[Lldb-commits] [lldb] [lldb][Windows] Return EOF from PipeWindows::Read on a closed write end (PR #207017)

[Charles Zablit via lldb-commits]

https://github.com/charles-zablit updated https://github.com/llvm/llvm-project/pull/207017

>From 218f97a8ace4b54d3d284542ba6590478cb069d5 Mon Sep 17 00:00:00 2001
From: Charles Zablit <c_zablit at apple.com>
Date: Wed, 1 Jul 2026 16:54:22 +0100
Subject: [PATCH 1/2] [lldb][Windows] Return EOF from PipeWindows::Read on a
 closed write end

---
 lldb/source/Host/windows/PipeWindows.cpp | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/lldb/source/Host/windows/PipeWindows.cpp b/lldb/source/Host/windows/PipeWindows.cpp
index e2a64e65cee00..abf608750e61a 100644
--- a/lldb/source/Host/windows/PipeWindows.cpp
+++ b/lldb/source/Host/windows/PipeWindows.cpp
@@ -291,8 +291,15 @@ llvm::Expected<size_t> PipeWindows::Read(void *buf, size_t size,
     return bytes_read;
 
   DWORD failure_error = ::GetLastError();
-  if (failure_error != ERROR_IO_PENDING)
+  switch (failure_error) {
+  case ERROR_BROKEN_PIPE:
+  case ERROR_HANDLE_EOF:
+    return 0;
+  case ERROR_IO_PENDING:
+    break;
+  default:
     return Status(failure_error, eErrorTypeWin32).takeError();
+  }
 
   DWORD timeout_msec =
       timeout ? std::chrono::ceil<std::chrono::milliseconds>(*timeout).count()
@@ -319,8 +326,13 @@ llvm::Expected<size_t> PipeWindows::Read(void *buf, size_t size,
 
   // Now we call GetOverlappedResult setting bWait to false, since we've
   // already waited as long as we're willing to.
-  if (!::GetOverlappedResult(m_read, &m_read_overlapped, &bytes_read, FALSE))
-    return Status(::GetLastError(), eErrorTypeWin32).takeError();
+  if (!::GetOverlappedResult(m_read, &m_read_overlapped, &bytes_read, FALSE)) {
+    DWORD overlapped_error = ::GetLastError();
+    if (overlapped_error == ERROR_BROKEN_PIPE ||
+        overlapped_error == ERROR_HANDLE_EOF)
+      return 0;
+    return Status(overlapped_error, eErrorTypeWin32).takeError();
+  }
 
   return bytes_read;
 }

>From f05eae2fabc6d4011028ea3aca9183730775b90d Mon Sep 17 00:00:00 2001
From: Charles Zablit <c_zablit at apple.com>
Date: Wed, 1 Jul 2026 17:57:16 +0100
Subject: [PATCH 2/2] add comment

---
 lldb/source/Host/windows/PipeWindows.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lldb/source/Host/windows/PipeWindows.cpp b/lldb/source/Host/windows/PipeWindows.cpp
index abf608750e61a..d69a28cd69324 100644
--- a/lldb/source/Host/windows/PipeWindows.cpp
+++ b/lldb/source/Host/windows/PipeWindows.cpp
@@ -292,6 +292,9 @@ llvm::Expected<size_t> PipeWindows::Read(void *buf, size_t size,
 
   DWORD failure_error = ::GetLastError();
   switch (failure_error) {
+  // A closed write end is EOF, not an error. POSIX read() returns 0
+  // in this case. Mirror that so cross-platform callers can detect EOF
+  // uniformly.
   case ERROR_BROKEN_PIPE:
   case ERROR_HANDLE_EOF:
     return 0;
@@ -328,6 +331,7 @@ llvm::Expected<size_t> PipeWindows::Read(void *buf, size_t size,
   // already waited as long as we're willing to.
   if (!::GetOverlappedResult(m_read, &m_read_overlapped, &bytes_read, FALSE)) {
     DWORD overlapped_error = ::GetLastError();
+    // See above: a closed write end is end-of-file, not an error.
     if (overlapped_error == ERROR_BROKEN_PIPE ||
         overlapped_error == ERROR_HANDLE_EOF)
       return 0;