Add a convenience function pb_get_encoded_size()

There is minimal size penalty from this, and it is probably much more
intuitive to use than PB_OSTREAM_SIZING itself.

This has been suggested before also, but I ended up refusing it back
them. Reconsidering it now, I see that an intuitive API is much better
than any amount of documentation explaining a non-intuitive API.

Update issue 16
Status: FixedInGit

pb_encode.c

@@ -378,6 +378,17 @@ bool pb_encode_delimited(pb_ostream_t *stream, const pb_field_t fields[], const
     return pb_encode_submessage(stream, fields, src_struct);
 }
 
+bool pb_get_encoded_size(size_t *size, const pb_field_t fields[], const void *src_struct)
+{
+    pb_ostream_t stream = PB_OSTREAM_SIZING;
+    
+    if (!pb_encode(&stream, fields, src_struct))
+        return false;
+    
+    *size = stream.bytes_written;
+    return true;
+}
+
 /********************
  * Helper functions *
  ********************/

pb_encode.h

@@ -71,6 +71,10 @@ bool pb_encode(pb_ostream_t *stream, const pb_field_t fields[], const void *src_
  */
 bool pb_encode_delimited(pb_ostream_t *stream, const pb_field_t fields[], const void *src_struct);
 
+/* Encode the message to get the size of the encoded data, but do not store
+ * the data. */
+bool pb_get_encoded_size(size_t *size, const pb_field_t fields[], const void *src_struct);
+
 /**************************************
  * Functions for manipulating streams *
  **************************************/

tests/encode_unittests/encode_unittests.c

@@ -281,6 +281,15 @@ int main()
         TEST(WRITES(pb_encode_delimited(&s, IntegerContainer_fields, &msg),
                     "\x09\x0A\x07\x0A\x05\x01\x02\x03\x04\x05"))
     }
+
+    {
+        IntegerContainer msg = {{5, {1,2,3,4,5}}};
+        size_t size;
+        
+        COMMENT("Test pb_get_encoded_size.")
+        TEST(pb_get_encoded_size(&size, IntegerContainer_fields, &msg) &&
+             size == 9);
+    }
     
     {
         uint8_t buffer[10];