Pass extrametadata as record instead of keys and values

We define extrametadata as record schema. Currently it has only json schema and its length. We can add more if we need any useful thing.

We needed to pass json schema since avro writer omits field-ids while converting schema to json. Now, when we pass the json schema, it will use it instead with filled field-ids.

lang/c/src/datafile.c

@@ -81,12 +81,14 @@ static int write_header(avro_file_writer_t w, avro_value_t *extra_meta)
 	avro_writer_t schema_writer;
 	const avro_encoding_t *enc = &avro_binary_encoding;
 	int64_t schema_len;
-	size_t extra_meta_index;
-	size_t extra_meta_size = 0;
 
+	const char *json_schema = NULL;
+	size_t json_schema_len = 0;
 	if (extra_meta != NULL)
 	{
-		check(rval, avro_value_get_size(extra_meta, &extra_meta_size));
+		avro_value_t meta_schema = {0};
+		check(rval, avro_value_get_by_name(extra_meta, "avroschema", &meta_schema, NULL));
+		check(rval, avro_value_get_string(&meta_schema, &json_schema, &json_schema_len));
 	}
 
 	/* Generate random sync */
@@ -95,34 +97,30 @@ static int write_header(avro_file_writer_t w, avro_value_t *extra_meta)
 	check(rval, avro_write(w->writer, "Obj", 3));
 	check(rval, avro_write(w->writer, &version, 1));
 
-	check(rval, enc->write_long(w->writer, 2 + extra_meta_size));
+	check(rval, enc->write_long(w->writer, 2));
 	check(rval, enc->write_string(w->writer, "avro.codec"));
 	check(rval, enc->write_bytes(w->writer, w->codec->name, strlen(w->codec->name)));
 	check(rval, enc->write_string(w->writer, "avro.schema"));
 	schema_writer =
 	    avro_writer_memory(&w->schema_buf[0], sizeof(w->schema_buf));
-	rval = avro_schema_to_json(w->writers_schema, schema_writer);
+
+	if (json_schema) {
+		rval = avro_write(schema_writer, (char *)json_schema, strlen(json_schema));
+	}
+	else {
+		rval = avro_schema_to_json(w->writers_schema, schema_writer);
+	}
+
 	if (rval) {
 		avro_writer_free(schema_writer);
 		return rval;
 	}
+
 	schema_len = avro_writer_tell(schema_writer);
 	avro_writer_free(schema_writer);
 	check(rval,
 	      enc->write_bytes(w->writer, w->schema_buf, schema_len));
 
-	for (extra_meta_index = 0; extra_meta_index < extra_meta_size; extra_meta_index++) {
-		avro_value_t child;
-		const char *key;
-		const void *value;
-		size_t value_len;
-
-		check(rval, avro_value_get_by_index(extra_meta, extra_meta_index, &child, &key));
-		check(rval, avro_value_get_bytes(&child, &value, &value_len));
-		check(rval, enc->write_string(w->writer, key));
-		check(rval, enc->write_bytes(w->writer, value, value_len));
-	}
-
 	check(rval, enc->write_long(w->writer, 0));
 	return write_sync(w);
 }