bookhoard/cover_image_serving_plan.md

# Cover & File Serving - Implementation Plan

## Overview

Fix file and cover image serving to support:
1. Multiple library folders in docker compose (flexible mount points)
2. Keep files with books (no hardcoded paths)
3. Store relative paths in database (for both files AND covers)
4. Serve everything via authenticated API endpoints
5. Mobile app compatibility (same auth for all requests)

## Architecture

### Current Behavior
- File path stored as absolute: `/app/uploads/Jane Austen/Pride and Prejudice/book.epub`
- Cover path stored as absolute: `/app/uploads/Jane Austen/Pride and Prejudice/cover.jpg`
- Frontend uses path directly - doesn't work (browser can't access container paths)
- No route serves `/app/uploads/*`

### Target Behavior
- File path stored as relative: `Jane Austen/Pride and Prejudice/book.epub`
- Cover path stored as relative: `Jane Austen/Pride and Prejudice/cover.jpg`
- Handler resolves relative path using library folder base path
- Authenticated static-style handler serves files: `/uploads/library-{id}/path/to/file`
- Backend resolves full URLs in API/SSR responses (one source of truth)
- Works with mobile apps, Kobo, KOReader devices via same endpoints

### URL Format
To handle same relative paths in different libraries, use:
```
/uploads/library-{library_id}/relative/path
```
- Requires JWT authentication (like API endpoints)
- Works for both covers and book files
- Single handler handles all file serving

### Universal Path Resolution
All handlers use the same `LibraryService.ResolveMediaPath()` function:
- MediaHandler (downloads)
- OPDSHandler (device cover images)
- Future handlers

This ensures one source of truth for path resolution.

---

## Phase 1: Update Scanner to Store Relative Paths (Files AND Covers)

### File: `internal/services/media_scanner.go`

#### Change 1: Store relative file path

**Location**: Where metadata.FilePath is set (multiple locations)

**Current code**:
```go
metadata.FilePath = path  // path is absolute like /app/uploads/Author/Book/file.epub
```

**New code**:
```go
metadata.FilePath = s.getRelativePath(path)
```

#### Change 2: Store relative cover path

**Location**: Around lines 514-517, 641-651, 832-837, 1056-1067, 1472

**Current code** (example at line 514-517):
```go
if len(coverImage) > 0 && metadata.CoverPath == "" {
    coverPath := path + ".cover.jpg"
    if err := os.WriteFile(coverPath, coverImage, 0644); err == nil {
        metadata.CoverPath = coverPath
    }
}
```

**New code**:
```go
if len(coverImage) > 0 && metadata.CoverPath == "" {
    coverPath := path + ".cover.jpg"
    if err := os.WriteFile(coverPath, coverImage, 0644); err == nil {
        // Store relative path - derive from library folder base
        metadata.CoverPath = s.getRelativePath(coverPath)
    }
}
```

#### Change 3: Add helper function

**Add new function** in `internal/services/media_scanner.go`:

```go
// getRelativePath converts absolute filesystem path to relative path
// using the library folder base path
func (s *MediaScanner) getRelativePath(absolutePath string) string {
    // Get the base folder paths from scanner
    for _, baseFolder := range s.folders {
        // Check if path is within this base folder
        if strings.HasPrefix(absolutePath, baseFolder) {
            // Return relative path (without leading slash)
            relPath := strings.TrimPrefix(absolutePath, baseFolder)
            // Remove leading slash if present
            relPath = strings.TrimPrefix(relPath, "/")
            return relPath
        }
    }
    // Fallback: if no match, return as-is (shouldn't happen)
    return absolutePath
}
```

**Note**: This uses `s.folders` which is already populated in the scanner.

#### Change 4: Update force rescan path handling

**Location**: Around line 1472 (in the force rescan/update flow)

Apply same `getRelativePath()` conversion when updating existing items.

