Line 1 is the “request line”. It is always composed of 3 fields :
- a METHOD : GET
- a URI : /serv/login.php?lang=en&profile=2
- a version tag : HTTP/1.1
All of them are delimited by what the standard calls LWS (linear white spaces), which are commonly spaces, but can also be tabs or line feeds/carriage returns followed by spaces/tabs. The method itself cannot contain any colon (‘:’) and is limited to alphabetic letters. All those various combinations make it desirable that HAProxy performs the splitting itself rather than leaving it to the user to write a complex or inaccurate regular expression.
The URI itself can have several forms :
- A “relative URI” :
- An “absolute URI”, also called a “URL” :
- a star (‘*’) :
- an address:port combination : 192.168.0.12:80
It is a complete URL without the host part. This is generally what is received by servers, reverse proxies and transparent proxies.
It is composed of a “scheme” (the protocol name followed by ‘://’), a host name or address, optionally a colon (‘:’) followed by a port number, then a relative URI beginning at the first slash (‘/’) after the address part.
This is generally what proxies receive, but a server supporting HTTP/1.1 must accept this form too.
This form is only accepted in association with the OPTIONS method and is not reliable. It is used to inquiry a next hop’s capabilities.
This is used with the CONNECT method, which is used to establish TCP tunnels through HTTP proxies, generally for HTTPS, but sometimes for other protocols too.
In a relative URI, two sub-parts are identified. The part before the question mark is called the “path”. It is typically the relative path to static objects on the server. The part after the question mark is called the “query string”.
It is mostly used with GET requests sent to dynamic scripts and is very specific to the language, framework or application in use.