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mojo/public/c/include/mojo/system/message_pipe.h

-// Copyright 2014 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.
-
-// This file contains types/constants and functions specific to message pipes.
-//
-// Note: This header should be compilable as C.
-
-#ifndef MOJO_PUBLIC_C_INCLUDE_MOJO_SYSTEM_MESSAGE_PIPE_H_
-#define MOJO_PUBLIC_C_INCLUDE_MOJO_SYSTEM_MESSAGE_PIPE_H_
-
-#include <mojo/macros.h>
-#include <mojo/result.h>
-#include <mojo/system/handle.h>
-
-// |MojoCreateMessagePipeOptions|: Used to specify creation parameters for a
-// message pipe to |MojoCreateMessagePipe()|.
-//   |uint32_t struct_size|: Set to the size of the
-//       |MojoCreateMessagePipeOptions| struct. (Used to allow for future
-//       extensions.)
-//   |MojoCreateMessagePipeOptionsFlags flags|: Reserved for future use.
-//       |MOJO_CREATE_MESSAGE_PIPE_OPTIONS_FLAG_NONE|: No flags; default mode.
-
-typedef uint32_t MojoCreateMessagePipeOptionsFlags;
-
-#define MOJO_CREATE_MESSAGE_PIPE_OPTIONS_FLAG_NONE \
-  ((MojoCreateMessagePipeOptionsFlags)0)
-
-MOJO_STATIC_ASSERT(MOJO_ALIGNOF(int64_t) == 8, "int64_t has weird alignment");
-struct MOJO_ALIGNAS(8) MojoCreateMessagePipeOptions {
-  uint32_t struct_size;
-  MojoCreateMessagePipeOptionsFlags flags;
-};
-MOJO_STATIC_ASSERT(sizeof(struct MojoCreateMessagePipeOptions) == 8,
-                   "MojoCreateMessagePipeOptions has wrong size");
-
-// |MojoWriteMessageFlags|: Used to specify different modes to
-// |MojoWriteMessage()|.
-//   |MOJO_WRITE_MESSAGE_FLAG_NONE| - No flags; default mode.
-
-typedef uint32_t MojoWriteMessageFlags;
-
-#define MOJO_WRITE_MESSAGE_FLAG_NONE ((MojoWriteMessageFlags)0)
-
-// |MojoReadMessageFlags|: Used to specify different modes to
-// |MojoReadMessage()|.
-//   |MOJO_READ_MESSAGE_FLAG_NONE| - No flags; default mode.
-//   |MOJO_READ_MESSAGE_FLAG_MAY_DISCARD| - If the message is unable to be read
-//       for whatever reason (e.g., the caller-supplied buffer is too small),
-//       discard the message (i.e., simply dequeue it).
-
-typedef uint32_t MojoReadMessageFlags;
-
-#define MOJO_READ_MESSAGE_FLAG_NONE ((MojoReadMessageFlags)0)
-#define MOJO_READ_MESSAGE_FLAG_MAY_DISCARD ((MojoReadMessageFlags)1 << 0)
-
-MOJO_BEGIN_EXTERN_C
-
-// |MojoCreateMessagePipe()|: Creates a message pipe, which is a bidirectional
-// communication channel for framed data (i.e., messages). Messages can contain
-// plain data and/or Mojo handles.
-//
-// |options| may be set to null for a message pipe with the default options.
-//
-// On success, |*message_pipe_handle0| and |*message_pipe_handle1| are set to
-// handles for the two endpoints (ports) for the message pipe. Both handles have
-// (at least) the following rights: |MOJO_HANDLE_RIGHT_TRANSFER|,
-// |MOJO_HANDLE_RIGHT_READ|, |MOJO_HANDLE_RIGHT_WRITE|,
-// |MOJO_HANDLE_RIGHT_GET_OPTIONS|, and |MOJO_HANDLE_RIGHT_SET_OPTIONS|.
-//
-// Returns:
-//   |MOJO_RESULT_OK| on success.
-//   |MOJO_RESULT_INVALID_ARGUMENT| if some argument was invalid (e.g.,
-//       |*options| is invalid).
-//   |MOJO_RESULT_RESOURCE_EXHAUSTED| if a process/system/quota/etc. limit has
-//       been reached.
-//   |MOJO_RESULT_UNIMPLEMENTED| if an unsupported flag was set in |*options|.
-MojoResult MojoCreateMessagePipe(
-    const struct MojoCreateMessagePipeOptions* MOJO_RESTRICT
-        options,                                      // Optional in.
-    MojoHandle* MOJO_RESTRICT message_pipe_handle0,   // Out.
-    MojoHandle* MOJO_RESTRICT message_pipe_handle1);  // Out.
-
-// |MojoWriteMessage()|: Writes a message to the message pipe endpoint given by
-// |message_pipe_handle| (which must have the |MOJO_HANDLE_RIGHT_WRITE| right),
-// with message data specified by |bytes| of size |num_bytes| and attached
-// handles specified by |handles| of count |num_handles|, and options specified
-// by |flags|. If there is no message data, |bytes| may be null, in which case
-// |num_bytes| must be zero. If there are no attached handles, |handles| may be
-// null, in which case |num_handles| must be zero.
-//
-// If handles are attached, on success the handles will no longer be valid (the
-// receiver will receive equivalent, but logically different, handles) and any
-// ongoing two-phase operations (e.g., for data pipes) on them will be aborted.
-// Handles to be sent should not be in simultaneous use (e.g., on another
-// thread). On failure, any handles to be attached will remain valid (and
-// two-phase operations will not be aborted).
