502 Bad gateway when using Transfer encoding Python

Question

I'm trying to build a barebones HTTP/1.1 client using just sockets. Whenever i try to use Transfer-encoding: chuncked, the code give me following status:502 Bad Gateway.

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print ("socket successfully created.")
host_ip = socket.gethostbyname('www.google.com')
s.connect((host_ip,80))
op = "GET / HTTP/1.1\r\nHost: www.google.com\r\nTransfer-encoding: chunked\r\nConnection: close\r\n\r\n"
s.sendall(op.encode('utf-8'))
print(s.recv(500000))
s.close()

This is giving me following o/p:

socket successfully created.
b'HTTP/1.1 502 Bad Gateway\r\nContent-Type: text/html; charset=UTF-8\r\nReferrer-Policy: no-referrer\r\nContent-Length: 1613\r\nDate: Sat, 23 Sep 2017 00:42:04 GMT\r\nConnection: close\r\n\r\n<!DOCTYPE html>\n<html lang=en>\n  <meta charset=utf-8>\n  <meta name=viewport content="initial-scale=1, minimum-scale=1, width=device-width">\n  <title>Error 502 (Server Error)!!1</title>\n  <style>\n    *{margin:0;padding:0}html,code{font:15px/22px arial,sans-serif}html{background:#fff;color:#222;padding:15px}body{margin:7% auto 0;max-width:390px;min-height:180px;padding:30px 0 15px}* > body{background:url(//www.google.com/images/errors/robot.png) 100% 5px no-repeat;padding-right:205px}p{margin:11px 0 22px;overflow:hidden}ins{color:#777;text-decoration:none}a img{border:0}@media screen and (max-width:772px){body{background:none;margin-top:0;max-width:none;padding-right:0}}#logo{background:url(//www.google.com/images/branding/googlelogo/1x/googlelogo_color_150x54dp.png) no-repeat;margin-left:-5px}@media only screen and (min-resolution:192dpi){#logo{background:url(//www.google.com/images/branding/googlelogo/2x/googlelogo_color_150x54dp.png) no-repeat 0% 0%/100% 100%;-moz-border-image:url(//www.google.com/images/branding/googlelogo/2x/googlelogo_color_150x54dp.png) 0}}@media only screen and (-webkit-min-device-pixel-ratio:2){#logo{background:url(//www.google.com/images/branding/googlelogo/2x/googlelogo_color_150x54dp.png) no-repeat;-webkit-background-size:100% 100%}}#logo{display:inline-block;height:54px;width:150px}\n  </style>\n  <a href=//www.google.com/><span id=logo aria-label=Google></span></a>\n  <p><b>502.</b> <ins>That\xe2\x80\x99s an error.</ins>\n  <p>The server encountered a temporary error and could not complete your request.<p>Please try again in 30 seconds.  <ins>That\xe2\x80\x99s all we know.</ins>\n'

If I remove the 'Transfer-encoding: chunked' header, it works fine.

score 2 · Answer 1 · answered Sep 23 '17 at 04:44

It is not clear why you are using Transfer-Encoding: chunked in the first place. You are doing a GET request which means that there is no request body, i.e. no request content. And if there is no content the non-existing content can not be encoded.

Apart from that: chunked Transfer-Encoding is only defined with HTTP/1.1 but not with HTTP/1.0. If the server supports only HTTP/1.0 it will not understand what you mean. And, even many system which claim to support HTTP/1.1 does not understand Transfer-Encoding within a request because this is seldom used, i.e. browsers don't use it. Thus you can only use chunked Transfer-Encoding if you can be sure that the server itself and any middleboxes in between (i.e. firewall, load balancer, reverse proxy...) will support it.

502 Bad gateway when using Transfer encoding Python

1 Answers1