Implement limitedRead function for client side

MaxBytesReader is only documented for server side reads, so we're using
a local limitedRead function instead that uses an io.LimitedReader.

Declared limits in a commented constant

client/lib/rendezvous.go

@@ -11,6 +11,7 @@ package lib
 import (
 	"bytes"
 	"errors"
+	"io"
 	"io/ioutil"
 	"log"
 	"net/http"
@@ -23,6 +24,7 @@ const (
 	BrokerError503        string = "No snowflake proxies currently available."
 	BrokerError400        string = "You sent an invalid offer in the request."
 	BrokerErrorUnexpected string = "Unexpected error, no answer."
+	readLimit                    = 100000 //Maximum number of bytes to be read from an HTTP response
 )
 
 // Signalling Channel to the Broker.
@@ -64,6 +66,23 @@ func NewBrokerChannel(broker string, front string, transport http.RoundTripper)
 	return bc
 }
 
+func limitedRead(r io.Reader, limit int64) ([]byte, error) {
+	p, err := ioutil.ReadAll(&io.LimitedReader{r, limit})
+	if err != nil {
+		return p, err
+	}
+
+	//Check to see if limit was exceeded
+	var tmp [1]byte
+	_, err = io.ReadFull(r, tmp[:])
+	if err == io.EOF {
+		err = nil
+	} else if err == nil {
+		err = io.ErrUnexpectedEOF
+	}
+	return p, err
+}
+
 // Roundtrip HTTP POST using WebRTC SessionDescriptions.
 //
 // Send an SDP offer to the broker, which assigns a proxy and responds
@@ -91,7 +110,7 @@ func (bc *BrokerChannel) Negotiate(offer *webrtc.SessionDescription) (
 
 	switch resp.StatusCode {
 	case http.StatusOK:
-		body, err := ioutil.ReadAll(http.MaxBytesReader(nil, resp.Body, 100000))
+		body, err := limitedRead(resp.Body, readLimit)
 		if nil != err {
 			return nil, err
 		}