client.py

import pycurl
import cStringIO

c = pycurl.Curl()

c.setopt(pycurl.VERBOSE, 1)

dummydata = "HI THIS IS SOME DATA"

c.setopt(pycurl.URL, "http://127.0.0.1:9000/noreadbody")
c.setopt(pycurl.UPLOAD, 1)
c.setopt(pycurl.READFUNCTION, cStringIO.StringIO(dummydata).read)
c.setopt(pycurl.INFILESIZE, len(dummydata))
c.setopt(pycurl.HTTPHEADER, ["Expect: 100-continue"])
c.perform()

c.setopt(pycurl.URL, "http://127.0.0.1:9000/readbody")
c.setopt(pycurl.UPLOAD, 1)
c.setopt(pycurl.READFUNCTION, cStringIO.StringIO(dummydata).read)
c.setopt(pycurl.INFILESIZE, len(dummydata))
c.setopt(pycurl.HTTPHEADER, ["Expect: 100-continue"])
c.perform()

server.go

package main

import (
    "fmt"
    "io"
    "io/ioutil"
    "net/http"
)

func hello(w http.ResponseWriter, r *http.Request) {
    if r.URL.Path == "/readbody" {
        ioutil.ReadAll(r.Body)
    }
    io.WriteString(w, "Hello world!")
}

func main() {
    http.HandleFunc("/", hello)
    http.ListenAndServe(":9000", nil)
}

xoutput.txt

* About to connect() to 127.0.0.1 port 9000 (#0)
*   Trying 127.0.0.1... * connected
> PUT /noreadbody HTTP/1.1
User-Agent: PycURL/7.22.0
Host: 127.0.0.1:9000
Accept: */*
Content-Length: 20
Expect: 100-continue

< HTTP/1.1 200 OK
< Date: Thu, 02 Jul 2015 20:18:06 GMT
< Content-Length: 12
< Content-Type: text/plain; charset=utf-8
< 
* Connection #0 to host 127.0.0.1 left intact
* Re-using existing connection! (#0) with host 127.0.0.1
* Connected to 127.0.0.1 (127.0.0.1) port 9000 (#0)
> PUT /readbody HTTP/1.1
User-Agent: PycURL/7.22.0
Host: 127.0.0.1:9000
Accept: */*
Content-Length: 20
Expect: 100-continue

< HTTP/1.1 400 Bad Request
* no chunk, no close, no size. Assume close to signal end
< 
* Closing connection #0