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// Copyright 2013 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.
#ifndef MOJO_SYSTEM_MESSAGE_IN_TRANSIT_H_
#define MOJO_SYSTEM_MESSAGE_IN_TRANSIT_H_
#include <stdint.h>
#include <vector>
#include "base/macros.h"
#include "base/memory/scoped_ptr.h"
#include "mojo/system/dispatcher.h"
#include "mojo/system/system_impl_export.h"
namespace mojo {
namespace system {
class Channel;
// This class is used to represent data in transit. It is thread-unsafe.
//
// |MessageInTransit| buffers:
//
// A |MessageInTransit| can be serialized by writing the main buffer and then,
// if it has one, the secondary buffer. Both buffers are
// |kMessageAlignment|-byte aligned and a multiple of |kMessageAlignment| bytes
// in size.
//
// The main buffer consists of the header (of type |Header|, which is an
// internal detail of this class) followed immediately by the message data
// (accessed by |bytes()| and of size |num_bytes()|, and also
// |kMessageAlignment|-byte aligned), and then any padding needed to make the
// main buffer a multiple of |kMessageAlignment| bytes in size.
//
// The secondary buffer consists first of a table of |HandleTableEntry|s (each
// of which is already a multiple of |kMessageAlignment| in size), followed by
// data needed for the |HandleTableEntry|s: A |HandleTableEntry| consists of an
// offset (in bytes, relative to the start of the secondary buffer; we guarantee
// that it's a multiple of |kMessageAlignment|), and a size (in bytes).
class MOJO_SYSTEM_IMPL_EXPORT MessageInTransit {
public:
typedef uint16_t Type;
// Messages that are forwarded to |MessagePipeEndpoint|s.
static const Type kTypeMessagePipeEndpoint = 0;
// Messages that are forwarded to |MessagePipe|s.
static const Type kTypeMessagePipe = 1;
// Messages that are consumed by the channel.
static const Type kTypeChannel = 2;
typedef uint16_t Subtype;
// Subtypes for type |kTypeMessagePipeEndpoint|:
static const Subtype kSubtypeMessagePipeEndpointData = 0;
// Subtypes for type |kTypeMessagePipe|:
static const Subtype kSubtypeMessagePipePeerClosed = 0;
// Subtypes for type |kTypeChannel|:
static const Subtype kSubtypeChannelRunMessagePipeEndpoint = 0;
typedef uint32_t EndpointId;
// Never a valid endpoint ID.
static const EndpointId kInvalidEndpointId = 0;
// Messages (the header and data) must always be aligned to a multiple of this
// quantity (which must be a power of 2).
static const size_t kMessageAlignment = 8;
// Forward-declare |Header| so that |View| can use it:
private:
struct Header;
public:
// This represents a view of serialized message data in a raw buffer.
class MOJO_SYSTEM_IMPL_EXPORT View {
public:
// Constructs a view from the given buffer of the given size. (The size must
// be as provided by |MessageInTransit::GetNextMessageSize()|.) The buffer
// must remain alive/unmodified through the lifetime of this object.
// |buffer| should be |kMessageAlignment|-byte aligned.
View(size_t message_size, const void* buffer);
// API parallel to that for |MessageInTransit| itself (mostly getters for
// header data).
const void* main_buffer() const { return buffer_; }
size_t main_buffer_size() const {
return RoundUpMessageAlignment(sizeof(Header) + header()->num_bytes);
}
const void* secondary_buffer() const {
return (total_size() > main_buffer_size()) ?
static_cast<const char*>(buffer_) + main_buffer_size() : NULL;
}
size_t secondary_buffer_size() const {
return total_size() - main_buffer_size();
}
size_t total_size() const { return header()->total_size; }
uint32_t num_bytes() const { return header()->num_bytes; }
const void* bytes() const {
return static_cast<const char*>(buffer_) + sizeof(Header);
}
uint32_t num_handles() const { return header()->num_handles; }
Type type() const { return header()->type; }
Subtype subtype() const { return header()->subtype; }
EndpointId source_id() const { return header()->source_id; }
EndpointId destination_id() const { return header()->destination_id; }
private:
const Header* header() const { return static_cast<const Header*>(buffer_); }
const void* const buffer_;
// Though this struct is trivial, disallow copy and assign, since it doesn't
// own its data. (If you're copying/assigning this, you're probably doing
// something wrong.)
DISALLOW_COPY_AND_ASSIGN(View);
};
// |bytes| is optional; if null, the message data will be zero-initialized.
MessageInTransit(Type type,
Subtype subtype,
uint32_t num_bytes,
uint32_t num_handles,
const void* bytes);
// Constructs a |MessageInTransit| from a |View|.
explicit MessageInTransit(const View& message_view);
~MessageInTransit();
// Gets the size of the next message from |buffer|, which has |buffer_size|
// bytes currently available, returning true and setting |*next_message_size|
// on success. |buffer| should be aligned on a |kMessageAlignment| boundary
// (and on success, |*next_message_size| will be a multiple of
// |kMessageAlignment|).
