File Upload

File Upload

Upload files to Bknd storage using the MediaApi SDK or REST endpoints.

Prerequisites

• Media module enabled in Bknd config
• Storage adapter configured (S3, R2, Cloudinary, or local)
• bknd package installed
• For entity uploads: target entity has media() field defined

When to Use UI Mode

• Admin panel > Media section > drag-and-drop upload
• Quick testing of storage configuration
• One-off file uploads without code

When to Use Code Mode

• Programmatic uploads from frontend
• Upload with progress tracking
• Attach files to entity records
• Custom upload UI components

Step-by-Step: UI Approach

Step 1: Open Admin Panel

Navigate to http://localhost:7654 (or your Bknd URL).

Step 2: Go to Media Section

Click "Media" in sidebar to access file management.

Step 3: Upload Files

• Drag files into the upload area, OR
• Click "Upload" button and select files

Step 4: Verify Upload

Files appear in the list with name, size, type, and date.

Step-by-Step: Code Approach

Basic File Upload

import { Api } from "bknd";

const api = new Api({ host: "http://localhost:7654" });

// From File object (browser)
const input = document.querySelector('input[type="file"]');
const file = input.files[0];

const { ok, data, error } = await api.media.upload(file);

if (ok) {
  console.log("Uploaded:", data.name);
  console.log("Size:", data.meta.size);
  console.log("Type:", data.meta.type);
}

Upload with Custom Filename

const { ok, data } = await api.media.upload(file, {
  filename: "custom-name.png",
});

Upload from URL

// Direct URL string
const { ok, data } = await api.media.upload("https://example.com/​image.png");

// Or from fetch Response
const response = await fetch("https://example.com/​image.png");
const { ok, data } = await api.media.upload(response);

Upload to Entity Field

Attach file directly to an entity record:

// Assumes "posts" entity has a media() field called "cover_image"
const { ok, data } = await api.media.uploadToEntity(
  "posts",           // entity name
  123,               // record ID
  "cover_image",     // field name
  file,
  { overwrite: true }  // replace existing file
);

if (ok) {
  console.log("File attached:", data.result.cover_image);
}

React Integration

Simple File Input

function FileUpload({ onUploaded }) {
  const { api } = useApp();  // or your Api instance
  const [uploading, setUploading] = useState(false);
  const [error, setError] = useState(null);

  const handleChange = async (e) => {
    const file = e.target.files?.[0];
    if (!file) return;

    setUploading(true);
    setError(null);

    const { ok, data, error } = await api.media.upload(file);

    setUploading(false);

    if (ok) {
      onUploaded(data);
    } else {
      setError(error?.message || "Upload failed");
    }
  };

  return (
    <div>
      <input
        type="file"
        onChange={handleChange}
        disabled={uploading}
      />
      {uploading && <span>Uploading...</​span>}
      {error && <span style={{ color: "red" }}>{error}</​span>}
    </​div>
  );
}

Image Upload with Preview

function ImageUpload({ value, onChange }) {
  const { api } = useApp();
  const [preview, setPreview] = useState(value);
  const [uploading, setUploading] = useState(false);

  const handleChange = async (e) => {
    const file = e.target.files?.[0];
    if (!file) return;

    // Show local preview immediately
    const localUrl = URL.createObjectURL(file);
    setPreview(localUrl);

    setUploading(true);
    const { ok, data } = await api.media.upload(file);
    setUploading(false);

    if (ok) {
      // Clean up local preview
      URL.revokeObjectURL(localUrl);
      // Use server URL
      onChange(data.name);
    }
  };

  return (
    <div>
      {preview && (
        <img
          src={preview}
          alt="Preview"
          style={{ maxWidth: 200, opacity: uploading ? 0.5 : 1 }}
        />
      )}
      <input type="file" accept="image/​*" onChange={handleChange} />
      {uploading && <span>Uploading...</​span>}
    </​div>
  );
}

