reftable: (de)serialization for the polymorphic record type.

The reftable format is structured as a sequence of blocks, and each block
contains a sequence of prefix-compressed key-value records. There are 4 types of
records, and they have similarities in how they must be handled. This is
achieved by introducing a polymorphic 'record' type that encapsulates ref, log,
index and object records.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: hanwen

Makefile

@@ -2453,7 +2453,9 @@ REFTABLE_OBJS += reftable/basics.o
 REFTABLE_OBJS += reftable/error.o
 REFTABLE_OBJS += reftable/blocksource.o
 REFTABLE_OBJS += reftable/publicbasics.o
+REFTABLE_OBJS += reftable/record.o
 
+REFTABLE_TEST_OBJS += reftable/record_test.o
 REFTABLE_TEST_OBJS += reftable/test_framework.o
 REFTABLE_TEST_OBJS += reftable/basics_test.o
 

reftable/constants.h

@@ -0,0 +1,21 @@
+/*
+Copyright 2020 Google LLC
+
+Use of this source code is governed by a BSD-style
+license that can be found in the LICENSE file or at
+https://developers.google.com/open-source/licenses/bsd
+*/
+
+#ifndef CONSTANTS_H
+#define CONSTANTS_H
+
+#define BLOCK_TYPE_LOG 'g'
+#define BLOCK_TYPE_INDEX 'i'
+#define BLOCK_TYPE_REF 'r'
+#define BLOCK_TYPE_OBJ 'o'
+#define BLOCK_TYPE_ANY 0
+
+#define MAX_RESTARTS ((1 << 16) - 1)
+#define DEFAULT_BLOCK_SIZE 4096
+
+#endif