mongoose/docs/c-api/http.h/mg_http_parse_header.md

title	decl_name	symbol_kind	signature
mg_http_parse_header()	mg_http_parse_header	func	int mg_http_parse_header(struct mg_str *hdr, const char *var_name, char *buf, size_t buf_size);

Parse HTTP header hdr. Find variable var_name and store it's value in the buffer buf, buf_size. Return 0 if variable not found, non-zero otherwise.

This function is supposed to parse cookies, authentication headers, etcetera. Example (error handling omitted):

char user[20];
struct mg_str *hdr = mg_get_http_header(hm, "Authorization");
mg_http_parse_header(hdr, "username", user, sizeof(user));

Return length of the variable's value. If buffer is not large enough, or variable not found, 0 is returned.