Structured Message Decode: Validate Content Length

sdk/storage/Azure.Storage.Common/src/Shared/StructuredMessageDecodingStream.cs

@@ -89,9 +89,12 @@ public override long Position
     }
 
     public StructuredMessageDecodingStream(
-        Stream innerStream)
+        Stream innerStream,
+        long? expectedStreamLength = default)
     {
         Argument.AssertNotNull(innerStream, nameof(innerStream));
+
+        _innerStreamLength = expectedStreamLength ?? -1;
         _innerBufferedStream = new BufferedStream(innerStream);
 
         // Assumes stream will be structured message 1.0. Will validate this when consuming stream.
@@ -366,9 +369,19 @@ private int ProcessStreamHeader(ReadOnlySpan<byte> span)
     {
         StructuredMessage.V1_0.ReadStreamHeader(
             span.Slice(0, _streamHeaderLength),
-            out _innerStreamLength,
+            out long streamLength,
             out _flags,
             out _totalSegments);
+
+        if (_innerStreamLength > 0 && streamLength != _innerStreamLength)
+        {
+            throw Errors.InvalidStructuredMessage("Unexpected message size.");
+        }
+        else
+        {
+            _innerStreamLength = streamLength;
+        }
+
         if (_flags.HasFlag(StructuredMessage.Flags.StorageCrc64))
         {
             _segmentFooterLength = _flags.HasFlag(StructuredMessage.Flags.StorageCrc64) ? StructuredMessage.Crc64Length : 0;

sdk/storage/Azure.Storage.Common/tests/StructuredMessageDecodingStreamTests.cs

@@ -227,6 +227,46 @@ public void BadStreamWrongSegmentNum()
             Assert.That(async () => await CopyStream(decodingStream, Stream.Null), Throws.InnerException.TypeOf<InvalidDataException>());
         }
 
+        [Test]
+        [Combinatorial]
+        public async Task BadStreamWrongContentLength(
+            [Values(-1, 1)] int difference,
+            [Values(true, false)] bool lengthProvided)
+        {
+            byte[] originalData = new byte[1024];
+            new Random().NextBytes(originalData);
+            byte[] encodedData = StructuredMessageHelper.MakeEncodedData(originalData, 256, Flags.StorageCrc64);
+
+            BinaryPrimitives.WriteInt64LittleEndian(
+                new Span<byte>(encodedData, V1_0.StreamHeaderMessageLengthOffset, 8),
+                encodedData.Length + difference);
+
+            Stream decodingStream = new StructuredMessageDecodingStream(
+                new MemoryStream(encodedData),
+                lengthProvided ? (long?)encodedData.Length : default);
+
+            // manual try/catch with tiny buffer to validate the proccess failed mid-stream rather than the end
+            const int copyBufferSize = 4;
+            bool caught = false;
+            try
+            {
+                await CopyStream(decodingStream, Stream.Null, copyBufferSize);
+            }
+            catch (CopyStreamException ex)
+            {
+                caught = true;
+                if (lengthProvided)
+                {
+                    Assert.That(ex.TotalCopied, Is.EqualTo(0));
+                }
+                else
+                {
+                    Assert.That(ex.TotalCopied, Is.EqualTo(originalData.Length));
+                }
+            }
+            Assert.That(caught);
+        }
+
         [Test]
         public void BadStreamMissingExpectedStreamFooter()
         {