-//
-// Returns:
-//   |MOJO_RESULT_OK| on success (i.e., the message was enqueued).
-//   |MOJO_RESULT_INVALID_ARGUMENT| if some argument was invalid (e.g., if
-//       |message_pipe_handle| is not a valid handle, or some of the
-//       requirements above are not satisfied).
-//   |MOJO_RESULT_PERMISSION_DENIED| if |message_pipe_handle| does not have the
-//       |MOJO_HANDLE_RIGHT_WRITE| right or if one of the handles to be sent
-//       does not have the |MOJO_HANDLE_RIGHT_TRANSFER| right.
-//   |MOJO_RESULT_RESOURCE_EXHAUSTED| if some system limit has been reached, or
-//       the number of handles to send is too large (TODO(vtl): reconsider the
-//       latter case).
-//   |MOJO_RESULT_FAILED_PRECONDITION| if the other endpoint has been closed.
-//       Note that closing an endpoint is not necessarily synchronous (e.g.,
-//       across processes), so this function may succeed even if the other
-//       endpoint has been closed (in which case the message would be dropped).
-//   |MOJO_RESULT_UNIMPLEMENTED| if an unsupported flag was set in |*options|.
-//   |MOJO_RESULT_BUSY| if |message_pipe_handle| is currently in use in some
-//       transaction (that, e.g., may result in it being invalidated, such as
-//       being sent in a message), or if some handle to be sent is currently in
-//       use.
-//
-// Note: |MOJO_RESULT_BUSY| is generally "preferred" over
-// |MOJO_RESULT_PERMISSION_DENIED|. E.g., if a handle to be sent both is busy
-// and does not have the transfer right, then the result will be "busy".
-//
-// TODO(vtl): We'll also report |MOJO_RESULT_BUSY| if a (data pipe
-// producer/consumer) handle to be sent is in a two-phase write/read). But
-// should we? (For comparison, there's no such provision in |MojoClose()|.)
-// https://github.com/domokit/mojo/issues/782
-//
-// TODO(vtl): Add a notion of capacity for message pipes, and return
-// |MOJO_RESULT_SHOULD_WAIT| if the message pipe is full.
-MojoResult MojoWriteMessage(MojoHandle message_pipe_handle,  // In.
-                            const void* bytes,               // Optional in.
-                            uint32_t num_bytes,              // In.
-                            const MojoHandle* handles,       // Optional in.
-                            uint32_t num_handles,            // In.
-                            MojoWriteMessageFlags flags);    // In.
-
-// |MojoReadMessage()|: Reads the next message from the message pipe endpoint
-// given by |message_pipe_handle| (which must have the |MOJO_HANDLE_RIGHT_READ|
-// right) or indicates the size of the message if it cannot fit in the provided
-// buffers. The message will be read in its entirety or not at all; if it is
-// not, it will remain enqueued unless the |MOJO_READ_MESSAGE_FLAG_MAY_DISCARD|
-// flag was passed. At most one message will be consumed from the queue, and the
-// return value will indicate whether a message was successfully read.
-//
-// |num_bytes| and |num_handles| are optional in/out parameters that on input
-// must be set to the sizes of the |bytes| and |handles| arrays, and on output
-// will be set to the actual number of bytes or handles contained in the
-// message (even if the message was not retrieved due to being too large).
-// Either |num_bytes| or |num_handles| may be null if the message is not
-// expected to contain the corresponding type of data, but such a call would
-// fail with |MOJO_RESULT_RESOURCE_EXHAUSTED| if the message in fact did
-// contain that type of data.
-//
-// |bytes| and |handles| will receive the contents of the message, if it is
-// retrieved. Either or both may be null, in which case the corresponding size
-// parameter(s) must also be set to zero or passed as null.
-//
-// Returns:
-//   |MOJO_RESULT_OK| on success (i.e., a message was actually read).
-//   |MOJO_RESULT_INVALID_ARGUMENT| if some argument was invalid.
-//   |MOJO_RESULT_FAILED_PRECONDITION| if the other endpoint has been closed.
-//   |MOJO_RESULT_PERMISSION_DENIED| if |message_pipe_handle| does not have the
-//       |MOJO_HANDLE_RIGHT_READ| right.
-//   |MOJO_RESULT_RESOURCE_EXHAUSTED| if the message was too large to fit in the
-//       provided buffer(s). The message will have been left in the queue or
-//       discarded, depending on flags.
-//   |MOJO_RESULT_SHOULD_WAIT| if no message was available to be read.
-//   |MOJO_RESULT_BUSY| if |message_pipe_handle| is currently in use in some
-//       transaction (that, e.g., may result in it being invalidated, such as
-//       being sent in a message).
-//
-// TODO(vtl): Reconsider the |MOJO_RESULT_RESOURCE_EXHAUSTED| error code; should
-// distinguish this from the hitting-system-limits case.
-MojoResult MojoReadMessage(
-    MojoHandle message_pipe_handle,       // In.
-    void* MOJO_RESTRICT bytes,            // Optional out.
-    uint32_t* MOJO_RESTRICT num_bytes,    // Optional in/out.
-    MojoHandle* MOJO_RESTRICT handles,    // Optional out.
-    uint32_t* MOJO_RESTRICT num_handles,  // Optional in/out.
-    MojoReadMessageFlags flags);          // In.
-
-MOJO_END_EXTERN_C
-
-#endif  // MOJO_PUBLIC_C_INCLUDE_MOJO_SYSTEM_MESSAGE_PIPE_H_