mdns: minor(?) stack usage and performance improvement by letting mdns_readname_loop() copy from pbuf to struct (instead of pbuf->buffer->struct)

src/apps/mdns/mdns.c

@@ -261,15 +261,8 @@ struct mdns_answer {
   u16_t rd_offset;
 };
 
-/**
- * Add a label part to a domain
- * @param domain The domain to add a label to
- * @param label The label to add, like <hostname>, 'local', 'com' or ''
- * @param len The length of the label
- * @return ERR_OK on success, an err_t otherwise if label too long
- */
 err_t
-mdns_domain_add_label(struct mdns_domain *domain, const char *label, u8_t len)
+mdns_domain_add_label_base(struct mdns_domain *domain, u8_t len)
 {
   if (len > MDNS_LABEL_MAXLEN) {
     return ERR_VAL;
@@ -283,6 +276,23 @@ mdns_domain_add_label(struct mdns_domain *domain, const char *label, u8_t len)
   }
   domain->name[domain->length] = len;
   domain->length++;
+  return ERR_OK;
+}
+
+/**
+ * Add a label part to a domain
+ * @param domain The domain to add a label to
+ * @param label The label to add, like <hostname>, 'local', 'com' or ''
+ * @param len The length of the label
+ * @return ERR_OK on success, an err_t otherwise if label too long
+ */
+err_t
+mdns_domain_add_label(struct mdns_domain *domain, const char *label, u8_t len)
+{
+  err_t err = mdns_domain_add_label_base(domain, len);
+  if (err != ERR_OK) {
+    return err;
+  }
   if (len) {
     MEMCPY(&domain->name[domain->length], label, len);
     domain->length += len;
@@ -290,6 +300,27 @@ mdns_domain_add_label(struct mdns_domain *domain, const char *label, u8_t len)
   return ERR_OK;
 }
 
+/**
+ * Add a label part to a domain (@see mdns_domain_add_label but copy directly from pbuf)
+ */
+static err_t
+mdns_domain_add_label_pbuf(struct mdns_domain *domain, const struct pbuf *p, u16_t offset, u8_t len)
+{
+  err_t err = mdns_domain_add_label_base(domain, len);
+  if (err != ERR_OK) {
+    return err;
+  }
+  if (len) {
+    if (pbuf_copy_partial(p, &domain->name[domain->length], len, offset) != len) {
+      /* take back the ++ done before */
+      domain->length--;
+      return ERR_ARG;
+    }
+    domain->length += len;
+  }
+  return ERR_OK;
+}
+
 /**
  * Internal readname function with max 6 levels of recursion following jumps
  * while decompressing name
@@ -333,22 +364,16 @@ mdns_readname_loop(struct pbuf *p, u16_t offset, struct mdns_domain *domain, uns
 
     /* normal label */
     if (c <= MDNS_LABEL_MAXLEN) {
-      u8_t label[MDNS_LABEL_MAXLEN];
       err_t res;
 
       if (c + domain->length >= MDNS_DOMAIN_MAXLEN) {
         return MDNS_READNAME_ERROR;
       }
-      if (c != 0) {
-        if (pbuf_copy_partial(p, label, c, offset) != c) {
-          return MDNS_READNAME_ERROR;
-        }
-        offset += c;
-      }
-      res = mdns_domain_add_label(domain, (char *) label, c);
+      res = mdns_domain_add_label_pbuf(domain, p, offset, c);
       if (res != ERR_OK) {
         return MDNS_READNAME_ERROR;
       }
+      offset += c;
     } else {
       /* bad length byte */
       return MDNS_READNAME_ERROR;