Fix GITHUB_STEP_SUMMARY size limit exceeded with non-ASCII characters

GitHubActionsTestLogger.Tests/MtpSummarySpecs.cs

@@ -386,4 +386,66 @@ public async Task I_can_try_to_use_the_logger_to_produce_a_summary_when_the_outp
         testOutput.WriteLine("Summary output:");
         testOutput.WriteLine(summaryOutput);
     }
+
+    [Fact]
+    public async Task I_can_try_to_use_the_logger_to_produce_a_summary_when_the_output_file_is_nearly_full_and_content_contains_non_ascii_characters_and_get_a_truncated_summary_within_the_size_limit()
+    {
+        // Arrange
+        using var testResultsDir = TempDirectory.Create();
+        using var summaryFile = TempFile.Create();
+
+        const int prefillSize = 1024 * 1024 - 250;
+        File.WriteAllZeroes(summaryFile.Path, prefillSize);
+
+        using var commandWriter = new StringWriter();
+
+        // Use a file-backed StreamWriter so that the file path is exposed internally
+        await using var summaryFileStream = File.Open(
+            summaryFile.Path,
+            FileMode.Append,
+            FileAccess.Write,
+            FileShare.ReadWrite
+        );
+
+        await using var summaryWriter = new StreamWriter(summaryFileStream);
+
+        var builder = await TestApplication.CreateBuilderAsync([
+            "--results-directory",
+            testResultsDir.Path,
+            "--report-github",
+            "--report-github-summary-include-passed",
+        ]);
+
+        // Use non-ASCII characters in test names (each Chinese character is 3 bytes in UTF-8,
+        // so truncating by char count instead of byte count would exceed the size limit)
+        builder.RegisterFakeTests(
+            new TestNodeBuilder()
+                .SetDisplayName(new string('一', 100))
+                .SetOutcome(TestOutcome.Failed)
+                .Build(),
+            new TestNodeBuilder()
+                .SetDisplayName(new string('二', 100))
+                .SetOutcome(TestOutcome.Failed)
+                .Build()
+        );
+
+        builder.AddGitHubActionsReporting(commandWriter, summaryWriter);
+
+        // Act
+        var app = await builder.BuildAsync();
+        await app.RunAsync();
+
+        await summaryWriter.FlushAsync();
+
+        // Assert
+        var commandOutput = commandWriter.ToString();
+        var summaryFileSize = new FileInfo(summaryFile.Path).Length;
+
+        commandOutput.Should().ContainAll("::warning", "truncated");
+        summaryFileSize.Should().BeLessThanOrEqualTo(1024 * 1024);
+
+        testOutput.WriteLine($"Summary file size: {summaryFileSize}");
+        testOutput.WriteLine("Command output:");
+        testOutput.WriteLine(commandOutput);
+    }
 }

GitHubActionsTestLogger.Tests/VsTestSummarySpecs.cs

@@ -431,4 +431,65 @@ public async Task I_can_try_to_use_the_logger_to_produce_a_summary_when_the_outp
         testOutput.WriteLine("Summary output:");
         testOutput.WriteLine(summaryOutput);
     }
+
+    [Fact]
+    public async Task I_can_try_to_use_the_logger_to_produce_a_summary_when_the_output_file_is_nearly_full_and_content_contains_non_ascii_characters_and_get_a_truncated_summary_within_the_size_limit()
+    {
+        // Arrange
+        using var summaryFile = TempFile.Create();
+
+        const int prefillSize = 1024 * 1024 - 250;
+        File.WriteAllZeroes(summaryFile.Path, prefillSize);
+
+        using var commandWriter = new StringWriter();
+
+        var events = new FakeTestLoggerEvents();
+        var logger = new VsTestLogger();
+
+        // Use a file-backed StreamWriter so that the file path is exposed internally
+        using var summaryFileStream = File.Open(
+            summaryFile.Path,
+            FileMode.Append,
+            FileAccess.Write,
+            FileShare.ReadWrite
+        );
+
+        using var summaryWriter = new StreamWriter(summaryFileStream);
+
+        logger.Initialize(
+            events,
+            new Dictionary<string, string?> { ["summary-include-passed"] = "true" },
+            commandWriter,
+            summaryWriter
+        );
+
+        // Act
+        // Use non-ASCII characters in test names (each Chinese character is 3 bytes in UTF-8,
+        // so truncating by char count instead of byte count would exceed the size limit)
+        events.SimulateTestRun(
+            new TestResultBuilder()
+                .SetDisplayName(new string('一', 100))
+                .SetFullyQualifiedName("TestProject.SomeTests.Test1")
+                .SetOutcome(TestOutcome.Failed)
+                .Build(),
+            new TestResultBuilder()
+                .SetDisplayName(new string('二', 100))
+                .SetFullyQualifiedName("TestProject.SomeTests.Test2")
+                .SetOutcome(TestOutcome.Failed)
+                .Build()
+        );
+
+        await summaryWriter.FlushAsync();
+
+        // Assert
+        var commandOutput = commandWriter.ToString();
+        var summaryFileSize = new FileInfo(summaryFile.Path).Length;
+
+        commandOutput.Should().ContainAll("::warning", "truncated");
+        summaryFileSize.Should().BeLessThanOrEqualTo(1024 * 1024);
+
+        testOutput.WriteLine($"Summary file size: {summaryFileSize}");
+        testOutput.WriteLine("Command output:");
+        testOutput.WriteLine(commandOutput);
+    }
 }

GitHubActionsTestLogger/GitHub/GitHubWorkflow.cs

@@ -86,6 +86,25 @@ await CreateAnnotationAsync(
             column
         );
 
+    private static string TruncateToUtf8ByteCount(string value, int byteLimit)
+    {
+        if (byteLimit <= 0)
+            return string.Empty;
+
+        if (Encoding.UTF8.GetByteCount(value) <= byteLimit)
+            return value;
+
+        var bytes = Encoding.UTF8.GetBytes(value);
+        var limit = byteLimit;
+
+        // If the byte at 'limit' is a UTF-8 continuation byte (10xxxxxx), back up to the start
+        // of the multi-byte sequence so we don't split a character in the middle.
+        while (limit > 0 && (bytes[limit] & 0xC0) == 0x80)
+            limit--;
+
+        return Encoding.UTF8.GetString(bytes, 0, limit);
+    }
+
     private string TruncateSummary(string content)
     {
         // Try to extract the underlying file path from the summary writer to monitor file size
@@ -122,7 +141,8 @@ private string TruncateSummary(string content)
                 && requiredSize <= availableSize
                     ? content
                 // There is enough space to fit some of the content
-                : availableSize > 0 && requiredSize > availableSize ? content[..availableSize]
+                : availableSize > 0 && requiredSize > availableSize
+                    ? TruncateToUtf8ByteCount(content, availableSize)
                 // There is no space at all
                 : string.Empty;
         }
@@ -155,7 +175,7 @@ If you have multiple summary providers in the same step (e.g. running multiple t
         await summaryWriter.WriteLineAsync();
         await summaryWriter.WriteLineAsync();
 
-        await summaryWriter.WriteLineAsync(content);
+        await summaryWriter.WriteLineAsync(truncated);
         await summaryWriter.FlushAsync();
     }
 }