text: // 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.
  
  #ifndef MOJO_SYSTEM_TRANSPORT_DATA_H_
  #define MOJO_SYSTEM_TRANSPORT_DATA_H_
  
  #include <stdint.h>
  
  #include <vector>
  
  #include "base/macros.h"
  #include "base/memory/aligned_memory.h"
  #include "base/memory/scoped_ptr.h"
  #include "build/build_config.h"
  #include "mojo/embedder/platform_handle.h"
  #include "mojo/embedder/platform_handle_vector.h"
  #include "mojo/system/dispatcher.h"
  #include "mojo/system/system_impl_export.h"
  
  namespace mojo {
  namespace system {
  
  class Channel;
  
  // This class is used by |MessageInTransit| to represent handles (|Dispatcher|s)
  // in various stages of serialization.
  //
  // The stages are:
  //   - Before reaching |TransportData|: Turn |DispatcherTransport|s into
  //     |Dispatcher|s that are "owned" by (and attached to) a |MessageInTransit|.
  //     This invalidates the handles in the space of the sending application
  //     (and, e.g., if another thread is waiting on such a handle, it'll be
  //     notified of this invalidation).
  //   - Serialize these dispatchers into the |TransportData|: First, for each
  //     attached dispatcher, there's an entry in the |TransportData|'s "handle
  //     table", which points to a segment of (dispatcher-type-dependent) data.
  //   - During the serialization of the dispatchers, |PlatformHandle|s may be
  //     detached from the dispatchers and attached to the |TransportData|.
  //   - Before sending the |MessageInTransit|, including its main buffer and the
  //     |TransportData|'s buffer, the |Channel| sends any |PlatformHandle|s (in a
  //     platform-, and possibly sandbox-situation-, specific way) first. In doing
  //     so, it appends a "platform handle table" to the |TransportData|
  //     containing information about how to deserialize these |PlatformHandle|s.
  //   - Finally, at this point, to send the |MessageInTransit|, there only
  //     remains "inert" data: the |MessageInTransit|'s main buffer and data from
  //     the |TransportData|, consisting of the "handle table" (one entry for each
  //     attached dispatcher), dispatcher-type-specific data (one segment for each
  //     entry in the "handle table"), and the "platform handle table" (one entry
  //     for each attached |PlatformHandle|).
  //
  // To receive a message (|MessageInTransit|), the "reverse" happens:
  //   - On POSIX, receive and buffer |PlatformHandle|s (i.e., FDs), which were
  //     sent before the "inert" data.
  //   - Receive the "inert" data from the |MessageInTransit|. Examine its
  //     "platform handle table". On POSIX, match its entries with the buffered
  //     |PlatformHandle|s, which were previously received. On Windows, do what's
  //     necessary to obtain |PlatformHandle|s (e.g.: i. if the sender is fully
  //     trusted and able to duplicate handle into the receiver, then just pick
  //     out the |HANDLE| value; ii. if the receiver is fully trusted and able to
  //     duplicate handles from the receiver, do the |DuplicateHandle()|; iii.
  //     otherwise, talk to a broker to get handles). Reattach all the
  //     |PlatformHandle|s to the |MessageInTransit|.
  //   - For each entry in the "handle table", use serialized dispatcher data to
  //     reconstitute a dispatcher, taking ownership of associated
  //     |PlatformHandle|s (and detaching them). Attach these dispatchers to the
  //     |MessageInTransit|.
  //   - At this point, the |MessageInTransit| consists of its main buffer
  //     (primarily the data payload) and the attached dispatchers; the
  //     |TransportData| can be discarded.
  //   - When |MojoReadMessage()| is to give data to the application, attach the
  //     dispatchers to the (global, "core") handle table, getting handles; give
  //     the application the data payload and these handles.
  //
  // TODO(vtl): Everything above involving |PlatformHandle|s.
  class MOJO_SYSTEM_IMPL_EXPORT TransportData {
   public:
    // The maximum size of a single serialized dispatcher. This must be a multiple
    // of |kMessageAlignment|.
    static const size_t kMaxSerializedDispatcherSize = 10000;
  
