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In AtomicFile, work relative to the destination's parent directory. This is more robust against concurrent filesystem reorganization and avoids path length issues.

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This commit is contained in:
Jonathan S 2020-03-25 22:17:41 -05:00
parent f7f563ea53
commit a779a96d38
1 changed files with 21 additions and 20 deletions
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41
lib/std/fs.zig
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@ -118,38 +118,30 @@ pub fn copyFileAbsolute(source_path: []const u8, dest_path: []const u8, args: Co
/// TODO update this API to avoid a getrandom syscall for every operation.
pub const AtomicFile = struct {
file: File,
tmp_path_buf: [MAX_PATH_BYTES - 1:0]u8,
// TODO either replace this with rand_buf or use []u16 on Windows
tmp_path_buf: [TMP_PATH_LEN:0]u8,
dest_path: []const u8,
file_open: bool,
file_exists: bool,
close_dir_on_deinit: bool,
dir: Dir,
const InitError = File.OpenError;
const TMP_PATH_LEN = base64.Base64Encoder.calcSize(12);
/// TODO rename this. Callers should go through Dir API
pub fn init2(dest_path: []const u8, mode: File.Mode, dir: Dir) InitError!AtomicFile {
const dirname = path.dirname(dest_path);
pub fn init2(dest_path: []const u8, mode: File.Mode, dir: Dir, close_dir_on_deinit: bool) InitError!AtomicFile {
var rand_buf: [12]u8 = undefined;
const dirname_component_len = if (dirname) |d| d.len + 1 else 0;
const encoded_rand_len = comptime base64.Base64Encoder.calcSize(rand_buf.len);
const tmp_path_len = dirname_component_len + encoded_rand_len;
var tmp_path_buf: [MAX_PATH_BYTES - 1:0]u8 = undefined;
if (tmp_path_len > tmp_path_buf.len) return error.NameTooLong;
if (dirname) |dn| {
mem.copy(u8, tmp_path_buf[0..], dn);
tmp_path_buf[dn.len] = path.sep;
}
tmp_path_buf[tmp_path_len] = 0;
const tmp_path_slice = tmp_path_buf[0..tmp_path_len :0];
var tmp_path_buf: [TMP_PATH_LEN:0]u8 = undefined;
tmp_path_buf[base64.Base64Encoder.calcSize(12)] = 0;
while (true) {
try crypto.randomBytes(rand_buf[0..]);
base64_encoder.encode(tmp_path_slice[dirname_component_len..tmp_path_len], &rand_buf);
base64_encoder.encode(&tmp_path_buf, &rand_buf);
const file = dir.createFileC(
tmp_path_slice,
&tmp_path_buf,
.{ .mode = mode, .exclusive = true },
) catch |err| switch (err) {
error.PathAlreadyExists => continue,
@ -162,6 +154,7 @@ pub const AtomicFile = struct {
.dest_path = dest_path,
.file_open = true,
.file_exists = true,
.close_dir_on_deinit = close_dir_on_deinit,
.dir = dir,
};
}
@ -169,7 +162,7 @@ pub const AtomicFile = struct {
/// Deprecated. Use `Dir.atomicFile`.
pub fn init(dest_path: []const u8, mode: File.Mode) InitError!AtomicFile {
return init2(dest_path, mode, cwd());
return cwd().atomicFile(dest_path, .{ .mode = mode });
}
/// always call deinit, even after successful finish()
@ -182,6 +175,9 @@ pub const AtomicFile = struct {
self.dir.deleteFileC(&self.tmp_path_buf) catch {};
self.file_exists = false;
}
if (self.close_dir_on_deinit) {
self.dir.close();
}
self.* = undefined;
}
@ -1281,7 +1277,12 @@ pub const Dir = struct {
/// `dest_path` must remain valid for the lifetime of `AtomicFile`.
/// Call `AtomicFile.finish` to atomically replace `dest_path` with contents.
pub fn atomicFile(self: Dir, dest_path: []const u8, options: AtomicFileOptions) !AtomicFile {
return AtomicFile.init2(dest_path, options.mode, self);
if (path.dirname(dest_path)) |dirname| {
const dir = try self.openDir(dirname, .{});
return AtomicFile.init2(path.basename(dest_path), options.mode, dir, true);
} else {
return AtomicFile.init2(dest_path, options.mode, self, false);
}
}
};