Allow $repo expansion in 'Server' config lines

Small change (addition of a 'strreplace' function) which replaces
any $repo tokens found in a server line with the name of the repo
or section being processed.

While this is more simplistic than suggestions on flyspray, it works
and I think it is cleaner.  Merits can be discussed further.

Ref: FS#6389

Signed-off-by: Aaron Griffin <aaronmgriffin@gmail.com>

lib/libalpm/alpm.c

@@ -1059,11 +1059,15 @@ int SYMEXPORT alpm_parse_config(char *file, alpm_cb_db_register callback, const
 					}
 				} else {
 					if(strcmp(origkey, "Server") == 0 || strcmp(key, "SERVER") == 0) {
-						/* add to the list */
+						/* let's attempt a replacement for the current repo */
-						if(alpm_db_setserver(db, ptr) != 0) {
+						char *server = _alpm_strreplace(ptr, "$repo", section);
+
+						if(alpm_db_setserver(db, server) != 0) {
 							/* pm_errno is set by alpm_db_setserver */
 							return(-1);
 						}
+
+						free(server);
 					} else {
 						RET_ERR(PM_ERR_CONF_BAD_SYNTAX, -1);
 					}

lib/libalpm/util.c

@@ -205,6 +205,51 @@ char *_alpm_strtrim(char *str)
 	return(str);
 }
 
+/* Helper function for _alpm_strreplace */
+static void _strnadd(char **str, const char *append, unsigned int count)
+{
+	if(*str) {
+		*str = realloc(*str, strlen(*str) + count + 1);
+	} else {
+		*str = calloc(sizeof(char), count + 1);
+	}
+
+	strncat(*str, append, count);
+}
+
+/* Replace all occurances of 'needle' with 'replace' in 'str', returning
+ * a new string (must be free'd) */
+char *_alpm_strreplace(const char *str, const char *needle, const char *replace)
+{
+	const char *p, *q;
+	p = q = str;
+
+	char *newstr = NULL;
+	unsigned int needlesz = strlen(needle),
+							 replacesz = strlen(replace);
+
+	while (1) {
+		q = strstr(p, needle);
+		if(!q) { /* not found */ 
+			if(*p) {
+				/* add the rest of 'p' */
+				_strnadd(&newstr, p, strlen(p));
+			}
+			break;
+		} else { /* found match */
+			if(q > p){
+				/* add chars between this occurance and last occurance, if any */
+				_strnadd(&newstr, p, q - p);
+			}
+			_strnadd(&newstr, replace, replacesz);
+			p = q + needlesz;
+		}
+	}
+
+	return newstr;
+}
+
+
 /* Create a lock file
 */
 int _alpm_lckmk(const char *file)

lib/libalpm/util.h

@@ -48,6 +48,7 @@ int _alpm_makepath(const char *path);
 int _alpm_copyfile(const char *src, const char *dest);
 char *_alpm_strtoupper(char *str);
 char *_alpm_strtrim(char *str);
+char *_alpm_strreplace(const char *str, const char *needle, const char *replace);
 int _alpm_lckmk(const char *file);
 int _alpm_lckrm(const char *file);
 int _alpm_unpack(const char *archive, const char *prefix, const char *fn);