Mojo: Factor MessageInTransit secondary buffer stuff out into a separate class.

mojo/system/transport_data.cc

Index: mojo/system/transport_data.cc
diff --git a/mojo/system/transport_data.cc b/mojo/system/transport_data.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b3c48458e30c529af0b4a602ed95b8cdc8867f9b
--- /dev/null
+++ b/mojo/system/transport_data.cc
@@ -0,0 +1,255 @@
+// 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.
+
+#include "mojo/system/transport_data.h"
+
+#include <string.h>
+
+#include "base/compiler_specific.h"
+#include "base/logging.h"
+#include "mojo/system/constants.h"
+#include "mojo/system/message_in_transit.h"
+
+namespace mojo {
+namespace system {
+
+STATIC_CONST_MEMBER_DEFINITION const size_t
+    TransportData::kMaxSerializedDispatcherSize;
+STATIC_CONST_MEMBER_DEFINITION const size_t
+    TransportData::kMaxSerializedDispatcherPlatformHandles;
+
+// In additional to the header, for each attached (Mojo) handle there'll be a
+// handle table entry and serialized dispatcher data.
+// static
+const size_t TransportData::kMaxBufferSize =
+    sizeof(Header) + kMaxMessageNumHandles * (sizeof(HandleTableEntry) +
+                                              kMaxSerializedDispatcherSize);
+
+// static
+const size_t TransportData::kMaxPlatformHandles =
+    kMaxMessageNumHandles * kMaxSerializedDispatcherPlatformHandles;
+
+struct TransportData::PrivateStructForCompileAsserts {
+  // The size of |Header| must be a multiple of the alignment.
+  COMPILE_ASSERT(sizeof(Header) % MessageInTransit::kMessageAlignment == 0,
+                 sizeof_MessageInTransit_Header_invalid);
+
+  // The maximum serialized dispatcher size must be a multiple of the alignment.
+  COMPILE_ASSERT(kMaxSerializedDispatcherSize %
+                     MessageInTransit::kMessageAlignment == 0,
+                 kMaxSerializedDispatcherSize_not_a_multiple_of_alignment);
+
+  // The size of |HandleTableEntry| must be a multiple of the alignment.
+  COMPILE_ASSERT(sizeof(HandleTableEntry) %
+                     MessageInTransit::kMessageAlignment == 0,
+                 sizeof_MessageInTransit_HandleTableEntry_invalid);
+};
+
+TransportData::TransportData(
+    scoped_ptr<std::vector<scoped_refptr<Dispatcher> > > dispatchers,
+    Channel* channel)
+    : buffer_size_(0) {
+  DCHECK(dispatchers);
+  DCHECK(channel);
+
+  const size_t num_handles = dispatchers->size();
+  DCHECK_GT(num_handles, 0u);
+
+  // The offset to the start of the (Mojo) handle table.
+  const size_t handle_table_start_offset = sizeof(Header);
+  // The offset to the start of the serialized dispatcher data.
+  const size_t serialized_dispatcher_start_offset =
+      handle_table_start_offset + num_handles * sizeof(HandleTableEntry);
+  // The estimated size of the secondary buffer. We compute this estimate below.
+  // It must be at least as big as the (eventual) actual size.
