For a 30MB file we saw difference of about 3minutes+ with Go net/http when compared to Curl.
Condition/Environment: When network is slow.

Is this reproducible with client and server being on the same machine ? Would like to investigate this on my laptop.

@agnivade Yes this is continuously reproducible, provided we delay the n/w.

Oh, I see this is for http. Could you also kindly check for http2 client and see if you get similar results ?

This would help us pin-point the issue faster.

I tested with http2 transport and there is a small difference between Go code and Curl.
Network Condition: Down:400kbit/s Up:400kbit/s RTT:200ms
Ex: 1MB file - Avg upload speed Curl ~25s Go ~29s
10MB - Avg upload speed Curl ~7m:30s Go ~7m:56s

@subbu05 have you had a chance to run the same code using http.DefaultTransport which is the core of the Client? That could help us narrow down where the bottleneck is.

/cc @bradfitz

@meirf I tested with http.DefaultTransport and I see curl and golang client file upload are all most ~same rate.

@subbu05 using your exact code as the client and the below Go code as the server, I am not seeing any difference in performance vs curl. Can you please show us the exact command you are using to run https://github.com/sashgorokhov/docker-nginx-webdav?

Go server:

package main

import (
	"fmt"
	"io"
	"net/http"
	"os"
	"log"
)

func main() {
	http.HandleFunc("/file.txt", uploadHandler)
	http.ListenAndServe(":9080", nil)
}

func uploadHandler(w http.ResponseWriter, r *http.Request) {
	log.Printf("uploadHandler start")
	file, err := os.Create("./result")
	if err != nil {
		panic(err)
	}
	n, err := io.Copy(file, r.Body)
	if err != nil {
		panic(err)
	}

	w.Write([]byte(fmt.Sprintf("%d bytes are recieved.\n", n)))
	log.Printf("uploadHandler end")
}

curl -X PUT -H "Content-Type: application/octet-stream" --data-binary '@file1mb.txt' http://127.0.0.1:9080/file.txt

@meirf
Steps:
0. Install throttle - https://github.com/sitespeedio/throttle

1. Started the nginx container - docker run --name webdav -p 9080:80 -v /media:/media -d sashgorokhov/webdav
2. to mimic the latency in the network run the command throttle --profile 3gslow
3. run curl command - time curl -X PUT -T file.txt "http://localhost:9080/file1.txt"
4. run go client with same file.txt to the url http://localhost:9080/file2.txt (capture the time)

Observed:
30Mb file upload - I am seeing 3 minutes+ difference between curl and go.

@meirf, the title of this bug no longer makes sense, since DefaultClient uses DefaultTransport. I don't see how they could have different speeds.