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
|
using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;
using System.IO;
using System.Reflection;
namespace Google.ProtocolBuffers {
/// <summary>
/// Iterates over data created using a <see cref="MessageStreamWriter{T}" />.
/// Unlike MessageStreamWriter, this class is not usually constructed directly with
/// a stream; instead it is provided with a way of opening a stream when iteration
/// is started. The stream is closed when the iteration is completed or the enumerator
/// is disposed. (This occurs naturally when using <c>foreach</c>.)
/// </summary>
public class MessageStreamIterator<TMessage> : IEnumerable<TMessage>
where TMessage : IMessage<TMessage> {
private readonly StreamProvider streamProvider;
private readonly ExtensionRegistry extensionRegistry;
/// <summary>
/// Delegate created via reflection trickery (once per type) to create a builder
/// and read a message from a CodedInputStream with it. Note that unlike in Java,
/// there's one static field per constructed type.
/// </summary>
private static readonly Func<CodedInputStream, ExtensionRegistry, TMessage> messageReader = BuildMessageReader();
/// <summary>
/// Any exception (within reason) thrown within messageReader is caught and rethrown in the constructor.
/// This makes life a lot simpler for the caller.
/// </summary>
private static Exception typeInitializationException;
/// <summary>
/// Creates the delegate later used to read messages. This is only called once per type, but to
/// avoid exceptions occurring at confusing times, if this fails it will set typeInitializationException
/// to the appropriate error and return null.
/// </summary>
private static Func<CodedInputStream, ExtensionRegistry, TMessage> BuildMessageReader() {
try {
Type builderType = FindBuilderType();
// Yes, it's redundant to find this again, but it's only the once...
MethodInfo createBuilderMethod = typeof(TMessage).GetMethod("CreateBuilder", Type.EmptyTypes);
Delegate builderBuilder = Delegate.CreateDelegate(
typeof(Func<>).MakeGenericType(builderType), null, createBuilderMethod);
MethodInfo buildMethod = typeof(MessageStreamIterator<TMessage>)
.GetMethod("BuildImpl", BindingFlags.Static | BindingFlags.NonPublic)
.MakeGenericMethod(typeof(TMessage), builderType);
return (Func<CodedInputStream, ExtensionRegistry, TMessage>)Delegate.CreateDelegate(
typeof(Func<CodedInputStream, ExtensionRegistry, TMessage>), builderBuilder, buildMethod);
} catch (ArgumentException e) {
typeInitializationException = e;
} catch (InvalidOperationException e) {
typeInitializationException = e;
} catch (InvalidCastException e) {
// Can't see why this would happen, but best to know about it.
typeInitializationException = e;
}
return null;
}
/// <summary>
/// Works out the builder type for TMessage, or throws an ArgumentException to explain why it can't.
/// This will check
/// </summary>
private static Type FindBuilderType() {
MethodInfo createBuilderMethod = typeof(TMessage).GetMethod("CreateBuilder", Type.EmptyTypes);
if (createBuilderMethod == null) {
throw new ArgumentException("Message type " + typeof(TMessage).FullName + " has no CreateBuilder method.");
}
if (createBuilderMethod.ReturnType == typeof(void)) {
throw new ArgumentException("CreateBuilder method in " + typeof(TMessage).FullName + " has void return type");
}
Type builderType = createBuilderMethod.ReturnType;
Type messageInterface = typeof(IMessage<,>).MakeGenericType(typeof(TMessage), builderType);
Type builderInterface = typeof(IBuilder<,>).MakeGenericType(typeof(TMessage), builderType);
if (Array.IndexOf(typeof(TMessage).GetInterfaces(), messageInterface) == -1) {
throw new ArgumentException("Message type " + typeof(TMessage) + " doesn't implement " + messageInterface.FullName);
}
if (Array.IndexOf(builderType.GetInterfaces(), builderInterface) == -1) {
throw new ArgumentException("Builder type " + typeof(TMessage) + " doesn't implement " + builderInterface.FullName);
}
return builderType;
}
/// <summary>
/// Method we'll use to build messageReader, with the first parameter fixed to TMessage.CreateBuilder. Note that we
/// have to introduce another type parameter (TMessage2) as we can't constrain TMessage for just a single method
/// (and we can't do it at the type level because we don't know TBuilder). However, by constraining TMessage2
/// to not only implement IMessage appropriately but also to derive from TMessage2, we can avoid doing a cast
/// for every message; the implicit reference conversion will be fine. In practice, TMessage2 and TMessage will
/// be the same type when we construct the generic method by reflection.
/// </summary>
private static TMessage BuildImpl<TMessage2, TBuilder>(Func<TBuilder> builderBuilder, CodedInputStream input, ExtensionRegistry registry)
where TBuilder : IBuilder<TMessage2, TBuilder>
where TMessage2 : TMessage, IMessage<TMessage2, TBuilder> {
TBuilder builder = builderBuilder();
input.ReadMessage(builder, registry);
return builder.Build();
}
private static readonly uint ExpectedTag = WireFormat.MakeTag(1, WireFormat.WireType.LengthDelimited);
private MessageStreamIterator(StreamProvider streamProvider, ExtensionRegistry extensionRegistry) {
if (messageReader == null) {
throw typeInitializationException;
}
this.streamProvider = streamProvider;
this.extensionRegistry = extensionRegistry;
}
/// <summary>
/// Creates a new instance which uses the same stream provider as this one,
/// but the specified extension registry.
/// </summary>
public MessageStreamIterator<TMessage> WithExtensionRegistry(ExtensionRegistry newRegistry) {
return new MessageStreamIterator<TMessage>(streamProvider, newRegistry);
}
public static MessageStreamIterator<TMessage> FromFile(string file) {
return new MessageStreamIterator<TMessage>(() => File.OpenRead(file), ExtensionRegistry.Empty);
}
public static MessageStreamIterator<TMessage> FromStreamProvider(StreamProvider streamProvider) {
return new MessageStreamIterator<TMessage>(streamProvider, ExtensionRegistry.Empty);
}
public IEnumerator<TMessage> GetEnumerator() {
using (Stream stream = streamProvider()) {
CodedInputStream input = CodedInputStream.CreateInstance(stream);
uint tag;
while ((tag = input.ReadTag()) != 0) {
if (tag != ExpectedTag) {
throw InvalidProtocolBufferException.InvalidMessageStreamTag();
}
yield return messageReader(input, extensionRegistry);
}
}
}
IEnumerator IEnumerable.GetEnumerator() {
return GetEnumerator();
}
}
}
|
