feat(uploads): add native resumable upload support

Implement a native chunked resumable upload API and frontend integration
to support reliable large file uploads.

Changes include:
- Added a 3-step resumable upload API flow (create session, upload chunks, complete session).
- Introduced configuration options for chunk size, retention hours, and toggling the feature.
- Updated the frontend to utilize resumable uploads with progress tracking.
- Configured temporary chunk storage under `data/tmp/uploads` with automatic cleanup.
- Documented the API flow and configuration in the README.

.env.example

@@ -9,6 +9,9 @@ WARPBOX_CLEANUP_ENABLED=true
 WARPBOX_CLEANUP_EVERY=1h
 WARPBOX_THUMBNAIL_ENABLED=true
 WARPBOX_THUMBNAIL_EVERY=1m
+WARPBOX_RESUMABLE_UPLOADS_ENABLED=true
+WARPBOX_RESUMABLE_CHUNK_MB=64
+WARPBOX_RESUMABLE_RETENTION_HOURS=1
 WARPBOX_MAX_UPLOAD_SIZE_MB=16384
 WARPBOX_ANONYMOUS_UPLOADS_ENABLED=true
 WARPBOX_ANONYMOUS_MAX_UPLOAD_MB=512

README.md

@@ -33,6 +33,9 @@ Upload policy defaults are also configured in megabytes and can later be changed
 - `WARPBOX_SHORT_WINDOW_SECONDS=60`
 - `WARPBOX_ANONYMOUS_STORAGE_BACKEND=local`
 - `WARPBOX_USER_STORAGE_BACKEND=local`
+- `WARPBOX_RESUMABLE_UPLOADS_ENABLED=true`
+- `WARPBOX_RESUMABLE_CHUNK_MB=8`
+- `WARPBOX_RESUMABLE_RETENTION_HOURS=24`
 - `WARPBOX_TRUSTED_PROXIES=` controls whether forwarded client IP headers are accepted only from specific proxy IPs/CIDRs. See [SECURITY_PROXY.md](./SECURITY_PROXY.md).
 
 Runtime data is configured with `WARPBOX_DATA_DIR` and defaults to `./data` in the dev environment.
@@ -43,6 +46,10 @@ Large uploads are expected to take minutes on normal home/server connections. Ke
 mid-upload; `WARPBOX_READ_HEADER_TIMEOUT=15s` still protects header reads from slowloris-style
 connections.
 
+Browser uploads use Warpbox-native resumable uploads by default. Chunks are stored temporarily under
+`data/tmp/uploads/{session_id}` and then streamed into the selected storage backend when the upload
+is completed. Stale sessions are cleaned by the cleanup job after `WARPBOX_RESUMABLE_RETENTION_HOURS`.
+
 Background jobs are enabled with `WARPBOX_JOBS_ENABLED=true`. Individual jobs can be toggled with
 `WARPBOX_CLEANUP_ENABLED` and `WARPBOX_THUMBNAIL_ENABLED`, and their schedules are configured with
 `WARPBOX_CLEANUP_EVERY` and `WARPBOX_THUMBNAIL_EVERY`.
@@ -242,6 +249,31 @@ ShareX selection — which ShareX sends as separate back-to-back requests — la
 link. The shipped `.sxcu` sets `X-Warpbox-Batch: sharex`; remove that header for one box per file.
 Requests without the header behave exactly as before.
 
+### Resumable API flow
+
+Custom clients can use the resumable JSON API for large files:
+
+```bash
+# 1. Create a resumable session from file metadata.
+curl -s http://localhost:8080/api/v1/uploads/resumable \
+  -H 'Accept: application/json' \
+  -H 'Content-Type: application/json' \
+  -d '{"files":[{"name":"large.bin","size":1048576,"contentType":"application/octet-stream"}],"expiresMinutes":1440}'
+
+# 2. Upload exact-sized chunks using the returned sessionId, file id, and chunkSize.
+dd if=./large.bin bs=8388608 count=1 skip=0 2>/dev/null | \
+  curl -X PUT --data-binary @- \
+  http://localhost:8080/api/v1/uploads/resumable/SESSION_ID/files/FILE_ID/chunks/0
+
+# 3. Complete the session after all chunks are present.
+curl -X POST -H 'Accept: application/json' \
+  http://localhost:8080/api/v1/uploads/resumable/SESSION_ID/complete
+```
+
+The complete response is the same JSON shape as `POST /api/v1/upload`, including `boxUrl`,
+`manageUrl`, `deleteUrl`, and file URLs. Send `Authorization: Bearer <token>` on every resumable
+request to upload as an account.
+
 ## Stage 4 Accounts + Personal Boxes
 
 - `/register` bootstraps the first admin account only when no users exist.
@@ -275,6 +307,7 @@ Warpbox keeps local runtime data under the configured data directory:
 
 - `data/files/{box_id}/@each@{file_id}.ext` - uploaded file contents when the local backend is selected.
 - `data/files/{box_id}/@thumb@{file_id}.jpg` - generated previews when the local backend is selected.
+- `data/tmp/uploads/{session_id}` - temporary chunks for unfinished resumable uploads.
 - `data/db/warpbox.bbolt` - bbolt metadata database for boxes and file records.
 - `data/db/warpbox.bbolt` also stores users, sessions, invites, and collections.
 - `data/db/warpbox.bbolt` stores upload policy settings and daily usage records keyed by plain IP

backend/libs/config/config.go

@@ -30,6 +30,9 @@ type Config struct {
 	CleanupEvery            time.Duration
 	ThumbnailEnabled        bool
 	ThumbnailEvery          time.Duration
+	ResumableUploadsEnabled bool
+	ResumableChunkSize      int64
+	ResumableRetention      time.Duration
 	MaxUploadSize           int64
 	DefaultSettings         SettingsDefaults
 }
@@ -75,6 +78,9 @@ func Load() (Config, error) {
 		CleanupEvery:            envDuration("WARPBOX_CLEANUP_EVERY", time.Hour),
 		ThumbnailEnabled:        envBool("WARPBOX_THUMBNAIL_ENABLED", true),
 		ThumbnailEvery:          envDuration("WARPBOX_THUMBNAIL_EVERY", time.Minute),
+		ResumableUploadsEnabled: envBool("WARPBOX_RESUMABLE_UPLOADS_ENABLED", true),
+		ResumableChunkSize:      envMegabytes("WARPBOX_RESUMABLE_CHUNK_MB", 8),
+		ResumableRetention:      time.Duration(envInt("WARPBOX_RESUMABLE_RETENTION_HOURS", 24)) * time.Hour,
 		MaxUploadSize:           envMegabytes("WARPBOX_MAX_UPLOAD_SIZE_MB", 2048), // 2 GiB default.
 		DefaultSettings: SettingsDefaults{
 			AnonymousUploadsEnabled: envBool("WARPBOX_ANONYMOUS_UPLOADS_ENABLED", true),
@@ -103,6 +109,12 @@ func Load() (Config, error) {
 	if cfg.MaxUploadSize <= 0 {
 		return Config{}, fmt.Errorf("WARPBOX_MAX_UPLOAD_SIZE_MB must be positive")
 	}
+	if cfg.ResumableChunkSize <= 0 {
+		return Config{}, fmt.Errorf("WARPBOX_RESUMABLE_CHUNK_MB must be positive")
+	}
+	if cfg.ResumableRetention <= 0 {
+		return Config{}, fmt.Errorf("WARPBOX_RESUMABLE_RETENTION_HOURS must be positive")
+	}
 	if !validUnlimitedMegabyteLimit(cfg.DefaultSettings.AnonymousMaxUploadMB) ||
 		!validUnlimitedMegabyteLimit(cfg.DefaultSettings.AnonymousDailyUploadMB) ||
 		!validUnlimitedMegabyteLimit(cfg.DefaultSettings.UserDailyUploadMB) ||

backend/libs/config/config_test.go

@@ -68,4 +68,13 @@ func TestLoadDefaultsUseLargeUploadFriendlyTimeouts(t *testing.T) {
 	if cfg.WriteTimeout != 0 {
 		t.Fatalf("WriteTimeout = %s, want 0 for long uploads", cfg.WriteTimeout)
 	}
+	if !cfg.ResumableUploadsEnabled {
+		t.Fatalf("ResumableUploadsEnabled = false, want true")
+	}
+	if cfg.ResumableChunkSize != 8*1024*1024 {
+		t.Fatalf("ResumableChunkSize = %d, want 8 MiB", cfg.ResumableChunkSize)
+	}
+	if cfg.ResumableRetention != 24*time.Hour {
+		t.Fatalf("ResumableRetention = %s, want 24h", cfg.ResumableRetention)
+	}
 }

backend/libs/handlers/app.go

@@ -141,6 +141,12 @@ func (a *App) RegisterRoutes(mux *http.ServeMux) {
 	mux.HandleFunc("GET /api/v1/schemas/upload-request.json", a.UploadRequestSchema)
 	mux.HandleFunc("GET /api/v1/schemas/upload-response.json", a.UploadResponseSchema)
 	mux.HandleFunc("POST /api/v1/upload", a.Upload)
+	mux.HandleFunc("POST /api/v1/uploads/resumable", a.CreateResumableUpload)
+	mux.HandleFunc("GET /api/v1/uploads/resumable/{sessionID}", a.ResumableUploadStatus)
+	mux.HandleFunc("POST /api/v1/uploads/resumable/{sessionID}/files", a.AddResumableFiles)
+	mux.HandleFunc("PUT /api/v1/uploads/resumable/{sessionID}/files/{fileID}/chunks/{index}", a.PutResumableChunk)
+	mux.HandleFunc("POST /api/v1/uploads/resumable/{sessionID}/complete", a.CompleteResumableUpload)
+	mux.HandleFunc("DELETE /api/v1/uploads/resumable/{sessionID}", a.CancelResumableUpload)
 	mux.HandleFunc("GET /emoji/{pack}/{file}", a.EmojiAsset)
 	mux.Handle("GET /static/", a.Static())
 }

