reftable/stack: adapt stack_filename() to handle allocation failures

The `stack_filename()` function cannot pass any errors to the caller as it
has a `void` return type. Adapt it and its callers such that we can
handle errors and start handling allocation failures.

There are two interesting edge cases in `reftable_stack_destroy()` and
`reftable_addition_close()`. Both of these are trying to tear down their
respective structures, and while doing so they try to unlink some of the
tables they have been keeping alive. Any earlier attempts to do that may
fail on Windows because it keeps us from deleting such tables while they
are still open, and thus we re-try on close. It's okay and even expected
that this can fail when the tables are still open by another process, so
we handle the allocation failures gracefully and just skip over any file
whose name we couldn't figure out.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Taylor Blau <me@ttaylorr.com>

Author: pks-t

reftable/stack.c

@@ -31,13 +31,16 @@ static void reftable_addition_close(struct reftable_addition *add);
 static int reftable_stack_reload_maybe_reuse(struct reftable_stack *st,
 					     int reuse_open);
 
-static void stack_filename(struct reftable_buf *dest, struct reftable_stack *st,
-			   const char *name)
+static int stack_filename(struct reftable_buf *dest, struct reftable_stack *st,
+			  const char *name)
 {
+	int err;
 	reftable_buf_reset(dest);
-	reftable_buf_addstr(dest, st->reftable_dir);
-	reftable_buf_addstr(dest, "/");
-	reftable_buf_addstr(dest, name);
+	if ((err = reftable_buf_addstr(dest, st->reftable_dir)) < 0 ||
+	    (err = reftable_buf_addstr(dest, "/")) < 0 ||
+	    (err = reftable_buf_addstr(dest, name)) < 0)
+		return err;
+	return 0;
 }
 
 static ssize_t reftable_fd_write(void *arg, const void *data, size_t sz)
@@ -211,13 +214,16 @@ void reftable_stack_destroy(struct reftable_stack *st)
 		struct reftable_buf filename = REFTABLE_BUF_INIT;
 		for (i = 0; i < st->readers_len; i++) {
 			const char *name = reader_name(st->readers[i]);
+			int try_unlinking = 1;
+
 			reftable_buf_reset(&filename);
 			if (names && !has_name(names, name)) {
-				stack_filename(&filename, st, name);
+				if (stack_filename(&filename, st, name) < 0)
+					try_unlinking = 0;
 			}
 			reftable_reader_decref(st->readers[i]);
 
-			if (filename.len) {
+			if (try_unlinking && filename.len) {
 				/* On Windows, can only unlink after closing. */
 				unlink(filename.buf);
 			}
@@ -310,7 +316,10 @@ static int reftable_stack_reload_once(struct reftable_stack *st,
 
 		if (!rd) {
 			struct reftable_block_source src = { NULL };
-			stack_filename(&table_path, st, name);
+
+			err = stack_filename(&table_path, st, name);
+			if (err < 0)
+				goto done;
 
 			err = reftable_block_source_from_file(&src,
 							      table_path.buf);
@@ -341,7 +350,11 @@ static int reftable_stack_reload_once(struct reftable_stack *st,
 	for (i = 0; i < cur_len; i++) {
 		if (cur[i]) {
 			const char *name = reader_name(cur[i]);
-			stack_filename(&table_path, st, name);
+
+			err = stack_filename(&table_path, st, name);
+			if (err < 0)
+				goto done;
+
 			reftable_reader_decref(cur[i]);
 			unlink(table_path.buf);
 		}
@@ -700,8 +713,8 @@ static void reftable_addition_close(struct reftable_addition *add)
 	size_t i;
 
 	for (i = 0; i < add->new_tables_len; i++) {
-		stack_filename(&nm, add->stack, add->new_tables[i]);
-		unlink(nm.buf);
+		if (!stack_filename(&nm, add->stack, add->new_tables[i]))
+			unlink(nm.buf);
 		reftable_free(add->new_tables[i]);
 		add->new_tables[i] = NULL;
 	}
@@ -851,7 +864,9 @@ int reftable_addition_add(struct reftable_addition *add,
 	if (err < 0)
 		goto done;
 
-	stack_filename(&temp_tab_file_name, add->stack, next_name.buf);
+	err = stack_filename(&temp_tab_file_name, add->stack, next_name.buf);
+	if (err < 0)
+		goto done;
 	reftable_buf_addstr(&temp_tab_file_name, ".temp.XXXXXX");
 
 	tab_file = mks_tempfile(temp_tab_file_name.buf);
@@ -900,7 +915,10 @@ int reftable_addition_add(struct reftable_addition *add,
 	if (err < 0)
 		goto done;
 	reftable_buf_addstr(&next_name, ".ref");
-	stack_filename(&tab_file_name, add->stack, next_name.buf);
+
+	err = stack_filename(&tab_file_name, add->stack, next_name.buf);
+	if (err < 0)
+		goto done;
 
 	/*
 	  On windows, this relies on rand() picking a unique destination name.
@@ -954,7 +972,9 @@ static int stack_compact_locked(struct reftable_stack *st,
 	if (err < 0)
 		goto done;
 
-	stack_filename(&tab_file_path, st, next_name.buf);
+	err = stack_filename(&tab_file_path, st, next_name.buf);
+	if (err < 0)
+		goto done;
 	reftable_buf_addstr(&tab_file_path, ".temp.XXXXXX");
 
 	tab_file = mks_tempfile(tab_file_path.buf);
@@ -1174,7 +1194,9 @@ static int stack_compact_range(struct reftable_stack *st,
 	}
 
 	for (i = last + 1; i > first; i--) {
-		stack_filename(&table_name, st, reader_name(st->readers[i - 1]));
+		err = stack_filename(&table_name, st, reader_name(st->readers[i - 1]));
+		if (err < 0)
+			goto done;
 
 		err = hold_lock_file_for_update(&table_locks[nlocks],
 						table_name.buf, LOCK_NO_DEREF);
@@ -1383,7 +1405,10 @@ static int stack_compact_range(struct reftable_stack *st,
 			goto done;
 
 		reftable_buf_addstr(&new_table_name, ".ref");
-		stack_filename(&new_table_path, st, new_table_name.buf);
+
+		err = stack_filename(&new_table_path, st, new_table_name.buf);
+		if (err < 0)
+			goto done;
 
 		err = rename_tempfile(&new_table, new_table_path.buf);
 		if (err < 0) {
@@ -1677,7 +1702,10 @@ static void remove_maybe_stale_table(struct reftable_stack *st, uint64_t max,
 	struct reftable_block_source src = { NULL };
 	struct reftable_reader *rd = NULL;
 	struct reftable_buf table_path = REFTABLE_BUF_INIT;
-	stack_filename(&table_path, st, name);
+
+	err = stack_filename(&table_path, st, name);
+	if (err < 0)
+		goto done;
 
 	err = reftable_block_source_from_file(&src, table_path.buf);
 	if (err < 0)