File API - C# SDK Documentation

Overview

The File API provides endpoints for downloading and accessing files stored in collection records. It supports thumbnail generation for images, protected file access with tokens, and force download options.

Key Features:

Download files from collection records
Generate thumbnails for images (crop, fit, resize)
Protected file access with short-lived tokens
Force download option for any file type
Automatic content-type detection
Support for Range requests and caching

Backend Endpoints:

GET /api/files/{collection}/{recordId}/{filename} - Download/fetch file
POST /api/files/token - Generate protected file token

Download / Fetch File

Downloads a single file resource from a record.

Basic Usage

using Bosbase;

var pb = new BosbaseClient("http://127.0.0.1:8090");

// Get a record with a file field
var record = await pb.Collection("posts").GetOneAsync("RECORD_ID");

// Get the file URL
var image = record["image"]?.ToString();
var fileUrl = pb.Files.GetUrl(record, image ?? "");

// Use the URL (e.g., in a web browser or download)
Console.WriteLine($"File URL: {fileUrl}");

File URL Structure

The file URL follows this pattern:

/api/files/{collectionIdOrName}/{recordId}/{filename}

Example:

http://127.0.0.1:8090/api/files/posts/abc123/photo_xyz789.jpg

Using in Web Applications

<!-- Direct image display -->
<img src="http://127.0.0.1:8090/api/files/posts/abc123/photo_xyz789.jpg" alt="Photo" />

<!-- Download link -->
<a href="http://127.0.0.1:8090/api/files/posts/abc123/document.pdf" download>Download PDF</a>

<!-- Video player -->
<video src="http://127.0.0.1:8090/api/files/posts/abc123/video.mp4" controls></video>

Thumbnails

Generate thumbnails for image files on-the-fly.

Thumbnail Formats

The following thumbnail formats are supported:

Format	Example	Description
`WxH`	`100x300`	Crop to WxH viewbox (from center)
`WxHt`	`100x300t`	Crop to WxH viewbox (from top)
`WxHb`	`100x300b`	Crop to WxH viewbox (from bottom)
`WxHf`	`100x300f`	Fit inside WxH viewbox (without cropping)
`0xH`	`0x300`	Resize to H height preserving aspect ratio
`Wx0`	`100x0`	Resize to W width preserving aspect ratio

Using Thumbnails

var record = await pb.Collection("example").GetOneAsync("RECORD_ID");
var image = record["image"]?.ToString();

if (image != null)
{
    // Get thumbnail URL
    var thumbUrl = pb.Files.GetUrl(record, image, thumb: "100x100");

    // Different thumbnail sizes
    var smallThumb = pb.Files.GetUrl(record, image, thumb: "50x50");
    var mediumThumb = pb.Files.GetUrl(record, image, thumb: "200x200");
    var largeThumb = pb.Files.GetUrl(record, image, thumb: "500x500");

    // Fit thumbnail (no cropping)
    var fitThumb = pb.Files.GetUrl(record, image, thumb: "200x200f");

    // Resize to specific width
    var widthThumb = pb.Files.GetUrl(record, image, thumb: "300x0");

    // Resize to specific height
    var heightThumb = pb.Files.GetUrl(record, image, thumb: "0x200");
}

Thumbnail Examples in HTML

<!-- Small thumbnail -->
<img src="http://127.0.0.1:8090/api/files/posts/abc123/photo.jpg?thumb=100x100" alt="Thumbnail" />

<!-- Medium thumbnail with fit -->
<img src="http://127.0.0.1:8090/api/files/posts/abc123/photo.jpg?thumb=300x300f" alt="Photo" />

<!-- Responsive thumbnail -->
<img 
  src="http://127.0.0.1:8090/api/files/posts/abc123/photo.jpg?thumb=400x400" 
  srcset="
    http://127.0.0.1:8090/api/files/posts/abc123/photo.jpg?thumb=200x200 200w,
    http://127.0.0.1:8090/api/files/posts/abc123/photo.jpg?thumb=400x400 400w,
    http://127.0.0.1:8090/api/files/posts/abc123/photo.jpg?thumb=800x800 800w
  "
  sizes="(max-width: 600px) 200px, (max-width: 1200px) 400px, 800px"
  alt="Responsive image"
/>