backend/libs/handlers/resumable.go

@@ -0,0 +1,328 @@
+package handlers
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+
+	"warpbox.dev/backend/libs/helpers"
+	"warpbox.dev/backend/libs/jobs"
+	"warpbox.dev/backend/libs/services"
+)
+
+type resumableCreateRequest struct {
+	Files             []services.ResumableFileInput `json:"files"`
+	MaxDays           int                           `json:"maxDays"`
+	ExpiresMinutes    int                           `json:"expiresMinutes"`
+	MaxDownloads      int                           `json:"maxDownloads"`
+	Password          string                        `json:"password"`
+	ObfuscateMetadata bool                          `json:"obfuscateMetadata"`
+	CollectionID      string                        `json:"collectionId"`
+}
+
+type resumableSessionResponse struct {
+	SessionID string                   `json:"sessionId"`
+	ChunkSize int64                    `json:"chunkSize"`
+	Status    string                   `json:"status"`
+	BoxID     string                   `json:"boxId,omitempty"`
+	ExpiresAt string                   `json:"expiresAt"`
+	Files     []services.ResumableFile `json:"files"`
+}
+
+func (a *App) CreateResumableUpload(w http.ResponseWriter, r *http.Request) {
+	if !a.cfg.ResumableUploadsEnabled {
+		helpers.WriteJSONError(w, http.StatusForbidden, "resumable uploads are disabled")
+		return
+	}
+	user, loggedIn, authErr := a.currentUserWithAuthError(r)
+	if authErr != nil {
+		a.logger.Warn("resumable upload rejected invalid bearer token", withRequestLogAttrs(r, "source", "user-upload", "severity", "warn", "code", 4011)...)
+		helpers.WriteJSONError(w, http.StatusUnauthorized, "invalid bearer token")
+		return
+	}
+	isAdminUpload := loggedIn && user.Role == services.UserRoleAdmin
+	settings, policy, ok := a.loadUploadPolicyForAPI(w, r, user, loggedIn)
+	if !ok {
+		return
+	}
+	if !loggedIn && !settings.AnonymousUploadsEnabled {
+		a.logger.Warn("resumable anonymous upload rejected disabled", withRequestLogAttrs(r, "source", "user-upload", "severity", "warn", "code", 4013)...)
+		helpers.WriteJSONError(w, http.StatusForbidden, "anonymous uploads are disabled")
+		return
+	}
+	rateKey := uploadRateKey(r, user, loggedIn)
+	if !isAdminUpload && policy.ShortRequests > 0 && !a.rateLimiter.Allow("upload:"+rateKey, policy.ShortRequests, policy.ShortWindow, time.Now().UTC()) {
+		a.logger.Warn("resumable upload rate limited", withRequestLogAttrs(r, "source", "user-upload", "severity", "warn", "code", 4291, "user_id", user.ID)...)
+		helpers.WriteJSONError(w, http.StatusTooManyRequests, "too many upload requests, please slow down")
+		return
+	}
+
+	var payload resumableCreateRequest
+	if err := json.NewDecoder(r.Body).Decode(&payload); err != nil {
+		helpers.WriteJSONError(w, http.StatusBadRequest, "upload session request could not be read")
+		return
+	}
+	fileSizes := make([]int64, 0, len(payload.Files))
+	var totalBytes int64
+	for _, file := range payload.Files {
+		fileSizes = append(fileSizes, file.Size)
+		totalBytes += file.Size
+	}
+	if !isAdminUpload {
+		if status, message := a.checkUploadPolicyForSizes(r, user, loggedIn, settings, policy, fileSizes, totalBytes); message != "" {
+			a.logger.Warn("resumable upload rejected by policy", withRequestLogAttrs(r, "source", "quota", "severity", "warn", "code", status, "user_id", user.ID, "message", message, "bytes", totalBytes, "files", len(payload.Files))...)
+			helpers.WriteJSONError(w, status, message)
+			return
+		}
+		if status, message := a.checkBoxCreationPolicy(r, user, loggedIn, policy); message != "" {
+			a.logger.Warn("resumable upload rejected by box policy", withRequestLogAttrs(r, "source", "quota", "severity", "warn", "code", status, "user_id", user.ID, "message", message, "bytes", totalBytes, "files", len(payload.Files))...)
+			helpers.WriteJSONError(w, status, message)
+			return
+		}
+	}
+
+	opts, err := a.resumableUploadOptions(r, payload, user, loggedIn, isAdminUpload, policy)
+	if err != nil {
+		helpers.WriteJSONError(w, http.StatusRequestEntityTooLarge, err.Error())
+		return
+	}
+	session, err := a.uploadService.CreateResumableSession(payload.Files, opts, a.cfg.ResumableChunkSize, a.cfg.ResumableRetention)
+	if err != nil {
+		a.logger.Warn("resumable session create failed", withRequestLogAttrs(r, "source", "user-upload", "severity", "warn", "code", 4002, "user_id", user.ID, "error", err.Error())...)
+		helpers.WriteJSONError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	a.logger.Info("resumable upload session created", withRequestLogAttrs(r, "source", "user-upload", "severity", "user_activity", "code", 2002, "user_id", user.ID, "session_id", session.ID, "files", len(session.Files), "bytes", totalBytes, "anonymous", !loggedIn)...)
+	helpers.WriteJSON(w, http.StatusCreated, resumableResponse(session))
+}
+
+func (a *App) ResumableUploadStatus(w http.ResponseWriter, r *http.Request) {
+	session, ok := a.authorizedResumableSession(w, r)
+	if !ok {
+		return
+	}
+	helpers.WriteJSON(w, http.StatusOK, resumableResponse(session))
+}
+
+func (a *App) AddResumableFiles(w http.ResponseWriter, r *http.Request) {
+	session, ok := a.authorizedResumableSession(w, r)
+	if !ok {
+		return
+	}
+	user, loggedIn, _ := a.currentUserWithAuthError(r)
+	isAdminUpload := loggedIn && user.Role == services.UserRoleAdmin
+	settings, policy, ok := a.loadUploadPolicyForAPI(w, r, user, loggedIn)
+	if !ok {
+		return
+	}
+	var payload struct {
+		Files []services.ResumableFileInput `json:"files"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&payload); err != nil {
+		helpers.WriteJSONError(w, http.StatusBadRequest, "upload files request could not be read")
+		return
+	}
+	fileSizes := make([]int64, 0, len(session.Files)+len(payload.Files))
+	var totalBytes int64
+	for _, file := range session.Files {
+		fileSizes = append(fileSizes, file.Size)
+		totalBytes += file.Size
+	}
+	for _, file := range payload.Files {
+		fileSizes = append(fileSizes, file.Size)
+		totalBytes += file.Size
+	}
+	if !isAdminUpload {
+		if status, message := a.checkUploadPolicyForSizes(r, user, loggedIn, settings, policy, fileSizes, totalBytes); message != "" {
+			helpers.WriteJSONError(w, status, message)
+			return
+		}
+	}
+	updated, err := a.uploadService.AddResumableFiles(session.ID, payload.Files)
+	if err != nil {
+		helpers.WriteJSONError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	a.logger.Info("resumable upload files added", withRequestLogAttrs(r, "source", "user-upload", "severity", "user_activity", "code", 2006, "session_id", session.ID, "added", len(updated.Files)-len(session.Files), "files", len(updated.Files))...)
+	helpers.WriteJSON(w, http.StatusOK, resumableResponse(updated))
+}
+
+func (a *App) PutResumableChunk(w http.ResponseWriter, r *http.Request) {
+	session, ok := a.authorizedResumableSession(w, r)
+	if !ok {
+		return
+	}
+	fileID := r.PathValue("fileID")
+	index, err := strconv.Atoi(r.PathValue("index"))
+	if err != nil {
+		helpers.WriteJSONError(w, http.StatusBadRequest, "chunk index is invalid")
+		return
+	}
+	updated, err := a.uploadService.PutResumableChunk(r.Context(), session.ID, fileID, index, r.Body)
+	if err != nil {
+		a.logger.Warn("resumable chunk failed", withRequestLogAttrs(r, "source", "user-upload", "severity", "warn", "code", 4003, "session_id", session.ID, "file_id", fileID, "chunk", index, "error", err.Error())...)
+		helpers.WriteJSONError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	a.logger.Info("resumable chunk uploaded", withRequestLogAttrs(r, "source", "user-upload", "severity", "user_activity", "code", 2003, "session_id", session.ID, "file_id", fileID, "chunk", index)...)
+	helpers.WriteJSON(w, http.StatusOK, resumableResponse(updated))
+}
+
+func (a *App) CompleteResumableUpload(w http.ResponseWriter, r *http.Request) {
+	session, ok := a.authorizedResumableSession(w, r)
+	if !ok {
+		return
+	}
+	user, loggedIn, _ := a.currentUserWithAuthError(r)
+	isAdminUpload := loggedIn && user.Role == services.UserRoleAdmin
+	settings, policy, ok := a.loadUploadPolicyForAPI(w, r, user, loggedIn)
+	if !ok {
+		return
+	}
+	fileSizes := make([]int64, 0, len(session.Files))
+	var totalBytes int64
+	for _, file := range session.Files {
+		fileSizes = append(fileSizes, file.Size)
+		totalBytes += file.Size
+	}
+	if !isAdminUpload {
+		if status, message := a.checkUploadPolicyForSizes(r, user, loggedIn, settings, policy, fileSizes, totalBytes); message != "" {
+			helpers.WriteJSONError(w, status, message)
+			return
+		}
+		if status, message := a.checkBoxCreationPolicy(r, user, loggedIn, policy); message != "" {
+			helpers.WriteJSONError(w, status, message)
+			return
+		}
+		if status, message := a.checkStorageBackendCapacity(session.Options.StorageBackendID, settings, totalBytes); message != "" {
+			helpers.WriteJSONError(w, status, message)
+			return
+		}
+	}
+	result, completed, err := a.uploadService.CompleteResumableSession(r.Context(), session.ID)
+	if err != nil {
+		a.logger.Warn("resumable upload complete failed", withRequestLogAttrs(r, "source", "user-upload", "severity", "warn", "code", 4004, "session_id", session.ID, "error", err.Error())...)
+		helpers.WriteJSONError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	if !isAdminUpload {
+		if err := a.recordUploadUsage(r, user, loggedIn, totalBytes, 1); err != nil {
+			a.logger.Warn("failed to record resumable upload usage", "source", "quota", "severity", "warn", "code", 4404, "error", err.Error())
+		}
+		if err := a.settingsService.CleanupUsage(time.Now().UTC(), settings.UsageRetentionDays); err != nil {
+			a.logger.Warn("failed to cleanup upload usage", "source", "quota", "severity", "warn", "code", 4405, "error", err.Error())
+		}
+	}
+	jobs.GenerateThumbnailsForBoxAsync(a.uploadService, a.logger, result.BoxID)
+	a.logger.Info("resumable upload completed", withRequestLogAttrs(r, "source", "user-upload", "severity", "user_activity", "code", 2004, "user_id", user.ID, "session_id", completed.ID, "box_id", result.BoxID, "files", len(result.Files), "bytes", totalBytes, "admin", isAdminUpload, "anonymous", !loggedIn)...)
+	helpers.WriteJSON(w, http.StatusCreated, result)
+}
+
+func (a *App) CancelResumableUpload(w http.ResponseWriter, r *http.Request) {
+	session, ok := a.authorizedResumableSession(w, r)
+	if !ok {
+		return
+	}
+	if err := a.uploadService.CancelResumableSession(session.ID); err != nil {
+		helpers.WriteJSONError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+	a.logger.Info("resumable upload cancelled", withRequestLogAttrs(r, "source", "user-upload", "severity", "user_activity", "code", 2005, "session_id", session.ID)...)
+	w.WriteHeader(http.StatusNoContent)
+}
+
+func (a *App) authorizedResumableSession(w http.ResponseWriter, r *http.Request) (services.ResumableSession, bool) {
+	user, loggedIn, authErr := a.currentUserWithAuthError(r)
+	if authErr != nil {
+		helpers.WriteJSONError(w, http.StatusUnauthorized, "invalid bearer token")
+		return services.ResumableSession{}, false
+	}
+	session, err := a.uploadService.GetResumableSession(r.PathValue("sessionID"))
+	if err != nil {
+		helpers.WriteJSONError(w, http.StatusNotFound, "upload session not found")
+		return services.ResumableSession{}, false
+	}
+	if loggedIn {
+		if session.Options.OwnerID != user.ID {
+			helpers.WriteJSONError(w, http.StatusForbidden, "upload session not found")
+			return services.ResumableSession{}, false
+		}
+		return session, true
+	}
+	if session.Options.OwnerID != "" || session.Options.CreatorIP != uploadClientIP(r) {
+		helpers.WriteJSONError(w, http.StatusForbidden, "upload session not found")
+		return services.ResumableSession{}, false
+	}
+	return session, true
+}
+
+func (a *App) loadUploadPolicyForAPI(w http.ResponseWriter, r *http.Request, user services.User, loggedIn bool) (services.UploadPolicySettings, services.EffectiveUploadPolicy, bool) {
+	settings, err := a.settingsService.UploadPolicy()
+	if err != nil {
+		a.logger.Error("failed to load upload policy", "source", "settings", "severity", "error", "code", 5006, "error", err.Error())
+		helpers.WriteJSONError(w, http.StatusInternalServerError, "upload policy could not be loaded")
+		return services.UploadPolicySettings{}, services.EffectiveUploadPolicy{}, false
+	}
+	return settings, a.effectiveUploadPolicy(settings, user, loggedIn), true
+}
+
+func (a *App) resumableUploadOptions(r *http.Request, payload resumableCreateRequest, user services.User, loggedIn, isAdminUpload bool, policy services.EffectiveUploadPolicy) (services.UploadOptions, error) {
+	var ownerID string
+	var collectionID string
+	if loggedIn {
+		ownerID = user.ID
+		collectionID = strings.TrimSpace(payload.CollectionID)
+		if !a.authService.CollectionOwnedBy(collectionID, user.ID) {
+			return services.UploadOptions{}, fmt.Errorf("collection not found")
+		}
+	}
+	unlimitedExpiry := isAdminUpload || policy.MaxDays < 0
+	rawMaxDays := payload.MaxDays
+	maxDays := rawMaxDays
+	if maxDays <= 0 {
+		maxDays = 7
+		if policy.MaxDays > 0 && policy.MaxDays < maxDays {
+			maxDays = policy.MaxDays
+		}
+	}
+	expiresMinutes := payload.ExpiresMinutes
+	if expiresMinutes < 0 || rawMaxDays < 0 {
+		if !unlimitedExpiry {
+			return services.UploadOptions{}, fmt.Errorf("expiration cannot exceed %d days", policy.MaxDays)
+		}
+		expiresMinutes = -1
+	} else if !unlimitedExpiry {
+		if maxDays > policy.MaxDays {
+			return services.UploadOptions{}, fmt.Errorf("expiration cannot exceed %d days", policy.MaxDays)
+		}
+		if expiresMinutes > 0 && expiresMinutes > policy.MaxDays*24*60 {
+			return services.UploadOptions{}, fmt.Errorf("expiration cannot exceed %d days", policy.MaxDays)
+		}
+	}
+	return services.UploadOptions{
+		MaxDays:           maxDays,
+		ExpiresInMinutes:  expiresMinutes,
+		MaxDownloads:      payload.MaxDownloads,
+		Password:          payload.Password,
+		ObfuscateMetadata: payload.ObfuscateMetadata,
+		OwnerID:           ownerID,
+		CollectionID:      collectionID,
+		SkipSizeLimit:     isAdminUpload || policy.MaxUploadMB < 0,
+		CreatorIP:         uploadClientIP(r),
+		StorageBackendID:  policy.StorageBackendID,
+	}, nil
+}
+
+func resumableResponse(session services.ResumableSession) resumableSessionResponse {
+	return resumableSessionResponse{
+		SessionID: session.ID,
+		ChunkSize: session.ChunkSize,
+		Status:    session.Status,
+		BoxID:     session.BoxID,
+		ExpiresAt: session.ExpiresAt.Format(time.RFC3339),
+		Files:     session.Files,
+	}
+}

