MultipartWriter

protocol MultipartWriter<OutboundBody> : Sendable

Overview

Writers conforming to this protocol can serialize multipart data by writing boundaries, headers, and body chunks in the proper multipart format. The protocol supports both streaming and buffered writing approaches.

Implementing a Custom Writer

Here’s an example of implementing a custom writer that accumulates data in memory:

struct MemoryMultipartWriter: MultipartWriter {
    typealias OutboundBody = [UInt8]

    let boundary: String
    private var buffer: [UInt8] = []

    init(boundary: String) {
        self.boundary = boundary
    }

    mutating func write(bytes: some Collection<UInt8> & Sendable) async throws {
        buffer.append(contentsOf: bytes)
    }

    mutating func finish() async throws {
        try await writeBoundary(end: true)
    }

    var data: [UInt8] {
        buffer
    }
}

// Usage example:
var writer = MemoryMultipartWriter(boundary: "boundary123")
try await writer.writeBoundary()
try await writer.writeHeaders([.contentType: "text/plain"])
try await writer.writeBodyChunk("Hello, world!".utf8)
try await writer.finish()
let result = writer.data