Cleanup exception message (#12623)

Author: BrennanConroy

src/SignalR/clients/csharp/Client/test/UnitTests/ServerSentEventsParserTests.cs

@@ -43,14 +43,14 @@ public void ParseSSEMessageSuccessCases(string encodedMessage, string expectedMe
         }
 
         [Theory]
-        [InlineData("data: T\n", "Unexpected '\n' in message. A '\n' character can only be used as part of the newline sequence '\r\n'")]
+        [InlineData("data: T\n", "Unexpected '\\n' in message. A '\\n' character can only be used as part of the newline sequence '\\r\\n'")]
         [InlineData("data: T\r\ndata: Hello, World\r\r\n\n", "There was an error in the frame format")]
-        [InlineData("data: T\r\ndata: Hello, World\n\n", "Unexpected '\n' in message. A '\n' character can only be used as part of the newline sequence '\r\n'")]
+        [InlineData("data: T\r\ndata: Hello, World\n\n", "Unexpected '\\n' in message. A '\\n' character can only be used as part of the newline sequence '\\r\\n'")]
         [InlineData("data: T\r\nfoo: Hello, World\r\n\r\n", "Expected the message prefix 'data: '")]
         [InlineData("foo: T\r\ndata: Hello, World\r\n\r\n", "Expected the message prefix 'data: '")]
         [InlineData("food: T\r\ndata: Hello, World\r\n\r\n", "Expected the message prefix 'data: '")]
         [InlineData("data: T\r\ndata: Hello, World\r\n\n", "There was an error in the frame format")]
-        [InlineData("data: T\r\ndata: Hello\n, World\r\n\r\n", "Unexpected '\n' in message. A '\n' character can only be used as part of the newline sequence '\r\n'")]
+        [InlineData("data: T\r\ndata: Hello\n, World\r\n\r\n", "Unexpected '\\n' in message. A '\\n' character can only be used as part of the newline sequence '\\r\\n'")]
         [InlineData("data: Hello, World\r\n\r\\", "Expected a \\r\\n frame ending")]
         [InlineData("data: Major\r\ndata:  Key\rndata:  Alert\r\n\r\\", "Expected a \\r\\n frame ending")]
         [InlineData("data: Major\r\ndata:  Key\r\ndata:  Alert\r\n\r\\", "Expected a \\r\\n frame ending")]
@@ -138,14 +138,14 @@ public async Task ParseMessageAcrossMultipleReadsSuccess(string[] messageParts,
         }
 
         [Theory]
-        [InlineData("data: T", "\n", "Unexpected '\n' in message. A '\n' character can only be used as part of the newline sequence '\r\n'")]
+        [InlineData("data: T", "\n", "Unexpected '\\n' in message. A '\\n' character can only be used as part of the newline sequence '\\r\\n'")]
         [InlineData("data: T\r\n", "data: Hello, World\r\r\n\n", "There was an error in the frame format")]
-        [InlineData("data: T\r\n", "data: Hello, World\n\n", "Unexpected '\n' in message. A '\n' character can only be used as part of the newline sequence '\r\n'")]
+        [InlineData("data: T\r\n", "data: Hello, World\n\n", "Unexpected '\\n' in message. A '\\n' character can only be used as part of the newline sequence '\\r\\n'")]
         [InlineData("data: T\r\nf", "oo: Hello, World\r\n\r\n", "Expected the message prefix 'data: '")]
         [InlineData("foo", ": T\r\ndata: Hello, World\r\n\r\n", "Expected the message prefix 'data: '")]
         [InlineData("food:", " T\r\ndata: Hello, World\r\n\r\n", "Expected the message prefix 'data: '")]
         [InlineData("data: T\r\ndata: Hello, W", "orld\r\n\n", "There was an error in the frame format")]
-        [InlineData("data: T\r\nda", "ta: Hello\n, World\r\n\r\n", "Unexpected '\n' in message. A '\n' character can only be used as part of the newline sequence '\r\n'")]
+        [InlineData("data: T\r\nda", "ta: Hello\n, World\r\n\r\n", "Unexpected '\\n' in message. A '\\n' character can only be used as part of the newline sequence '\\r\\n'")]
         [InlineData("data: ", "T\r\ndata: Major\r\ndata:  Key\r\ndata:  Alert\r\n\r\\", "Expected a \\r\\n frame ending")]
         [InlineData("data: B\r\ndata: SGVs", "bG8sIFdvcmxk\r\n\n\n", "There was an error in the frame format")]
         public async Task ParseMessageAcrossMultipleReadsFailure(string encodedMessagePart1, string encodedMessagePart2, string expectedMessage)

src/SignalR/clients/csharp/Http.Connections.Client/src/Internal/ServerSentEventsMessageParser.cs

@@ -29,7 +29,6 @@ public ParseResult ParseMessage(ReadOnlySequence<byte> buffer, out SequencePosit
             message = null;
 
             var start = consumed;
-            var end = examined;
 
             while (buffer.Length > 0)
             {
@@ -77,7 +76,7 @@ public ParseResult ParseMessage(ReadOnlySequence<byte> buffer, out SequencePosit
                 // data: bar\r\n
                 else if (line[line.Length - _sseLineEnding.Length] != ByteCR)
                 {
-                    throw new FormatException("Unexpected '\n' in message. A '\n' character can only be used as part of the newline sequence '\r\n'");
+                    throw new FormatException("Unexpected '\\n' in message. A '\\n' character can only be used as part of the newline sequence '\\r\\n'");
                 }
                 else
                 {