Thumbnail Behavior

Image Files Only: Thumbnails are only generated for image files (PNG, JPG, JPEG, GIF, WEBP)
Non-Image Files: For non-image files, the thumb parameter is ignored and the original file is returned
Caching: Thumbnails are cached and reused if already generated
Fallback: If thumbnail generation fails, the original file is returned
Field Configuration: Thumb sizes must be defined in the file field’s thumbs option or use default 100x100

Protected Files

Protected files require a special token for access, even if you’re authenticated.

Getting a File Token

// Must be authenticated first
await pb.Collection("users").AuthWithPasswordAsync("user@example.com", "password");

// Get file token
var token = await pb.Files.GetTokenAsync();

Console.WriteLine(token); // Short-lived JWT token

Using Protected File Token

// Get protected file URL with token
var record = await pb.Collection("example").GetOneAsync("RECORD_ID");
var document = record["privateDocument"]?.ToString();

if (document != null)
{
    var protectedFileUrl = pb.Files.GetUrl(record, document, token: token);

    // Use the URL (e.g., download or display)
    Console.WriteLine($"Protected file URL: {protectedFileUrl}");
}

Protected File Example

async Task<string?> DisplayProtectedImageAsync(string recordId)
{
    // Authenticate
    await pb.Collection("users").AuthWithPasswordAsync("user@example.com", "password");
    
    // Get record
    var record = await pb.Collection("documents").GetOneAsync(recordId);
    
    // Get file token
    var token = await pb.Files.GetTokenAsync();
    
    // Get protected file URL
    var thumbnail = record["thumbnail"]?.ToString();
    if (thumbnail != null)
    {
        var imageUrl = pb.Files.GetUrl(record, thumbnail, token: token, thumb: "300x300");
        return imageUrl;
    }
    
    return null;
}

Token Lifetime

File tokens are short-lived (typically expires after a few minutes)
Tokens are associated with the authenticated user/superuser
Generate a new token if the previous one expires

Force Download

Force files to download instead of being displayed in the browser.

var record = await pb.Collection("example").GetOneAsync("RECORD_ID");
var document = record["document"]?.ToString();

if (document != null)
{
    // Force download
    var downloadUrl = pb.Files.GetUrl(record, document, download: true);
    Console.WriteLine($"Download URL: {downloadUrl}");
}

Download Parameter Values

// These all force download:
pb.Files.GetUrl(record, filename, download: true);

// These allow inline display (default):
pb.Files.GetUrl(record, filename, download: false);
pb.Files.GetUrl(record, filename); // No download parameter

Complete Examples

Example 1: Image Gallery

async Task DisplayImageGalleryAsync(string recordId)
{
    var record = await pb.Collection("posts").GetOneAsync(recordId);
    
    var images = record["images"] as List<object?> ?? new List<object?>();
    if (images.Count == 0 && record["image"] != null)
    {
        images = new List<object?> { record["image"] };
    }
    
    foreach (var imageObj in images)
    {
        var filename = imageObj?.ToString();
        if (filename == null) continue;

        // Thumbnail for gallery
        var thumbUrl = pb.Files.GetUrl(record, filename, thumb: "200x200");
        
        // Full image URL
        var fullUrl = pb.Files.GetUrl(record, filename);
        
        Console.WriteLine($"Thumbnail: {thumbUrl}");
        Console.WriteLine($"Full image: {fullUrl}");
    }
}

Example 2: File Download Handler

async Task<string> GetDownloadUrlAsync(string recordId, string filename)
{
    var record = await pb.Collection("documents").GetOneAsync(recordId);
    
    // Get download URL
    var downloadUrl = pb.Files.GetUrl(record, filename, download: true);
    
    return downloadUrl;
}

Example 3: Protected File Viewer

async Task<string?> ViewProtectedFileAsync(string recordId)
{
    // Authenticate
    if (!pb.AuthStore.IsValid())
    {
        await pb.Collection("users").AuthWithPasswordAsync("user@example.com", "password");
    }
    