+  size_t estimated_size = serialized_dispatcher_start_offset;
+  size_t num_platform_handles = 0;
+#if DCHECK_IS_ON
+  std::vector<size_t> all_max_sizes(num_handles);
+  std::vector<size_t> all_max_platform_handles(num_handles);
+#endif
+  for (size_t i = 0; i < num_handles; i++) {
+    if (Dispatcher* dispatcher = (*dispatchers)[i].get()) {
+      size_t max_size = 0;
+      size_t max_platform_handles = 0;
+      Dispatcher::TransportDataAccess::StartSerialize(
+              dispatcher, channel, &max_size, &max_platform_handles);
+
+      DCHECK_LE(max_size, kMaxSerializedDispatcherSize);
+      estimated_size += MessageInTransit::RoundUpMessageAlignment(max_size);
+      DCHECK_LE(estimated_size, kMaxBufferSize);
+
+      DCHECK_LE(max_platform_handles,
+                kMaxSerializedDispatcherPlatformHandles);
+      num_platform_handles += max_platform_handles;
+      DCHECK_LE(num_platform_handles, kMaxPlatformHandles);
+
+#if DCHECK_IS_ON
+      all_max_sizes[i] = max_size;
+      all_max_platform_handles[i] = max_platform_handles;
+#endif
+    }
+  }
+
+  buffer_.reset(static_cast<char*>(
+      base::AlignedAlloc(estimated_size, MessageInTransit::kMessageAlignment)));
+  // Entirely clear out the secondary buffer, since then we won't have to worry
+  // about clearing padding or unused space (e.g., if a dispatcher fails to
+  // serialize).
+  memset(buffer_.get(), 0, estimated_size);
+
+  if (num_platform_handles > 0) {
+    DCHECK(!platform_handles_);
+    platform_handles_.reset(new std::vector<embedder::PlatformHandle>());
+  }
+
+  Header* header = reinterpret_cast<Header*>(buffer_.get());
+  header->num_handles = static_cast<uint32_t>(num_handles);
+  // TODO(vtl): platform_handle_table_offset and num_platform_handles
+
+  HandleTableEntry* handle_table = reinterpret_cast<HandleTableEntry*>(
+      buffer_.get() + handle_table_start_offset);
+  size_t current_offset = serialized_dispatcher_start_offset;
+  for (size_t i = 0; i < num_handles; i++) {
+    Dispatcher* dispatcher = (*dispatchers)[i].get();
+    if (!dispatcher) {
+      COMPILE_ASSERT(Dispatcher::kTypeUnknown == 0,
+                     value_of_Dispatcher_kTypeUnknown_must_be_zero);
+      continue;
+    }
+
+#if DCHECK_IS_ON
+    size_t old_platform_handles_size =
+        platform_handles_ ? platform_handles_->size() : 0;
+#endif
+
+    void* destination = buffer_.get() + current_offset;
+    size_t actual_size = 0;
+    if (Dispatcher::TransportDataAccess::EndSerializeAndClose(
+            dispatcher, channel, destination, &actual_size,
+            platform_handles_.get())) {
+      handle_table[i].type = static_cast<int32_t>(dispatcher->GetType());
+      handle_table[i].offset = static_cast<uint32_t>(current_offset);
+      handle_table[i].size = static_cast<uint32_t>(actual_size);
+
+#if DCHECK_IS_ON
+      DCHECK_LE(actual_size, all_max_sizes[i]);
+      DCHECK_LE(platform_handles_ ? (platform_handles_->size() -
+                                         old_platform_handles_size) : 0,
+                all_max_platform_handles[i]);
+#endif
+    } else {
+      // Nothing to do on failure, since |buffer_| was cleared, and
+      // |kTypeUnknown| is zero. The handle was simply closed.
+      LOG(ERROR) << "Failed to serialize handle to remote message pipe";
+    }
+
+    current_offset += MessageInTransit::RoundUpMessageAlignment(actual_size);
+    DCHECK_LE(current_offset, estimated_size);
+    DCHECK_LE(platform_handles_ ? platform_handles_->size() : 0,
+              num_platform_handles);
+  }
+
+  // There's no aligned realloc, so it's no good way to release unused space (if
+  // we overshot our estimated space requirements).
+  buffer_size_ = current_offset;
+
+  // |dispatchers_| will be destroyed as it goes out of scope.
