+/* In proto3, all fields are optional and are only encoded if their value is "non-zero".
+ * This function implements the check for the zero value. */
+static bool pb_check_proto3_default_value(const pb_field_t *field, const void *pData)
+{
+ if (PB_ATYPE(field->type) == PB_ATYPE_STATIC)
+ {
+ if (PB_LTYPE(field->type) == PB_LTYPE_BYTES)
+ {
+ const pb_bytes_array_t *bytes = (const pb_bytes_array_t*)pData;
+ return bytes->size == 0;
+ }
+ else if (PB_LTYPE(field->type) == PB_LTYPE_STRING)
+ {
+ return *(const char*)pData == '\0';
+ }
+ else if (PB_LTYPE(field->type) == PB_LTYPE_FIXED_LENGTH_BYTES)
+ {
+ /* Fixed length bytes is only empty if its length is fixed
+ * as 0. Which would be pretty strange, but we can check
+ * it anyway. */
+ return field->data_size == 0;
+ }
+ else if (PB_LTYPE(field->type) == PB_LTYPE_SUBMESSAGE)
+ {
+ /* Check all fields in the submessage to find if any of them
+ * are non-zero. The comparison cannot be done byte-per-byte
+ * because the C struct may contain padding bytes that must
+ * be skipped.
+ */
+ pb_field_iter_t iter;
+ if (pb_field_iter_begin(&iter, (const pb_field_t*)field->ptr, pb_const_cast(pData)))
+ {
+ do
+ {
+ if (!pb_check_proto3_default_value(iter.pos, iter.pData))
+ {
+ return false;
+ }
+ } while (pb_field_iter_next(&iter));
+ }
+ return true;
+ }
+ }
+
+ {
+ /* Catch-all branch that does byte-per-byte comparison for zero value.
+ *
+ * This is for all pointer fields, and for static PB_LTYPE_VARINT,
+ * UVARINT, SVARINT, FIXED32, FIXED64, EXTENSION fields, and also
+ * callback fields. These all have integer or pointer value which
+ * can be compared with 0.
+ */
+ pb_size_t i;
+ const char *p = (const char*)pData;
+ for (i = 0; i < field->data_size; i++)
+ {
+ if (p[i] != 0)
+ {
+ return false;
+ }
+ }
+
+ return true;
+ }
+}
+
+/* Encode a field with static or pointer allocation, i.e. one whose data
+ * is available to the encoder directly. */
+static bool checkreturn encode_basic_field(pb_ostream_t *stream,