1#region Copyright notice and license
2// Protocol Buffers - Google's data interchange format
3// Copyright 2008 Google Inc.  All rights reserved.
4// https://developers.google.com/protocol-buffers/
5//
6// Redistribution and use in source and binary forms, with or without
7// modification, are permitted provided that the following conditions are
8// met:
9//
10//     * Redistributions of source code must retain the above copyright
11// notice, this list of conditions and the following disclaimer.
12//     * Redistributions in binary form must reproduce the above
13// copyright notice, this list of conditions and the following disclaimer
14// in the documentation and/or other materials provided with the
15// distribution.
16//     * Neither the name of Google Inc. nor the names of its
17// contributors may be used to endorse or promote products derived from
18// this software without specific prior written permission.
19//
20// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
21// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
22// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
23// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
24// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
25// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
26// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
27// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
28// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
29// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
30// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
31#endregion
32
33using System;
34using System.Buffers;
35using System.IO;
36using System.Runtime.CompilerServices;
37using System.Security;
38
39namespace Google.Protobuf
40{
41    /// <summary>
42    /// Abstraction for writing to a steam / IBufferWriter
43    /// </summary>
44    [SecuritySafeCritical]
45    internal struct WriteBufferHelper
46    {
47        private IBufferWriter<byte> bufferWriter;
48        private CodedOutputStream codedOutputStream;
49
50        public CodedOutputStream CodedOutputStream => codedOutputStream;
51
52        /// <summary>
53        /// Initialize an instance with a coded output stream.
54        /// This approach is faster than using a constructor because the instance to initialize is passed by reference
55        /// and we can write directly into it without copying.
56        /// </summary>
57        [MethodImpl(MethodImplOptions.AggressiveInlining)]
58        public static void Initialize(CodedOutputStream codedOutputStream, out WriteBufferHelper instance)
59        {
60            instance.bufferWriter = null;
61            instance.codedOutputStream = codedOutputStream;
62        }
63
64        /// <summary>
65        /// Initialize an instance with a buffer writer.
66        /// This approach is faster than using a constructor because the instance to initialize is passed by reference
67        /// and we can write directly into it without copying.
68        /// </summary>
69        [MethodImpl(MethodImplOptions.AggressiveInlining)]
70        public static void Initialize(IBufferWriter<byte> bufferWriter, out WriteBufferHelper instance, out Span<byte> buffer)
71        {
72            instance.bufferWriter = bufferWriter;
73            instance.codedOutputStream = null;
74            buffer = default;  // TODO: initialize the initial buffer so that the first write is not via slowpath.
75        }
76
77        /// <summary>
78        /// Initialize an instance with a buffer represented by a single span (i.e. buffer cannot be refreshed)
79        /// This approach is faster than using a constructor because the instance to initialize is passed by reference
80        /// and we can write directly into it without copying.
81        /// </summary>
82        [MethodImpl(MethodImplOptions.AggressiveInlining)]
83        public static void InitializeNonRefreshable(out WriteBufferHelper instance)
84        {
85            instance.bufferWriter = null;
86            instance.codedOutputStream = null;
87        }
88
89        /// <summary>
90        /// Verifies that SpaceLeft returns zero.
91        /// </summary>
92        [MethodImpl(MethodImplOptions.AggressiveInlining)]
93        public static void CheckNoSpaceLeft(ref WriterInternalState state)
94        {
95            if (GetSpaceLeft(ref state) != 0)
96            {
97                throw new InvalidOperationException("Did not write as much data as expected.");
98            }
99        }
100
101        /// <summary>
102        /// If writing to a flat array, returns the space left in the array. Otherwise,
103        /// throws an InvalidOperationException.
104        /// </summary>
105        [MethodImpl(MethodImplOptions.AggressiveInlining)]
106        public static int GetSpaceLeft(ref WriterInternalState state)
107        {
108            if (state.writeBufferHelper.codedOutputStream?.InternalOutputStream == null && state.writeBufferHelper.bufferWriter == null)
109            {
110                return state.limit - state.position;
111            }
112            else
113            {
114                throw new InvalidOperationException(
115                    "SpaceLeft can only be called on CodedOutputStreams that are " +
116                        "writing to a flat array or when writing to a single span.");
117            }
118        }
119
120        [MethodImpl(MethodImplOptions.NoInlining)]
121        public static void RefreshBuffer(ref Span<byte> buffer, ref WriterInternalState state)
122        {
123            if (state.writeBufferHelper.codedOutputStream?.InternalOutputStream != null)
124            {
125                // because we're using coded output stream, we know that "buffer" and codedOutputStream.InternalBuffer are identical.
126                state.writeBufferHelper.codedOutputStream.InternalOutputStream.Write(state.writeBufferHelper.codedOutputStream.InternalBuffer, 0, state.position);
127                // reset position, limit stays the same because we are reusing the codedOutputStream's internal buffer.
128                state.position = 0;
129            }
130            else if (state.writeBufferHelper.bufferWriter != null)
131            {
132                // commit the bytes and get a new buffer to write to.
133                state.writeBufferHelper.bufferWriter.Advance(state.position);
134                state.position = 0;
135                buffer = state.writeBufferHelper.bufferWriter.GetSpan();
136                state.limit = buffer.Length;
137            }
138            else
139            {
140                // We're writing to a single buffer.
141                throw new CodedOutputStream.OutOfSpaceException();
142            }
143        }
144
145        [MethodImpl(MethodImplOptions.AggressiveInlining)]
146        public static void Flush(ref Span<byte> buffer, ref WriterInternalState state)
147        {
148            if (state.writeBufferHelper.codedOutputStream?.InternalOutputStream != null)
149            {
150                // because we're using coded output stream, we know that "buffer" and codedOutputStream.InternalBuffer are identical.
151                state.writeBufferHelper.codedOutputStream.InternalOutputStream.Write(state.writeBufferHelper.codedOutputStream.InternalBuffer, 0, state.position);
152                state.position = 0;
153            }
154            else if (state.writeBufferHelper.bufferWriter != null)
155            {
156                // calling Advance invalidates the current buffer and we must not continue writing to it,
157                // so we set the current buffer to point to an empty Span. If any subsequent writes happen,
158                // the first subsequent write will trigger refresing of the buffer.
159                state.writeBufferHelper.bufferWriter.Advance(state.position);
160                state.position = 0;
161                state.limit = 0;
162                buffer = default;  // invalidate the current buffer
163            }
164        }
165    }
166}