Upload with Progress Tracking

For large files, use XHR for progress:

function ProgressUpload({ onUploaded }) {
  const { api } = useApp();
  const [progress, setProgress] = useState(0);
  const [uploading, setUploading] = useState(false);

  const uploadWithProgress = (file) => {
    return new Promise((resolve, reject) => {
      const xhr = new XMLHttpRequest();
      const url = api.media.getFileUploadUrl({ path: file.name });

      xhr.upload.addEventListener("progress", (e) => {
        if (e.lengthComputable) {
          setProgress(Math.round((e.loaded / e.total) * 100));
        }
      });

      xhr.addEventListener("load", () => {
        if (xhr.status >= 200 && xhr.status < 300) {
          resolve(JSON.parse(xhr.responseText));
        } else {
          reject(new Error(xhr.statusText));
        }
      });

      xhr.addEventListener("error", () => reject(new Error("Upload failed")));

      xhr.open("POST", url);
      xhr.setRequestHeader("Content-Type", file.type);

      // Add auth if using header transport
      const token = api.getAuthState().token;
      if (token) {
        xhr.setRequestHeader("Authorization", `Bearer ${token}`);
      }

      xhr.send(file);
    });
  };

  const handleChange = async (e) => {
    const file = e.target.files?.[0];
    if (!file) return;

    setUploading(true);
    setProgress(0);

    try {
      const result = await uploadWithProgress(file);
      onUploaded(result);
    } catch (err) {
      console.error("Upload failed:", err);
    } finally {
      setUploading(false);
    }
  };

  return (
    <div>
      <input type="file" onChange={handleChange} disabled={uploading} />
      {uploading && (
        <div>
          <progress value={progress} max={100} />
          <span>{progress}%</​span>
        </​div>
      )}
    </​div>
  );
}

Avatar Upload Component

Complete avatar upload with entity attachment:

function AvatarUpload({ userId, currentAvatar }) {
  const { api } = useApp();
  const [preview, setPreview] = useState(currentAvatar);
  const [uploading, setUploading] = useState(false);

  const handleChange = async (e) => {
    const file = e.target.files?.[0];
    if (!file) return;

    // Validate image
    if (!file.type.startsWith("image/")) {
      alert("Please select an image file");
      return;
    }

    if (file.size > 5 * 1024 * 1024) {
      alert("Image must be under 5MB");
      return;
    }

    setPreview(URL.createObjectURL(file));
    setUploading(true);

    const { ok, data } = await api.media.uploadToEntity(
      "users",
      userId,
      "avatar",
      file,
      { overwrite: true }
    );

    setUploading(false);

    if (ok) {
      setPreview(data.result.avatar);
    }
  };

  return (
    <div>
      <img
        src={preview || "/​default-avatar.png"}
        alt="Avatar"
        style={{
          width: 100,
          height: 100,
          borderRadius: "50%",
          opacity: uploading ? 0.5 : 1
        }}
      />
      <label>
        <input
          type="file"
          accept="image/​*"
          onChange={handleChange}
          disabled={uploading}
          style={{ display: "none" }}
        />
        <button type="button" disabled={uploading}>
          {uploading ? "Uploading..." : "Change Avatar"}
        </​button>
      </​label>
    </​div>
  );
}

REST API

Upload Endpoint

# Basic upload (filename in path)
curl -X POST \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: image/​png" \
  --data-binary @image.png \
  http://localhost:7654/​api/​media/​upload/​image.png

# Upload to entity field
curl -X POST \
  -H "Authorization: Bearer $TOKEN" \
  -H "Content-Type: image/​jpeg" \
  --data-binary @photo.jpg \
  "http://localhost:7654/​api/​media/​entity/​users/​123/​avatar?overwrite=true"

Response Format

{
  "name": "image.png",
  "meta": {
    "type": "image/​png",
    "size": 24680,
    "width": 800,
    "height": 600
  },
  "etag": "abc123...",
  "state": {
    "name": "image.png",
    "path": "image.png"
  }
}

Entity Media Field

Define a media field to link files to records:

import { em, entity, text, media } from "bknd";

const schema = em({
  posts: entity("posts", {
    title: text(),
    cover_image: media(),  // Stores file reference
  }),

  users: entity("users", {
    name: text(),
    avatar: media(),
  }),
});

Media fields store the filename, not the file content.

