How to Customize Content-Type for Individual Form Fields in Go\'s Multipart Form?

Customizing Content-Type for Multipart Form Fields in Go

This question pertains to customizing the Content-Type for individual form fields within a multipart form created using the Go mime/multipart package. While the original code creates the multipart form, it assumes a default "application/octet-stream" Content-Type. The goal is to set a specific Content-Type for a specific field, such as "audio/wav;rate=8000" for an audio file.

The native mime/multipart package does not provide explicit support for setting the Content-Type for individual fields. However, a custom implementation can be used to achieve this.

<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 creates a new form part with the desired Content-Type. The original code can be modified to use this function:

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

Now, the API will receive the multipart form with the appropriate Content-Type for the audio file. The resulting form data will resemble the following:

--0c4c6b408a5a8bf7a37060e54f4febd6083fd6758fd4b3975c4e2ea93732
Content-Disposition: form-data; name="file"; filename="helloWorld.wav"
Content-Type: audio/wav;rate=8000
[audio file data]
--0c4c6b408a5a8bf7a37060e54f4febd6083fd6758fd4b3975c4e2ea93732--

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