Decoding a oneof case in nanopb

pb_union_decode.c

typedef struct pb_union_s
{
	const uint32_t tag;
	const pb_msgdesc_t* submsg_desc;
	pb_istream_t stream;
} pb_union_t;

const pb_union_t getUnionType(uint8_t buffer[], size_t size)
{
	pb_istream_t stream = pb_istream_from_buffer(buffer, size);
	pb_wire_type_t wire_type;			
	uint32_t tag;
	bool eof;

	while (pb_decode_tag(&stream, &wire_type, &tag, &eof))
	{
		if (wire_type == PB_WT_STRING)
		{
			pb_field_iter_t iter;
			if (pb_field_iter_begin(&iter, fields, NULL) &&
				pb_field_iter_find(&iter, tag))
			{
				//Found oneof
				pb_union_t unionType = { tag, iter.submsg_desc, stream };
				return unionType;
			}
		}

		//Next
		pb_skip_field(&stream, wire_type);
	}

	return { 0, 0, 0 };
}

bool decodeUnion(void* message, pb_union_t& unionType) 
{
    pb_istream_t substream;
    bool status;
    if (!pb_make_string_substream(&unionType.stream, &substream))
      return false;

    status = pb_decode(&substream, unionType.submsg_desc, message);
    pb_close_string_substream(&unionType.stream, &substream);
    return status;
}