Change ReadTag and PeekTag to just use 0 as a return value for "end of stream", rather than using an awkward out parameter.

This simplifies quite a lot of code.

Generated code in next commit.

7 files changed, 52 insertions, 62 deletions

diff --git a/csharp/src/Google.Protobuf.Test/CodedInputStreamExtensions.cs b/csharp/src/Google.Protobuf.Test/CodedInputStreamExtensions.cs
index 408c7cb9..23af2887 100644
--- a/csharp/src/Google.Protobuf.Test/CodedInputStreamExtensions.cs
+++ b/csharp/src/Google.Protobuf.Test/CodedInputStreamExtensions.cs
@@ -38,8 +38,7 @@ namespace Google.Protobuf
     {
         public static void AssertNextTag(this CodedInputStream input, uint expectedTag)
         {
-            uint tag;
-            Assert.IsTrue(input.ReadTag(out tag));
+            uint tag = input.ReadTag();
             Assert.AreEqual(expectedTag, tag);
         }
 
diff --git a/csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs b/csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs
index 6e25fa37..c4c92efd 100644
--- a/csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs
+++ b/csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs
@@ -279,9 +279,7 @@ namespace Google.Protobuf
             ms.Position = 0;

 

             CodedInputStream input = new CodedInputStream(ms);

-            uint testtag;

-            Assert.IsTrue(input.ReadTag(out testtag));

-            Assert.AreEqual(tag, testtag);

+            Assert.AreEqual(tag, input.ReadTag());

 

             // TODO(jonskeet): Should this be ArgumentNullException instead?

             Assert.Throws<InvalidProtocolBufferException>(() => input.ReadBytes());

@@ -377,9 +375,7 @@ namespace Google.Protobuf
 

             CodedInputStream input = new CodedInputStream(ms);

 

-            uint actualTag;

-            Assert.IsTrue(input.ReadTag(out actualTag));

-            Assert.AreEqual(tag, actualTag);

+            Assert.AreEqual(tag, input.ReadTag());

             string text = input.ReadString();

             Assert.AreEqual('\ufffd', text[0]);

         }

@@ -430,15 +426,21 @@ namespace Google.Protobuf
                 ms.Position = 0;

                 CodedInputStream input = new CodedInputStream(ms, new byte[ms.Length / 2]);

 

-                uint tag;

-                Assert.IsTrue(input.ReadTag(out tag));

+                uint tag = input.ReadTag();

                 Assert.AreEqual(1, WireFormat.GetTagFieldNumber(tag));

                 Assert.AreEqual(100, input.ReadBytes().Length);

 

-                Assert.IsTrue(input.ReadTag(out tag));

+                tag = input.ReadTag();

                 Assert.AreEqual(2, WireFormat.GetTagFieldNumber(tag));

                 Assert.AreEqual(100, input.ReadBytes().Length);

             }

         }

+

+        [Test]

+        public void Tag0Throws()

+        {

+            var input = new CodedInputStream(new byte[] { 0 });

+            Assert.Throws<InvalidProtocolBufferException>(() => input.ReadTag());

+        }

     }

 }
\ No newline at end of file
diff --git a/csharp/src/Google.Protobuf.Test/CodedOutputStreamTest.cs b/csharp/src/Google.Protobuf.Test/CodedOutputStreamTest.cs
index af329174..c1bf7bd6 100644
--- a/csharp/src/Google.Protobuf.Test/CodedOutputStreamTest.cs
+++ b/csharp/src/Google.Protobuf.Test/CodedOutputStreamTest.cs
@@ -335,15 +335,16 @@ namespace Google.Protobuf
             // Now test Input stream:

             {

                 CodedInputStream cin = new CodedInputStream(new MemoryStream(bytes), new byte[50]);

-                uint tag;

                 Assert.AreEqual(0, cin.Position);

                 // Field 1:

-                Assert.IsTrue(cin.ReadTag(out tag) && tag >> 3 == 1);

+                uint tag = cin.ReadTag();

+                Assert.AreEqual(1, tag >> 3);

                 Assert.AreEqual(1, cin.Position);

                 Assert.AreEqual(500, cin.ReadInt32());

                 Assert.AreEqual(3, cin.Position);

                 //Field 2:

-                Assert.IsTrue(cin.ReadTag(out tag) && tag >> 3 == 2);

+                tag = cin.ReadTag();

+                Assert.AreEqual(2, tag >> 3);

                 Assert.AreEqual(4, cin.Position);

                 int childlen = cin.ReadLength();

                 Assert.AreEqual(120, childlen);

