1 files changed, 291 insertions, 170 deletions

diff --git a/reftable/writer.c b/reftable/writer.c
index 2e322a5683..be0fae6cb2 100644
--- a/reftable/writer.c
+++ b/reftable/writer.c
@@ -49,8 +49,14 @@ static int padded_write(struct reftable_writer *w, uint8_t *data, size_t len,
 {
 	int n = 0;
 	if (w->pending_padding > 0) {
-		uint8_t *zeroed = reftable_calloc(w->pending_padding);
-		int n = w->write(w->write_arg, zeroed, w->pending_padding);
+		uint8_t *zeroed;
+		int n;
+
+		zeroed = reftable_calloc(w->pending_padding, sizeof(*zeroed));
+		if (!zeroed)
+			return -1;
+
+		n = w->write(w->write_arg, zeroed, w->pending_padding);
 		if (n < 0)
 			return n;
 
@@ -102,43 +108,61 @@ static int writer_write_header(struct reftable_writer *w, uint8_t *dest)
 	return header_size(writer_version(w));
 }
 
-static void writer_reinit_block_writer(struct reftable_writer *w, uint8_t typ)
+static int writer_reinit_block_writer(struct reftable_writer *w, uint8_t typ)
 {
-	int block_start = 0;
-	if (w->next == 0) {
+	int block_start = 0, ret;
+
+	if (w->next == 0)
 		block_start = header_size(writer_version(w));
-	}
 
-	strbuf_release(&w->last_key);
-	block_writer_init(&w->block_writer_data, typ, w->block,
-			  w->opts.block_size, block_start,
-			  hash_size(w->opts.hash_id));
+	reftable_buf_reset(&w->last_key);
+	ret = block_writer_init(&w->block_writer_data, typ, w->block,
+				w->opts.block_size, block_start,
+				hash_size(w->opts.hash_id));
+	if (ret < 0)
+		return ret;
+
 	w->block_writer = &w->block_writer_data;
 	w->block_writer->restart_interval = w->opts.restart_interval;
-}
 
-static struct strbuf reftable_empty_strbuf = STRBUF_INIT;
+	return 0;
+}
 
-struct reftable_writer *
-reftable_new_writer(ssize_t (*writer_func)(void *, const void *, size_t),
-		    void *writer_arg, struct reftable_write_options *opts)
+int reftable_writer_new(struct reftable_writer **out,
+			ssize_t (*writer_func)(void *, const void *, size_t),
+			int (*flush_func)(void *),
+			void *writer_arg, const struct reftable_write_options *_opts)
 {
-	struct reftable_writer *wp =
-		reftable_calloc(sizeof(struct reftable_writer));
-	strbuf_init(&wp->block_writer_data.last_key, 0);
-	options_set_defaults(opts);
-	if (opts->block_size >= (1 << 24)) {
-		/* TODO - error return? */
-		abort();
+	struct reftable_write_options opts = {0};
+	struct reftable_writer *wp;
+
+	wp = reftable_calloc(1, sizeof(*wp));
+	if (!wp)
+		return REFTABLE_OUT_OF_MEMORY_ERROR;
+
+	if (_opts)
+		opts = *_opts;
+	options_set_defaults(&opts);
+	if (opts.block_size >= (1 << 24))
+		BUG("configured block size exceeds 16MB");
+
+	reftable_buf_init(&wp->block_writer_data.last_key);
+	reftable_buf_init(&wp->last_key);
+	reftable_buf_init(&wp->scratch);
+	REFTABLE_CALLOC_ARRAY(wp->block, opts.block_size);
+	if (!wp->block) {
+		reftable_free(wp);
+		return REFTABLE_OUT_OF_MEMORY_ERROR;
 	}
-	wp->last_key = reftable_empty_strbuf;
-	wp->block = reftable_calloc(opts->block_size);
 	wp->write = writer_func;
 	wp->write_arg = writer_arg;
-	wp->opts = *opts;
+	wp->opts = opts;
+	wp->flush = flush_func;
 	writer_reinit_block_writer(wp, BLOCK_TYPE_REF);
 
-	return wp;
+	*out = wp;
+
+	return 0;
 }
 
 void reftable_writer_set_limits(struct reftable_writer *w, uint64_t min,
@@ -148,16 +172,27 @@ void reftable_writer_set_limits(struct reftable_writer *w, uint64_t min,
 	w->max_update_index = max;
 }
 