backend/libs/handlers/upload.go

@@ -228,11 +228,22 @@ func (a *App) checkUploadPolicy(r *http.Request, user services.User, loggedIn bo
 	if len(files) == 0 {
 		return 0, ""
 	}
+	sizes := make([]int64, 0, len(files))
+	for _, file := range files {
+		sizes = append(sizes, file.Size)
+	}
+	return a.checkUploadPolicyForSizes(r, user, loggedIn, settings, policy, sizes, totalBytes)
+}
+
+func (a *App) checkUploadPolicyForSizes(r *http.Request, user services.User, loggedIn bool, settings services.UploadPolicySettings, policy services.EffectiveUploadPolicy, fileSizes []int64, totalBytes int64) (int, string) {
+	if len(fileSizes) == 0 {
+		return 0, ""
+	}
 	now := time.Now().UTC()
 	if policy.MaxUploadMB > 0 {
 		maxBytes := services.MegabytesToBytes(policy.MaxUploadMB)
-		for _, file := range files {
+		for _, fileSize := range fileSizes {
-			if file.Size > maxBytes {
+			if fileSize > maxBytes {
 				return http.StatusRequestEntityTooLarge, "file exceeds upload size limit"
 			}
 		}

backend/libs/handlers/upload_stage3_test.go

@@ -2,6 +2,7 @@ package handlers
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"io"
 	"log/slog"
@@ -10,8 +11,10 @@ import (
 	"net/http/httptest"
 	"os"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"testing"
+	"time"
 
 	"warpbox.dev/backend/libs/config"
 	"warpbox.dev/backend/libs/services"
@@ -103,6 +106,196 @@ func TestUploadTextResponseReturnsOnlyBoxURL(t *testing.T) {
 	}
 }
 
+func TestResumableUploadFlowCreatesNormalBox(t *testing.T) {
+	app, cleanup := newTestApp(t)
+	defer cleanup()
+
+	createBody := `{"files":[{"name":"note.txt","size":11,"contentType":"text/plain"}],"expiresMinutes":60}`
+	createRequest := httptest.NewRequest(http.MethodPost, "/api/v1/uploads/resumable", strings.NewReader(createBody))
+	createRequest.Header.Set("Accept", "application/json")
+	createResponse := httptest.NewRecorder()
+	app.CreateResumableUpload(createResponse, createRequest)
+	if createResponse.Code != http.StatusCreated {
+		t.Fatalf("create status = %d, body = %s", createResponse.Code, createResponse.Body.String())
+	}
+	var session struct {
+		SessionID string `json:"sessionId"`
+		ChunkSize int64  `json:"chunkSize"`
+		Files     []struct {
+			ID             string `json:"id"`
+			ChunkCount     int    `json:"chunkCount"`
+			UploadedChunks []int  `json:"uploadedChunks"`
+		} `json:"files"`
+	}
+	if err := json.Unmarshal(createResponse.Body.Bytes(), &session); err != nil {
+		t.Fatalf("json.Unmarshal session returned error: %v", err)
+	}
+	if session.SessionID == "" || session.ChunkSize != 4 || len(session.Files) != 1 || session.Files[0].ChunkCount != 3 {
+		t.Fatalf("unexpected session response: %+v", session)
+	}
+
+	chunks := map[int]string{1: "o wo", 0: "hell", 2: "rld"}
+	for index, body := range chunks {
+		request := httptest.NewRequest(http.MethodPut, "/api/v1/uploads/resumable/"+session.SessionID+"/files/"+session.Files[0].ID+"/chunks/"+strconv.Itoa(index), strings.NewReader(body))
+		request.SetPathValue("sessionID", session.SessionID)
+		request.SetPathValue("fileID", session.Files[0].ID)
+		request.SetPathValue("index", strconv.Itoa(index))
+		response := httptest.NewRecorder()
+		app.PutResumableChunk(response, request)
+		if response.Code != http.StatusOK {
+			t.Fatalf("chunk %d status = %d, body = %s", index, response.Code, response.Body.String())
+		}
+	}
+
+	completeRequest := httptest.NewRequest(http.MethodPost, "/api/v1/uploads/resumable/"+session.SessionID+"/complete", nil)
+	completeRequest.SetPathValue("sessionID", session.SessionID)
+	completeResponse := httptest.NewRecorder()
+	app.CompleteResumableUpload(completeResponse, completeRequest)
+	if completeResponse.Code != http.StatusCreated {
+		t.Fatalf("complete status = %d, body = %s", completeResponse.Code, completeResponse.Body.String())
+	}
+	var payload services.UploadResult
+	if err := json.Unmarshal(completeResponse.Body.Bytes(), &payload); err != nil {
+		t.Fatalf("json.Unmarshal result returned error: %v", err)
+	}
+	box, err := app.uploadService.GetBox(payload.BoxID)
+	if err != nil {
+		t.Fatalf("GetBox returned error: %v", err)
+	}
+	if len(box.Files) != 1 || box.Files[0].Name != "note.txt" || box.Files[0].Size != 11 {
+		t.Fatalf("unexpected box files: %+v", box.Files)
+	}
+	object, err := app.uploadService.OpenFileObject(context.Background(), box, box.Files[0])
+	if err != nil {
+		t.Fatalf("OpenFileObject returned error: %v", err)
+	}
+	data, err := io.ReadAll(object.Body)
+	object.Body.Close()
+	if err != nil {
+		t.Fatalf("ReadAll returned error: %v", err)
+	}
+	if string(data) != "hello world" {
+		t.Fatalf("uploaded body = %q", string(data))
+	}
+}
+
+func TestResumableUploadRequiresAllChunks(t *testing.T) {
+	app, cleanup := newTestApp(t)
+	defer cleanup()
+
+	createRequest := httptest.NewRequest(http.MethodPost, "/api/v1/uploads/resumable", strings.NewReader(`{"files":[{"name":"note.txt","size":8,"contentType":"text/plain"}]}`))
+	createResponse := httptest.NewRecorder()
+	app.CreateResumableUpload(createResponse, createRequest)
+	if createResponse.Code != http.StatusCreated {
+		t.Fatalf("create status = %d, body = %s", createResponse.Code, createResponse.Body.String())
+	}
+	var session struct {
+		SessionID string `json:"sessionId"`
+		Files     []struct {
+			ID string `json:"id"`
+		} `json:"files"`
+	}
+	if err := json.Unmarshal(createResponse.Body.Bytes(), &session); err != nil {
+		t.Fatalf("json.Unmarshal session returned error: %v", err)
+	}
+	chunkRequest := httptest.NewRequest(http.MethodPut, "/api/v1/uploads/resumable/"+session.SessionID+"/files/"+session.Files[0].ID+"/chunks/0", strings.NewReader("hell"))
+	chunkRequest.SetPathValue("sessionID", session.SessionID)
+	chunkRequest.SetPathValue("fileID", session.Files[0].ID)
+	chunkRequest.SetPathValue("index", "0")
+	chunkResponse := httptest.NewRecorder()
+	app.PutResumableChunk(chunkResponse, chunkRequest)
+	if chunkResponse.Code != http.StatusOK {
+		t.Fatalf("chunk status = %d, body = %s", chunkResponse.Code, chunkResponse.Body.String())
+	}
+
+	completeRequest := httptest.NewRequest(http.MethodPost, "/api/v1/uploads/resumable/"+session.SessionID+"/complete", nil)
+	completeRequest.SetPathValue("sessionID", session.SessionID)
+	completeResponse := httptest.NewRecorder()
+	app.CompleteResumableUpload(completeResponse, completeRequest)
+	if completeResponse.Code != http.StatusBadRequest {
+		t.Fatalf("complete status = %d, body = %s", completeResponse.Code, completeResponse.Body.String())
+	}
+}
+
+func TestResumableUploadCanAddFilesToExistingSession(t *testing.T) {
+	app, cleanup := newTestApp(t)
+	defer cleanup()
+
+	createBody := `{"files":[{"name":"one.txt","size":4,"contentType":"text/plain","fingerprint":"one"}],"expiresMinutes":60}`
+	createRequest := httptest.NewRequest(http.MethodPost, "/api/v1/uploads/resumable", strings.NewReader(createBody))
+	createResponse := httptest.NewRecorder()
+	app.CreateResumableUpload(createResponse, createRequest)
+	if createResponse.Code != http.StatusCreated {
+		t.Fatalf("create status = %d, body = %s", createResponse.Code, createResponse.Body.String())
+	}
+	var session struct {
+		SessionID string `json:"sessionId"`
+		Files     []struct {
+			ID string `json:"id"`
+		} `json:"files"`
+	}
+	if err := json.Unmarshal(createResponse.Body.Bytes(), &session); err != nil {
+		t.Fatalf("json.Unmarshal session returned error: %v", err)
+	}
+	firstChunk := httptest.NewRequest(http.MethodPut, "/api/v1/uploads/resumable/"+session.SessionID+"/files/"+session.Files[0].ID+"/chunks/0", strings.NewReader("one!"))
+	firstChunk.SetPathValue("sessionID", session.SessionID)
+	firstChunk.SetPathValue("fileID", session.Files[0].ID)
+	firstChunk.SetPathValue("index", "0")
+	firstChunkResponse := httptest.NewRecorder()
+	app.PutResumableChunk(firstChunkResponse, firstChunk)
+	if firstChunkResponse.Code != http.StatusOK {
+		t.Fatalf("first chunk status = %d, body = %s", firstChunkResponse.Code, firstChunkResponse.Body.String())
+	}
+
+	addRequest := httptest.NewRequest(http.MethodPost, "/api/v1/uploads/resumable/"+session.SessionID+"/files", strings.NewReader(`{"files":[{"name":"two.txt","size":4,"contentType":"text/plain","fingerprint":"two"}]}`))
+	addRequest.SetPathValue("sessionID", session.SessionID)
+	addResponse := httptest.NewRecorder()
+	app.AddResumableFiles(addResponse, addRequest)
+	if addResponse.Code != http.StatusOK {
+		t.Fatalf("add status = %d, body = %s", addResponse.Code, addResponse.Body.String())
+	}
+	var updated struct {
+		Files []struct {
+			ID             string `json:"id"`
+			Name           string `json:"name"`
+			UploadedChunks []int  `json:"uploadedChunks"`
+		} `json:"files"`
+	}
+	if err := json.Unmarshal(addResponse.Body.Bytes(), &updated); err != nil {
+		t.Fatalf("json.Unmarshal updated returned error: %v", err)
+	}
+	if len(updated.Files) != 2 || len(updated.Files[0].UploadedChunks) != 1 {
+		t.Fatalf("unexpected updated session: %+v", updated)
+	}
+	secondChunk := httptest.NewRequest(http.MethodPut, "/api/v1/uploads/resumable/"+session.SessionID+"/files/"+updated.Files[1].ID+"/chunks/0", strings.NewReader("two!"))
+	secondChunk.SetPathValue("sessionID", session.SessionID)
+	secondChunk.SetPathValue("fileID", updated.Files[1].ID)
+	secondChunk.SetPathValue("index", "0")
+	secondChunkResponse := httptest.NewRecorder()
+	app.PutResumableChunk(secondChunkResponse, secondChunk)
+	if secondChunkResponse.Code != http.StatusOK {
+		t.Fatalf("second chunk status = %d, body = %s", secondChunkResponse.Code, secondChunkResponse.Body.String())
+	}
+	completeRequest := httptest.NewRequest(http.MethodPost, "/api/v1/uploads/resumable/"+session.SessionID+"/complete", nil)
+	completeRequest.SetPathValue("sessionID", session.SessionID)
+	completeResponse := httptest.NewRecorder()
+	app.CompleteResumableUpload(completeResponse, completeRequest)
+	if completeResponse.Code != http.StatusCreated {
+		t.Fatalf("complete status = %d, body = %s", completeResponse.Code, completeResponse.Body.String())
+	}
+	var payload services.UploadResult
+	if err := json.Unmarshal(completeResponse.Body.Bytes(), &payload); err != nil {
+		t.Fatalf("json.Unmarshal result returned error: %v", err)
+	}
+	box, err := app.uploadService.GetBox(payload.BoxID)
+	if err != nil {
+		t.Fatalf("GetBox returned error: %v", err)
+	}
+	if len(box.Files) != 2 {
+		t.Fatalf("box file count = %d, want 2", len(box.Files))
+	}
+}
+
 func TestManageBoxAndDeleteFlow(t *testing.T) {
 	app, cleanup := newTestApp(t)
 	defer cleanup()
@@ -221,6 +414,9 @@ func newTestApp(t *testing.T) (*App, func()) {
 		StaticDir:               staticDir,
 		TemplateDir:             templateDir,
 		MaxUploadSize:           1024 * 1024,
+		ResumableUploadsEnabled: true,
+		ResumableChunkSize:      4,
+		ResumableRetention:      time.Hour,
 		DefaultSettings: config.SettingsDefaults{
 			AnonymousUploadsEnabled: true,
 			AnonymousMaxUploadMB:    1,

