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@mattetti
Last active March 6, 2024 08:07
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Example of doing a multipart upload in Go (golang)
package main
import (
"bytes"
"fmt"
"io"
"log"
"mime/multipart"
"net/http"
"os"
"path/filepath"
)
// Creates a new file upload http request with optional extra params
func newfileUploadRequest(uri string, params map[string]string, paramName, path string) (*http.Request, error) {
file, err := os.Open(path)
if err != nil {
return nil, err
}
defer file.Close()
body := &bytes.Buffer{}
writer := multipart.NewWriter(body)
part, err := writer.CreateFormFile(paramName, filepath.Base(path))
if err != nil {
return nil, err
}
_, err = io.Copy(part, file)
for key, val := range params {
_ = writer.WriteField(key, val)
}
err = writer.Close()
if err != nil {
return nil, err
}
req, err := http.NewRequest("POST", uri, body)
req.Header.Set("Content-Type", writer.FormDataContentType())
return req, err
}
func main() {
path, _ := os.Getwd()
path += "/test.pdf"
extraParams := map[string]string{
"title": "My Document",
"author": "Matt Aimonetti",
"description": "A document with all the Go programming language secrets",
}
request, err := newfileUploadRequest("https://google.com/upload", extraParams, "file", "/tmp/doc.pdf")
if err != nil {
log.Fatal(err)
}
client := &http.Client{}
resp, err := client.Do(request)
if err != nil {
log.Fatal(err)
} else {
body := &bytes.Buffer{}
_, err := body.ReadFrom(resp.Body)
if err != nil {
log.Fatal(err)
}
resp.Body.Close()
fmt.Println(resp.StatusCode)
fmt.Println(resp.Header)
fmt.Println(body)
}
}
@shuaihanhungry
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@e7
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e7 commented Jul 12, 2018

@themihai I'm wondering it too, do you have solution?

@tcr-ableton
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My two cents: using file.Stat is an triggers an unnecessary system call. You could use filepath.Base(path) in order to obtain the filename.

@ramadani
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great solution @bacongobbler, big thanks

@melissafzhang
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I'm having similar issue as @vicbaily528 where the content type is an octet stream. Any ideas how to get around this?

@jk2K
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jk2K commented Feb 25, 2019

var bodyContent []byte
resp.Body.Read(bodyContent)
resp.Body.Close()
fmt.Println(bodyContent)

not work,

body, _ := ioutil.ReadAll(res.Body)
fmt.Println(res)
fmt.Println(string(body))

work well

@yzhanginwa
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Didn't work at first. Just used wireshark and found there is no content-type in the request.

@omerkaya1
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omerkaya1 commented Apr 17, 2019

Thanks for this example.
It helped a lot.
However, if I may, I'd like to contribute to this discussion in the hope that it'll be of use to others and save them time.

As was already pointed out by @ghost when it comes to large files, it's inconvenient to use a buffer, as it consumes a lot of resources.

Luckily, there's a solution. After googling for a while I encountered this article where the idea of in-memory piping is leveraged for multipart uploading.
The advantages of this approach are tremendous in my point of view.
Another example can be found here.
I hope it'll be helpful.
Cheers.

@030
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030 commented May 31, 2019

@jacksonwbrito
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Thanks a lot!

I had the same problem as @vicbaily528 and @melissafzhang, after take a look at mime/multipart/writer.go I decide to replace the CreateFormFile function for a custom one:

func MyCreateFormFile(fieldname, filename, contentType string) (io.Writer, error) {
        h := make(textproto.MIMEHeader)
	h.Set("Content-Disposition", fmt.Sprintf(`form-data; name="%s"; filename="%s"`, escapeQuotes(fieldname), escapeQuotes(filename)))
	h.Set("Content-Type", escapeQuotes(contentType))
	return w.CreatePart(h)
}

this worked for me, I hope it can help you or others who have the same problem.

@prayuditb
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@mattetti, thanks for helpful gist and as @mkaz mentioned, adding Content-Type header works for me

@sebnyberg
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sebnyberg commented Aug 18, 2020

Yet another example:

func uploadFileMultipart(url string, path string) (*http.Response, error) {
	f, err := os.OpenFile(path, os.O_RDONLY, 0644)
	if err != nil {
		return nil, err
	}

	// Reduce number of syscalls when reading from disk.
	bufferedFileReader := bufio.NewReader(f)
	defer f.Close()

	// Create a pipe for writing from the file and reading to
	// the request concurrently.
	bodyReader, bodyWriter := io.Pipe()
	formWriter := multipart.NewWriter(bodyWriter)

	// Store the first write error in writeErr.
	var (
		writeErr error
		errOnce  sync.Once
	)
	setErr := func(err error) {
		if err != nil {
			errOnce.Do(func() { writeErr = err })
		}
	}
	go func() {
		partWriter, err := formWriter.CreateFormFile("file", path)
		setErr(err)
		_, err = io.Copy(partWriter, bufferedFileReader)
		setErr(err)
		setErr(formWriter.Close())
		setErr(bodyWriter.Close())
	}()

	req, err := http.NewRequest(http.MethodPut, url, bodyReader)
	if err != nil {
		return nil, err
	}
	req.Header.Add("Content-Type", formWriter.FormDataContentType())

	// This operation will block until both the formWriter
	// and bodyWriter have been closed by the goroutine,
	// or in the event of a HTTP error.
	resp, err := http.DefaultClient.Do(req)

	if writeErr != nil {
		return nil, writeErr
	}

	return resp, err
}

@faddat
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faddat commented Sep 27, 2020

thank you.

@donnol
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donnol commented Oct 15, 2020

Can I upload two or more files one times?

@mirisbowring
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mirisbowring commented Nov 1, 2020

@donnol - jep, just call the "createFormFile" function multiple times

@toannd96
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toannd96 commented Mar 5, 2021

@vikfrank
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Thanks a lot.. This is really useful.

@pablodz
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pablodz commented Aug 12, 2022

Really useful, it works

@pforpramit
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@sebnyberg Hello, just wanted to understand about the comment "This operation will block until both the formWriter...". Could you please explain, thank you!

@sebnyberg
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sebnyberg commented Dec 22, 2022

@sebnyberg Hello, just wanted to understand about the comment "This operation will block until both the formWriter...". Could you please explain, thank you!

Sure. The request reads from the provided reader until it returns io.EOF. For an io.Pipe, the reader-end will return io.EOF after the write-end is closed. That's what is meant by "blocking". If the bodyWriter is not closed, the the request will last forever (until conn timeout).

https://pkg.go.dev/io#PipeWriter.Close

Closing the formWriter isn't strictly necessary to send the request. However, the formWriters Close() writes a trailer to the multipart message that is required for the request to be valid.

https://pkg.go.dev/mime/multipart#Writer.Close

@pforpramit
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@sebnyberg Thank you very much! :)

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