+static void writer_release(struct reftable_writer *w)
+{
+	if (w) {
+		reftable_free(w->block);
+		w->block = NULL;
+		block_writer_release(&w->block_writer_data);
+		w->block_writer = NULL;
+		writer_clear_index(w);
+		reftable_buf_release(&w->last_key);
+		reftable_buf_release(&w->scratch);
+	}
+}
+
 void reftable_writer_free(struct reftable_writer *w)
 {
-	if (!w)
-		return;
-	reftable_free(w->block);
+	writer_release(w);
 	reftable_free(w);
 }
 
 struct obj_index_tree_node {
-	struct strbuf hash;
+	struct reftable_buf hash;
 	uint64_t *offsets;
 	size_t offset_len;
 	size_t offset_cap;
@@ -165,90 +200,119 @@ struct obj_index_tree_node {
 
 #define OBJ_INDEX_TREE_NODE_INIT    \
 	{                           \
-		.hash = STRBUF_INIT \
+		.hash = REFTABLE_BUF_INIT \
 	}
 
 static int obj_index_tree_node_compare(const void *a, const void *b)
 {
-	return strbuf_cmp(&((const struct obj_index_tree_node *)a)->hash,
+	return reftable_buf_cmp(&((const struct obj_index_tree_node *)a)->hash,
 			  &((const struct obj_index_tree_node *)b)->hash);
 }
 
-static void writer_index_hash(struct reftable_writer *w, struct strbuf *hash)
+static int writer_index_hash(struct reftable_writer *w, struct reftable_buf *hash)
 {
 	uint64_t off = w->next;
-
 	struct obj_index_tree_node want = { .hash = *hash };
+	struct obj_index_tree_node *key;
+	struct tree_node *node;
 
-	struct tree_node *node = tree_search(&want, &w->obj_index_tree,
-					     &obj_index_tree_node_compare, 0);
-	struct obj_index_tree_node *key = NULL;
+	node = tree_search(w->obj_index_tree, &want, &obj_index_tree_node_compare);
 	if (!node) {
 		struct obj_index_tree_node empty = OBJ_INDEX_TREE_NODE_INIT;
-		key = reftable_malloc(sizeof(struct obj_index_tree_node));
+		int err;
+
+		key = reftable_malloc(sizeof(*key));
+		if (!key)
+			return REFTABLE_OUT_OF_MEMORY_ERROR;
+
 		*key = empty;
 
-		strbuf_reset(&key->hash);
-		strbuf_addbuf(&key->hash, hash);
-		tree_search((void *)key, &w->obj_index_tree,
-			    &obj_index_tree_node_compare, 1);
+		reftable_buf_reset(&key->hash);
+		err = reftable_buf_add(&key->hash, hash->buf, hash->len);
+		if (err < 0)
+			return err;
+		tree_insert(&w->obj_index_tree, key,
+			    &obj_index_tree_node_compare);
 	} else {
 		key = node->key;
 	}
 
-	if (key->offset_len > 0 && key->offsets[key->offset_len - 1] == off) {
-		return;
-	}
-
-	if (key->offset_len == key->offset_cap) {
-		key->offset_cap = 2 * key->offset_cap + 1;
-		key->offsets = reftable_realloc(
-			key->offsets, sizeof(uint64_t) * key->offset_cap);
-	}
+	if (key->offset_len > 0 && key->offsets[key->offset_len - 1] == off)
+		return 0;
 
+	REFTABLE_ALLOC_GROW(key->offsets, key->offset_len + 1, key->offset_cap);
+	if (!key->offsets)
+		return REFTABLE_OUT_OF_MEMORY_ERROR;
 	key->offsets[key->offset_len++] = off;
+
+	return 0;
 }
 
 static int writer_add_record(struct reftable_writer *w,
 			     struct reftable_record *rec)
 {
-	struct strbuf key = STRBUF_INIT;
-	int err = -1;
-	reftable_record_key(rec, &key);
-	if (strbuf_cmp(&w->last_key, &key) >= 0) {
+	int err;
+
+	err = reftable_record_key(rec, &w->scratch);
+	if (err < 0)
+		goto done;
+
+	if (reftable_buf_cmp(&w->last_key, &w->scratch) >= 0) {
 		err = REFTABLE_API_ERROR;
 		goto done;
 	}
 
