go-multipart-composer

Prepares bodies of HTTP requests with MIME multipart messages according to RFC7578 without reading entire file contents to memory. Instead of writing files to a multipart writer right away, it collects readers for each part of the form and lets them stream to the network once the request has been sent. Avoids buffering of the request body simpler than with goroutines and pipes. See the documentation for more information.

Installation

Add this package to go.mod and go.sub in your Go project:

go get github.com/prantlf/go-multipart-composer

Usage

Upload a file with comment:

import (
  "net/http"
  composer "github.com/prantlf/go-multipart-composer"
)
// compose a multipart form-data content
comp := composer.NewComposer()
comp.AddField("comment", "a comment")
err := comp.AddFile("file", "test.txt")
// post a request with the generated content type and body
resp, err := http.DefaultClient.Post("http://host.com/upload",
  comp.FormDataContentType(), comp.DetachReader())

If the server does not support chunked encoding and requires Content-=Length in the header:

comp := composer.NewComposer()
comp.AddField("comment", "a comment")
err := comp.AddFile("file", "test.txt")
reqBody, contentLength, err := comp.DetachReaderWithSize()
if err != nil {
  comp.Close() // DetachReaderWithSize does not close the composer on failure
  log.Fatal(err)
}
// post a request with the generated body, content type and content length
req, err := http.NewRequest("POST", "http://host.com/upload", reqBody)
req.Header.Add("Content-Type", comp.FormDataContentType())
req.ContentLength = contentLength
resp, err := http.DefaultClient.Do(request)

See the documentation for the full interface.