backend/libs/jobs/cleanup.go

@@ -22,6 +22,14 @@ func newCleanupJob(cfg config.Config, logger *slog.Logger, uploadService *servic
 			if cleaned > 0 {
 				logger.Info("cleanup job complete", "source", "housekeeping", "severity", "user_activity", "code", 2202, "cleaned", cleaned)
 			}
+			cleanedUploads, err := uploadService.CleanupExpiredResumableSessions(time.Now().UTC())
+			if err != nil {
+				logger.Warn("resumable upload cleanup failed", "source", "housekeeping", "severity", "warn", "code", 4204, "error", err.Error())
+				return
+			}
+			if cleanedUploads > 0 {
+				logger.Info("resumable uploads cleaned", "source", "housekeeping", "severity", "user_activity", "code", 2204, "cleaned", cleanedUploads)
+			}
 			if banService != nil {
 				cleanedEvents, err := banService.CleanupAbuseEvents(time.Now().UTC())
 				if err != nil {
@@ -37,7 +45,12 @@ func newCleanupJob(cfg config.Config, logger *slog.Logger, uploadService *servic
 }
 
 func RunCleanupNow(uploadService *services.UploadService, logger *slog.Logger) (int, error) {
-	return cleanupUnavailableBoxes(uploadService, logger)
+	cleaned, err := cleanupUnavailableBoxes(uploadService, logger)
+	if err != nil {
+		return cleaned, err
+	}
+	cleanedUploads, err := uploadService.CleanupExpiredResumableSessions(time.Now().UTC())
+	return cleaned + cleanedUploads, err
 }
 
 func cleanupUnavailableBoxes(uploadService *services.UploadService, logger *slog.Logger) (int, error) {