---

## Phase 2: Create Path Resolution Helper (Service Layer)

### File: `internal/services/library_service.go` (or new file)

Create a reusable function that resolves relative paths to absolute filesystem paths:

```go
// ResolveMediaPath resolves a relative path to absolute filesystem path
// using the library's configured folder(s)
func (s *LibraryService) ResolveMediaPath(ctx context.Context, libraryID pgtype.UUID, relativePath string) (string, error) {
    // Get library folders for this library
    folders, err := s.db.GetLibraryFolders(ctx, libraryID)
    if err != nil || len(folders) == 0 {
        return "", fmt.Errorf("no library folders found for library")
    }

    // Try each folder - find one where the relative path makes sense
    for _, folder := range folders {
        fullPath := filepath.Join(folder.FolderPath, relativePath)
        if _, err := os.Stat(fullPath); err == nil {
            return fullPath, nil
        }
    }

    // Fallback: use first folder (file might not exist yet during scan)
    if len(folders) > 0 {
        return filepath.Join(folders[0].FolderPath, relativePath), nil
    }

    return "", fmt.Errorf("could not resolve path")
}
```

---

## Phase 3: Add URL Resolution Helper to MediaHandler

### Strategy

Use `LibraryService.ResolveMediaPath()` to resolve paths. Add a simple wrapper in the handler for convenience.

### File: `internal/handlers/media.go`

Add helper method that uses the service:

```go
// getFullFilePath returns the absolute filesystem path for a media item
// Uses LibraryService for resolution (one source of truth)
func (mh *MediaHandler) getFullFilePath(ctx context.Context, libraryID pgtype.UUID, relativePath string) (string, error) {
    if relativePath == "" {
        return "", fmt.Errorf("no file path")
    }
    
    // Check if already absolute (backward compatibility)
    if filepath.IsAbs(relativePath) {
        return relativePath, nil
    }
    
    // Use service for resolution (one source of truth)
    return mh.libraryService.ResolveMediaPath(ctx, libraryID, relativePath)
}
```

Note: The handler already has `libraryService` injected, so this just calls through to it.

---

## Phase 4: Update Download Handler to Use Relative Paths

### File: `internal/handlers/media.go`

#### Modify DownloadBook function

**Current code** (line 103-144):
```go
func (h *MediaHandler) DownloadBook(c echo.Context) error {
    // ...
    mediaItem, err := h.db.GetMediaItem(c.Request().Context(), pgBookUUID)
    if err != nil {
        return c.JSON(http.StatusNotFound, map[string]string{"error": "book not found"})
    }

    if _, err := os.Stat(mediaItem.FilePath); os.IsNotExist(err) {
        return c.JSON(http.StatusNotFound, map[string]string{"error": "book file not found on disk"})
    }

    file, err := os.Open(mediaItem.FilePath)
    // ...
}
```

**New code**:
```go
func (h *MediaHandler) DownloadBook(c echo.Context) error {
    // ...
    mediaItem, err := h.db.GetMediaItem(c.Request().Context(), pgBookUUID)
    if err != nil {
        return c.JSON(http.StatusNotFound, map[string]string{"error": "book not found"})
    }

    // Resolve relative path to absolute filesystem path
    fullPath, err := h.getFullFilePath(c.Request().Context(), mediaItem.LibraryID, mediaItem.FilePath)
    if err != nil {
        return c.JSON(http.StatusNotFound, map[string]string{"error": "book file not found on disk"})
    }

    if _, err := os.Stat(fullPath); os.IsNotExist(err) {
        return c.JSON(http.StatusNotFound, map[string]string{"error": "book file not found on disk"})
    }

    file, err := os.Open(fullPath)
    // ...
}
```

---

## Phase 5: Create Authenticated File Serving Handler

### File: `internal/handlers/media.go`

Create a single handler that serves both covers and book files:

```go
// ServeFile serves files (covers or books) via /uploads/library-{id}/path
// Requires JWT authentication
func (mh *MediaHandler) ServeFile(c echo.Context) error {
    // URL format: /uploads/library-{libraryID}/{relativePath}
    path := c.Param("*")  // Gets everything after /uploads/library-{id}/
    
    // Extract library ID from path
    parts := strings.SplitN(path, "/", 2)
    if len(parts) < 2 {
        return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid path"})
    }
    
    libraryIDStr := strings.TrimPrefix(parts[0], "library-")
    libraryUUID, err := uuid.Parse(libraryIDStr)
    if err != nil {
        return c.JSON(http.StatusBadRequest, map[string]string{"error": "invalid library ID"})
    }
    
    relativePath := parts[1]
    
    // Resolve using service
    fullPath, err := mh.getFullFilePath(c.Request().Context(), pgtype.UUID{Bytes: libraryUUID, Valid: true}, relativePath)
    if err != nil {
        return c.JSON(http.StatusNotFound, map[string]string{"error": "file not found"})
    }
    
    // Check if file exists
    if _, err := os.Stat(fullPath); os.IsNotExist(err) {
        return c.JSON(http.StatusNotFound, map[string]string{"error": "file not found"})
    }
    
    // Determine content type
    ext := strings.ToLower(filepath.Ext(fullPath))
    contentType := "application/octet-stream"
    if ext == ".jpg" || ext == ".jpeg" {
        contentType = "image/jpeg"
    } else if ext == ".png" {
        contentType = "image/png"
    } else if ext == ".webp" {
        contentType = "image/webp"
    } else if ext == ".epub" {
        contentType = "application/epub+zip"
    } else if ext == ".pdf" {
        contentType = "application/pdf"
    }
    
    c.Response().Header().Set("Content-Type", contentType)
    c.Response().Header().Set("Cache-Control", "public, max-age=86400")
    return c.File(fullPath)
}
```

