Mojo: Move message pipe types/constants/functions from mojo/public/c/system/core.h to .../message_p…

mojo/public/c/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_SYSTEM_MESSAGE_PIPE_H_
+#define MOJO_PUBLIC_C_SYSTEM_MESSAGE_PIPE_H_
+
+#include "mojo/public/c/system/system_export.h"
+#include "mojo/public/c/system/types.h"
+
+// |MojoWriteMessageFlags|: Used to specify different modes to
+// |MojoWriteMessage()|.
+//   |MOJO_WRITE_MESSAGE_FLAG_NONE| - No flags; default mode.
+
+typedef uint32_t MojoWriteMessageFlags;
+
+#ifdef __cplusplus
+const MojoWriteMessageFlags MOJO_WRITE_MESSAGE_FLAG_NONE = 0;
+#else
+#define MOJO_WRITE_MESSAGE_FLAG_NONE ((MojoWriteMessageFlags) 0)
+#endif
+
+// |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;
+
+#ifdef __cplusplus
+const MojoReadMessageFlags MOJO_READ_MESSAGE_FLAG_NONE = 0;
+const MojoReadMessageFlags MOJO_READ_MESSAGE_FLAG_MAY_DISCARD = 1 << 0;
+#else
+#define MOJO_READ_MESSAGE_FLAG_NONE ((MojoReadMessageFlags) 0)
+#define MOJO_READ_MESSAGE_FLAG_MAY_DISCARD ((MojoReadMessageFlags) 1 << 0)
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Note: See the comment in functions.h about the meaning of the "optional"
+// label for pointer parameters.
+
+// 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. On success, |*message_pipe_handle0| and |*message_pipe_handle1| are
+// set to handles for the two endpoints (ports) for the message pipe.
+//
+// Returns:
+//   |MOJO_RESULT_OK| on success.
+//   |MOJO_RESULT_INVALID_ARGUMENT| if |message_pipe_handle0| and/or
+//       |message_pipe_handle1| do not appear to be valid pointers.
+//   |MOJO_RESULT_RESOURCE_EXHAUSTED| if a process/system/quota/etc. limit has
+//       been reached.
+//
+// TODO(vtl): Add an options struct pointer argument.
+MOJO_SYSTEM_EXPORT MojoResult MojoCreateMessagePipe(
+    MojoHandle* message_pipe_handle0,  // Out.
+    MojoHandle* message_pipe_handle1);  // Out.
+
+// Writes a message to the message pipe endpoint given by |message_pipe_handle|,
+// 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). Handles
+// to be sent should not be in simultaneous use (e.g., on another thread).
+//
+// 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_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 be succeed even if the other
+//       endpoint has been closed (in which case the message would be dropped).
+//   |MOJO_RESULT_BUSY| if some handle to be sent is currently in use.
+//
+// TODO(vtl): Add a notion of capacity for message pipes, and return
+// |MOJO_RESULT_SHOULD_WAIT| if the message pipe is full.
+MOJO_SYSTEM_EXPORT MojoResult MojoWriteMessage(
+    MojoHandle message_pipe_handle,
+    const void* bytes,  // Optional.
+    uint32_t num_bytes,
+    const MojoHandle* handles,  // Optional.
+    uint32_t num_handles,
+    MojoWriteMessageFlags flags);
+
+// Reads a message from the message pipe endpoint given by
+// |message_pipe_handle|; also usable to query the size of the next message or
+// discard the next message. |bytes|/|*num_bytes| indicate the buffer/buffer
+// size to receive the message data (if any) and |handles|/|*num_handles|
+// indicate the buffer/maximum handle count to receive the attached handles (if
+// any).
+//
+// |num_bytes| and |num_handles| are optional "in-out" parameters. If non-null,
+// on return |*num_bytes| and |*num_handles| will usually indicate the number
+// of bytes and number of attached handles in the "next" message, respectively,
+// whether that message was read or not. (If null, the number of bytes/handles
+// is treated as zero.)
+//
+// If |bytes| is null, then |*num_bytes| must be zero, and similarly for
+// |handles| and |*num_handles|.
+//
+// Partial reads are NEVER done. Either a full read is done and |MOJO_RESULT_OK|
+// returned, or the read is NOT done and |MOJO_RESULT_RESOURCE_EXHAUSTED| is
+// returned (if |MOJO_READ_MESSAGE_FLAG_MAY_DISCARD| was set, the message is
+// also discarded in this case).
+//
+// 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_RESOURCE_EXHAUSTED| if one of the buffers to receive the
+//       message/attached handles (|bytes|/|*num_bytes| or
+//       |handles|/|*num_handles|) was too small. (TODO(vtl): Reconsider this
+//       error code; should distinguish this from the hitting-system-limits
+//       case.)
+//   |MOJO_RESULT_SHOULD_WAIT| if no message was available to be read.
+MOJO_SYSTEM_EXPORT MojoResult MojoReadMessage(
+    MojoHandle message_pipe_handle,
+    void* bytes,  // Optional out.
+    uint32_t* num_bytes,  // Optional in/out.
+    MojoHandle* handles,  // Optional out.
+    uint32_t* num_handles,  // Optional in/out.
+    MojoReadMessageFlags flags);
+
+#ifdef __cplusplus
+}  // extern "C"
+#endif
+
+#endif  // MOJO_PUBLIC_C_SYSTEM_MESSAGE_PIPE_H_