+}
+
+TransportData::~TransportData() {
+  if (platform_handles_) {
+    for (size_t i = 0; i < platform_handles_->size(); i++)
+      (*platform_handles_)[i].CloseIfNecessary();
+  }
+}
+
+// static
+const char* TransportData::ValidateBuffer(const void* buffer,
+                                          size_t buffer_size) {
+  DCHECK(buffer);
+  DCHECK_GT(buffer_size, 0u);
+
+  // Always make sure that the buffer size is sane; if it's not, someone's
+  // messing with us.
+  if (buffer_size < sizeof(Header) || buffer_size > kMaxBufferSize ||
+      buffer_size % MessageInTransit::kMessageAlignment != 0)
+    return "Invalid message secondary buffer size";
+
+  const Header* header = static_cast<const Header*>(buffer);
+  const size_t num_handles = header->num_handles;
+  if (num_handles == 0)
+    return "Message has no handles attached, but secondary buffer present";
+
+  // Sanity-check |num_handles| (before multiplying it against anything).
+  if (num_handles > kMaxMessageNumHandles)
+    return "Message handle payload too large";
+
+  if (buffer_size < sizeof(Header) + num_handles * sizeof(HandleTableEntry))
+    return "Message secondary buffer too small";
+
+  // TODO(vtl): Check |platform_handle_table_offset| and |num_platform_handles|
+  // once they're used.
+  if (header->platform_handle_table_offset != 0 ||
+      header->num_platform_handles != 0)
+    return "Bad message secondary buffer header values";
+
+  const HandleTableEntry* handle_table =
+      reinterpret_cast<const HandleTableEntry*>(
+          static_cast<const char*>(buffer) + sizeof(Header));
+  static const char kInvalidSerializedDispatcher[] =
+      "Message contains invalid serialized dispatcher";
+  for (size_t i = 0; i < num_handles; i++) {
+    size_t offset = handle_table[i].offset;
+    if (offset % MessageInTransit::kMessageAlignment != 0)
+      return kInvalidSerializedDispatcher;
+
+    size_t size = handle_table[i].size;
+    if (size > kMaxSerializedDispatcherSize || size > buffer_size)
+      return kInvalidSerializedDispatcher;
+
+    // Note: This is an overflow-safe check for |offset + size > buffer_size|
+    // (we know that |size <= buffer_size| from the previous check).
+    if (offset > buffer_size - size)
+      return kInvalidSerializedDispatcher;
+  }
+
+  return NULL;
+}
+
+// static
+scoped_ptr<std::vector<scoped_refptr<Dispatcher> > >
+    TransportData::DeserializeDispatchersFromBuffer(const void* buffer,
+                                                    size_t buffer_size,
+                                                    Channel* channel) {
+  DCHECK(buffer);
+  DCHECK_GT(buffer_size, 0u);
+  DCHECK(channel);
+
+  const Header* header = static_cast<const Header*>(buffer);
+  const size_t num_handles = header->num_handles;
+  scoped_ptr<std::vector<scoped_refptr<Dispatcher> > > dispatchers(
+      new std::vector<scoped_refptr<Dispatcher> >(num_handles));
+
+  const HandleTableEntry* handle_table =
+      reinterpret_cast<const HandleTableEntry*>(
+          static_cast<const char*>(buffer) + sizeof(Header));
+  for (size_t i = 0; i < num_handles; i++) {
+    size_t offset = handle_table[i].offset;
+    size_t size = handle_table[i].size;
+    // Should already have been checked by |ValidateBuffer()|:
+    DCHECK_EQ(offset % MessageInTransit::kMessageAlignment, 0u);
+    DCHECK_LE(offset, buffer_size);
+    DCHECK_LE(offset + size, buffer_size);
+
+    const void* source = static_cast<const char*>(buffer) + offset;
+    (*dispatchers)[i] = Dispatcher::TransportDataAccess::Deserialize(
+        channel, handle_table[i].type, source, size);
+  }
+
+  return dispatchers.Pass();
+}
+
+}  // namespace system
+}  // namespace mojo