Send multipart form-data with cURL in Swift
Paste a curl command that sends multipart form-data and get idiomatic Swift code. We pick the right serialization for URLSession and set the correct Content-Type.
Quick answer
To convert a cURL command to Swift, paste it into the Toolpaper workbench below. It parses the command in your browser and emits idiomatic Swift code — headers, query string, request body, authentication (Bearer, Basic, API key), and cookies are all wired up automatically. No data is uploaded; conversion is fully client-side.
Prefer a different target? See the full cURL to Swift reference, or jump to the same guide in JavaScript, Node.js, or Python.
import Foundation
let session = URLSession.shared
var request = URLRequest(url: URL(string: "https://api.example.com/upload")!)
request.httpMethod = "POST"
// Multipart body — Swift has no built-in helper. Consider Alamofire for real uploads.
let boundary = "----ToolpaperBoundary\(UUID().uuidString)"
request.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
var body = Data()
body.append("--\(boundary)\r\n".data(using: .utf8)!)
body.append("Content-Disposition: form-data; name=\"file\"; filename=\"/path/to/photo.png\"\r\n".data(using: .utf8)!)
body.append("Content-Type: application/octet-stream\r\n\r\n".data(using: .utf8)!)
body.append(try Data(contentsOf: URL(fileURLWithPath: "/path/to/photo.png")))
body.append("\r\n".data(using: .utf8)!)
body.append("--\(boundary)\r\n".data(using: .utf8)!)
body.append("Content-Disposition: form-data; name=\"caption\"\r\n\r\nHello".data(using: .utf8)!)
body.append("\r\n".data(using: .utf8)!)
body.append("--\(boundary)--\r\n".data(using: .utf8)!)
request.httpBody = body
let (data, response) = try await session.data(for: request)
print(String(data: data, encoding: .utf8) ?? "")
// Note: to disable redirects, implement URLSessionTaskDelegate.urlSession(_:task:willPerformHTTPRedirection:...) and return nil.Example
A representative curl command for this scenario. Paste your own above to convert an exact match.
curl -X POST https://api.example.com/upload \
-F "file=@/path/to/photo.png" \
-F "caption=Hello"Implementation notes
- Content-Type is detected from -H headers first, then inferred from the body shape when the header is missing.
- Each -F flag becomes a distinct part; file@ paths are surfaced as URLSession file handles so the multipart boundary stays valid.
- Charset directives on Content-Type (e.g. application/json; charset=utf-8) survive the round trip.
Common mistakes
- Setting Content-Type manually and then also using URLSession's helper — you end up with duplicate headers or the wrong one wins.
- Forgetting @ in -F "file=@upload.png" — without it curl sends the literal string, not the file. The generator flags this.
- Trusting the browser DevTools "Copy as cURL" to preserve charset — it often drops it. Clean panel restores common defaults.
Common questions
- How is multipart form-data encoded in the generated Swift?
- -F flags translate to multipart form-data with proper boundary handling — files={...} in Python, MultipartFormDataContent in C#, MultipartBody.Part in Java/Kotlin.
- Does it preserve Content-Type?
- Yes. The Content-Type header is honored and matched against the body so serialization stays consistent.
- Is anything uploaded?
- No. Parsing and generation happen entirely in your browser.
More payload types in Swift
Swift hub →The same guide in other languages
All guides →In JavaScript
/how-to/send-multipart-with-curl-in-javascript
In Node.js
/how-to/send-multipart-with-curl-in-node
In Python
/how-to/send-multipart-with-curl-in-python
In Go
/how-to/send-multipart-with-curl-in-go
In PHP
/how-to/send-multipart-with-curl-in-php
In Ruby
/how-to/send-multipart-with-curl-in-ruby
In Rust
/how-to/send-multipart-with-curl-in-rust
In Java
/how-to/send-multipart-with-curl-in-java
Full Swift reference on the cURL to Swift hub, or open the main converter for all 18 targets.