-	strbuf_reset(&w->last_key);
-	strbuf_addbuf(&w->last_key, &key);
+	reftable_buf_reset(&w->last_key);
+	err = reftable_buf_add(&w->last_key, w->scratch.buf, w->scratch.len);
+	if (err < 0)
+		goto done;
+
 	if (!w->block_writer) {
-		writer_reinit_block_writer(w, reftable_record_type(rec));
+		err = writer_reinit_block_writer(w, reftable_record_type(rec));
+		if (err < 0)
+			goto done;
 	}
 
-	assert(block_writer_type(w->block_writer) == reftable_record_type(rec));
+	if (block_writer_type(w->block_writer) != reftable_record_type(rec))
+		BUG("record of type %d added to writer of type %d",
+		    reftable_record_type(rec), block_writer_type(w->block_writer));
 
-	if (block_writer_add(w->block_writer, rec) == 0) {
+	/*
+	 * Try to add the record to the writer. If this succeeds then we're
+	 * done. Otherwise the block writer may have hit the block size limit
+	 * and needs to be flushed.
+	 */
+	if (!block_writer_add(w->block_writer, rec)) {
 		err = 0;
 		goto done;
 	}
 
+	/*
+	 * The current block is full, so we need to flush and reinitialize the
+	 * writer to start writing the next block.
+	 */
 	err = writer_flush_block(w);
-	if (err < 0) {
+	if (err < 0)
+		goto done;
+	err = writer_reinit_block_writer(w, reftable_record_type(rec));
+	if (err < 0)
 		goto done;
-	}
 
-	writer_reinit_block_writer(w, reftable_record_type(rec));
+	/*
+	 * Try to add the record to the writer again. If this still fails then
+	 * the record does not fit into the block size.
+	 *
+	 * TODO: it would be great to have `block_writer_add()` return proper
+	 *       error codes so that we don't have to second-guess the failure
+	 *       mode here.
+	 */
 	err = block_writer_add(w->block_writer, rec);
-	if (err == -1) {
-		/* we are writing into memory, so an error can only mean it
-		 * doesn't fit. */
+	if (err) {
 		err = REFTABLE_ENTRY_TOO_BIG_ERROR;
 		goto done;
 	}
 
 done:
-	strbuf_release(&key);
 	return err;
 }
 
@@ -261,11 +325,10 @@ int reftable_writer_add_ref(struct reftable_writer *w,
 			.ref = *ref
 		},
 	};
-	int err = 0;
+	int err;
 
-	if (!ref->refname)
-		return REFTABLE_API_ERROR;
-	if (ref->update_index < w->min_update_index ||
+	if (!ref->refname ||
+	    ref->update_index < w->min_update_index ||
 	    ref->update_index > w->max_update_index)
 		return REFTABLE_API_ERROR;
 
@@ -273,24 +336,36 @@ int reftable_writer_add_ref(struct reftable_writer *w,
 
 	err = writer_add_record(w, &rec);
 	if (err < 0)
-		return err;
+		goto out;
 
 	if (!w->opts.skip_index_objects && reftable_ref_record_val1(ref)) {
-		struct strbuf h = STRBUF_INIT;
-		strbuf_add(&h, (char *)reftable_ref_record_val1(ref),
-			   hash_size(w->opts.hash_id));
-		writer_index_hash(w, &h);
-		strbuf_release(&h);
+		reftable_buf_reset(&w->scratch);
+		err = reftable_buf_add(&w->scratch, (char *)reftable_ref_record_val1(ref),
+				       hash_size(w->opts.hash_id));
+		if (err < 0)
+			goto out;
+
+		err = writer_index_hash(w, &w->scratch);
+		if (err < 0)
+			goto out;
 	}
 
 	if (!w->opts.skip_index_objects && reftable_ref_record_val2(ref)) {
-		struct strbuf h = STRBUF_INIT;
-		strbuf_add(&h, reftable_ref_record_val2(ref),
-			   hash_size(w->opts.hash_id));
-		writer_index_hash(w, &h);
-		strbuf_release(&h);
+		reftable_buf_reset(&w->scratch);
+		err = reftable_buf_add(&w->scratch, reftable_ref_record_val2(ref),
+				       hash_size(w->opts.hash_id));
+		if (err < 0)
+			goto out;
+
+		err = writer_index_hash(w, &w->scratch);
+		if (err < 0)
+			goto out;
 	}
-	return 0;
+
+	err = 0;
+
+out:
+	return err;
 }
 