### File: `internal/router/media.go`

**Location**: After existing media routes

```go
// File serving - authenticated
// Note: Must be registered LAST as it's a wildcard route
protected.GET("/uploads/library-:id/*", cfg.MediaHandler.ServeFile)
```

**Important**: This route must be registered LAST because `/*` is a wildcard that matches everything.

---

## Phase 6: Update OPDS Handler for Device Support

### File: `internal/handlers/opds.go`

#### Modify GetCoverImage function

**Current code** (around line 477-549):
```go
func (h *OPDSHandler) GetCoverImage(c echo.Context) error {
    // ...
    coverPath := mediaItem.CoverImagePath.String
    
    // Check if file exists
    if _, err := os.Stat(coverPath); os.IsNotExist(err) {
        return c.NoContent(http.StatusNoContent)
    }
    
    // Open file
    file, err := os.Open(coverPath)
    // ...
}
```

**New code**:
```go
func (h *OPDSHandler) GetCoverImage(c echo.Context) error {
    // ...
    coverPath := mediaItem.CoverImagePath.String
    
    // Resolve relative path using library service
    fullPath, err := h.libraryService.ResolveMediaPath(c.Request().Context(), mediaItem.LibraryID, coverPath)
    if err != nil {
        return c.NoContent(http.StatusNoContent)
    }
    
    // Check if file exists
    if _, err := os.Stat(fullPath); os.IsNotExist(err) {
        return c.NoContent(http.StatusNoContent)
    }
    
    // Open file
    file, err := os.Open(fullPath)
    // ...
}
```

**Note**: OPDSHandler already has `libraryService` injected, so it can use the same resolution logic.

**If OPDSHandler doesn't have libraryService**, add it:

```go
type OPDSHandler struct {
    db                *database.Queries
    libraryService    *services.LibraryService
    conversionService interface {...}
}

func NewOPDSHandler(db *database.Queries, libraryService *services.LibraryService, conversionService ...) *OPDSHandler {
    return &OPDSHandler{
        db:             db,
        libraryService: libraryService,
        conversionService: conversionService,
    }
}
```

---

## Phase 7: Frontend - No Changes Needed (SSR)

The existing frontend code should work without modification:

- **dashboard.templ**: Uses `item.CoverImagePath` directly in SSR
- **dashboard.ts**: Uses `book.cover_image_path` from API response
- **bookshelf.ts**: Uses `book.cover_image_path` from API response

**Note**: Backend resolves URLs when building API responses, so frontend just uses the URL directly - no extra requests.

---

## Phase 8: Backward Compatibility

Handle existing absolute paths in database:

### Option A: Migration (One-time)
Create a script to convert existing absolute paths to relative paths using known library folder paths.

### Option B: Runtime Resolution (No migration)
Add backward compatibility in handlers:

```go
func (mh *MediaHandler) getFullFilePath(ctx context.Context, libraryID pgtype.UUID, relativePath string) (string, error) {
    // Already absolute? Use as-is (backward compatibility)
    if filepath.IsAbs(relativePath) {
        return relativePath, nil
    }
    
    // Otherwise resolve as relative path
    return mh.libraryService.ResolveMediaPath(ctx, libraryID, relativePath)
}
```

