Python Extract JSON from HTTP Response

Question

Say I have the following HTTP request:

GET /4 HTTP/1.1
Host: graph.facebook.com

And the server returns the following response:

HTTP/1.1 200 OK
Access-Control-Allow-Origin: *
Cache-Control: private, no-cache, no-store, must-revalidate
Content-Type: text/javascript; charset=UTF-8
ETag: "539feb8aee5c3d20a2ebacd02db380b27243b255"
Expires: Sat, 01 Jan 2000 00:00:00 GMT
Pragma: no-cache
X-FB-Rev: 1070755
X-FB-Debug: pC4b0ONpdhLwBn6jcabovcZf44bkfKSEguNsVKuSI1I=
Date: Wed, 08 Jan 2014 01:22:36 GMT
Connection: keep-alive
Content-Length: 172

{"id":"4","name":"Mark Zuckerberg","first_name":"Mark","last_name":"Zuckerberg","link":"http:\/\/www.facebook.com\/zuck","username":"zuck","gender":"male","locale":"en_US"}

Since the Content-Lengh header depends on the length of the content, I cannot simply split by the Content-Length: 172 string. How can I extract the JSON and headers separately? They are both important to my program. I am using this code to get the response:

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(("graph.facebook.com", 80))
s.send("GET /"+str(id)+"/picture HTTP/1.1\r\nHost: graph.facebook.com\r\n\r\n")
data = s.recv(1024)
s.close()
json_string = (somehow extract this)
userdata = json.loads(json_string)

Answer 1

The easy way to do this is to use an HTTP library. For example:

import json
import urllib2

r = urllib2.urlopen("http://graph.facebook.com/{}/picture".format(id))
json_string = r.read()
userdata = json.loads(json_string)

If you really want to parse it yourself, the HTTP protocol guarantees that headers and body are separated by an empty line, and that this will be the first empty line anywhere in the response, so it's not that hard:

data = s.recv(1024)
header, _, json_string = data.partition('\r\n\r\n')
userdata = json.loads(json_string)

There are some obvious down sides to this—as written, your code won't work if the response is longer than 1K, or if the kernel doesn't give you the whole response in a single recv (which it's never guaranteed to do), or if the server redirects you or gives you a 100 CONTINUE before the real response, or if the server decides to send back a chunked or MIME-multipart or other response instead of a flat body, or…