backend/libs/services/resumable.go

@@ -0,0 +1,454 @@
+package services
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"time"
+
+	"go.etcd.io/bbolt"
+)
+
+var resumableUploadsBucket = []byte("resumable_uploads")
+
+const (
+	ResumableStatusUploading = "uploading"
+	ResumableStatusCompleted = "completed"
+	ResumableStatusCancelled = "cancelled"
+)
+
+type ResumableFileInput struct {
+	Name        string `json:"name"`
+	Size        int64  `json:"size"`
+	ContentType string `json:"contentType"`
+	Fingerprint string `json:"fingerprint,omitempty"`
+}
+
+type ResumableSession struct {
+	ID        string          `json:"id"`
+	Options   UploadOptions   `json:"options"`
+	Files     []ResumableFile `json:"files"`
+	ChunkSize int64           `json:"chunkSize"`
+	Status    string          `json:"status"`
+	BoxID     string          `json:"boxId,omitempty"`
+	CreatedAt time.Time       `json:"createdAt"`
+	UpdatedAt time.Time       `json:"updatedAt"`
+	ExpiresAt time.Time       `json:"expiresAt"`
+}
+
+type ResumableFile struct {
+	ID             string `json:"id"`
+	Name           string `json:"name"`
+	Size           int64  `json:"size"`
+	ContentType    string `json:"contentType"`
+	Fingerprint    string `json:"fingerprint,omitempty"`
+	ChunkCount     int    `json:"chunkCount"`
+	UploadedChunks []int  `json:"uploadedChunks"`
+}
+
+func (s *UploadService) ensureResumableBucket() error {
+	return s.db.Update(func(tx *bbolt.Tx) error {
+		_, err := tx.CreateBucketIfNotExists(resumableUploadsBucket)
+		return err
+	})
+}
+
+func (s *UploadService) CreateResumableSession(files []ResumableFileInput, opts UploadOptions, chunkSize int64, retention time.Duration) (ResumableSession, error) {
+	if len(files) == 0 {
+		return ResumableSession{}, fmt.Errorf("no files were uploaded")
+	}
+	if chunkSize <= 0 {
+		return ResumableSession{}, fmt.Errorf("chunk size must be positive")
+	}
+	if retention <= 0 {
+		return ResumableSession{}, fmt.Errorf("retention must be positive")
+	}
+	if strings.TrimSpace(opts.Password) != "" {
+		opts.PasswordSalt, opts.PasswordHash = hashPassword(opts.Password)
+		opts.Password = ""
+	}
+	sessionFiles, err := s.resumableFilesFromInput(files, opts, chunkSize, nil)
+	if err != nil {
+		return ResumableSession{}, err
+	}
+	now := time.Now().UTC()
+	session := ResumableSession{
+		ID:        randomID(12),
+		Options:   opts,
+		Files:     sessionFiles,
+		ChunkSize: chunkSize,
+		Status:    ResumableStatusUploading,
+		CreatedAt: now,
+		UpdatedAt: now,
+		ExpiresAt: now.Add(retention),
+	}
+	if err := s.saveResumableSession(session); err != nil {
+		return ResumableSession{}, err
+	}
+	return session, nil
+}
+
+func (s *UploadService) AddResumableFiles(sessionID string, files []ResumableFileInput) (ResumableSession, error) {
+	if len(files) == 0 {
+		return s.GetResumableSession(sessionID)
+	}
+	session, err := s.GetResumableSession(sessionID)
+	if err != nil {
+		return ResumableSession{}, err
+	}
+	if err := resumableSessionWritable(session); err != nil {
+		return ResumableSession{}, err
+	}
+	existing := make(map[string]bool)
+	for _, file := range session.Files {
+		existing[resumableFileKey(file.Name, file.Size, file.Fingerprint)] = true
+	}
+	newFiles, err := s.resumableFilesFromInput(files, session.Options, session.ChunkSize, existing)
+	if err != nil {
+		return ResumableSession{}, err
+	}
+	if len(newFiles) == 0 {
+		return session, nil
+	}
+	session.Files = append(session.Files, newFiles...)
+	session.UpdatedAt = time.Now().UTC()
+	if err := s.saveResumableSession(session); err != nil {
+		return ResumableSession{}, err
+	}
+	return session, nil
+}
+
+func (s *UploadService) GetResumableSession(id string) (ResumableSession, error) {
+	var session ResumableSession
+	err := s.db.View(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(resumableUploadsBucket)
+		if bucket == nil {
+			return os.ErrNotExist
+		}
+		data := bucket.Get([]byte(id))
+		if data == nil {
+			return os.ErrNotExist
+		}
+		return json.Unmarshal(data, &session)
+	})
+	if err != nil {
+		return ResumableSession{}, err
+	}
+	return session, nil
+}
+
+func (s *UploadService) PutResumableChunk(ctx context.Context, sessionID, fileID string, index int, body io.Reader) (ResumableSession, error) {
+	session, err := s.GetResumableSession(sessionID)
+	if err != nil {
+		return ResumableSession{}, err
+	}
+	if err := resumableSessionWritable(session); err != nil {
+		return ResumableSession{}, err
+	}
+	fileIndex := -1
+	for i, file := range session.Files {
+		if file.ID == fileID {
+			fileIndex = i
+			break
+		}
+	}
+	if fileIndex < 0 {
+		return ResumableSession{}, os.ErrNotExist
+	}
+	file := session.Files[fileIndex]
+	if index < 0 || index >= file.ChunkCount {
+		return ResumableSession{}, fmt.Errorf("chunk index is invalid")
+	}
+	expectedSize := expectedChunkSize(file.Size, session.ChunkSize, index)
+	chunkDir := s.resumableFileDir(session.ID, file.ID)
+	if err := os.MkdirAll(chunkDir, 0o755); err != nil {
+		return ResumableSession{}, err
+	}
+	chunkPath := s.resumableChunkPath(session.ID, file.ID, index)
+	tempPath := chunkPath + ".tmp"
+	target, err := os.OpenFile(tempPath, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0o600)
+	if err != nil {
+		return ResumableSession{}, err
+	}
+	written, copyErr := io.Copy(target, io.LimitReader(body, expectedSize+1))
+	closeErr := target.Close()
+	if copyErr != nil {
+		_ = os.Remove(tempPath)
+		return ResumableSession{}, copyErr
+	}
+	if closeErr != nil {
+		_ = os.Remove(tempPath)
+		return ResumableSession{}, closeErr
+	}
+	if written != expectedSize {
+		_ = os.Remove(tempPath)
+		return ResumableSession{}, fmt.Errorf("chunk size mismatch")
+	}
+	if err := os.Rename(tempPath, chunkPath); err != nil {
+		_ = os.Remove(tempPath)
+		return ResumableSession{}, err
+	}
+	session.Files[fileIndex].UploadedChunks = addChunkIndex(session.Files[fileIndex].UploadedChunks, index)
+	session.UpdatedAt = time.Now().UTC()
+	if err := s.saveResumableSession(session); err != nil {
+		return ResumableSession{}, err
+	}
+	return session, nil
+}
+
+func (s *UploadService) CompleteResumableSession(ctx context.Context, sessionID string) (UploadResult, ResumableSession, error) {
+	session, err := s.GetResumableSession(sessionID)
+	if err != nil {
+		return UploadResult{}, ResumableSession{}, err
+	}
+	if err := resumableSessionWritable(session); err != nil {
+		return UploadResult{}, ResumableSession{}, err
+	}
+	staged, cleanup, err := s.assembleResumableFiles(ctx, session)
+	if err != nil {
+		return UploadResult{}, ResumableSession{}, err
+	}
+	defer cleanup()
+
+	result, err := s.CreateBoxFromIncoming(staged, session.Options)
+	if err != nil {
+		return UploadResult{}, ResumableSession{}, err
+	}
+	if err := os.RemoveAll(s.resumableSessionDir(session.ID)); err != nil {
+		return UploadResult{}, ResumableSession{}, err
+	}
+	session.Status = ResumableStatusCompleted
+	session.BoxID = result.BoxID
+	session.UpdatedAt = time.Now().UTC()
+	if err := s.saveResumableSession(session); err != nil {
+		return UploadResult{}, ResumableSession{}, err
+	}
+	return result, session, nil
+}
+
+func (s *UploadService) CancelResumableSession(sessionID string) error {
+	session, err := s.GetResumableSession(sessionID)
+	if err != nil {
+		return err
+	}
+	session.Status = ResumableStatusCancelled
+	session.UpdatedAt = time.Now().UTC()
+	if err := s.saveResumableSession(session); err != nil {
+		return err
+	}
+	return os.RemoveAll(s.resumableSessionDir(session.ID))
+}
+
+func (s *UploadService) CleanupExpiredResumableSessions(now time.Time) (int, error) {
+	candidates := make([]ResumableSession, 0)
+	err := s.db.View(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(resumableUploadsBucket)
+		if bucket == nil {
+			return nil
+		}
+		return bucket.ForEach(func(_, value []byte) error {
+			var session ResumableSession
+			if err := json.Unmarshal(value, &session); err != nil {
+				return err
+			}
+			if !session.ExpiresAt.After(now) || session.Status != ResumableStatusUploading {
+				candidates = append(candidates, session)
+			}
+			return nil
+		})
+	})
+	if err != nil {
+		return 0, err
+	}
+	for _, session := range candidates {
+		if err := os.RemoveAll(s.resumableSessionDir(session.ID)); err != nil {
+			return 0, err
+		}
+	}
+	err = s.db.Update(func(tx *bbolt.Tx) error {
+		bucket := tx.Bucket(resumableUploadsBucket)
+		if bucket == nil {
+			return nil
+		}
+		for _, session := range candidates {
+			if err := bucket.Delete([]byte(session.ID)); err != nil {
+				return err
+			}
+		}
+		return nil
+	})
+	return len(candidates), err
+}
+
+func (s *UploadService) saveResumableSession(session ResumableSession) error {
+	if err := s.ensureResumableBucket(); err != nil {
+		return err
+	}
+	return s.db.Update(func(tx *bbolt.Tx) error {
+		data, err := json.Marshal(session)
+		if err != nil {
+			return err
+		}
+		return tx.Bucket(resumableUploadsBucket).Put([]byte(session.ID), data)
+	})
+}
+
+func (s *UploadService) resumableFilesFromInput(files []ResumableFileInput, opts UploadOptions, chunkSize int64, existing map[string]bool) ([]ResumableFile, error) {
+	sessionFiles := make([]ResumableFile, 0, len(files))
+	for _, file := range files {
+		file.Name = filepath.Base(strings.TrimSpace(file.Name))
+		if file.Name == "." || file.Name == "" {
+			return nil, fmt.Errorf("file name is required")
+		}
+		if file.Size < 0 {
+			return nil, fmt.Errorf("file size is invalid")
+		}
+		fingerprint := strings.TrimSpace(file.Fingerprint)
+		key := resumableFileKey(file.Name, file.Size, fingerprint)
+		if existing != nil && existing[key] {
+			continue
+		}
+		if !opts.SkipSizeLimit {
+			if err := s.ValidateSize(file.Size); err != nil {
+				return nil, err
+			}
+		}
+		chunks := int((file.Size + chunkSize - 1) / chunkSize)
+		if chunks == 0 {
+			chunks = 1
+		}
+		sessionFiles = append(sessionFiles, ResumableFile{
+			ID:          randomID(8),
+			Name:        file.Name,
+			Size:        file.Size,
+			ContentType: strings.TrimSpace(file.ContentType),
+			Fingerprint: fingerprint,
+			ChunkCount:  chunks,
+		})
+		if existing != nil {
+			existing[key] = true
+		}
+	}
+	return sessionFiles, nil
+}
+
+func resumableFileKey(name string, size int64, fingerprint string) string {
+	return strings.TrimSpace(fingerprint) + "|" + filepath.Base(strings.TrimSpace(name)) + "|" + fmt.Sprintf("%d", size)
+}
+
+func (s *UploadService) assembleResumableFiles(ctx context.Context, session ResumableSession) ([]IncomingFile, func(), error) {
+	assembledDir := filepath.Join(s.resumableSessionDir(session.ID), "assembled")
+	if err := os.MkdirAll(assembledDir, 0o755); err != nil {
+		return nil, func() {}, err
+	}
+	cleanup := func() {
+		_ = os.RemoveAll(assembledDir)
+	}
+	staged := make([]IncomingFile, 0, len(session.Files))
+	for _, file := range session.Files {
+		if len(file.UploadedChunks) != file.ChunkCount {
+			cleanup()
+			return nil, func() {}, fmt.Errorf("file %s is missing chunks", file.Name)
+		}
+		assembledPath := filepath.Join(assembledDir, file.ID)
+		target, err := os.OpenFile(assembledPath, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0o600)
+		if err != nil {
+			cleanup()
+			return nil, func() {}, err
+		}
+		var written int64
+		for i := 0; i < file.ChunkCount; i++ {
+			select {
+			case <-ctx.Done():
+				_ = target.Close()
+				cleanup()
+				return nil, func() {}, ctx.Err()
+			default:
+			}
+			chunk, err := os.Open(s.resumableChunkPath(session.ID, file.ID, i))
+			if err != nil {
+				_ = target.Close()
+				cleanup()
+				return nil, func() {}, fmt.Errorf("file %s is missing chunks", file.Name)
+			}
+			n, copyErr := io.Copy(target, chunk)
+			closeErr := chunk.Close()
+			if copyErr != nil {
+				_ = target.Close()
+				cleanup()
+				return nil, func() {}, copyErr
+			}
+			if closeErr != nil {
+				_ = target.Close()
+				cleanup()
+				return nil, func() {}, closeErr
+			}
+			written += n
+		}
+		if err := target.Close(); err != nil {
+			cleanup()
+			return nil, func() {}, err
+		}
+		if written != file.Size {
+			cleanup()
+			return nil, func() {}, fmt.Errorf("assembled file size mismatch")
+		}
+		staged = append(staged, StagedUploadFile{
+			Filename: file.Name,
+			FileSize: file.Size,
+			MIMEType: file.ContentType,
+			Path:     assembledPath,
+		})
+	}
+	return staged, cleanup, nil
+}
+
+func resumableSessionWritable(session ResumableSession) error {
+	if session.Status != ResumableStatusUploading {
+		return fmt.Errorf("upload session is not active")
+	}
+	if !session.ExpiresAt.After(time.Now().UTC()) {
+		return fmt.Errorf("upload session expired")
+	}
+	return nil
+}
+
+func expectedChunkSize(fileSize, chunkSize int64, index int) int64 {
+	offset := int64(index) * chunkSize
+	remaining := fileSize - offset
+	if remaining < 0 {
+		return 0
+	}
+	if remaining > chunkSize {
+		return chunkSize
+	}
+	return remaining
+}
+
+func addChunkIndex(chunks []int, index int) []int {
+	for _, chunk := range chunks {
+		if chunk == index {
+			return chunks
+		}
+	}
+	chunks = append(chunks, index)
+	sort.Ints(chunks)
+	return chunks
+}
+
+func (s *UploadService) resumableSessionDir(sessionID string) string {
+	return filepath.Join(s.dataDir, "tmp", "uploads", sessionID)
+}
+
+func (s *UploadService) resumableFileDir(sessionID, fileID string) string {
+	return filepath.Join(s.resumableSessionDir(sessionID), fileID)
+}
+
+func (s *UploadService) resumableChunkPath(sessionID, fileID string, index int) string {
+	return filepath.Join(s.resumableFileDir(sessionID, fileID), fmt.Sprintf("%06d.part", index))
+}

backend/libs/services/upload.go

@@ -42,6 +42,8 @@ type UploadOptions struct {
 	ExpiresInMinutes  int
 	MaxDownloads      int
 	Password          string
+	PasswordSalt      string
+	PasswordHash      string
 	ObfuscateMetadata bool
 	OwnerID           string
 	CollectionID      string
@@ -50,6 +52,56 @@ type UploadOptions struct {
 	StorageBackendID  string
 }
 
+type IncomingFile interface {
+	Name() string
+	Size() int64
+	ContentType() string
+	Open() (io.ReadCloser, error)
+}
+
+type multipartIncomingFile struct {
+	header *multipart.FileHeader
+}
+
+func (f multipartIncomingFile) Name() string {
+	return f.header.Filename
+}
+
+func (f multipartIncomingFile) Size() int64 {
+	return f.header.Size
+}
+
+func (f multipartIncomingFile) ContentType() string {
+	return f.header.Header.Get("Content-Type")
+}
+
+func (f multipartIncomingFile) Open() (io.ReadCloser, error) {
+	return f.header.Open()
+}
+
+type StagedUploadFile struct {
+	Filename string
+	FileSize int64
+	MIMEType string
+	Path     string
+}
+
+func (f StagedUploadFile) Name() string {
+	return f.Filename
+}
+
+func (f StagedUploadFile) Size() int64 {
+	return f.FileSize
+}
+
+func (f StagedUploadFile) ContentType() string {
+	return f.MIMEType
+}
+
+func (f StagedUploadFile) Open() (io.ReadCloser, error) {
+	return os.Open(f.Path)
+}
+
 type Box struct {
 	ID               string    `json:"id"`
 	OwnerID          string    `json:"ownerId,omitempty"`
@@ -198,6 +250,10 @@ func (s *UploadService) ValidateSize(size int64) error {
 }
 
 func (s *UploadService) CreateBox(files []*multipart.FileHeader, opts UploadOptions) (UploadResult, error) {
+	return s.CreateBoxFromIncoming(multipartIncomingFiles(files), opts)
+}
+
+func (s *UploadService) CreateBoxFromIncoming(files []IncomingFile, opts UploadOptions) (UploadResult, error) {
 	if len(files) == 0 {
 		return UploadResult{}, fmt.Errorf("no files were uploaded")
 	}
@@ -232,13 +288,16 @@ func (s *UploadService) CreateBox(files []*multipart.FileHeader, opts UploadOpti
 	}
 	deleteToken := randomID(32)
 	box.DeleteTokenHash = deleteTokenHash(box.ID, deleteToken)
-	if strings.TrimSpace(opts.Password) != "" {
+	if strings.TrimSpace(opts.PasswordHash) != "" {
+		box.PasswordSalt = opts.PasswordSalt
+		box.PasswordHash = opts.PasswordHash
+	} else if strings.TrimSpace(opts.Password) != "" {
 		salt, hash := hashPassword(opts.Password)
 		box.PasswordSalt = salt
 		box.PasswordHash = hash
 	}
 
-	if err := s.writeFilesToBox(&box, files, opts); err != nil {
+	if err := s.writeIncomingFilesToBox(&box, files, opts); err != nil {
 		return UploadResult{}, err
 	}
 
