-f/--format: support percent decoding

Convert percent hexcodes when format mode is enabled:

    m:chat:to@example.com:from@example.com:01234=%30%31%32%33%34

src/xmppipe.c

@@ -1282,11 +1282,27 @@ xmppipe_send_stanza(xmppipe_state_t *state, char *buf0, size_t len)
         return;
     }
 
-    type = tok[1];
-    to = tok[2];
-    body = tok[4];
+    type = xmppipe_fmt_decode(tok[1]);
+
+    if (type == NULL)
+        goto XMPPIPE_ERR;
+
+    to = xmppipe_fmt_decode(tok[2]);
+
+    if (to == NULL)
+        goto XMPPIPE_ERR;
+
+    body = xmppipe_fmt_decode(tok[4]);
+
+    if (body == NULL)
+        goto XMPPIPE_ERR;
 
     xmppipe_send_message(state, to, type, body, strlen(body));
+
+XMPPIPE_ERR:
+    free(type);
+    free(to);
+    free(body);
 }
 
     void

src/xmppipe.h

@@ -104,6 +104,8 @@ typedef struct {
 int xmppipe_fmt_init();
 char *xmppipe_fmt(const char *);
 char *xmppipe_nfmt(const char *, size_t);
+char *xmppipe_fmt_decode(const char *);
+char *xmppipe_nfmt_decode(const char *, size_t);
 int xmppipe_set_nonblock(int fd);
 
 char *xmppipe_servername(char *);

src/xmppipe_fmt.c

@@ -13,6 +13,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 #include "xmppipe.h"
+#include "errno.h"
 
 static unsigned char rfc3986[256];
 
@@ -56,3 +57,51 @@ xmppipe_fmt(const char *s)
 {
     return xmppipe_nfmt(s, strlen(s));
 }
+
+    char *
+xmppipe_nfmt_decode(const char *s, size_t len)
+{
+    char *buf = xmppipe_calloc(len+1, 1);
+    char *p = buf;
+    size_t i = 0;
+    char fmt[3] = {0};
+    char *endptr;
+
+    for (i = 0; i < len; i++) {
+        unsigned char c = s[i];
+        if (c == '%') {
+            unsigned char n = 0;
+
+            if (i + 2 > len) goto XMPPIPE_ERR;
+
+            (void)memcpy(fmt, s+i+1, 2);
+
+            errno = 0;
+            n = strtol(fmt, &endptr, 16);
+
+            if ( (errno != 0) || (endptr == fmt))
+                goto XMPPIPE_ERR;
+
+            *p++ = n;
+            i += 2;
+        }
+        else {
+            *p++ = c;
+        }
+    }
+
+    return buf;
+
+XMPPIPE_ERR:
+    free(buf);
+    return NULL;
+}
+
+    char *
+xmppipe_fmt_decode(const char *s)
+{
+    if (s == NULL)
+        return NULL;
+
+    return xmppipe_nfmt_decode(s, strlen(s));
+}