Prototype of Files service.

services/files/types.mojom

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module mojo.files;
+
+// Error codes used by the file manager.
+// TODO(vtl): Add more (to, e.g., cover all of errno).
+enum Error {
+  OK = 0,
+  UNKNOWN,
+  INVALID_ARGUMENT,
+  PERMISSION_DENIED,
+  OUT_OF_RANGE,
+  UNIMPLEMENTED,
+  CLOSED,
+  UNAVAILABLE,
+  INTERNAL,
+};
+
+// Used to explain the meaning of an offset within a file.
+enum Whence {
+  // Offset is from current position in the file.
+  FROM_CURRENT = 0,
+  // Offset is relative to the beginning of the file.
+  FROM_START,
+  // Offset is relative to the end of the file.
+  FROM_END,
+};
+
+// Describes (idealized) wall-clock time, since Unix epoch (i.e., since
+// "1970-01-01 00:00 UTC", ignoring leap seconds and that UTC as we know it
+// started in 1972).
+// TODO(vtl): Should probably be moved out of mojo.files (maybe to mojo.time?).
+struct Timespec {
+  int64 seconds;
+  int32 nanoseconds;  // Always in the interval [0, 10^9).
+};
+
+// Used for |Touch()| calls. If |now| is set, |timespec| must be null (the time
+// "now" will be used). Otherwise, |timespec| must not be null.
+// TODO(vtl): Use a union instead, when that becomes possible.

[qsr, 2015/03/02 12:46:40]

I am missing something obvious, but why do you need the boolean at all?

[viettrungluu, 2015/03/02 18:10:59]

Really, this should be turned into a union, once those are ready for prime time,
so I'd prefer to keep the explicit bool.

[qsr, 2015/03/03 11:56:44]

What would the union looks like? The same as this? This is still kind of weird,
because you won't care about the value of the boolean. Isn't the following
struct exactly what you need:

struct TimespecOrNow {
  Timespec? timespec;
}

and you specify that a null timespec means Now.

You can then have the 3 states you need -> A null TimespecOrNow is no info, a
non-null TimespecOrNow with a null timespec is now, and a non-null timespec is
the value of the timespec.

I am not sure the union makes it clearer, unless you have another idea about
what the |now| will be.

[viettrungluu, 2015/03/03 18:50:35]

Yeah, I'm not super-happy about it. Really, what I want is a union with a unary
"now" choice. I don't like having a struct containing only a nullable struct for
this purpose -- it's a just a bit too weird/unclear.

I could make now a "unary enum" for the purposes of such a union, but our enums
are currently always extensible and only weakly typed.

+struct TimespecOrNow {
+  bool now;
+  Timespec? timespec;
+};
+
+// Describes various information about a file or directory (for |Stat()|). Note
+// that access/modification times may be set arbitrarily (by those with
+// appropriate capabilities) and may not reflect reality.
+struct FileInformation {
+  // Size of the file, in bytes.
+  int64 size;

[qsr, 2015/03/02 12:46:40]

What does size mean for a directory?

[viettrungluu, 2015/03/02 18:10:59]

That's a good question (to be pondered). stat(2) doesn't really say, so it's
probably undefined according to POSIX. Maybe we should define it to be zero.

[viettrungluu, 2015/03/03 18:50:35]

(I defined it to be zero for directories.)

+  // Last access time, if available/supported.
+  Timespec? atime;
+  // Last modification time, if available/supported.
+  Timespec? mtime;
+};
+
+// File and directory open flags (at least one of |kOpenFlagRead| and
+// |kOpenFlagWrite| is required):
+// Opens the file/directory for reading.
+const uint32 kOpenFlagRead = 0x1;
+// Opens the file/directory for writing.
+const uint32 kOpenFlagWrite = 0x2;
+// Only meaningful together with |kOpenFlagWrite|: creates the file if
+// necessary.
+const uint32 kOpenFlagCreate = 0x4;
+// Only meaningful together with |kOpenFlagCreate|: requires file/directory to
+// be created, failing if it already exists.
+const uint32 kOpenFlagExclusive = 0x8;
+// Only meaningful for files, together with |kOpenFlagWrite|: writes will always
+// append to the file.
+const uint32 kOpenFlagAppend = 0x10;
+// Only meaningful for files, together with |kOpenFlagWrite|: truncates the
+// file.
+const uint32 kOpenFlagTruncate = 0x20;
+
+// File types.
+enum FileType {
+  UNKNOWN = 0,
+  REGULAR_FILE,
+  DIRECTORY,
+};
+
+// Describes a directory entry (i.e., a single member of a directory).
+struct DirectoryEntry {
+  FileType type;
+  string name;
+};
+
+// Deletion flags:
+// Only delete if the path refers to a file/non-directory (by default, will
+// delete files and directories).
+const uint32 kDeleteFlagFileOnly = 0x1;
+// Only delete if the path refers to a directory.
+const uint32 kDeleteFlagDirectoryOnly = 0x2;
+// Recursively delete (neither of the two flags above may be specified).
+const uint32 kDeleteFlagRecursive = 0x4;