Allow all valid (and only valid) characters in URL scheme for url_open()

The URL specification allows letters, numbers, plus, hyphen, and period
in the scheme part.  The isalpha() test would allow additional characters
depending on locale settings while rejecting numbers and punctuation.

Originally committed as revision 24306 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/avio.c

@@ -167,29 +167,21 @@ int url_open_protocol (URLContext **puc, struct URLProtocol *up,
     return ret;
 }
 
+#define URL_SCHEME_CHARS                        \
+    "abcdefghijklmnopqrstuvwxyz"                \
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"                \
+    "0123456789+-."
+
 int url_alloc(URLContext **puc, const char *filename, int flags)
 {
     URLProtocol *up;
-    const char *p;
-    char proto_str[128], *q;
-
-    p = filename;
-    q = proto_str;
-    while (*p != '\0' && *p != ':') {
-        /* protocols can only contain alphabetic chars */
-        if (!isalpha(*p))
-            goto file_proto;
-        if ((q - proto_str) < sizeof(proto_str) - 1)
-            *q++ = *p;
-        p++;
-    }
-    /* if the protocol has length 1, we consider it is a dos drive */
-    if (*p == '\0' || is_dos_path(filename)) {
-    file_proto:
+    char proto_str[128];
+    size_t proto_len = strspn(filename, URL_SCHEME_CHARS);
+
+    if (filename[proto_len] != ':' || is_dos_path(filename))
         strcpy(proto_str, "file");
-    } else {
-        *q = '\0';
-    }
+    else
+        av_strlcpy(proto_str, filename, FFMIN(proto_len+1, sizeof(proto_str)));
 
     up = first_protocol;
     while (up != NULL) {