reftable/block: create public interface for reading blocks

While users of the reftable library wouldn't generally require access to
individual blocks in a reftable table, there are valid usecases where
one may require low-level access to them. One such upcoming usecase in
the Git codebase is to implement consistency checks for the reftable
library where we want to verify each block individually.

Create a public interface for reading blocks. The interface isn't yet
complete and lacks e.g. a way to read individual records from a block.
Such missing functionality will be backfilled in subsequent commits.

Note that this change also requires us to expose `reftable_buf`, which
is used by the `reftable_block_first_key()` function.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/reftable/reftable-basics.h b/reftable/reftable-basics.h
index ed7c7c9ac2..6d73f19c85 100644
--- a/reftable/reftable-basics.h
+++ b/reftable/reftable-basics.h
@@ -11,6 +11,14 @@
 
 #include <stddef.h>
 
+/* A buffer that contains arbitrary byte slices. */
+struct reftable_buf {
+	size_t alloc;
+	size_t len;
+	char *buf;
+};
+#define REFTABLE_BUF_INIT { 0 }
+
 /*
  * Hash functions understood by the reftable library. Note that the values are
  * arbitrary and somewhat random such that we can easily detect cases where the