@@ -261,6 +320,10 @@ func (s *UploadService) CreateBox(files []*multipart.FileHeader, opts UploadOpti
 // selection into a single box). The box keeps its original expiry, password and
 // other settings; only the new files are written.
 func (s *UploadService) AppendFiles(boxID string, files []*multipart.FileHeader, opts UploadOptions) (UploadResult, error) {
+	return s.AppendIncomingFiles(boxID, multipartIncomingFiles(files), opts)
+}
+
+func (s *UploadService) AppendIncomingFiles(boxID string, files []IncomingFile, opts UploadOptions) (UploadResult, error) {
 	if len(files) == 0 {
 		return UploadResult{}, fmt.Errorf("no files were uploaded")
 	}
@@ -268,7 +331,7 @@ func (s *UploadService) AppendFiles(boxID string, files []*multipart.FileHeader,
 	if err != nil {
 		return UploadResult{}, err
 	}
-	if err := s.writeFilesToBox(&box, files, opts); err != nil {
+	if err := s.writeIncomingFilesToBox(&box, files, opts); err != nil {
 		return UploadResult{}, err
 	}
 	if err := s.SaveBox(box); err != nil {
@@ -289,14 +352,26 @@ func (s *UploadService) AppendFiles(boxID string, files []*multipart.FileHeader,
 // appends the file metadata to box.Files. The box's StorageBackendID determines
 // where files land, so it works for both new and existing boxes.
 func (s *UploadService) writeFilesToBox(box *Box, files []*multipart.FileHeader, opts UploadOptions) error {
+	return s.writeIncomingFilesToBox(box, multipartIncomingFiles(files), opts)
+}
+
+func multipartIncomingFiles(files []*multipart.FileHeader) []IncomingFile {
+	incoming := make([]IncomingFile, 0, len(files))
+	for _, file := range files {
+		incoming = append(incoming, multipartIncomingFile{header: file})
+	}
+	return incoming
+}
+
+func (s *UploadService) writeIncomingFilesToBox(box *Box, files []IncomingFile, opts UploadOptions) error {
 	backend, err := s.storage.Backend(box.StorageBackendID)
 	if err != nil {
 		return err
 	}
 
-	for _, header := range files {
+	for _, incoming := range files {
 		if !opts.SkipSizeLimit {
-			if err := s.ValidateSize(header.Size); err != nil {
+			if err := s.ValidateSize(incoming.Size()); err != nil {
 				return err
 			}
 		}
@@ -306,15 +381,15 @@ func (s *UploadService) writeFilesToBox(box *Box, files []*multipart.FileHeader,
 			maxSize = 0
 		}
 
-		file, err := header.Open()
+		file, err := incoming.Open()
 		if err != nil {
 			return err
 		}
 
 		fileID := randomID(8)
-		storedName := "@each@" + fileID + strings.ToLower(filepath.Ext(header.Filename))
+		storedName := "@each@" + fileID + strings.ToLower(filepath.Ext(incoming.Name()))
 		objectKey := boxObjectKey(box.ID, storedName)
-		contentType := header.Header.Get("Content-Type")
+		contentType := incoming.ContentType()
 		if contentType == "" {
 			buffer := make([]byte, 512)
 			n, _ := file.Read(buffer)
@@ -324,7 +399,7 @@ func (s *UploadService) writeFilesToBox(box *Box, files []*multipart.FileHeader,
 			}
 		}
 
-		if err := s.writeUploadedObject(context.Background(), backend, objectKey, file, header.Size, maxSize, contentType); err != nil {
+		if err := s.writeUploadedObject(context.Background(), backend, objectKey, file, incoming.Size(), maxSize, contentType); err != nil {
 			file.Close()
 			return err
 		}
@@ -332,9 +407,9 @@ func (s *UploadService) writeFilesToBox(box *Box, files []*multipart.FileHeader,
 
 		box.Files = append(box.Files, File{
 			ID:          fileID,
-			Name:        filepath.Base(header.Filename),
+			Name:        filepath.Base(incoming.Name()),
 			StoredName:  storedName,
-			Size:        header.Size,
+			Size:        incoming.Size(),
 			ContentType: contentType,
 			PreviewKind: previewKind(contentType),
 			ObjectKey:   objectKey,
@@ -931,21 +1006,17 @@ func writeUploadedFile(path string, source multipart.File, maxSize int64) error
 	return nil
 }
 
-func (s *UploadService) writeUploadedObject(ctx context.Context, backend StorageBackend, key string, source multipart.File, size, maxSize int64, contentType string) error {
+func (s *UploadService) writeUploadedObject(ctx context.Context, backend StorageBackend, key string, source io.Reader, size, maxSize int64, contentType string) error {
 	var reader io.Reader = source
+	putSize := size
 	if maxSize > 0 {
-		reader = io.LimitReader(source, maxSize+1)
+		if size > maxSize {
-		var buffer bytes.Buffer
-		written, err := io.Copy(&buffer, reader)
-		if err != nil {
-			return err
-		}
-		if written > maxSize {
 			return fmt.Errorf("file exceeds max upload size")
 		}
-		return backend.Put(ctx, key, bytes.NewReader(buffer.Bytes()), written, contentType)
+		reader = io.LimitReader(source, maxSize)
+		putSize = size
 	}
-	return backend.Put(ctx, key, reader, size, contentType)
+	return backend.Put(ctx, key, reader, putSize, contentType)
 }
 
 func boxObjectKey(boxID, name string) string {

backend/libs/services/upload_test.go

@@ -126,6 +126,166 @@ func TestLocalStorageBackendAndLegacyFallback(t *testing.T) {
 	object.Body.Close()
 }
 
+func TestResumableSessionUploadOutOfOrderAndComplete(t *testing.T) {
+	service := newTestUploadService(t)
+	session, err := service.CreateResumableSession([]ResumableFileInput{{
+		Name:        "note.txt",
+		Size:        11,
+		ContentType: "text/plain",
+		Fingerprint: "sha256:first-chunk",
+	}}, UploadOptions{MaxDays: 1, Password: "secret"}, 4, time.Hour)
+	if err != nil {
+		t.Fatalf("CreateResumableSession returned error: %v", err)
+	}
+	if session.Options.Password != "" || session.Options.PasswordHash == "" || session.Options.PasswordSalt == "" {
+		t.Fatalf("resumable session did not hash password before storage: %+v", session.Options)
+	}
+	if session.Files[0].ChunkCount != 3 {
+		t.Fatalf("ChunkCount = %d, want 3", session.Files[0].ChunkCount)
+	}
+	if session.Files[0].Fingerprint != "sha256:first-chunk" {
+		t.Fatalf("Fingerprint = %q", session.Files[0].Fingerprint)
+	}
+	for index, body := range map[int]string{2: "rld", 0: "hell", 1: "o wo"} {
+		updated, err := service.PutResumableChunk(testContext(), session.ID, session.Files[0].ID, index, strings.NewReader(body))
+		if err != nil {
+			t.Fatalf("PutResumableChunk(%d) returned error: %v", index, err)
+		}
+		if len(updated.Files[0].UploadedChunks) == 0 {
+			t.Fatalf("UploadedChunks was not updated")
+		}
+	}
+	result, completed, err := service.CompleteResumableSession(testContext(), session.ID)
+	if err != nil {
+		t.Fatalf("CompleteResumableSession returned error: %v", err)
+	}
+	if completed.Status != ResumableStatusCompleted || completed.BoxID != result.BoxID {
+		t.Fatalf("completed session = %+v, result = %+v", completed, result)
+	}
+	box := getTestBox(t, service, result.BoxID)
+	if box.PasswordHash == "" || box.PasswordSalt == "" || box.PasswordHash != session.Options.PasswordHash {
+		t.Fatalf("completed box did not preserve hashed password")
+	}
+	object, err := service.OpenFileObject(testContext(), box, box.Files[0])
+	if err != nil {
+		t.Fatalf("OpenFileObject returned error: %v", err)
+	}
+	data, err := io.ReadAll(object.Body)
+	object.Body.Close()
+	if err != nil {
+		t.Fatalf("ReadAll returned error: %v", err)
+	}
+	if string(data) != "hello world" {
+		t.Fatalf("object body = %q", string(data))
+	}
+	if _, err := os.Stat(service.resumableSessionDir(session.ID)); !os.IsNotExist(err) {
+		t.Fatalf("resumable temp dir after complete error = %v, want os.ErrNotExist", err)
+	}
+}
+
+func TestResumableCompleteRejectsMissingChunks(t *testing.T) {
+	service := newTestUploadService(t)
+	session, err := service.CreateResumableSession([]ResumableFileInput{{
+		Name:        "note.txt",
+		Size:        8,
+		ContentType: "text/plain",
+	}}, UploadOptions{MaxDays: 1}, 4, time.Hour)
+	if err != nil {
+		t.Fatalf("CreateResumableSession returned error: %v", err)
+	}
+	if _, err := service.PutResumableChunk(testContext(), session.ID, session.Files[0].ID, 0, strings.NewReader("hell")); err != nil {
+		t.Fatalf("PutResumableChunk returned error: %v", err)
+	}
+	if _, _, err := service.CompleteResumableSession(testContext(), session.ID); err == nil {
+		t.Fatalf("CompleteResumableSession accepted missing chunks")
+	}
+}
+
+func TestResumableSessionCanAddFilesBeforeComplete(t *testing.T) {
+	service := newTestUploadService(t)
+	session, err := service.CreateResumableSession([]ResumableFileInput{{
+		Name:        "one.txt",
+		Size:        4,
+		ContentType: "text/plain",
+		Fingerprint: "one",
+	}}, UploadOptions{MaxDays: 1}, 4, time.Hour)
+	if err != nil {
+		t.Fatalf("CreateResumableSession returned error: %v", err)
+	}
+	if _, err := service.PutResumableChunk(testContext(), session.ID, session.Files[0].ID, 0, strings.NewReader("one!")); err != nil {
+		t.Fatalf("PutResumableChunk one returned error: %v", err)
+	}
+	updated, err := service.AddResumableFiles(session.ID, []ResumableFileInput{{
+		Name:        "two.txt",
+		Size:        4,
+		ContentType: "text/plain",
+		Fingerprint: "two",
+	}})
+	if err != nil {
+		t.Fatalf("AddResumableFiles returned error: %v", err)
+	}
+	if len(updated.Files) != 2 {
+		t.Fatalf("files after add = %d, want 2", len(updated.Files))
+	}
+	if updated.Files[0].UploadedChunks[0] != 0 {
+		t.Fatalf("existing uploaded chunk was not preserved: %+v", updated.Files[0])
+	}
+	if _, err := service.AddResumableFiles(session.ID, []ResumableFileInput{{
+		Name:        "two.txt",
+		Size:        4,
+		ContentType: "text/plain",
+		Fingerprint: "two",
+	}}); err != nil {
+		t.Fatalf("duplicate AddResumableFiles returned error: %v", err)
+	}
+	updated, err = service.GetResumableSession(session.ID)
+	if err != nil {
+		t.Fatalf("GetResumableSession returned error: %v", err)
+	}
+	if len(updated.Files) != 2 {
+		t.Fatalf("duplicate add changed file count to %d", len(updated.Files))
+	}
+	if _, err := service.PutResumableChunk(testContext(), session.ID, updated.Files[1].ID, 0, strings.NewReader("two!")); err != nil {
+		t.Fatalf("PutResumableChunk two returned error: %v", err)
+	}
+	result, _, err := service.CompleteResumableSession(testContext(), session.ID)
+	if err != nil {
+		t.Fatalf("CompleteResumableSession returned error: %v", err)
+	}
+	box := getTestBox(t, service, result.BoxID)
+	if len(box.Files) != 2 {
+		t.Fatalf("completed box file count = %d, want 2", len(box.Files))
+	}
+}
+
+func TestResumableCleanupRemovesExpiredSessionsAndChunks(t *testing.T) {
+	service := newTestUploadService(t)
+	session, err := service.CreateResumableSession([]ResumableFileInput{{
+		Name:        "note.txt",
+		Size:        4,
+		ContentType: "text/plain",
+	}}, UploadOptions{MaxDays: 1}, 4, time.Millisecond)
+	if err != nil {
+		t.Fatalf("CreateResumableSession returned error: %v", err)
+	}
+	if _, err := service.PutResumableChunk(testContext(), session.ID, session.Files[0].ID, 0, strings.NewReader("hell")); err != nil {
+		t.Fatalf("PutResumableChunk returned error: %v", err)
+	}
+	cleaned, err := service.CleanupExpiredResumableSessions(time.Now().UTC().Add(time.Hour))
+	if err != nil {
+		t.Fatalf("CleanupExpiredResumableSessions returned error: %v", err)
+	}
+	if cleaned != 1 {
+		t.Fatalf("cleaned = %d, want 1", cleaned)
+	}
+	if _, err := service.GetResumableSession(session.ID); !os.IsNotExist(err) {
+		t.Fatalf("GetResumableSession after cleanup error = %v, want os.ErrNotExist", err)
+	}
+	if _, err := os.Stat(service.resumableSessionDir(session.ID)); !os.IsNotExist(err) {
+		t.Fatalf("resumable temp dir after cleanup error = %v, want os.ErrNotExist", err)
+	}
+}
+
 func TestContaboStorageConfigAllowsDisplayNamesWithSpaces(t *testing.T) {
 	service := newTestUploadService(t)
 	cfg, err := service.Storage().CreateS3Backend(StorageBackendConfig{

