Prototype of Files service.

services/files/file.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.
+
+// TODO(vtl): notes to self:
+//  - file offsets, file positions, and file sizes are int64 (though positions
+//    and sizes must always be non-negative)
+//  - buffer size parameters (for read/write) are uint32
+
+module mojo.files;
+
+import "services/files/types.mojom";
+
+// TODO(vtl): Write comments.
+interface File {
+  Close() => (Error err);
+
+  // Reads (at most) |num_bytes_to_read| from the location specified by
+  // |offset|/|whence|. On success, |bytes_read| is set to the data read.
+  // TODO(vtl): Define/clarify behavior when less than |num_bytes_to_read| bytes
+  // are read.
+  Read(uint32 num_bytes_to_read, int64 offset, Whence whence)
+      => (Error error, array<uint8>? bytes_read);
+
+  // Writes |bytes_to_write| to the location specified by |offset|/|whence|.
+  // TODO(vtl): Clarify behavior when |num_bytes_written| is less than the size
+  // of |bytes_to_write|.
+  Write(array<uint8> bytes_to_write, int64 offset, Whence whence)
+      => (Error error, uint32 num_bytes_written);
+
+  // TODO(vtl): We definitely want 64 bits for |num_bytes_to_read|; but do we
+  // want it to be signed (this is consistent with |size| values, but
+  // inconsistent with 32-bit |num_bytes_to_read| values)? Do we want to have
+  // separate "read to end" versus "tail" (i.e., keep on reading as more data is
+  // appended) modes, and how would those be signalled?
+  ReadToStream(handle<data_pipe_producer> source,
+               int64 offset,
+               Whence whence,
+               int64 num_bytes_to_read) => (Error error);
+  WriteFromStream(handle<data_pipe_consumer> sink, int64 offset, Whence whence)
+      => (Error error);
+
+  // Gets the current file position. On success, |position| is the current
+  // offset (in bytes) from the beginning of the file).
+  Tell() => (Error error, int64 position);
+
+  // Sets the current file position to that specified by |offset|/|whence|. On
+  // success, |position| is the offset (in bytes) from the beginning of the
+  // file.
+  Seek(int64 offset, Whence whence) => (Error error, int64 position);
+
+  // Gets information about this file. On success, |file_information| is
+  // non-null and will contain this information.
+  Stat() => (Error error, FileInformation? file_information);
+
+  // Truncates this file to the size specified by |size| (in bytes).
+  Truncate(int64 size) => (Error error);
+
+  // Updates this file's atime and/or mtime to the time specified by |atime| (or
+  // |mtime|, respectively), which may also indicate "now". If |atime| or
+  // |mtime| is null, then the corresponding time is not modified.
+  Touch(TimespecOrNow? atime, TimespecOrNow? mtime) => (Error error);
+
+  // Creates a new |File| instance, which shares the same "file description".
+  // I.e., the access mode, etc. (as specified to |Directory::OpenFile()| by the
+  // |open_flags| argument) as well as file position.
+  Dup(File& file) => (Error error);
+
+  // TODO(vtl): What are the rules for reopening (w.r.t. changing mode/flags).
+  // E.g., obviously can go from "read-write" to "read", but reverse? (probably
+  // not), can remove "append"? (probably not?). Do we allow "truncate"?
+  Reopen(File& file, uint32 open_flags) => (Error error);
+
+  // TODO(vtl): probably should have access flags (but also exec?); how do these
+  // relate to access mode?
+  AsBuffer() => (Error error, handle<shared_buffer>? buffer);
+
+  // TODO(vtl): Add a "watch"?
+};