aboutsummaryrefslogtreecommitdiffhomepage
path: root/include/grpcpp/impl/codegen/proto_buffer_writer.h
blob: fdff4676b048812be315021626ccb169168e9da6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
/*
 *
 * Copyright 2018 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

#ifndef GRPCPP_IMPL_CODEGEN_PROTO_BUFFER_WRITER_H
#define GRPCPP_IMPL_CODEGEN_PROTO_BUFFER_WRITER_H

#include <type_traits>

#include <grpc/impl/codegen/grpc_types.h>
#include <grpc/impl/codegen/slice.h>
#include <grpcpp/impl/codegen/byte_buffer.h>
#include <grpcpp/impl/codegen/config_protobuf.h>
#include <grpcpp/impl/codegen/core_codegen_interface.h>
#include <grpcpp/impl/codegen/serialization_traits.h>
#include <grpcpp/impl/codegen/status.h>

/// This header provides an object that writes bytes directly into a
/// grpc::ByteBuffer, via the ZeroCopyOutputStream interface

namespace grpc {

extern CoreCodegenInterface* g_core_codegen_interface;

// Forward declaration for testing use only
namespace internal {
class ProtoBufferWriterPeer;
}  // namespace internal

const int kProtoBufferWriterMaxBufferLength = 1024 * 1024;

/// This is a specialization of the protobuf class ZeroCopyOutputStream.
/// The principle is to give the proto layer one buffer of bytes at a time
/// that it can use to serialize the next portion of the message, with the
/// option to "backup" if more buffer is given than required at the last buffer.
///
/// Read more about ZeroCopyOutputStream interface here:
/// https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.io.zero_copy_stream#ZeroCopyOutputStream
class ProtoBufferWriter : public ::grpc::protobuf::io::ZeroCopyOutputStream {
 public:
  /// Constructor for this derived class
  ///
  /// \param[out] byte_buffer A pointer to the grpc::ByteBuffer created
  /// \param block_size How big are the chunks to allocate at a time
  /// \param total_size How many total bytes are required for this proto
  ProtoBufferWriter(ByteBuffer* byte_buffer, int block_size, int total_size)
      : block_size_(block_size),
        total_size_(total_size),
        byte_count_(0),
        have_backup_(false) {
    GPR_CODEGEN_ASSERT(!byte_buffer->Valid());
    /// Create an empty raw byte buffer and look at its underlying slice buffer
    grpc_byte_buffer* bp =
        g_core_codegen_interface->grpc_raw_byte_buffer_create(NULL, 0);
    byte_buffer->set_buffer(bp);
    slice_buffer_ = &bp->data.raw.slice_buffer;
  }

  ~ProtoBufferWriter() {
    if (have_backup_) {
      g_core_codegen_interface->grpc_slice_unref(backup_slice_);
    }
  }

  /// Give the proto library the next buffer of bytes and its size. It is
  /// safe for the caller to write from data[0, size - 1].
  bool Next(void** data, int* size) override {
    // Protobuf should not ask for more memory than total_size_.
    GPR_CODEGEN_ASSERT(byte_count_ < total_size_);
    // 1. Use the remaining backup slice if we have one
    // 2. Otherwise allocate a slice, up to the remaining length needed
    //    or our maximum allocation size
    // 3. Provide the slice start and size available
    // 4. Add the slice being returned to the slice buffer
    size_t remain = total_size_ - byte_count_;
    if (have_backup_) {
      /// If we have a backup slice, we should use it first
      slice_ = backup_slice_;
      have_backup_ = false;
      if (GRPC_SLICE_LENGTH(slice_) > remain) {
        GRPC_SLICE_SET_LENGTH(slice_, remain);
      }
    } else {
      // When less than a whole block is needed, only allocate that much.
      // But make sure the allocated slice is not inlined.
      size_t allocate_length =
          remain > static_cast<size_t>(block_size_) ? block_size_ : remain;
      slice_ = g_core_codegen_interface->grpc_slice_malloc(
          allocate_length > GRPC_SLICE_INLINED_SIZE
              ? allocate_length
              : GRPC_SLICE_INLINED_SIZE + 1);
    }
    *data = GRPC_SLICE_START_PTR(slice_);
    // On win x64, int is only 32bit
    GPR_CODEGEN_ASSERT(GRPC_SLICE_LENGTH(slice_) <= INT_MAX);
    byte_count_ += * size = (int)GRPC_SLICE_LENGTH(slice_);
    g_core_codegen_interface->grpc_slice_buffer_add(slice_buffer_, slice_);
    return true;
  }

  /// Backup by \a count bytes because Next returned more bytes than needed
  /// (only used in the last buffer). \a count must be less than or equal too
  /// the last buffer returned from next.
  void BackUp(int count) override {
    /// 1. Remove the partially-used last slice from the slice buffer
    /// 2. Split it into the needed (if any) and unneeded part
    /// 3. Add the needed part back to the slice buffer
    /// 4. Mark that we still have the remaining part (for later use/unref)
    GPR_CODEGEN_ASSERT(count <= static_cast<int>(GRPC_SLICE_LENGTH(slice_)));
    g_core_codegen_interface->grpc_slice_buffer_pop(slice_buffer_);
    if ((size_t)count == GRPC_SLICE_LENGTH(slice_)) {
      backup_slice_ = slice_;
    } else {
      backup_slice_ = g_core_codegen_interface->grpc_slice_split_tail(
          &slice_, GRPC_SLICE_LENGTH(slice_) - count);
      g_core_codegen_interface->grpc_slice_buffer_add(slice_buffer_, slice_);
    }
    // It's dangerous to keep an inlined grpc_slice as the backup slice, since
    // on a following Next() call, a reference will be returned to this slice
    // via GRPC_SLICE_START_PTR, which will not be an address held by
    // slice_buffer_.
    have_backup_ = backup_slice_.refcount != NULL;
    byte_count_ -= count;
  }

  /// Returns the total number of bytes written since this object was created.
  grpc::protobuf::int64 ByteCount() const override { return byte_count_; }

  // These protected members are needed to support internal optimizations.
  // they expose internal bits of grpc core that are NOT stable. If you have
  // a use case needs to use one of these functions, please send an email to
  // https://groups.google.com/forum/#!forum/grpc-io.
 protected:
  grpc_slice_buffer* slice_buffer() { return slice_buffer_; }
  void set_byte_count(int64_t byte_count) { byte_count_ = byte_count; }

 private:
  // friend for testing purposes only
  friend class internal::ProtoBufferWriterPeer;
  const int block_size_;  ///< size to alloc for each new \a grpc_slice needed
  const int total_size_;  ///< byte size of proto being serialized
  int64_t byte_count_;    ///< bytes written since this object was created
  grpc_slice_buffer*
      slice_buffer_;  ///< internal buffer of slices holding the serialized data
  bool have_backup_;  ///< if we are holding a backup slice or not
  grpc_slice backup_slice_;  ///< holds space we can still write to, if the
                             ///< caller has called BackUp
  grpc_slice slice_;         ///< current slice passed back to the caller
};

}  // namespace grpc

#endif  // GRPCPP_IMPL_CODEGEN_PROTO_BUFFER_WRITER_H