backend/static/css/20-upload.css

@@ -335,10 +335,13 @@ button {
 .file-progress-side {
   width: min(10rem, 32vw);
   display: grid;
+  grid-template-columns: minmax(0, 1fr) auto;
   gap: 0.35rem;
+  align-items: center;
 }
 
 .file-progress-percent {
+  grid-column: 1 / -1;
   color: var(--muted-foreground);
   font-size: 0.75rem;
   text-align: right;
@@ -349,6 +352,25 @@ button {
   margin-top: 0;
 }
 
+.upload-file-remove {
+  width: 1.65rem;
+  height: 1.65rem;
+  min-height: 1.65rem;
+  padding: 0;
+  border-color: var(--border);
+  border-radius: 999px;
+  color: var(--muted-foreground);
+  background: var(--surface-1);
+  font-size: 1rem;
+  line-height: 1;
+}
+
+.upload-file-remove:hover {
+  color: var(--foreground);
+  border-color: var(--primary);
+  background: var(--surface-1-hover);
+}
+
 .result-item small,
 .download-item small,
 .result-item code,

backend/static/js/40-upload.js

@@ -13,6 +13,7 @@
   const copyURL = document.querySelector("#copy-url");
   const openBox = document.querySelector("#open-box");
   const manageLink = document.querySelector("#manage-link");
+  const RESUMABLE_SESSIONS_KEY = "warpbox-resumable-sessions";
 
   if (!form || !dropZone || !fileInput) {
     return;
@@ -42,6 +43,7 @@
 
   let latestBoxURL = "";
   let selectedFiles = [];
+  let uploadLocked = false;
 
   ["dragenter", "dragover"].forEach((eventName) => {
     dropZone.addEventListener(eventName, (event) => {
@@ -57,33 +59,52 @@
     });
   });
 
-  dropZone.addEventListener("drop", (event) => {
+  document.addEventListener("dragover", (event) => {
-    if (event.dataTransfer && event.dataTransfer.files.length > 0) {
+    if (event.dataTransfer && Array.from(event.dataTransfer.types || []).includes("Files")) {
-      fileInput.files = event.dataTransfer.files;
+      event.preventDefault();
-      updateSelectedState(event.dataTransfer.files);
     }
   });
 
-  fileInput.addEventListener("change", () => updateSelectedState(fileInput.files));
+  document.addEventListener("drop", (event) => {
+    if (!event.dataTransfer || !event.dataTransfer.files.length) {
+      return;
+    }
+    event.preventDefault();
+    if (!dropZone.contains(event.target)) {
+      addSelectedFiles(event.dataTransfer.files);
+    }
+  });
+
+  dropZone.addEventListener("drop", (event) => {
+    if (event.dataTransfer && event.dataTransfer.files.length > 0) {
+      addSelectedFiles(event.dataTransfer.files);
+    }
+  });
+
+  fileInput.addEventListener("change", () => {
+    addSelectedFiles(fileInput.files);
+    fileInput.value = "";
+  });
 
   form.addEventListener("submit", async (event) => {
     event.preventDefault();
-    if (!fileInput.files || fileInput.files.length === 0) {
+    if (selectedFiles.length === 0) {
       updateStatus("Choose at least one file first.");
       return;
     }
 
     const submit = form.querySelector("button[type='submit']");
-    const formData = new FormData(form);
+    const formData = uploadFormData();
-    selectedFiles = Array.from(fileInput.files);
     renderQueue(selectedFiles, "queued");
     setLoading(true, submit);
 
     try {
-      const payload = await uploadWithProgress(form.action, formData, selectedFiles);
+      const payload = await uploadResumable(form.action, formData, selectedFiles);
       renderResult(payload);
       form.reset();
-      updateSelectedState([]);
+      selectedFiles = [];
+      fileInput.value = "";
+      updateSelectedState();
     } catch (error) {
       updateStatus(error.message || "Upload failed");
     } finally {
@@ -97,8 +118,27 @@
     });
   }
 
-  function updateSelectedState(files) {
+  function addSelectedFiles(files) {
-    selectedFiles = Array.from(files || []);
+    if (uploadLocked) {
+      return;
+    }
+    Array.from(files || []).forEach((file) => {
+      if (!selectedFiles.some((existing) => fileIdentity(existing) === fileIdentity(file))) {
+        selectedFiles.push(file);
+      }
+    });
+    updateSelectedState();
+  }
+
+  function removeSelectedFile(index) {
+    if (uploadLocked) {
+      return;
+    }
+    selectedFiles.splice(index, 1);
+    updateSelectedState();
+  }
+
+  function updateSelectedState() {
     const count = selectedFiles.length || 0;
     const title = dropZone.querySelector(".drop-title");
     if (title) {
@@ -116,6 +156,7 @@
   }
 
   function setLoading(isLoading, submit) {
+    uploadLocked = isLoading;
     if (progress) {
       progress.hidden = !isLoading;
     }
@@ -201,18 +242,294 @@
     });
   }
 
