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const AtomicFile = @This();
const std = @import("../std.zig");
const File = std.fs.File;
const Dir = std.fs.Dir;
const fs = std.fs;
const assert = std.debug.assert;
const posix = std.posix;
file_writer: File.Writer,
random_integer: u64,
dest_basename: []const u8,
file_open: bool,
file_exists: bool,
close_dir_on_deinit: bool,
dir: Dir,
pub const InitError = File.OpenError;
/// Note that the `Dir.atomicFile` API may be more handy than this lower-level function.
pub fn init(
dest_basename: []const u8,
mode: File.Mode,
dir: Dir,
close_dir_on_deinit: bool,
write_buffer: []u8,
) InitError!AtomicFile {
while (true) {
const random_integer = std.crypto.random.int(u64);
const tmp_sub_path = std.fmt.hex(random_integer);
const file = dir.createFile(&tmp_sub_path, .{ .mode = mode, .exclusive = true }) catch |err| switch (err) {
error.PathAlreadyExists => continue,
else => |e| return e,
};
return .{
.file_writer = file.writer(write_buffer),
.random_integer = random_integer,
.dest_basename = dest_basename,
.file_open = true,
.file_exists = true,
.close_dir_on_deinit = close_dir_on_deinit,
.dir = dir,
};
}
}
/// Always call deinit, even after a successful finish().
pub fn deinit(af: *AtomicFile) void {
if (af.file_open) {
af.file_writer.file.close();
af.file_open = false;
}
if (af.file_exists) {
const tmp_sub_path = std.fmt.hex(af.random_integer);
af.dir.deleteFile(&tmp_sub_path) catch {};
af.file_exists = false;
}
if (af.close_dir_on_deinit) {
af.dir.close();
}
af.* = undefined;
}
pub const FlushError = File.WriteError;
pub fn flush(af: *AtomicFile) FlushError!void {
af.file_writer.interface.flush() catch |err| switch (err) {
error.WriteFailed => return af.file_writer.err.?,
};
}
pub const RenameIntoPlaceError = posix.RenameError;
/// On Windows, this function introduces a period of time where some file
/// system operations on the destination file will result in
/// `error.AccessDenied`, including rename operations (such as the one used in
/// this function).
pub fn renameIntoPlace(af: *AtomicFile) RenameIntoPlaceError!void {
assert(af.file_exists);
if (af.file_open) {
af.file_writer.file.close();
af.file_open = false;
}
const tmp_sub_path = std.fmt.hex(af.random_integer);
try posix.renameat(af.dir.fd, &tmp_sub_path, af.dir.fd, af.dest_basename);
af.file_exists = false;
}
pub const FinishError = FlushError || RenameIntoPlaceError;
/// Combination of `flush` followed by `renameIntoPlace`.
pub fn finish(af: *AtomicFile) FinishError!void {
try af.flush();
try af.renameIntoPlace();
}
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