Pass buffer.End to AdvanceTo #27585 (#27586)

Author: Tratcher

src/Http/WebUtilities/src/FormPipeReader.cs

@@ -101,7 +101,7 @@ public async Task<Dictionary<string, StringValues>> ReadFormAsync(CancellationTo
                     }
                     catch
                     {
-                        _pipeReader.AdvanceTo(buffer.Start);
+                        _pipeReader.AdvanceTo(buffer.Start, buffer.End);
                         throw;
                     }
                 }

src/Http/WebUtilities/test/FormPipeReaderTests.cs

@@ -190,6 +190,31 @@ public async Task ReadFormAsync_ValueLengthLimitExceeded_Throw()
             Assert.Equal(Encoding.UTF8.GetBytes(content), readResult.Buffer.ToArray());
         }
 
+        [Fact]
+        public async Task ReadFormAsync_ValueLengthLimitExceededAcrossBufferBoundary_Throw()
+        {
+            Pipe bodyPipe = new Pipe();
+
+            var content1 = "foo=1&baz=1234567890";
+            var content2 = "1";
+
+            await bodyPipe.Writer.WriteAsync(Encoding.UTF8.GetBytes(content1));
+            await bodyPipe.Writer.FlushAsync();
+
+            var readTask = Assert.ThrowsAsync<InvalidDataException>(
+                () => ReadFormAsync(new FormPipeReader(bodyPipe.Reader) { ValueLengthLimit = 10 }));
+
+            await bodyPipe.Writer.WriteAsync(Encoding.UTF8.GetBytes(content2));
+            bodyPipe.Writer.Complete();
+
+            var exception = await readTask;
+            Assert.Equal("Form value length limit 10 exceeded.", exception.Message);
+
+            // The body pipe is still readable and has not advanced.
+            var readResult = await bodyPipe.Reader.ReadAsync();
+            Assert.Equal(Encoding.UTF8.GetBytes("baz=12345678901"), readResult.Buffer.ToArray());
+        }
+
         // https://en.wikipedia.org/wiki/Percent-encoding
         [Theory]
         [InlineData("++=hello", "  ", "hello")]