+  async function uploadResumable(fallbackUrl, formData, files) {
+    if (!window.fetch || typeof Blob === "undefined") {
+      return uploadWithProgress(fallbackUrl, formData, files);
+    }
+
+    updateStatus("Fingerprinting files...");
+    const fingerprints = await Promise.all(files.map((file) => fileFingerprint(file)));
+    const createPayload = {
+      files: files.map((file, index) => ({
+        name: file.name,
+        size: file.size,
+        contentType: file.type || "application/octet-stream",
+        fingerprint: fingerprints[index],
+      })),
+      expiresMinutes: parseInt(formData.get("expires_minutes") || "0", 10) || 0,
+      maxDownloads: parseInt(formData.get("max_downloads") || "0", 10) || 0,
+      password: formData.get("password") || "",
+      obfuscateMetadata: formData.get("obfuscate_metadata") === "on",
+      collectionId: formData.get("collection_id") || "",
+    };
+    const persistable = !createPayload.password;
+    let session = persistable ? await findResumableSession(createPayload) : null;
+    if (session) {
+      session = await addMissingResumableFiles(session, createPayload);
+    }
+    if (!session || session.status !== "uploading") {
+      try {
+        session = await createResumableSession(createPayload);
+      } catch (error) {
+        if ((error.message || "").toLowerCase().includes("resumable uploads are disabled")) {
+          return uploadWithProgress(fallbackUrl, formData, files);
+        }
+        throw error;
+      }
+      if (persistable) {
+        saveResumableSession(session, createPayload);
+      }
+    }
+    const sessionFiles = files.map((file, index) => matchSessionFile(session, createPayload.files[index]));
+    if (sessionFiles.some((file) => !file)) {
+      throw new Error("Upload session could not match the selected files");
+    }
+
+    updateStatus("Uploading...");
+    const totalBytes = files.reduce((sum, file) => sum + file.size, 0);
+    const completedByFile = new Array(files.length).fill(0);
+    sessionFiles.forEach((sessionFile, index) => {
+      completedByFile[index] = uploadedBytesForSessionFile(sessionFile, session.chunkSize);
+      setSingleFileProgress(index, files[index], percentForBytes(completedByFile[index], files[index].size));
+    });
+    setTotalProgress(percentForBytes(completedByFile.reduce((sum, bytes) => sum + bytes, 0), totalBytes));
+
+    for (let fileIndex = 0; fileIndex < files.length; fileIndex++) {
+      const file = files[fileIndex];
+      const sessionFile = sessionFiles[fileIndex];
+      const uploaded = new Set(sessionFile.uploadedChunks || []);
+      for (let chunkIndex = 0; chunkIndex < sessionFile.chunkCount; chunkIndex++) {
+        if (uploaded.has(chunkIndex)) {
+          continue;
+        }
+        const start = chunkIndex * session.chunkSize;
+        const end = Math.min(file.size, start + session.chunkSize);
+        await uploadChunk(session.sessionId, sessionFile.id, chunkIndex, file.slice(start, end), (loaded) => {
+          const currentTotal = completedByFile.reduce((sum, bytes) => sum + bytes, 0) + loaded;
+          setTotalProgress(percentForBytes(currentTotal, totalBytes));
+          setSingleFileProgress(fileIndex, file, percentForBytes(completedByFile[fileIndex] + loaded, file.size));
+          updateStatus(`${percentForBytes(currentTotal, totalBytes)}%`);
+        });
+        completedByFile[fileIndex] += end - start;
+        uploaded.add(chunkIndex);
+        sessionFile.uploadedChunks = Array.from(uploaded).sort((a, b) => a - b);
+        if (persistable) {
+          saveResumableSession(session, createPayload);
+        }
+      }
+      setSingleFileProgress(fileIndex, file, 100);
+    }
+
+    const resultPayload = await completeResumableSession(session.sessionId);
+    if (persistable) {
+      removeResumableSession(session.sessionId);
+    }
+    setTotalProgress(100);
+    setFileProgress(files, 100);
+    return resultPayload;
+  }
+
+  async function createResumableSession(payload) {
+    const response = await fetch("/api/v1/uploads/resumable", {
+      method: "POST",
+      headers: {
+        "Accept": "application/json",
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify(payload),
+    });
+    return readUploadJSON(response, "Upload session could not be created");
+  }
+
+  async function fetchResumableStatus(sessionID) {
+    const response = await fetch(`/api/v1/uploads/resumable/${encodeURIComponent(sessionID)}`, {
+      headers: { "Accept": "application/json" },
+    });
+    return readUploadJSON(response, "Upload session could not be resumed");
+  }
+
+  async function addResumableFiles(sessionID, files) {
+    const response = await fetch(`/api/v1/uploads/resumable/${encodeURIComponent(sessionID)}/files`, {
+      method: "POST",
+      headers: {
+        "Accept": "application/json",
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify({ files }),
+    });
+    return readUploadJSON(response, "Upload session files could not be added");
+  }
+
+  function uploadChunk(sessionID, fileID, chunkIndex, chunk, onProgress) {
+    return new Promise((resolve, reject) => {
+      const request = new XMLHttpRequest();
+      request.open("PUT", `/api/v1/uploads/resumable/${encodeURIComponent(sessionID)}/files/${encodeURIComponent(fileID)}/chunks/${chunkIndex}`);
+      request.setRequestHeader("Accept", "application/json");
+      request.upload.addEventListener("progress", (event) => {
+        if (event.lengthComputable && onProgress) {
+          onProgress(event.loaded);
+        }
+      });
+      request.addEventListener("load", () => {
+        if (request.status < 200 || request.status >= 300) {
+          let payload = {};
+          try {
+            payload = JSON.parse(request.responseText || "{}");
+          } catch (error) {
+            payload = {};
+          }
+          reject(new Error(payload.error || "Chunk upload failed"));
+          return;
+        }
+        resolve();
+      });
+      request.addEventListener("error", () => reject(new Error("Network error during chunk upload")));
+      request.addEventListener("abort", () => reject(new Error("Chunk upload aborted")));
+      request.send(chunk);
+    });
+  }
+
+  async function completeResumableSession(sessionID) {
+    const response = await fetch(`/api/v1/uploads/resumable/${encodeURIComponent(sessionID)}/complete`, {
+      method: "POST",
+      headers: { "Accept": "application/json" },
+    });
+    return readUploadJSON(response, "Upload could not be completed");
+  }
+
+  async function readUploadJSON(response, fallback) {
+    let payload = {};
+    try {
+      payload = await response.json();
+    } catch (error) {
+      payload = {};
+    }
+    if (!response.ok) {
+      throw new Error(payload.error || fallback);
+    }
+    return payload;
+  }
+
+  async function findResumableSession(payload) {
+    const records = loadResumableSessions();
+    const optionKey = resumableOptionKey(payload);
+    const selectedKeys = new Set(payload.files.map((file) => resumableFileKey(file)));
+    for (const record of records) {
+      if (record.optionKey !== optionKey) {
+        continue;
+      }
+      if (!record.files || !record.files.some((file) => selectedKeys.has(resumableFileKey(file)))) {
+        continue;
+      }
+      const session = await fetchResumableStatus(record.sessionId).catch(() => null);
+      if (!session || session.status !== "uploading") {
+        removeResumableSession(record.sessionId);
+        continue;
+      }
+      const sessionKeys = new Set(session.files.map((file) => resumableFileKey(file)));
+      const sessionHasOnlySelectedFiles = session.files.every((file) => selectedKeys.has(resumableFileKey(file)));
+      const selectedContainsSessionFile = Array.from(sessionKeys).some((key) => selectedKeys.has(key));
+      if (sessionHasOnlySelectedFiles && selectedContainsSessionFile) {
+        return session;
+      }
+    }
+    return null;
+  }
+
+  async function addMissingResumableFiles(session, payload) {
+    const existing = new Set(session.files.map((file) => resumableFileKey(file)));
+    const missing = payload.files.filter((file) => !existing.has(resumableFileKey(file)));
+    if (missing.length === 0) {
+      return session;
+    }
+    return addResumableFiles(session.sessionId, missing);
+  }
+
+  function matchSessionFile(session, file) {
+    const key = resumableFileKey(file);
+    return session.files.find((sessionFile) => resumableFileKey(sessionFile) === key) || null;
+  }
+
+  function resumableOptionKey(payload) {
+    return [
+      payload.expiresMinutes,
+      payload.maxDownloads,
+      payload.obfuscateMetadata ? "1" : "0",
+      payload.collectionId || "",
+    ].join(":");
+  }
+
+  function resumableFileKey(file) {
+    return [file.name, file.size, file.fingerprint || ""].join(":");
+  }
+
+  function loadResumableSessions() {
+    try {
+      const value = localStorage.getItem(RESUMABLE_SESSIONS_KEY);
+      const records = value ? JSON.parse(value) : [];
+      return Array.isArray(records) ? records : [];
+    } catch (error) {
+      return [];
+    }
+  }
+
+  function saveResumableSession(session, payload) {
+    try {
+      const records = loadResumableSessions().filter((record) => record.sessionId !== session.sessionId);
+      records.push({
+        sessionId: session.sessionId,
+        optionKey: resumableOptionKey(payload),
+        files: session.files.map((file) => ({
+          name: file.name,
+          size: file.size,
+          fingerprint: file.fingerprint || "",
+        })),
+        updatedAt: new Date().toISOString(),
+      });
+      localStorage.setItem(RESUMABLE_SESSIONS_KEY, JSON.stringify(records.slice(-25)));
+    } catch (error) {
+      /* ignore persistence failures */
+    }
+  }
+
+  function removeResumableSession(sessionID) {
+    try {
+      const records = loadResumableSessions().filter((record) => record.sessionId !== sessionID);
+      localStorage.setItem(RESUMABLE_SESSIONS_KEY, JSON.stringify(records));
+    } catch (error) {
+      /* ignore persistence failures */
+    }
+  }
+
+  function uploadedBytesForSessionFile(file, chunkSize) {
+    return (file.uploadedChunks || []).reduce((sum, index) => {
+      const start = index * chunkSize;
+      const end = Math.min(file.size, start + chunkSize);
+      return sum + Math.max(0, end - start);
+    }, 0);
+  }
+
+  function percentForBytes(bytes, total) {
+    if (!total) {
+      return 100;
+    }
+    return Math.max(0, Math.min(100, Math.round((bytes / total) * 100)));
+  }
+
   function renderQueue(files, status) {
     if (!uploadQueue) {
       return;
     }
     uploadQueue.hidden = files.length === 0;
     uploadQueue.replaceChildren();
-    files.forEach((file) => {
+    files.forEach((file, index) => {
       uploadQueue.append(createFileRow({
         name: file.name,
         meta: window.Warpbox.formatBytes(file.size),
         progress: status === "queued" ? 0 : 100,
         status,
+        index,
+        removable: status === "queued",
       }));
     });
   }
@@ -221,6 +538,7 @@
     const row = document.createElement("div");
     row.className = "result-item upload-file-row";
     row.dataset.fileName = file.name;
+    row.dataset.fileIndex = file.index || 0;
 
     const body = document.createElement("span");
     const name = document.createElement("strong");
@@ -242,11 +560,47 @@
     fill.style.transform = `scaleX(${file.progress / 100})`;
     bar.append(fill);
     side.append(percent, bar);
+    if (file.removable) {
+      const remove = document.createElement("button");
+      remove.className = "upload-file-remove";
+      remove.type = "button";
+      remove.setAttribute("aria-label", `Remove ${file.name}`);
+      remove.textContent = "×";
+      remove.addEventListener("click", () => removeSelectedFile(file.index || 0));
+      side.append(remove);
+    }
 
     row.append(body, side);
     return row;
   }
 
+  function uploadFormData() {
+    const formData = new FormData(form);
+    formData.delete("file");
+    selectedFiles.forEach((file) => {
+      formData.append("file", file, file.name);
+    });
+    return formData;
+  }
+
+  function fileIdentity(file) {
+    return [file.name, file.size, file.lastModified || 0].join(":");
+  }
+
+  async function fileFingerprint(file) {
+    if (!window.crypto || !window.crypto.subtle || !file.slice || typeof TextEncoder === "undefined") {
+      return fileIdentity(file);
+    }
+    const sampleSize = Math.min(file.size, 1024 * 1024);
+    const sample = await file.slice(0, sampleSize).arrayBuffer();
+    const metadata = new TextEncoder().encode([file.name, file.size, file.lastModified || 0, sampleSize].join(":"));
+    const combined = new Uint8Array(metadata.byteLength + sample.byteLength);
+    combined.set(metadata, 0);
+    combined.set(new Uint8Array(sample), metadata.byteLength);
+    const digest = await window.crypto.subtle.digest("SHA-256", combined);
+    return Array.from(new Uint8Array(digest)).map((byte) => byte.toString(16).padStart(2, "0")).join("");
+  }
+
   function setTotalProgress(percent) {
     if (totalProgressBar) {
       totalProgressBar.style.transform = `scaleX(${Math.max(0, Math.min(100, percent)) / 100})`;
@@ -271,4 +625,23 @@
       }
     });
   }
+
+  function setSingleFileProgress(index, file, progress) {
+    if (!uploadQueue) {
+      return;
+    }
+    const row = uploadQueue.querySelector(`.upload-file-row[data-file-index="${index}"]`);
+    if (!row) {
+      return;
+    }
+    const percent = row.querySelector(".file-progress-percent");
+    const fill = row.querySelector(".file-progress span");
+    const normalized = Math.max(0, Math.min(100, progress));
+    if (percent) {
+      percent.textContent = `${normalized}%`;
+    }
+    if (fill) {
+      fill.style.transform = `scaleX(${normalized / 100})`;
+    }
+  }
 })();

backend/templates/pages/api.html

@@ -14,6 +14,10 @@
         <h2>Endpoints</h2>
         <dl class="endpoint-list">
           <div><dt>Upload</dt><dd><code>POST /api/v1/upload</code></dd></div>
+          <div><dt>Resumable create</dt><dd><code>POST /api/v1/uploads/resumable</code></dd></div>
+          <div><dt>Resumable status</dt><dd><code>GET /api/v1/uploads/resumable/{sessionID}</code></dd></div>
+          <div><dt>Resumable chunk</dt><dd><code>PUT /api/v1/uploads/resumable/{sessionID}/files/{fileID}/chunks/{index}</code></dd></div>
+          <div><dt>Resumable complete</dt><dd><code>POST /api/v1/uploads/resumable/{sessionID}/complete</code></dd></div>
           <div><dt>Health</dt><dd><code>GET /health</code></dd></div>
           <div><dt>Request schema</dt><dd><a href="/api/v1/schemas/upload-request.json"><code>/api/v1/schemas/upload-request.json</code></a></dd></div>
           <div><dt>Response schema</dt><dd><a href="/api/v1/schemas/upload-response.json"><code>/api/v1/schemas/upload-response.json</code></a></dd></div>
@@ -21,6 +25,28 @@
       </div>
     </article>
 
+    <article class="card docs-card docs-card-wide">
+      <div class="card-content">
+        <h2>Resumable uploads</h2>
+        <p>Browser uploads use the resumable API by default. Custom clients can use the same flow: create a session with file metadata, upload exact-sized chunks, then complete the session. Chunks are temporary and are cleaned if the session expires.</p>
+        <pre><code># 1. Create a session.
+curl -s {{.Data.BaseURL}}/api/v1/uploads/resumable \
+  -H 'Accept: application/json' \
+  -H 'Content-Type: application/json' \
+  -d '{"files":[{"name":"report.pdf","size":1048576,"contentType":"application/pdf"}],"expiresMinutes":1440}'
+
+# 2. Upload each chunk using the returned sessionId, file id, and chunkSize.
+dd if=./report.pdf bs=8388608 count=1 skip=0 2>/dev/null | \
+  curl -X PUT --data-binary @- \
+  {{.Data.BaseURL}}/api/v1/uploads/resumable/SESSION_ID/files/FILE_ID/chunks/0
+
+# 3. Complete after all chunks are present. The response is the normal upload JSON.
+curl -X POST -H 'Accept: application/json' \
+  {{.Data.BaseURL}}/api/v1/uploads/resumable/SESSION_ID/complete</code></pre>
+        <p class="muted-copy">For authenticated uploads, send the same <code>Authorization: Bearer &lt;token&gt;</code> header on every resumable request. Incomplete chunks are stored under <code>data/tmp/uploads</code> before finalizing into the selected storage backend.</p>
+      </div>
+    </article>
+
     <article class="card docs-card">
       <div class="card-content">
         <h2>Curl upload</h2>

scripts/env/dev.env.example

@@ -9,6 +9,9 @@ WARPBOX_CLEANUP_ENABLED=true
 WARPBOX_CLEANUP_EVERY=1h
 WARPBOX_THUMBNAIL_ENABLED=true
 WARPBOX_THUMBNAIL_EVERY=1m
+WARPBOX_RESUMABLE_UPLOADS_ENABLED=true
+WARPBOX_RESUMABLE_CHUNK_MB=16
+WARPBOX_RESUMABLE_RETENTION_HOURS=1
 WARPBOX_MAX_UPLOAD_SIZE_MB=16384
 WARPBOX_ANONYMOUS_UPLOADS_ENABLED=true
 WARPBOX_ANONYMOUS_MAX_UPLOAD_MB=512