    // The maximum number of platform handles to attach for a single serialized
    // dispatcher.
    static const size_t kMaxSerializedDispatcherPlatformHandles = 2;
  
    // The maximum possible size of a valid transport data buffer.
    static const size_t kMaxBufferSize;
  
    // The maximum total number of platform handles that may be attached.
    static const size_t kMaxPlatformHandles;
  
    TransportData(scoped_ptr<DispatcherVector> dispatchers, Channel* channel);
  
  #if defined(OS_POSIX)
    // This is a hacky POSIX-only constructor to directly attach only platform
    // handles to a message, used by |RawChannelPosix| to split messages with too
    // many platform handles into multiple messages. |Header| will be present, but
    // be zero. (No other information will be attached, and
    // |RawChannel::GetSerializedPlatformHandleSize()| should return zero.)
    explicit TransportData(
        embedder::ScopedPlatformHandleVectorPtr platform_handles);
  #endif
  
    ~TransportData();
  
    const void* buffer() const { return buffer_.get(); }
    void* buffer() { return buffer_.get(); }
    size_t buffer_size() const { return buffer_size_; }
  
    uint32_t platform_handle_table_offset() const {
      return header()->platform_handle_table_offset;
    }
  
    // Gets attached platform-specific handles; this may return null if there are
    // none. Note that the caller may mutate the set of platform-specific handles.
    const embedder::PlatformHandleVector* platform_handles() const {
      return platform_handles_.get();
    }
    embedder::PlatformHandleVector* platform_handles() {
      return platform_handles_.get();
    }
  
    // Receive-side functions:
  
    // Checks if the given buffer (from the "wire") looks like a valid
    // |TransportData| buffer. (Should only be called if |buffer_size| is
    // nonzero.) Returns null if valid, and a pointer to a human-readable error
    // message (for debug/logging purposes) on error. Note: This checks the
    // validity of the handle table entries (i.e., does range checking), but does
    // not check that the validity of the actual serialized dispatcher
    // information.
    static const char* ValidateBuffer(size_t serialized_platform_handle_size,
                                      const void* buffer,
                                      size_t buffer_size);
  
    // Gets the platform handle table from a (valid) |TransportData| buffer (which
    // should have been validated using |ValidateBuffer()| first).
    static void GetPlatformHandleTable(const void* transport_data_buffer,
                                       size_t* num_platform_handles,
                                       const void** platform_handle_table);
  
    // Deserializes dispatchers from the given (serialized) transport data buffer
    // (typically from a |MessageInTransit::View|) and vector of platform handles.
    // |buffer| should be non-null and |buffer_size| should be nonzero.
    static scoped_ptr<DispatcherVector> DeserializeDispatchers(
        const void* buffer,
        size_t buffer_size,
        embedder::ScopedPlatformHandleVectorPtr platform_handles,
        Channel* channel);
  
   private:
    // To allow us to make compile-assertions about |Header|, etc. in the .cc
    // file.
    struct PrivateStructForCompileAsserts;
  
    // Header for the "secondary buffer"/"transport data". Must be a multiple of
    // |MessageInTransit::kMessageAlignment| in size. Must be POD.
    struct Header {
      uint32_t num_handles;
      // TODO(vtl): Not used yet:
      uint32_t platform_handle_table_offset;
      uint32_t num_platform_handles;
      uint32_t unused;
    };
  
    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 reinterpret_cast<const Header*>(buffer_.get());
    }
  
    size_t buffer_size_;
    scoped_ptr<char, base::AlignedFreeDeleter> buffer_;  // Never null.
  
    // Any platform-specific handles attached to this message (for inter-process
    // transport). The vector (if any) owns the handles that it contains (and is
    // responsible for closing them).
    // TODO(vtl): With C++11, change it to a vector of |ScopedPlatformHandles|.
    embedder::ScopedPlatformHandleVectorPtr platform_handles_;
  
    DISALLOW_COPY_AND_ASSIGN(TransportData);
  };
  
  }  // namespace system
  }  // namespace mojo
  
  #endif  // MOJO_SYSTEM_TRANSPORT_DATA_H_
  