urlapi: make Curl_is_absolute_url always use MAX_SCHEME_LEN

Instad of having all callers pass in the maximum length, always use
it. The passed in length is instead used only as the length of the
target buffer for to storing the scheme name in, if used.

Added the scheme max length restriction to the curl_url_set.3 man page.

Follow-up to 45bcb2eaa7

Closes #8047

docs/libcurl/curl_url_set.3

@@ -58,7 +58,8 @@ Pass a pointer to a null-terminated string to the \fIurl\fP parameter. The
 string must point to a correctly formatted "RFC 3986+" URL or be a NULL
 pointer.
 .IP CURLUPART_SCHEME
-Scheme cannot be URL decoded on set.
+Scheme cannot be URL decoded on set. libcurl only accepts setting schemes up
+to 40 bytes long.
 .IP CURLUPART_USER
 .IP CURLUPART_PASSWORD
 .IP CURLUPART_OPTIONS

lib/transfer.c

@@ -1631,7 +1631,7 @@ CURLcode Curl_follow(struct Curl_easy *data,
 
   if((type != FOLLOW_RETRY) &&
      (data->req.httpcode != 401) && (data->req.httpcode != 407) &&
-     Curl_is_absolute_url(newurl, NULL, MAX_SCHEME_LEN))
+     Curl_is_absolute_url(newurl, NULL, 0))
     /* If this is not redirect due to a 401 or 407 response and an absolute
        URL: don't allow a custom port number */
     disallowport = TRUE;

lib/url.c

@@ -1948,7 +1948,7 @@ static CURLcode parseurlandfillconn(struct Curl_easy *data,
     return CURLE_OUT_OF_MEMORY;
 
   if(data->set.str[STRING_DEFAULT_PROTOCOL] &&
-     !Curl_is_absolute_url(data->state.url, NULL, MAX_SCHEME_LEN)) {
+     !Curl_is_absolute_url(data->state.url, NULL, 0)) {
     char *url = aprintf("%s://%s", data->set.str[STRING_DEFAULT_PROTOCOL],
                         data->state.url);
     if(!url)

lib/urlapi-int.h

@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -22,8 +22,6 @@
  *
  ***************************************************************************/
 #include "curl_setup.h"
-/* scheme is not URL encoded, the longest libcurl supported ones are... */
-#define MAX_SCHEME_LEN 40
 
 bool Curl_is_absolute_url(const char *url, char *scheme, size_t buflen);
 

lib/urlapi.c

@@ -50,6 +50,9 @@
    ((str)[1] == ':' || (str)[1] == '|') && \
    ((str)[2] == '/' || (str)[2] == '\\' || (str)[2] == 0))
 
+/* scheme is not URL encoded, the longest libcurl supported ones are... */
+#define MAX_SCHEME_LEN 40
+
 /* Internal representation of CURLU. Point to URL-encoded strings. */
 struct Curl_URL {
   char *scheme;
@@ -228,21 +231,22 @@ static void strcpy_url(char *output, const char *url, bool relative)
 }
 
 /*
- * Returns true if the given URL is absolute (as opposed to relative) within
- * the buffer size. Returns the scheme in the buffer if TRUE and 'buf' is
- * non-NULL.
+ * Returns true if the given URL is absolute (as opposed to relative). Returns
+ * the scheme in the buffer if TRUE and 'buf' is non-NULL. The buflen must
+ * be larger than MAX_SCHEME_LEN if buf is set.
  */
 bool Curl_is_absolute_url(const char *url, char *buf, size_t buflen)
 {
   size_t i;
-
-  if(buf && buflen)
+  DEBUGASSERT(!buf || (buflen > MAX_SCHEME_LEN));
+  (void)buflen; /* only used in debug-builds */
+  if(buf)
     buf[0] = 0; /* always leave a defined value in buf */
 #ifdef WIN32
   if(STARTS_WITH_DRIVE_PREFIX(url))
     return FALSE;
 #endif
-  for(i = 0; i < buflen; ++i) {
+  for(i = 0; i < MAX_SCHEME_LEN; ++i) {
     char s = url[i];
     if(s && (ISALNUM(s) || (s == '+') || (s == '-') || (s == '.') )) {
       /* RFC 3986 3.1 explains:
@@ -817,7 +821,7 @@ static CURLUcode seturl(const char *url, CURLU *u, unsigned int flags)
   hostname = &path[urllen + 1];
   hostname[0] = 0;
 
-  if(Curl_is_absolute_url(url, schemebuf, sizeof(schemebuf) - 1)) {
+  if(Curl_is_absolute_url(url, schemebuf, sizeof(schemebuf))) {
     url_has_scheme = TRUE;
     schemelen = strlen(schemebuf);
   }
@@ -1530,7 +1534,7 @@ CURLUcode curl_url_set(CURLU *u, CURLUPart what,
     char *redired_url;
     CURLU *handle2;
 
-    if(Curl_is_absolute_url(part, NULL, MAX_SCHEME_LEN)) {
+    if(Curl_is_absolute_url(part, NULL, 0)) {
       handle2 = curl_url();
       if(!handle2)
         return CURLUE_OUT_OF_MEMORY;