Session *sn is the session that generated the request. The structure named by sn contains a pointer to a netbuf called inbuf. If the parameter buf is NULL, the function automatically uses inbuf.
Note that sn is an optional parameter that is used for error logs. Use NULL if you wish.
netbuf *buf is the network buffer to be scanned for HTTP headers.
char *t defines a string of length REQ_MAX_LINE. This is an optimization for the internal code to reduce usage of runtime stack.
pblock *headers is the parameter block to receive the headers.