 int reftable_writer_add_refs(struct reftable_writer *w,
@@ -330,7 +405,7 @@ int reftable_writer_add_log(struct reftable_writer *w,
 			    struct reftable_log_record *log)
 {
 	char *input_log_message = NULL;
-	struct strbuf cleaned_message = STRBUF_INIT;
+	struct reftable_buf cleaned_message = REFTABLE_BUF_INIT;
 	int err = 0;
 
 	if (log->value_type == REFTABLE_LOG_DELETION)
@@ -341,24 +416,34 @@ int reftable_writer_add_log(struct reftable_writer *w,
 
 	input_log_message = log->value.update.message;
 	if (!w->opts.exact_log_message && log->value.update.message) {
-		strbuf_addstr(&cleaned_message, log->value.update.message);
+		err = reftable_buf_addstr(&cleaned_message, log->value.update.message);
+		if (err < 0)
+			goto done;
+
 		while (cleaned_message.len &&
-		       cleaned_message.buf[cleaned_message.len - 1] == '\n')
-			strbuf_setlen(&cleaned_message,
-				      cleaned_message.len - 1);
+		       cleaned_message.buf[cleaned_message.len - 1] == '\n') {
+			err = reftable_buf_setlen(&cleaned_message,
+						  cleaned_message.len - 1);
+			if (err < 0)
+				goto done;
+		}
 		if (strchr(cleaned_message.buf, '\n')) {
 			/* multiple lines not allowed. */
 			err = REFTABLE_API_ERROR;
 			goto done;
 		}
-		strbuf_addstr(&cleaned_message, "\n");
+
+		err = reftable_buf_addstr(&cleaned_message, "\n");
+		if (err < 0)
+			goto done;
+
 		log->value.update.message = cleaned_message.buf;
 	}
 
 	err = reftable_writer_add_log_verbatim(w, log);
 	log->value.update.message = input_log_message;
 done:
-	strbuf_release(&cleaned_message);
+	reftable_buf_release(&cleaned_message);
 	return err;
 }
 
@@ -377,24 +462,45 @@ int reftable_writer_add_logs(struct reftable_writer *w,
 
 static int writer_finish_section(struct reftable_writer *w)
 {
+	struct reftable_block_stats *bstats = NULL;
 	uint8_t typ = block_writer_type(w->block_writer);
 	uint64_t index_start = 0;
 	int max_level = 0;
-	int threshold = w->opts.unpadded ? 1 : 3;
+	size_t threshold = w->opts.unpadded ? 1 : 3;
 	int before_blocks = w->stats.idx_stats.blocks;
-	int err = writer_flush_block(w);
-	int i = 0;
-	struct reftable_block_stats *bstats = NULL;
+	int err;
+
+	err = writer_flush_block(w);
 	if (err < 0)
 		return err;
 
+	/*
+	 * When the section we are about to index has a lot of blocks then the
+	 * index itself may span across multiple blocks, as well. This would
+	 * require a linear scan over index blocks only to find the desired
+	 * indexed block, which is inefficient. Instead, we write a multi-level
+	 * index where index records of level N+1 will refer to index blocks of
+	 * level N. This isn't constant time, either, but at least logarithmic.
+	 *
+	 * This loop handles writing this multi-level index. Note that we write
+	 * the lowest-level index pointing to the indexed blocks first. We then
+	 * continue writing additional index levels until the current level has
+	 * less blocks than the threshold so that the highest level will be at
+	 * the end of the index section.
+	 *
+	 * Readers are thus required to start reading the index section from
+	 * its end, which is why we set `index_start` to the beginning of the
+	 * last index section.
+	 */
 	while (w->index_len > threshold) {
 		struct reftable_index_record *idx = NULL;
-		int idx_len = 0;
+		size_t i, idx_len;
 
 		max_level++;
 		index_start = w->next;
-		writer_reinit_block_writer(w, BLOCK_TYPE_INDEX);
+		err = writer_reinit_block_writer(w, BLOCK_TYPE_INDEX);
+		if (err < 0)
+			return err;
 
 		idx = w->index;
 		idx_len = w->index_len;
@@ -409,48 +515,41 @@ static int writer_finish_section(struct reftable_writer *w)
 					.idx = idx[i],
 				},
 			};
-			if (block_writer_add(w->block_writer, &rec) == 0) {
-				continue;
-			}
 
