fix: avoid first-chance exception when getting length of non-seekable attachment streams

src/Sentry/Internal/Extensions/StreamExtensions.cs

@@ -110,7 +110,7 @@ public static Task WriteNewlineAsync(this Stream stream, CancellationToken cance
     {
         try
         {
-            return stream.Length;
+            return stream.CanSeek ? stream.Length : null;
         }
         catch
         {

test/Sentry.Tests/Internals/Extensions/StreamExtensionsTests.cs

@@ -46,4 +46,61 @@ public async Task ReadLineAsync_NoMaxLength_ReadsToTheEnd()
         // Assert
         Encoding.UTF8.GetString(result).Should().Be(line);
     }
+
+    [Fact]
+    public void TryGetLength_SeekableStream_ReturnsLength()
+    {
+        // Arrange
+        using var stream = new MemoryStream(new byte[42]);
+
+        // Act
+        var result = stream.TryGetLength();
+
+        // Assert
+        result.Should().Be(42);
+    }
+
+    [Fact]
+    public void TryGetLength_NonSeekableStream_ReturnsNull()
+    {
+        // Arrange
+        using var stream = new LengthlessStream();
+
+        // Act
+        var result = stream.TryGetLength();
+
+        // Assert
+        result.Should().BeNull();
+    }
+
+    [Fact]
+    public void TryGetLength_NonSeekableStreamReportingLength_ReturnsNull()
+    {
+        // Arrange
+        using var stream = new NonSeekableMemoryStream(new byte[42]);
+
+        // Act
+        var result = stream.TryGetLength();
+
+        // Assert
+        result.Should().BeNull();
+    }
+
+    [Fact]
+    public void TryGetLength_NullStream_ReturnsNull()
+    {
+        // Arrange
+        Stream stream = null;
+
+        // Act
+        var result = stream.TryGetLength();
+
+        // Assert
+        result.Should().BeNull();
+    }
+
+    private class NonSeekableMemoryStream(byte[] buffer) : MemoryStream(buffer)
+    {
+        public override bool CanSeek => false;
+    }
 }