@@ -353,19 +354,22 @@ namespace Google.Protobuf
                 // Now we are reading child message

                 {

                     // Field 11: numeric value: 500

-                    Assert.IsTrue(cin.ReadTag(out tag) && tag >> 3 == 11);

+                    tag = cin.ReadTag();

+                    Assert.AreEqual(11, tag >> 3);

                     Assert.AreEqual(6, cin.Position);

                     Assert.AreEqual(500, cin.ReadInt32());

                     Assert.AreEqual(8, cin.Position);

                     //Field 12: length delimited 120 bytes

-                    Assert.IsTrue(cin.ReadTag(out tag) && tag >> 3 == 12);

+                    tag = cin.ReadTag();

+                    Assert.AreEqual(12, tag >> 3);

                     Assert.AreEqual(9, cin.Position);

                     ByteString bstr = cin.ReadBytes();

                     Assert.AreEqual(110, bstr.Length);

                     Assert.AreEqual((byte) 109, bstr[109]);

                     Assert.AreEqual(120, cin.Position);

                     // Field 13: fixed numeric value: 501

-                    Assert.IsTrue(cin.ReadTag(out tag) && tag >> 3 == 13);

+                    tag = cin.ReadTag();

+                    Assert.AreEqual(13, tag >> 3);

                     // ROK - Previously broken here, this returned 126 failing to account for bufferSizeAfterLimit

                     Assert.AreEqual(121, cin.Position);

                     Assert.AreEqual(501, cin.ReadSFixed32());

@@ -375,7 +379,8 @@ namespace Google.Protobuf
                 cin.PopLimit(oldlimit);

                 Assert.AreEqual(125, cin.Position);

                 // Field 3: fixed numeric value: 501

-                Assert.IsTrue(cin.ReadTag(out tag) && tag >> 3 == 3);

+                tag = cin.ReadTag();

+                Assert.AreEqual(3, tag >> 3);

                 Assert.AreEqual(126, cin.Position);

                 Assert.AreEqual(501, cin.ReadSFixed32());

                 Assert.AreEqual(130, cin.Position);

diff --git a/csharp/src/Google.Protobuf.Test/Collections/RepeatedFieldTest.cs b/csharp/src/Google.Protobuf.Test/Collections/RepeatedFieldTest.cs
index 322100d0..8c804fdd 100644
--- a/csharp/src/Google.Protobuf.Test/Collections/RepeatedFieldTest.cs
+++ b/csharp/src/Google.Protobuf.Test/Collections/RepeatedFieldTest.cs
@@ -455,7 +455,7 @@ namespace Google.Protobuf.Collections
             Assert.AreEqual(0, output.SpaceLeft);
 
             CodedInputStream input = new CodedInputStream(bytes);
-            Assert.IsTrue(input.ReadTag(out tag));
+            tag = input.ReadTag();
 
             RepeatedField<SampleEnum> values = new RepeatedField<SampleEnum>();
             values.AddEntriesFrom(input, FieldCodec.ForEnum(tag, x => (int)x, x => (SampleEnum)x));
@@ -493,7 +493,7 @@ namespace Google.Protobuf.Collections
             Assert.AreEqual(0, output.SpaceLeft);
 
             CodedInputStream input = new CodedInputStream(bytes);
-            Assert.IsTrue(input.ReadTag(out tag));
+            tag = input.ReadTag();
 
             RepeatedField<SampleEnum> values = new RepeatedField<SampleEnum>();
             values.AddEntriesFrom(input, FieldCodec.ForEnum(tag, x => (int)x, x => (SampleEnum)x));
diff --git a/csharp/src/Google.Protobuf/CodedInputStream.cs b/csharp/src/Google.Protobuf/CodedInputStream.cs
index 5da03b5c..0e2495f1 100644
--- a/csharp/src/Google.Protobuf/CodedInputStream.cs
+++ b/csharp/src/Google.Protobuf/CodedInputStream.cs
@@ -254,37 +254,35 @@ namespace Google.Protobuf
         #region Reading of tags etc

 

         /// <summary>

-        /// Attempts to peek at the next field tag.

+        /// Peeks at the next field tag. This is like calling <see cref="ReadTag"/>, but the

+        /// tag is not consumed. (So a subsequent call to <see cref="ReadTag"/> will return the

+        /// same value.)

