Add pb_decode_noinit and use it from pb_dec_submessage.

This avoids double initialization when decoding nested submessages.

Update issue 28
Status: FixedInGit

3 files changed, 24 insertions, 4 deletions

diff --git a/docs/reference.rst b/docs/reference.rst
index ec9aec5d..371c155a 100644
--- a/docs/reference.rst
+++ b/docs/reference.rst
@@ -322,6 +322,16 @@ In addition to EOF, the pb_decode implementation supports terminating a message
 
 For optional fields, this function applies the default value and sets *has_<field>* to false if the field is not present.
 
+pb_decode_noinit
+----------------
+Same as `pb_decode`_, except does not apply the default values to fields. ::
+
+    bool pb_decode_noinit(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
+
+(parameters are the same as for `pb_decode`_.)
+
+The destination structure should be filled with zeros before calling this function. Doing a *memset* manually can be slightly faster than using `pb_decode`_ if you don't need any default values.
+
 pb_skip_varint
 --------------
 Skip a varint_ encoded integer without decoding it. ::
diff --git a/pb_decode.c b/pb_decode.c
index 9d65504c..601dc742 100644
--- a/pb_decode.c
+++ b/pb_decode.c
@@ -415,13 +415,11 @@ static void pb_message_set_to_defaults(const pb_field_t fields[], void *dest_str
  * Decode all fields *
  *********************/
 
-bool checkreturn pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct)
+bool checkreturn pb_decode_noinit(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct)
 {
     uint8_t fields_seen[(PB_MAX_REQUIRED_FIELDS + 7) / 8] = {0}; /* Used to check for required fields */
     pb_field_iterator_t iter;
     
-    pb_message_set_to_defaults(fields, dest_struct);
-    
     pb_field_init(&iter, fields, dest_struct);
     
     while (stream->bytes_left)
@@ -470,6 +468,12 @@ bool checkreturn pb_decode(pb_istream_t *stream, const pb_field_t fields[], void
     return true;
 }
 
+bool checkreturn pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct)
+{
+    pb_message_set_to_defaults(fields, dest_struct);
+    return pb_decode_noinit(stream, fields, dest_struct);
+}
+
 /* Field decoders */
 
 bool pb_decode_svarint(pb_istream_t *stream, int64_t *dest)
@@ -615,7 +619,7 @@ bool checkreturn pb_dec_submessage(pb_istream_t *stream, const pb_field_t *field
     if (field->ptr == NULL)
         PB_RETURN_ERROR(stream, "invalid field descriptor");
     
-    status = pb_decode(&substream, (pb_field_t*)field->ptr, dest);
+    status = pb_decode_noinit(&substream, (pb_field_t*)field->ptr, dest);
     pb_close_string_substream(stream, &substream);
     return status;
 }
diff --git a/pb_decode.h b/pb_decode.h
index ad45efbf..483665ee 100644
--- a/pb_decode.h
+++ b/pb_decode.h
@@ -48,6 +48,12 @@ bool pb_read(pb_istream_t *stream, uint8_t *buf, size_t count);
  */
 bool pb_decode(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
 
+/* Same as pb_decode, except does not initialize the destination structure
+ * to default values. This is slightly faster if you need no default values
+ * and just do memset(struct, 0, sizeof(struct)) yourself.
+ */
+bool pb_decode_noinit(pb_istream_t *stream, const pb_field_t fields[], void *dest_struct);
+
 /* --- Helper functions ---
  * You may want to use these from your caller or callbacks.
  */