**Recommended**: Option B - no database migration needed, handles both old and new data.

---

## Phase 8: Tests

### Unit Tests

#### File: `internal/handlers/media_test.go`

```go
// TestGetCoverImage_ValidItem tests successful cover image retrieval
func TestGetCoverImage_ValidItem(t *testing.T) {
    // Setup test server with mock database
    // Create a test cover image file
    // Call GetCoverImage
    // Verify response has correct Content-Type and status code
}

// TestGetCoverImage_NotFound tests 404 for non-existent media item
func TestGetCoverImage_NotFound(t *testing.T) {
    // Call with invalid UUID
    // Verify 404 response
}

// TestGetCoverImage_NoCover tests 404 when media item has no cover
func TestGetCoverImage_NoCover(t *testing.T) {
    // Create media item with empty cover_image_path
    // Verify 404 response
}

// TestGetFullFilePath_RelativePath tests relative path resolution
func TestGetFullFilePath_RelativePath(t *testing.T) {
    // Setup: Create library with folder /app/uploads
    // Media item with file_path: "Author/Book/book.epub"
    // Call getFullFilePath
    // Verify returns: "/app/uploads/Author/Book/book.epub"
}

// TestGetFullFilePath_AbsolutePath tests backward compatibility
func TestGetFullFilePath_AbsolutePath(t *testing.T) {
    // Media item with absolute file_path
    // Verify returns same path
}
```

### Scanner Tests

#### File: `internal/services/media_scanner_test.go`

```go
// TestGetRelativePath tests path conversion
func TestGetRelativePath(t *testing.T) {
    scanner := &MediaScanner{
        folders: []string{"/app/uploads", "/var/books"},
    }
    
    tests := []struct {
        absolute string
        expected string
    }{
        {"/app/uploads/Author/Book/epub", "Author/Book/epub"},
        {"/var/books/manga/Naruto/vol1", "manga/Naruto/vol1"},
        {"/other/path/file.pdf", "/other/path/file.pdf"}, // fallback
    }
    
    for _, tt := range tests {
        result := scanner.getRelativePath(tt.absolute)
        assert.Equal(t, tt.expected, result)
    }
}
```

### Integration Tests

#### File: `cmd/server/tests/cover_file_serving_test.go`

```go
package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"testing"
	"time"

	"github.com/stretchr/testify/require"
	"github.com/stretchr/testify/suite"
)
```

Note: The integration tests use `setupTestServer(s.T())` from `cmd/server/tests/test_helpers.go` as per PROJECT_GUIDELINES.md requirements.

### Bruno API Tests

Create new Bruno test files for the new endpoints:

#### File: `bruno/media-items/Get Cover Image.yml`

```yaml
info:
  name: Get Cover Image
  type: http
  seq: 1
http:
  method: GET
  url: '{{base_url}}/api/covers/{{media_item_id}}'
  auth: none

docs: |-
  ## Get Cover Image
  
  Retrieve the cover image for a media item. Requires authentication.
  
  **Method:** GET
  
  **Endpoint:** /api/covers/{id}
  
  **Authentication:** Bearer token required
  
  **Response:** Binary image data (JPEG, PNG, etc.)
  
  **Status Codes:**
  - 200: Success - returns image
  - 400: Invalid media item ID
  - 401: Unauthorized
  - 404: Media item not found or cover doesn't exist

Note: Uses `media_item_id` from environment variables.
```

#### File: `bruno/media-items/Download Media Item.yml` (Update existing)

Update the existing file to document that it now handles relative paths:

```yaml
info:
  name: Download Media Item
  type: http
  seq: 1
http:
  method: GET
  url: '{{base_url}}/api/media-items/{{media_item_id}}/download'
  auth: none

docs: |-
  ## Download Media Item
  
  Download a media item file (EPUB, PDF, CBZ, etc.) from Bookhoard server.
  
  **Method:** GET
  
  **Endpoint:** /api/media-items/{id}/download
  
  **Authentication:** Bearer token required
  
  **Path Resolution:** The handler resolves the relative file path stored in the
  database against the library's configured folder(s) to locate the actual file.
  
  **Backward Compatibility:** Supports both relative paths (new) and absolute
  paths (legacy data).
  
  **Response:** Binary file data with appropriate Content-Type header
  
  **Status Codes:**
  - 200: Success - returns file
  - 400: Invalid media item ID
  - 401: Unauthorized
  - 404: Media item not found or file doesn't exist on disk

Note: Uses `media_item_id` from environment variables.
```

