File API - Go 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

package main

import (
    "fmt"
    "log"
    
    bosbase "github.com/bosbase/go-sdk"
)

func main() {
    client := bosbase.New("http://127.0.0.1:8090")
    defer client.Close()
    
    // Get a record with a file field
    record, err := client.Collection("posts").GetOne("RECORD_ID", nil)
    if err != nil {
        log.Fatal(err)
    }
    
    // Get the file URL
    image, _ := record["image"].(string)
    fileUrl := client.Files.GetURL(record, image, nil)
    
    fmt.Println("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

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

record, err := client.Collection("posts").GetOne("RECORD_ID", nil)
if err != nil {
    log.Fatal(err)
}

image, _ := record["image"].(string)

// Get thumbnail URL
thumbUrl := client.Files.GetURL(record, image, &bosbase.FileURLOptions{
    Thumb: "100x100",
})

// Different thumbnail sizes
smallThumb := client.Files.GetURL(record, image, &bosbase.FileURLOptions{
    Thumb: "50x50",
})

mediumThumb := client.Files.GetURL(record, image, &bosbase.FileURLOptions{
    Thumb: "200x200",
})

largeThumb := client.Files.GetURL(record, image, &bosbase.FileURLOptions{
    Thumb: "500x500",
})

// Fit thumbnail (no cropping)
fitThumb := client.Files.GetURL(record, image, &bosbase.FileURLOptions{
    Thumb: "200x200f",
})

// Resize to specific width
widthThumb := client.Files.GetURL(record, image, &bosbase.FileURLOptions{
    Thumb: "300x0",
})

// Resize to specific height
heightThumb := client.Files.GetURL(record, image, &bosbase.FileURLOptions{
    Thumb: "0x200",
})

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
_, err := client.Collection("users").AuthWithPassword(
    "user@example.com", "password123", "", "", nil, nil, nil)
if err != nil {
    log.Fatal(err)
}

// Get file token
token, err := client.Files.GetToken(nil, nil, nil)
if err != nil {
    log.Fatal(err)
}

fmt.Println("File token:", token)

Using Protected File Token

// Get protected file URL with token
record, err := client.Collection("documents").GetOne("RECORD_ID", nil)
if err != nil {
    log.Fatal(err)
}

filename, _ := record["document"].(string)
protectedFileUrl := client.Files.GetURL(record, filename, &bosbase.FileURLOptions{
    Token: token,
})

fmt.Println("Protected file URL:", protectedFileUrl)

Protected File Example

func displayProtectedImage(client *bosbase.BosBase, recordID string) error {
    // Authenticate
    _, err := client.Collection("users").AuthWithPassword(
        "user@example.com", "password123", "", "", nil, nil, nil)
    if err != nil {
        return err
    }
    
    // Get record
    record, err := client.Collection("documents").GetOne(recordID, nil)
    if err != nil {
        return err
    }
    
    // Get file token
    token, err := client.Files.GetToken(nil, nil, nil)
    if err != nil {
        return err
    }
    
    // Get protected file URL
    filename, _ := record["thumbnail"].(string)
    imageUrl := client.Files.GetURL(record, filename, &bosbase.FileURLOptions{
        Token: token,
        Thumb: "300x300",
    })
    
    fmt.Println("Protected image URL:", imageUrl)
    return nil
}

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.

// Force download
downloadUrl := client.Files.GetURL(record, filename, &bosbase.FileURLOptions{
    Download: true,
})

fmt.Println("Download URL:", downloadUrl)

Complete Examples

Example 1: Image Gallery

func displayImageGallery(client *bosbase.BosBase, recordID string) error {
    record, err := client.Collection("posts").GetOne(recordID, nil)
    if err != nil {
        return err
    }
    
    var images []string
    if imgList, ok := record["images"].([]interface{}); ok {
        for _, img := range imgList {
            if imgStr, ok := img.(string); ok {
                images = append(images, imgStr)
            }
        }
    } else if img, ok := record["image"].(string); ok {
        images = []string{img}
    }
    
    for _, filename := range images {
        // Thumbnail for gallery
        thumbUrl := client.Files.GetURL(record, filename, &bosbase.FileURLOptions{
            Thumb: "200x200",
        })
        
        // Full image URL
        fullUrl := client.Files.GetURL(record, filename, nil)
        
        fmt.Printf("Thumbnail: %s\n", thumbUrl)
        fmt.Printf("Full image: %s\n", fullUrl)
    }
    
    return nil
}

Example 2: File Download Handler

func downloadFile(client *bosbase.BosBase, recordID, filename string) (string, error) {
    record, err := client.Collection("documents").GetOne(recordID, nil)
    if err != nil {
        return "", err
    }
    
    // Get download URL
    downloadUrl := client.Files.GetURL(record, filename, &bosbase.FileURLOptions{
        Download: true,
    })
    
    return downloadUrl, nil
}

Example 3: Protected File Viewer

func viewProtectedFile(client *bosbase.BosBase, recordID string) error {
    // Authenticate
    if !client.AuthStore.IsValid() {
        _, err := client.Collection("users").AuthWithPassword(
            "user@example.com", "password123", "", "", nil, nil, nil)
        if err != nil {
            return err
        }
    }
    
    // Get record
    record, err := client.Collection("private_docs").GetOne(recordID, nil)
    if err != nil {
        return err
    }
    
    // Get token
    token, err := client.Files.GetToken(nil, nil, nil)
    if err != nil {
        return err
    }
    
    // Get file URL
    filename, _ := record["file"].(string)
    fileUrl := client.Files.GetURL(record, filename, &bosbase.FileURLOptions{
        Token: token,
    })
    
    fmt.Println("Protected file URL:", fileUrl)
    return nil
}

Error Handling

func safeGetFileURL(client *bosbase.BosBase, record map[string]interface{}, filename string) (string, error) {
    fileUrl := client.Files.GetURL(record, filename, nil)
    
    if fileUrl == "" {
        return "", fmt.Errorf("invalid file URL")
    }
    
    return fileUrl, nil
}

// Protected file token error handling
func getProtectedFileUrl(client *bosbase.BosBase, record map[string]interface{}, filename string) (string, error) {
    // Get token
    token, err := client.Files.GetToken(nil, nil, nil)
    if err != nil {
        if clientErr, ok := err.(*bosbase.ClientResponseError); ok {
            switch clientErr.Status {
            case 401:
                return "", fmt.Errorf("not authenticated")
            case 403:
                return "", fmt.Errorf("no permission to access file")
            default:
                return "", fmt.Errorf("failed to get file token: %v", err)
            }
        }
        return "", err
    }
    
    // Get file URL
    return client.Files.GetURL(record, filename, &bosbase.FileURLOptions{
        Token: token,
    }), nil
}

Best Practices

Use Thumbnails for Lists: Use thumbnails when displaying images in lists/grids to reduce bandwidth
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