Server-Side Upload

Upload files in Bknd server context (seeds, flows):

// In seed function
export default defineConfig({
  options: {
    seed: async (ctx) => {
      const media = ctx.server?.modules.media;
      if (!media) return;

      // Upload from URL
      const response = await fetch("https://example.com/​default-avatar.png");
      const buffer = await response.arrayBuffer();

      await media.adapter.putObject(
        "default-avatar.png",
        new Uint8Array(buffer)
      );
    },
  },
});

Handling Upload Response

const { ok, data, error } = await api.media.upload(file);

if (!ok) {
  // Handle error
  if (error?.status === 413) {
    console.error("File too large");
  } else if (error?.status === 401) {
    console.error("Not authenticated");
  } else if (error?.status === 403) {
    console.error("No upload permission");
  } else {
    console.error("Upload failed:", error?.message);
  }
  return;
}

// Success - use data
console.log("Filename:", data.name);
console.log("MIME type:", data.meta.type);
console.log("Size (bytes):", data.meta.size);

// For images
if (data.meta.width && data.meta.height) {
  console.log("Dimensions:", data.meta.width, "x", data.meta.height);
}

Common Pitfalls

File Too Large (413 Error)

Problem: Upload fails with 413 status.

Fix: Increase body_max_size in config:

export default defineConfig({
  media: {
    enabled: true,
    body_max_size: 50 * 1024 * 1024,  // 50MB
    adapter: { ... },
  },
});

Missing Content-Type Header

Problem: File uploaded with wrong MIME type.

Fix: Always set Content-Type in REST uploads:

# WRONG - no content type
curl -X POST --data-binary @image.png .../​upload/​image.png

# CORRECT
curl -X POST \
  -H "Content-Type: image/​png" \
  --data-binary @image.png \
  .../​upload/​image.png

SDK handles this automatically from File object.

CORS Errors

Problem: Browser blocks upload to S3.

Fix: Configure CORS on storage bucket (not Bknd):

{
  "CORSRules": [{
    "AllowedOrigins": ["https://yourapp.com"],
    "AllowedMethods": ["GET", "PUT", "POST"],
    "AllowedHeaders": ["*"]
  }]
}

Auth Token Missing in XHR Upload

Problem: 401 error when using XHR progress upload.

Fix: Add Authorization header:

const token = api.getAuthState().token;
if (token) {
  xhr.setRequestHeader("Authorization", `Bearer ${token}`);
}

Media Field Not Defined

Problem: uploadToEntity fails with "field not found".

Fix: Ensure entity has media() field:

// WRONG - no media field
posts: entity("posts", {
  title: text(),
  cover_image: text(),  // This is just a string
}),

// CORRECT
posts: entity("posts", {
  title: text(),
  cover_image: media(),  // Proper media field
}),

Memory Issues with Large Files

Problem: Browser crashes on large file upload.

Fix: Use streaming or chunked upload:

// For very large files, consider chunked upload
// Bknd doesn't have native chunking, so use S3 presigned URLs
// or implement custom chunking endpoint

Verification

Test upload works correctly:

async function testUpload() {
  // 1. Check media enabled
  const { ok: listOk } = await api.media.listFiles();
  console.log("Media module enabled:", listOk);

  // 2. Test file upload
  const testFile = new File(["test"], "test.txt", { type: "text/​plain" });
  const { ok, data, error } = await api.media.upload(testFile);
  console.log("Upload result:", ok ? data.name : error);

  // 3. Verify file exists
  const { data: files } = await api.media.listFiles();
  const exists = files.some(f => f.key === "test.txt");
  console.log("File in list:", exists);

  // 4. Clean up
  if (exists) {
    await api.media.deleteFile("test.txt");
    console.log("Test file deleted");
  }
}

DOs and DON'Ts

DO:

• Validate file type/​size before upload
• Show upload progress for large files
• Handle all error cases (401, 403, 413)
• Use uploadToEntity for entity attachments
• Clean up object URLs after upload completes
• Set appropriate body_max_size limit

DON'T:

• Upload without auth when permissions require it
• Forget Content-Type header in REST uploads
• Store sensitive files without access control
• Allow unlimited file sizes in production
• Use local adapter in production

Related Skills

• bknd-storage-config - Configure storage backends
• bknd-serve-files - Serve uploaded files
• bknd-add-field - Add media field to entity
• bknd-crud-update - Update records with file references
• bknd-assign-permissions - Set media.create permission