S3 Upload GOLANG different behaviours

README.md

It seems that if you use a file reader as the reader of the request (even if you wrap it into another object), golang's request to S3 will always end with a 501 Not Implemented error response. If you load the same file in memory (e.g. a buffer) this doesn't happen and it works.

go run main.go buffer ./test-file <some presigned string>
works

go run main.go reader ./test-file <some presigned string>
invalid response code: 501 Not Implemented
<Error><Code>NotImplemented</Code><Message>A header you provided implies functionality that is not implemented</Message><Header>Transfer-Encoding</Header><RequestId>F2D54740EA621AA8</RequestId><HostId>uVkv+diBWzEO9xaCIXTj45mm5b6HhIkrcwmBSJxIoJ1XzJeOv+fbEphs58JK9PkTIriENefs41w=</HostId></Error>

main.go

package main

import (
	"bytes"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"os"
	"strconv"
)

func main() {
	if len(os.Args) != 4 {
		fmt.Fprintln(os.Stderr, "ARGS: <mode(buffer|reader)> <filepath> <pre-signedurl>")
		os.Exit(1)
	}

	file, err := os.Open(os.Args[2])
	if err != nil {
		fmt.Fprintln(os.Stderr, err.Error())
		os.Exit(1)
	}

	stat, err := file.Stat()
	if err != nil {
		fmt.Fprintln(os.Stderr, err.Error())
		os.Exit(1)
	}

	var request *http.Request

	switch os.Args[1] {
	case "buffer":
		request, err = requestFromBuffer(os.Args[3], file)
	case "reader":
		request, err = requestFromReader(os.Args[3], file)
	default:
		err = fmt.Errorf("invalid mode: %s", os.Args[1])
	}

	if err != nil {
		fmt.Fprintln(os.Stderr, err.Error())
		os.Exit(1)
	}

	request.Header.Add("Content-Length", strconv.FormatInt(stat.Size(), 10))

	if err := upload(request); err != nil {
		fmt.Fprintln(os.Stderr, err.Error())
		os.Exit(1)
	}

	fmt.Println("done")
}

func upload(req *http.Request) error {
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return fmt.Errorf("request failed: %w", err)
	}

	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := ioutil.ReadAll(resp.Body)
		return fmt.Errorf("invalid response code: %s | body: %s", resp.Status, string(body))
	}

	return nil
}

func requestFromReader(url string, r io.Reader) (*http.Request, error) {
	request, err := http.NewRequest("PUT", url, r)
	if err != nil {
		return nil, fmt.Errorf("failed to upload: %w", err)
	}

	return request, nil
}

func requestFromBuffer(url string, r io.Reader) (*http.Request, error) {
	body := bytes.NewBuffer([]byte{})
	// copy the file content to memory
	if _, err := io.Copy(body, r); err != nil {
		return nil, fmt.Errorf("failed to copy to buffer: %w", err)
	}

	request, err := http.NewRequest("PUT", url, body)
	if err != nil {
		return nil, fmt.Errorf("failed to upload: %w", err)
	}

	return request, nil
}