Keep Pipe readable after FormPipeReader error (#18939)

Author: halter73

src/Http/WebUtilities/src/FormPipeReader.cs

@@ -92,7 +92,15 @@ public async Task<Dictionary<string, StringValues>> ReadFormAsync(CancellationTo
 
                 if (!buffer.IsEmpty)
                 {
-                    ParseFormValues(ref buffer, ref accumulator, readResult.IsCompleted);
+                    try
+                    {
+                        ParseFormValues(ref buffer, ref accumulator, readResult.IsCompleted);
+                    }
+                    catch
+                    {
+                        _pipeReader.AdvanceTo(buffer.Start);
+                        throw;
+                    }
                 }
 
                 if (readResult.IsCompleted)

src/Http/WebUtilities/test/FormPipeReaderTests.cs

@@ -94,21 +94,32 @@ public async Task ReadFormAsync_ValueCountLimitMet_Success()
         [Fact]
         public async Task ReadFormAsync_ValueCountLimitExceeded_Throw()
         {
-            var bodyPipe = await MakePipeReader("foo=1&baz=2&bar=3&baz=4&baf=5");
+            var content = "foo=1&baz=2&bar=3&baz=4&baf=5";
+            var bodyPipe = await MakePipeReader(content);
 
             var exception = await Assert.ThrowsAsync<InvalidDataException>(
                 () => ReadFormAsync(new FormPipeReader(bodyPipe) { ValueCountLimit = 3 }));
             Assert.Equal("Form value count limit 3 exceeded.", exception.Message);
+
+            // The body pipe is still readable and has not advanced.
+            var readResult = await bodyPipe.ReadAsync();
+            Assert.Equal(Encoding.UTF8.GetBytes(content), readResult.Buffer.ToArray());
         }
 
         [Fact]
         public async Task ReadFormAsync_ValueCountLimitExceededSameKey_Throw()
         {
-            var bodyPipe = await MakePipeReader("baz=1&baz=2&baz=3&baz=4");
+            var content = "baz=1&baz=2&baz=3&baz=4";
+            var bodyPipe = await MakePipeReader(content);
 
             var exception = await Assert.ThrowsAsync<InvalidDataException>(
                 () => ReadFormAsync(new FormPipeReader(bodyPipe) { ValueCountLimit = 3 }));
             Assert.Equal("Form value count limit 3 exceeded.", exception.Message);
+
+
+            // The body pipe is still readable and has not advanced.
+            var readResult = await bodyPipe.ReadAsync();
+            Assert.Equal(Encoding.UTF8.GetBytes(content), readResult.Buffer.ToArray());
         }
 
         [Fact]
@@ -127,11 +138,16 @@ public async Task ReadFormAsync_KeyLengthLimitMet_Success()
         [Fact]
         public async Task ReadFormAsync_KeyLengthLimitExceeded_Throw()
         {
-            var bodyPipe = await MakePipeReader("foo=1&baz12345678=2");
+            var content = "foo=1&baz12345678=2";
+            var bodyPipe = await MakePipeReader(content);
 
             var exception = await Assert.ThrowsAsync<InvalidDataException>(
                 () => ReadFormAsync(new FormPipeReader(bodyPipe) { KeyLengthLimit = 10 }));
             Assert.Equal("Form key length limit 10 exceeded.", exception.Message);
+
+            // The body pipe is still readable and has not advanced.
+            var readResult = await bodyPipe.ReadAsync();
+            Assert.Equal(Encoding.UTF8.GetBytes(content), readResult.Buffer.ToArray());
         }
 
         [Fact]
@@ -150,11 +166,16 @@ public async Task ReadFormAsync_ValueLengthLimitMet_Success()
         [Fact]
         public async Task ReadFormAsync_ValueLengthLimitExceeded_Throw()
         {
-            var bodyPipe = await MakePipeReader("foo=1&baz=12345678901");
+            var content = "foo=1&baz=12345678901";
+            var bodyPipe = await MakePipeReader(content);
 
             var exception = await Assert.ThrowsAsync<InvalidDataException>(
                 () => ReadFormAsync(new FormPipeReader(bodyPipe) { ValueLengthLimit = 10 }));
             Assert.Equal("Form value length limit 10 exceeded.", exception.Message);
+
+            // The body pipe is still readable and has not advanced.
+            var readResult = await bodyPipe.ReadAsync();
+            Assert.Equal(Encoding.UTF8.GetBytes(content), readResult.Buffer.ToArray());
         }
 
         // https://en.wikipedia.org/wiki/Percent-encoding