// TODO(vtl): In |RawChannelPosix|, the alignment requirements are currently
// satisified on a faith-based basis.
static bool GetNextMessageSize(const void* buffer,
size_t buffer_size,
size_t* next_message_size);
// Makes this message "own" the given set of dispatchers. The dispatchers must
// not be referenced from anywhere else (in particular, not from the handle
// table), i.e., each dispatcher must have a reference count of 1. This
// message must not already have dispatchers.
void SetDispatchers(
scoped_ptr<std::vector<scoped_refptr<Dispatcher> > > dispatchers);
// Serializes any dispatchers to the secondary buffer. This message must not
// already have a secondary buffer (so this must only be called once). The
// caller must ensure (e.g., by holding on to a reference) that |channel|
// stays alive through the call.
void SerializeAndCloseDispatchers(Channel* channel);
// Deserializes any dispatchers from the secondary buffer. This message must
// not have any dispatchers attached.
// TODO(vtl): Having to copy the secondary buffer (in the constructor from a
// |View|) is suboptimal. Maybe this should just be done in the constructor?
void DeserializeDispatchers(Channel* channel);
// Gets the main buffer and its size (in number of bytes), respectively.
const void* main_buffer() const { return main_buffer_; }
size_t main_buffer_size() const { return main_buffer_size_; }
// Gets the secondary buffer and its size (in number of bytes), respectively.
const void* secondary_buffer() const { return secondary_buffer_; }
size_t secondary_buffer_size() const { return secondary_buffer_size_; }
// Gets the total size of the message (see comment in |Header|, below).
size_t total_size() const { return header()->total_size; }
// Gets the size of the message data.
uint32_t num_bytes() const { return header()->num_bytes; }
// Gets the message data (of size |num_bytes()| bytes).
const void* bytes() const {
return static_cast<const char*>(main_buffer_) + sizeof(Header);
}
void* bytes() { return static_cast<char*>(main_buffer_) + sizeof(Header); }
uint32_t num_handles() const { return header()->num_handles; }
Type type() const { return header()->type; }
Subtype subtype() const { return header()->subtype; }
EndpointId source_id() const { return header()->source_id; }
EndpointId destination_id() const { return header()->destination_id; }
void set_source_id(EndpointId source_id) { header()->source_id = source_id; }
void set_destination_id(EndpointId destination_id) {
header()->destination_id = destination_id;
}
// Gets the dispatchers attached to this message; this may return null if
// there are none. Note that the caller may mutate the set of dispatchers
// (e.g., take ownership of all the dispatchers, leaving the vector empty).
std::vector<scoped_refptr<Dispatcher> >* dispatchers() {
return dispatchers_.get();
}
// Returns true if this message has dispatchers attached.
bool has_dispatchers() const {
return dispatchers_.get() && !dispatchers_->empty();
}
// Rounds |n| up to a multiple of |kMessageAlignment|.
static inline size_t RoundUpMessageAlignment(size_t n) {
return (n + kMessageAlignment - 1) & ~(kMessageAlignment - 1);
}
private:
// To allow us to make assertions about |Header| in the .cc file.
struct PrivateStructForCompileAsserts;
// "Header" for the data. Must be a multiple of |kMessageAlignment| bytes in
// size. Must be POD.
struct Header {
// Total size of the message, including the header, the message data
// ("bytes") including padding (to make it a multiple of |kMessageAlignment|
// bytes), and serialized handle information. Note that this may not be the
// correct value if dispatchers are attached but
// |SerializeAndCloseDispatchers()| has not been called.
uint32_t total_size;
Type type; // 2 bytes.
Subtype subtype; // 2 bytes.
EndpointId source_id; // 4 bytes.
EndpointId destination_id; // 4 bytes.
// Size of actual message data.
uint32_t num_bytes;
// Number of handles "attached".
uint32_t num_handles;
};
struct HandleTableEntry {
int32_t type; // From |Dispatcher::Type| (|kTypeUnknown| for "invalid").
uint32_t offset; // Relative to the start of the secondary buffer.
uint32_t size; // (Not including any padding.)
uint32_t unused;
};
const Header* header() const {
return static_cast<const Header*>(main_buffer_);
}
Header* header() { return static_cast<Header*>(main_buffer_); }
void UpdateTotalSize();
size_t main_buffer_size_;
void* main_buffer_;
size_t secondary_buffer_size_;
void* secondary_buffer_; // May be null.
// Any dispatchers that may be attached to this message. These dispatchers
// should be "owned" by this message, i.e., have a ref count of exactly 1. (We
// allow a dispatcher entry to be null, in case it couldn't be duplicated for
// some reason.)
scoped_ptr<std::vector<scoped_refptr<Dispatcher> > > dispatchers_;
DISALLOW_COPY_AND_ASSIGN(MessageInTransit);
};
} // namespace system
} // namespace mojo
#endif // MOJO_SYSTEM_MESSAGE_IN_TRANSIT_H_