reftable/writer: handle allocation failures in reftable_new_writer()

Handle allocation failures in `reftable_new_writer()`. Adapt the
function to return an error code to return such failures. While at it,
rename it to match our code style as we have to touch up every callsite
anyway.

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

reftable/reftable-writer.h

@@ -90,11 +90,13 @@ struct reftable_stats {
 	int object_id_len;
 };
 
-/* reftable_new_writer creates a new writer */
-struct reftable_writer *
-reftable_new_writer(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;
+
+/* Create a new writer. */
+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);
 
 /* Set the range of update indices for the records we will add. When writing a
    table into a stack, the min should be at least

reftable/stack.c

@@ -808,8 +808,11 @@ int reftable_addition_add(struct reftable_addition *add,
 	}
 	tab_fd = get_tempfile_fd(tab_file);
 
-	wr = reftable_new_writer(reftable_fd_write, reftable_fd_flush, &tab_fd,
-				 &add->stack->opts);
+	err = reftable_writer_new(&wr, reftable_fd_write, reftable_fd_flush,
+				  &tab_fd, &add->stack->opts);
+	if (err < 0)
+		goto done;
+
 	err = write_table(wr, arg);
 	if (err < 0)
 		goto done;
@@ -898,8 +901,11 @@ static int stack_compact_locked(struct reftable_stack *st,
 		goto done;
 	}
 
-	wr = reftable_new_writer(reftable_fd_write, reftable_fd_flush,
-				 &tab_fd, &st->opts);
+	err = reftable_writer_new(&wr, reftable_fd_write, reftable_fd_flush,
+				  &tab_fd, &st->opts);
+	if (err < 0)
+		goto done;
+
 	err = stack_write_compact(st, wr, first, last, config);
 	if (err < 0)
 		goto done;

reftable/writer.c

@@ -117,13 +117,17 @@ static void writer_reinit_block_writer(struct reftable_writer *w, uint8_t typ)
 	w->block_writer->restart_interval = w->opts.restart_interval;
 }
 
-struct reftable_writer *
-reftable_new_writer(ssize_t (*writer_func)(void *, const void *, size_t),
-		    int (*flush_func)(void *),
-		    void *writer_arg, const 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(1, sizeof(*wp));
 	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;
@@ -134,13 +138,19 @@ reftable_new_writer(ssize_t (*writer_func)(void *, const void *, size_t),
 	strbuf_init(&wp->block_writer_data.last_key, 0);
 	strbuf_init(&wp->last_key, 0);
 	REFTABLE_CALLOC_ARRAY(wp->block, opts.block_size);
+	if (!wp->block) {
+		reftable_free(wp);
+		return REFTABLE_OUT_OF_MEMORY_ERROR;
+	}
 	wp->write = writer_func;
 	wp->write_arg = writer_arg;
 	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,

t/unit-tests/lib-reftable.c

@@ -22,9 +22,11 @@ static int strbuf_writer_flush(void *arg UNUSED)
 struct reftable_writer *t_reftable_strbuf_writer(struct strbuf *buf,
 						 struct reftable_write_options *opts)
 {
-	return reftable_new_writer(&strbuf_writer_write,
-				   &strbuf_writer_flush,
-				   buf, opts);
+	struct reftable_writer *writer;
+	int ret = reftable_writer_new(&writer, &strbuf_writer_write, &strbuf_writer_flush,
+				      buf, opts);
+	check(!ret);
+	return writer;
 }
 
 void t_reftable_write_to_buf(struct strbuf *buf,