    // Get record
    var record = await pb.Collection("private_docs").GetOneAsync(recordId);
    
    // Get token
    string? token;
    try
    {
        token = await pb.Files.GetTokenAsync();
    }
    catch (Exception error)
    {
        Console.Error.WriteLine($"Failed to get file token: {error}");
        return null;
    }
    
    // Get file URL
    var file = record["file"]?.ToString();
    if (file != null)
    {
        var fileUrl = pb.Files.GetUrl(record, file, token: token);
        return fileUrl;
    }
    
    return null;
}

Example 4: Multiple Files with Thumbnails

async Task DisplayFileListAsync(string recordId)
{
    var record = await pb.Collection("attachments").GetOneAsync(recordId);
    
    var files = record["files"] as List<object?> ?? new List<object?>();
    
    foreach (var fileObj in files)
    {
        var filename = fileObj?.ToString();
        if (filename == null) continue;
        
        // Check if it's an image
        var ext = Path.GetExtension(filename).ToLower();
        var isImage = new[] { ".jpg", ".jpeg", ".png", ".gif", ".webp" }.Contains(ext);
        
        if (isImage)
        {
            // Show thumbnail
            var thumbUrl = pb.Files.GetUrl(record, filename, thumb: "100x100");
            Console.WriteLine($"Thumbnail: {thumbUrl}");
        }
        
        // File download link
        var downloadUrl = pb.Files.GetUrl(record, filename, download: true);
        Console.WriteLine($"Download: {downloadUrl}");
    }
}

Error Handling

try
{
    var record = await pb.Collection("posts").GetOneAsync("RECORD_ID");
    var image = record["image"]?.ToString();
    
    if (string.IsNullOrEmpty(image))
    {
        throw new Exception("Invalid file URL");
    }
    
    var fileUrl = pb.Files.GetUrl(record, image);
    
    // Use the URL
    Console.WriteLine($"File URL: {fileUrl}");
    
}
catch (Exception error)
{
    Console.Error.WriteLine($"File access error: {error}");
}

Protected File Token Error Handling

async Task<string?> GetProtectedFileUrlAsync(Dictionary<string, object?> record, string filename)
{
    try
    {
        // Get token
        var token = await pb.Files.GetTokenAsync();
        
        // Get file URL
        return pb.Files.GetUrl(record, filename, token: token);
        
    }
    catch (ClientResponseError error)
    {
        if (error.Status == 401)
        {
            Console.Error.WriteLine("Not authenticated");
            // Redirect to login
        }
        else if (error.Status == 403)
        {
            Console.Error.WriteLine("No permission to access file");
        }
        else
        {
            Console.Error.WriteLine($"Failed to get file token: {error}");
        }
        return null;
    }
}

Best Practices

Use Thumbnails for Lists: Use thumbnails when displaying images in lists/grids to reduce bandwidth
Lazy Loading: Use lazy loading for images below the fold
Cache Tokens: Store file tokens and reuse them until they expire
Error Handling: Always handle file loading errors gracefully
Content-Type: Let the server handle content-type detection automatically
Range Requests: The API supports Range requests for efficient video/audio streaming
Caching: Files are cached with a 30-day cache-control header
Security: Always use tokens for protected files, never expose them in client-side code

Thumbnail Size Guidelines

Use Case	Recommended Size
Profile picture	`100x100` or `150x150`
List thumbnails	`200x200` or `300x300`
Card images	`400x400` or `500x500`
Gallery previews	`300x300f` (fit) or `400x400f`
Hero images	Use original or `800x800f`
Avatar	`50x50` or `75x75`

Limitations

Thumbnails: Only work for image files (PNG, JPG, JPEG, GIF, WEBP)
Protected Files: Require authentication to get tokens
Token Expiry: File tokens expire after a short period (typically minutes)
File Size: Large files may take time to generate thumbnails on first request
Thumb Sizes: Must match sizes defined in field configuration or use default 100x100

Files Upload and Handling - Uploading and managing files
API Records - Working with records
Collections - Collection configuration