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

title	decl_name	symbol_kind	signature
mg_url_decode()	mg_url_decode	func	int mg_url_decode(const char *src, int src_len, char *dst, int dst_len, int is_form_url_encoded);

Decode URL-encoded string.

Source string is specified by (src, src_len), and destination is (dst, dst_len). If is_form_url_encoded is non-zero, then + character is decoded as a blank space character. This function guarantees to \0-terminate the destination. If destination is too small, then source string is partially decoded and -1 is returned. Otherwise, a length of decoded string is returned, not counting final \0.