-			err = writer_flush_block(w);
+			err = writer_add_record(w, &rec);
 			if (err < 0)
 				return err;
+		}
 
-			writer_reinit_block_writer(w, BLOCK_TYPE_INDEX);
+		err = writer_flush_block(w);
+		if (err < 0)
+			return err;
 
-			err = block_writer_add(w->block_writer, &rec);
-			if (err != 0) {
-				/* write into fresh block should always succeed
-				 */
-				abort();
-			}
-		}
-		for (i = 0; i < idx_len; i++) {
-			strbuf_release(&idx[i].last_key);
-		}
+		for (i = 0; i < idx_len; i++)
+			reftable_buf_release(&idx[i].last_key);
 		reftable_free(idx);
 	}
 
+	/*
+	 * The index may still contain a number of index blocks lower than the
+	 * threshold. Clear it so that these entries don't leak into the next
+	 * index section.
+	 */
 	writer_clear_index(w);
 
-	err = writer_flush_block(w);
-	if (err < 0)
-		return err;
-
 	bstats = writer_reftable_block_stats(w, typ);
 	bstats->index_blocks = w->stats.idx_stats.blocks - before_blocks;
 	bstats->index_offset = index_start;
 	bstats->max_index_level = max_level;
 
 	/* Reinit lastKey, as the next section can start with any key. */
-	w->last_key.len = 0;
+	reftable_buf_reset(&w->last_key);
 
 	return 0;
 }
 
 struct common_prefix_arg {
-	struct strbuf *last;
+	struct reftable_buf *last;
 	int max;
 };
 
@@ -495,7 +594,10 @@ static void write_object_record(void *void_arg, void *key)
 	if (arg->err < 0)
 		goto done;
 
-	writer_reinit_block_writer(arg->w, BLOCK_TYPE_OBJ);
+	arg->err = writer_reinit_block_writer(arg->w, BLOCK_TYPE_OBJ);
+	if (arg->err < 0)
+		goto done;
+
 	arg->err = block_writer_add(arg->w->block_writer, &rec);
 	if (arg->err == 0)
 		goto done;
@@ -509,12 +611,12 @@ static void write_object_record(void *void_arg, void *key)
 done:;
 }
 
-static void object_record_free(void *void_arg, void *key)
+static void object_record_free(void *void_arg UNUSED, void *key)
 {
 	struct obj_index_tree_node *entry = key;
 
-	FREE_AND_NULL(entry->offsets);
-	strbuf_release(&entry->hash);
+	REFTABLE_FREE_AND_NULL(entry->offsets);
+	reftable_buf_release(&entry->hash);
 	reftable_free(entry);
 }
 
@@ -524,16 +626,18 @@ static int writer_dump_object_index(struct reftable_writer *w)
 	struct common_prefix_arg common = {
 		.max = 1,		/* obj_id_len should be >= 2. */
 	};
-	if (w->obj_index_tree) {
+	int err;
+
+	if (w->obj_index_tree)
 		infix_walk(w->obj_index_tree, &update_common, &common);
-	}
 	w->stats.object_id_len = common.max + 1;
 
-	writer_reinit_block_writer(w, BLOCK_TYPE_OBJ);
+	err = writer_reinit_block_writer(w, BLOCK_TYPE_OBJ);
+	if (err < 0)
+		return err;
 
-	if (w->obj_index_tree) {
+	if (w->obj_index_tree)
 		infix_walk(w->obj_index_tree, &write_object_record, &closure);
-	}
 
 	if (closure.err < 0)
 		return closure.err;
@@ -603,6 +707,12 @@ int reftable_writer_close(struct reftable_writer *w)
 	put_be32(p, crc32(0, footer, p - footer));
 	p += 4;
 
+	err = w->flush(w->write_arg);
+	if (err < 0) {
+		err = REFTABLE_IO_ERROR;
+		goto done;
+	}
+
 	err = padded_write(w, footer, footer_size(writer_version(w)), 0);
 	if (err < 0)
 		goto done;
@@ -613,82 +723,93 @@ int reftable_writer_close(struct reftable_writer *w)
 	}
 
 done:
-	/* free up memory. */
-	block_writer_release(&w->block_writer_data);
-	writer_clear_index(w);
-	strbuf_release(&w->last_key);
+	writer_release(w);
 	return err;
 }
 
 static void writer_clear_index(struct reftable_writer *w)
 {
-	int i = 0;
-	for (i = 0; i < w->index_len; i++) {
-		strbuf_release(&w->index[i].last_key);
-	}
-
-	FREE_AND_NULL(w->index);
+	for (size_t i = 0; w->index && i < w->index_len; i++)
+		reftable_buf_release(&w->index[i].last_key);
+	REFTABLE_FREE_AND_NULL(w->index);
 	w->index_len = 0;
 	w->index_cap = 0;
 }
 