         /// </summary>

-        public bool PeekNextTag(out uint fieldTag)

+        public uint PeekTag()

         {

             if (hasNextTag)

             {

-                fieldTag = nextTag;

-                return true;

+                return nextTag;

             }

 

             uint savedLast = lastTag;

-            hasNextTag = ReadTag(out nextTag);

-            lastTag = savedLast;

-            fieldTag = nextTag;

-            return hasNextTag;

+            nextTag = ReadTag();

+            hasNextTag = true;

+            lastTag = savedLast; // Undo the side effect of ReadTag

+            return nextTag;

         }

 

         /// <summary>

-        /// Attempts to read a field tag, returning false if we have reached the end

-        /// of the input data.

+        /// Reads a field tag, returning the tag of 0 for "end of stream".

         /// </summary>

-        /// <param name="fieldTag">The 'tag' of the field (id * 8 + wire-format)</param>

-        /// <returns>true if the next fieldTag was read</returns>

-        public bool ReadTag(out uint fieldTag)

+        /// <returns>The next field tag, or 0 for end of stream. (0 is never a valid tag.)</returns>

+        public uint ReadTag()

         {

             if (hasNextTag)

             {

-                fieldTag = nextTag;

-                lastTag = fieldTag;

+                lastTag = nextTag;

                 hasNextTag = false;

-                return true;

+                return lastTag;

             }

 

             // Optimize for the incredibly common case of having at least two bytes left in the buffer,

@@ -294,7 +292,7 @@ namespace Google.Protobuf
                 int tmp = buffer[bufferPos++];

                 if (tmp < 128)

                 {

-                    fieldTag = (uint)tmp;

+                    lastTag = (uint)tmp;

                 }

                 else

                 {

@@ -302,13 +300,13 @@ namespace Google.Protobuf
                     if ((tmp = buffer[bufferPos++]) < 128)

                     {

                         result |= tmp << 7;

-                        fieldTag = (uint) result;

+                        lastTag = (uint) result;

                     }

                     else

                     {

                         // Nope, rewind and go the potentially slow route.

                         bufferPos -= 2;

-                        fieldTag = ReadRawVarint32();

+                        lastTag = ReadRawVarint32();

                     }

                 }

             }

@@ -316,20 +314,18 @@ namespace Google.Protobuf
             {

                 if (IsAtEnd)

                 {

-                    fieldTag = 0;

-                    lastTag = fieldTag;

-                    return false;

+                    lastTag = 0;

+                    return 0; // This is the only case in which we return 0.

                 }

 

-                fieldTag = ReadRawVarint32();

+                lastTag = ReadRawVarint32();

             }

-            lastTag = fieldTag;

             if (lastTag == 0)

             {

                 // If we actually read zero, that's not a valid tag.

                 throw InvalidProtocolBufferException.InvalidTag();

             }

-            return true;

+            return lastTag;

         }

 

         /// <summary>

@@ -580,14 +576,10 @@ namespace Google.Protobuf
         /// </summary>

         public bool MaybeConsumeTag(uint tag)

         {

-            uint next;

-            if (PeekNextTag(out next))

+            if (PeekTag() == tag)

             {

-                if (next == tag)

-                {

-                    hasNextTag = false;

-                    return true;

-                }

+                hasNextTag = false;

+                return true;

             }

             return false;

         }

diff --git a/csharp/src/Google.Protobuf/Collections/MapField.cs b/csharp/src/Google.Protobuf/Collections/MapField.cs
index fed3d062..5eb2c2fc 100644
--- a/csharp/src/Google.Protobuf/Collections/MapField.cs
+++ b/csharp/src/Google.Protobuf/Collections/MapField.cs
@@ -627,12 +627,8 @@ namespace Google.Protobuf.Collections
                 public void MergeFrom(CodedInputStream input)
                 {
                     uint tag;
-                    while (input.ReadTag(out tag))
+                    while ((tag = input.ReadTag()) != 0)
                     {
-                        if (tag == 0)
-                        {
-                            throw InvalidProtocolBufferException.InvalidTag();
-                        }
                         if (tag == codec.keyCodec.Tag)
                         {
                             Key = codec.keyCodec.Read(input);
diff --git a/csharp/src/Google.Protobuf/FieldCodec.cs b/csharp/src/Google.Protobuf/FieldCodec.cs
index 1076c2a9..15d52c7d 100644
--- a/csharp/src/Google.Protobuf/FieldCodec.cs
+++ b/csharp/src/Google.Protobuf/FieldCodec.cs
@@ -298,12 +298,8 @@ namespace Google.Protobuf
 
                 uint tag;
                 T value = codec.DefaultValue;
-                while (input.ReadTag(out tag))
+                while ((tag = input.ReadTag()) != 0)
                 {
-                    if (tag == 0)
-                    {
-                        throw InvalidProtocolBufferException.InvalidTag();
-                    }
                     if (tag == codec.Tag)
                     {
                         value = codec.Read(input);