How to Set Specific Content-Type Headers for Multipart Form Fields in Go?

Configuring Content-Type Headers for Multipart Form Fields in Go

When submitting multipart forms with file uploads, it becomes necessary to specify the Content-Type header for the file fields to ensure proper handling by the receiving API. While setting global headers for the entire request using net/http is straightforward, setting individual headers for multipart form fields has proven challenging.

To overcome this, a custom function can be employed to create form fields with explicit Content-Type headers:

<code class="go">func CreateAudioFormFile(w *multipart.Writer, filename string) (io.Writer, error) {
  h := make(textproto.MIMEHeader)
  h.Set("Content-Disposition", fmt.Sprintf(`form-data; name="%s"; filename="%s"`, "file", filename))
  h.Set("Content-Type", "audio/wav;rate=8000")
  return w.CreatePart(h)
}</code>

This function takes the multipart writer and filename as input and returns an io.Writer into which the file data can be written. The implemented header sets the Content-Disposition and Content-Type as desired.

To set the Content-Type for a specific multipart form field, use the custom function as follows:

<code class="go">audioFile, _ := CreateAudioFormFile(writer, "helloWorld.wav")
io.Copy(audioFile, file)</code>

This approach effectively allows the Content-Type to be set for individual multipart form fields, enabling developers to seamlessly handle file uploads with specific content type requirements.

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