-static const int debug = 0;
-
 static int writer_flush_nonempty_block(struct reftable_writer *w)
 {
+	struct reftable_index_record index_record = {
+		.last_key = REFTABLE_BUF_INIT,
+	};
 	uint8_t typ = block_writer_type(w->block_writer);
-	struct reftable_block_stats *bstats =
-		writer_reftable_block_stats(w, typ);
-	uint64_t block_typ_off = (bstats->blocks == 0) ? w->next : 0;
-	int raw_bytes = block_writer_finish(w->block_writer);
-	int padding = 0;
-	int err = 0;
-	struct reftable_index_record ir = { .last_key = STRBUF_INIT };
+	struct reftable_block_stats *bstats;
+	int raw_bytes, padding = 0, err;
+	uint64_t block_typ_off;
+
+	/*
+	 * Finish the current block. This will cause the block writer to emit
+	 * restart points and potentially compress records in case we are
+	 * writing a log block.
+	 *
+	 * Note that this is still happening in memory.
+	 */
+	raw_bytes = block_writer_finish(w->block_writer);
 	if (raw_bytes < 0)
 		return raw_bytes;
 
-	if (!w->opts.unpadded && typ != BLOCK_TYPE_LOG) {
+	/*
+	 * By default, all records except for log records are padded to the
+	 * block size.
+	 */
+	if (!w->opts.unpadded && typ != BLOCK_TYPE_LOG)
 		padding = w->opts.block_size - raw_bytes;
-	}
 
-	if (block_typ_off > 0) {
+	bstats = writer_reftable_block_stats(w, typ);
+	block_typ_off = (bstats->blocks == 0) ? w->next : 0;
+	if (block_typ_off > 0)
 		bstats->offset = block_typ_off;
-	}
-
 	bstats->entries += w->block_writer->entries;
 	bstats->restarts += w->block_writer->restart_len;
 	bstats->blocks++;
 	w->stats.blocks++;
 
-	if (debug) {
-		fprintf(stderr, "block %c off %" PRIu64 " sz %d (%d)\n", typ,
-			w->next, raw_bytes,
-			get_be24(w->block + w->block_writer->header_off + 1));
-	}
-
-	if (w->next == 0) {
+	/*
+	 * If this is the first block we're writing to the table then we need
+	 * to also write the reftable header.
+	 */
+	if (!w->next)
 		writer_write_header(w, w->block);
-	}
 
 	err = padded_write(w, w->block, raw_bytes, padding);
 	if (err < 0)
 		return err;
 
-	if (w->index_cap == w->index_len) {
-		w->index_cap = 2 * w->index_cap + 1;
-		w->index = reftable_realloc(
-			w->index,
-			sizeof(struct reftable_index_record) * w->index_cap);
-	}
-
-	ir.offset = w->next;
-	strbuf_reset(&ir.last_key);
-	strbuf_addbuf(&ir.last_key, &w->block_writer->last_key);
-	w->index[w->index_len] = ir;
-
+	/*
+	 * Add an index record for every block that we're writing. If we end up
+	 * having more than a threshold of index records we will end up writing
+	 * an index section in `writer_finish_section()`. Each index record
+	 * contains the last record key of the block it is indexing as well as
+	 * the offset of that block.
+	 *
+	 * Note that this also applies when flushing index blocks, in which
+	 * case we will end up with a multi-level index.
+	 */
+	REFTABLE_ALLOC_GROW(w->index, w->index_len + 1, w->index_cap);
+	if (!w->index)
+		return REFTABLE_OUT_OF_MEMORY_ERROR;
+
+	index_record.offset = w->next;
+	reftable_buf_reset(&index_record.last_key);
+	err = reftable_buf_add(&index_record.last_key, w->block_writer->last_key.buf,
+			       w->block_writer->last_key.len);
+	if (err < 0)
+		return err;
+	w->index[w->index_len] = index_record;
 	w->index_len++;
+
 	w->next += padding + raw_bytes;
 	w->block_writer = NULL;
+
 	return 0;
 }