Too strict HTTP Status Line parsing

Alexander Zhuravlev <>
Tue Jun 1 23:22:29 CEST 2010


Hello,

I've tried to use lhttpc library (http://bitbucket.org/etc/lhttpc) to fetch
a resource (http://www.qype.com/review/1376848) and got the following
error:

{{http_error,"HTTP/1.1 200\r\n"},
	[{lhttpc_client,read_response,5},
	{lhttpc_client,execute,8},
	{lhttpc_client,request,9}]} 

I've checked lhttpc source code and found out that to receive and parse an HTTP
response it uses _standard_ erlang module gen_tcp on a socket in
{packet, http} mode. So it looks like the {http_error,"HTTP/1.1 200\r\n"} error was
in fact generated by erlang's http packet parsing code.

I found the following code in packet_parse_http function from
erts/emulator/beam/packet_parser.c file:

...
p0 = ptr;
while (n && SP(ptr)) {
	ptr++; n--;
}
if (ptr==p0) return -1;
...

As far as I understand "HTTP/1.1 200\r\n" line does not have any spaces
after the status code "200", and the function strips \r\n as a first step of
its operation. So the "while" cycle does not run and we get into the
"if (ptr==p0) branch" this basically leads to returning of 
{http_error, "HTTP/1.1 200\r\n"} atom up to the call stack.

Strictly speaking this is not a bug in erlang, but I suppose it
should take a more relaxed approach to HTTP Status Line parsing
and not return http_error if an HTTP response Status Line does not have
a Reason-phrase part.


More information about the erlang-questions mailing list