From 02f583d99fa5e2201d592c6be9aaa4886da69675 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Tue, 3 Nov 2026 03:25:47 +0000
Subject: [PATCH] [patch] End output lines only at CR, LF and CRLF

LineOutputHandler also split on NEL (U+0085), LS (U+2028), PS (U+2029) and
form feed, a set carried over from the old ReplaceLineEndings code. Tools
emit LS and PS raw inside JSON strings, so NDJSON records were cut in half,
and Latin-1 output split at every 0x85 byte. Lines now end where
Process.OutputDataReceived and StreamReader.ReadLine end them.

Behaviour change: a caller that relied on FF or NEL splitting now gets
those characters inside the line.

Fixes ktsu-dev/RunCommand#133

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017vfJW5RAKCxdwrsVmygQDP
---
 README.md                                 |  2 +-
 RunCommand.Test/LineOutputHandlerTests.cs | 41 +++++++++++++++++++++++
 RunCommand/LineOutputHandler.cs           |  8 +++--
 3 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index 6388281..2bad560 100644
--- a/README.md
+++ b/README.md
@@ -394,7 +394,7 @@ Processes output in raw, undelimited chunks as they arrive from the process.
 
 ### `LineOutputHandler`
 
-Inherits from `OutputHandler` and buffers incoming chunks, invoking the delegates once per complete line. Incomplete trailing data is held until the rest of the line arrives.
+Inherits from `OutputHandler` and buffers incoming chunks, invoking the delegates once per complete line. Incomplete trailing data is held until the rest of the line arrives. Lines end at LF, CR or CRLF, the same as `Process.OutputDataReceived` and `StreamReader.ReadLine`; NEL (U+0085), LS (U+2028), PS (U+2029) and form feed stay inside the line, so line-delimited JSON that carries them raw arrives one record per call.
 
 #### Constructor
 
diff --git a/RunCommand.Test/LineOutputHandlerTests.cs b/RunCommand.Test/LineOutputHandlerTests.cs
index b21b819..3b84635 100644
--- a/RunCommand.Test/LineOutputHandlerTests.cs
+++ b/RunCommand.Test/LineOutputHandlerTests.cs
@@ -164,6 +164,47 @@ public void HandleStandardOutputDataShouldSplitOnEveryLineEndingKind()
 		Assert.AreEqual("e", handler.outputBuffer.ToString());
 	}
 
+	[TestMethod]
+	[DataRow('\u2028', DisplayName = "LS")]
+	[DataRow('\u2029', DisplayName = "PS")]
+	[DataRow('\u0085', DisplayName = "NEL")]
+	[DataRow('\f', DisplayName = "FF")]
+	public void HandleStandardOutputDataShouldKeepAnUnusualSeparatorInsideTheLine(char separator)
+	{
+		// Arrange
+		string record = $"{{\"a\":\"x{separator}y\"}}";
+		List<string> lines = [];
+		LineOutputHandler handler = new(onStandardOutput: lines.Add);
+
+		// Act
+		handler.HandleStandardOutputData($"{record}\n{record}\n");
+
+		// Assert
+		string[] expected = [record, record];
+		Assert.AreSequenceEqual(expected, lines);
+	}
+
+	[TestMethod]
+	[DataRow('\u2028', DisplayName = "LS")]
+	[DataRow('\u2029', DisplayName = "PS")]
+	[DataRow('\u0085', DisplayName = "NEL")]
+	[DataRow('\f', DisplayName = "FF")]
+	public void HandleStandardErrorDataShouldKeepAnUnusualSeparatorOnAChunkBoundaryInsideTheLine(char separator)
+	{
+		// Arrange
+		List<string> lines = [];
+		LineOutputHandler handler = new(onStandardError: lines.Add);
+
+		// Act
+		handler.HandleStandardErrorData($"x{separator}");
+		handler.HandleStandardErrorData($"y\nz{separator}");
+		handler.HandleStandardErrorData("\n");
+
+		// Assert
+		string[] expected = [$"x{separator}y", $"z{separator}"];
+		Assert.AreSequenceEqual(expected, lines);
+	}
+
 	[TestMethod]
 	public void CompleteShouldDeliverTheFinalUnterminatedLine()
 	{
diff --git a/RunCommand/LineOutputHandler.cs b/RunCommand/LineOutputHandler.cs
index d04223a..fcf7212 100644
--- a/RunCommand/LineOutputHandler.cs
+++ b/RunCommand/LineOutputHandler.cs
@@ -200,9 +200,11 @@ private static void EmitLine(StringBuilder buffer, string data, int start, int e
 	}
 
 	/// <summary>
-	/// Determines whether a character other than CR ends a line, matching the set <c>string.ReplaceLineEndings</c> recognises.
+	/// Determines whether a character other than CR ends a line. Only LF does, matching
+	/// <c>Process.OutputDataReceived</c> and <c>StreamReader.ReadLine</c>: NEL, LS, PS and FF are ordinary characters,
+	/// since tools emit them raw inside JSON strings and a line-delimited record must arrive whole.
 	/// </summary>
 	/// <param name="c">The character to test.</param>
-	/// <returns><see langword="true"/> if <paramref name="c"/> is LF, NEL, LS, PS or FF; otherwise <see langword="false"/>.</returns>
-	private static bool IsLineBreak(char c) => c is '\n' or '\u0085' or '\u2028' or '\u2029' or '\f';
+	/// <returns><see langword="true"/> if <paramref name="c"/> is LF; otherwise <see langword="false"/>.</returns>
+	private static bool IsLineBreak(char c) => c == '\n';
 }