Beginner LevelREST APIs & Web Services
How do multi-part form uploads (multipart/form-data) work in REST APIs?
❓ Interview Prompt: Explain `multipart/form-data` MIME encoding, boundary separators, file streaming, and uploading binary files with metadata.
Uploading binary files (images, PDFs) along with JSON metadata in a single HTTP request uses 'multipart/form-data':
How It Works:
1
The 'Content-Type' header specifies a unique boundary string: 'Content-Type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxk'.
2
The request body is divided into parts separated by this boundary string.
3
Each part contains its own headers ('Content-Disposition: form-data; name="avatar"; filename="photo.png"', 'Content-Type: image/png') followed by raw binary bytes.
Code Implementation Example
http
POST /api/v1/users/42/avatar HTTP/1.1
Host: api.example.com
Content-Type: multipart/form-data; boundary=--Boundary123
--Boundary123
Content-Disposition: form-data; name="description"
Profile Picture
--Boundary123
Content-Disposition: form-data; name="file"; filename="avatar.jpg"
Content-Type: image/jpeg
<binary JPEG data bytes...>
--Boundary123--💡Multipart form data HTTP request carrying metadata and binary image payload.
🎯 Interview Key Takeaway
Use multipart/form-data with boundary strings to upload binary files alongside text metadata in HTTP requests.
#Multipart#File Upload#HTTP Payload#Beginner
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