From 0c38954e0033f4ef112fc2b6d8244c798dce30da Mon Sep 17 00:00:00 2001
From: Tristan Labelle <tristan@thebrowser.company>
Date: Wed, 14 Jun 2023 15:44:39 -0400
Subject: [PATCH] Clamp the length for WriteFile calls on win32 pipes.

---
 src/io.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/io.c b/src/io.c
index f853d9bbf..e31e28c82 100644
--- a/src/io.c
+++ b/src/io.c
@@ -2510,6 +2510,23 @@ _dispatch_operation_perform(dispatch_operation_t op)
 				}
 				bSuccess = TRUE;
 			} else if (GetFileType(hFile) == FILE_TYPE_PIPE) {
+				// WriteFile with more bytes than are available in the
+				// buffer of a NOWAIT pipe will immediately return 0,
+				// so clamp our requested write length to make progress.
+				IO_STATUS_BLOCK iosb;
+				FILE_PIPE_LOCAL_INFORMATION fpli;
+				NTSTATUS status = _dispatch_NtQueryInformationFile(hFile,
+						&iosb, &fpli, sizeof(fpli), FilePipeLocalInformation);
+				if (NT_SUCCESS(status)) {
+					// WriteQuotaAvailable is unreliable in the presence
+					// of a blocking reader, when it can return zero, so only
+					// account for it otherwise
+					if (fpli.WriteQuotaAvailable > 0) {
+						len = MIN(len, fpli.WriteQuotaAvailable);
+					}
+					len = MIN(len, fpli.OutboundQuota);
+				}
+
 				OVERLAPPED ovlOverlapped = {};
 				bSuccess = WriteFile(hFile, buf, (DWORD)len,
 						(LPDWORD)&processed, &ovlOverlapped);