---

## Phase 9: Documentation

### File: `docs/developer/api/media-items/get_cover_image.md`

```markdown
---
title: Get Cover Image
description: Retrieve the cover image for a media item
---

# Get Cover Image

Retrieve the cover image for a media item.

## Endpoint

`GET /api/covers/:id`

## Path Parameters

| Parameter | Type | Description |
|-----------|------|-------------|
| id | string | The media item ID (UUID) |

## Headers

| Header | Required | Description |
|--------|----------|-------------|
| Authorization | Yes | Bearer token |

## Response

- **200 OK**: Cover image returned
  - Content-Type: `image/jpeg`, `image/png`, etc.
  - Cache-Control: `public, max-age=86400`

- **400 Bad Request**: Invalid media item ID

- **404 Not Found**: 
  - Media item not found
  - No cover image configured
  - Cover image file not found on disk

## Example

```bash
curl -H "Authorization: Bearer YOUR_TOKEN" \
     http://localhost:8765/api/covers/550e8400-e29b-41d4-a716-446655440000 \
     --output cover.jpg
```

## Notes

- Cover images are stored relative to their library folder
- The API resolves the full path using the library's configured folder(s)
- Supports backward compatibility with existing absolute paths
- Images are cached for 24 hours by clients
- All endpoints require authentication (JWT)
```

### File: `docs/developer/api/media-items/download_book.md`

Update existing documentation to note:
- File paths are stored relative to library folders
- Handler resolves path at request time
- Backward compatible with existing absolute paths

---

## Summary of Changes

| Phase | File | Change |
|-------|------|--------|
| 1 | `internal/services/media_scanner.go` | Add `getRelativePath()` function; use for both file_path and cover_path |
| 2 | `internal/services/library_service.go` | Add `ResolveMediaPath()` function (one source of truth) |
| 3 | `internal/handlers/media.go` | Add `getFullFilePath()` helper that calls service |
| 4 | `internal/handlers/media.go` | Modify `DownloadBook` to use `getFullFilePath()` |
| 5 | `internal/handlers/media.go` | Add `ServeFile()` handler for authenticated static-style routes |
| 5 | `internal/router/media.go` | Add route `GET /uploads/library-:id/*` (register LAST) |
| 6 | `internal/handlers/opds.go` | Add `libraryService` to struct; update `GetCoverImage` to use service |
| 7 | Frontend files | No changes needed (backend resolves URLs) |
| 8 | Runtime resolution | Handles both absolute (old) and relative (new) paths |
| 9 | `internal/handlers/media_test.go` | Add unit tests for path resolution |
| 9 | `internal/services/media_scanner_test.go` | Add unit tests for `getRelativePath()` |
| 9 | `cmd/server/tests/cover_file_serving_test.go` | Add integration tests using test_helpers |
| 10 | `bruno/media-items/Get Cover Image.yml` | Add Bruno API test |
| 10 | `bruno/media-items/EPUB Download.yml` | Update to document relative path handling |
| 10 | `docs/developer/api/media-items/` | Update API documentation |

---

## Verification Steps

After implementation:

1. **Test new scan**: Add a new book with cover, verify:
   - Database `file_path` is relative (e.g., `Author/Book/book.epub`)
   - Database `cover_image_path` is relative (e.g., `Author/Book/cover.jpg`)
   - GET `/uploads/library-{id}/Author/Book/cover.jpg` returns the image
   - GET `/api/media-items/:id/download` returns the file

2. **Test existing data**: For items with absolute paths:
   - Downloads still work (backward compatibility)
   - Cover images still work (backward compatibility)

3. **Test multiple mount points**:
   - Library A with folder `/app/epubs`
   - Library B with folder `/var/manga`
   - Books in each resolve correctly via their library ID

4. **Test frontend**:
   - Dashboard shows cover images (SSR - initial load)
   - Library switch works (dynamic - uses resolved URLs)
   - Bookshelf shows cover images
   - Downloads work

5. **Test mobile app** (future):
   - Same JWT auth works for files and covers
   - `/uploads/library-{id}/...` URLs work

6. **Test device integration**:
   - Kobo devices can fetch cover images via OPDS
   - KOReader sync continues to work

---

## Flexibility for Users

Users can configure any mount point in docker-compose:

```yaml
services:
  bookhoard:
    volumes:
      - ./epubs:/app/epubs        # ebooks
      - ./manga:/var/manga       # manga
      - ./comics:/media/comics   # comics
```

The system stores relative paths, so it works with any configuration.