Make piping to subprocesses more robust on MS-Windows

* src/w32.c (sys_write): Don't write to a pipe more stuff than its
buffer can hold.  Don't return -1 if something has been written to
the pipe.  Zero out 'errno' before calling '_write', to avoid
returning a stale value.  (Bug#22344)
* src/w32proc.c (syms_of_ntproc) <w32-pipe-buffer-size>: New variable.
* src/w32.c (pipe2): Use it to request a user-defined size for the
pipe being created.

* etc/NEWS: Mention 'w32-pipe-buffer-size'.

* doc/emacs/msdos.texi (Windows Processes): Document
'w32-pipe-buffer-size'.

2 files changed, 38 insertions, 8 deletions

diff --git a/src/w32.c b/src/w32.c
index 4770718f5e3..ea3a9dafad5 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -8043,14 +8043,19 @@ pipe2 (int * phandles, int pipe2_flags)
 {
   int rc;
   unsigned flags;
+  unsigned pipe_size = 0;
 
   eassert (pipe2_flags == (O_BINARY | O_CLOEXEC));
 
+  /* Allow Lisp to override the default buffer size of the pipe.  */
+  if (w32_pipe_buffer_size > 0 && w32_pipe_buffer_size < UINT_MAX)
+    pipe_size = w32_pipe_buffer_size;
+
   /* make pipe handles non-inheritable; when we spawn a child, we
      replace the relevant handle with an inheritable one.  Also put
      pipes into binary mode; we will do text mode translation ourselves
      if required.  */
-  rc = _pipe (phandles, 0, _O_NOINHERIT | _O_BINARY);
+  rc = _pipe (phandles, pipe_size, _O_NOINHERIT | _O_BINARY);
 
   if (rc == 0)
     {
@@ -8632,15 +8637,35 @@ sys_write (int fd, const void * buffer, unsigned int count)
          http://thread.gmane.org/gmane.comp.version-control.git/145294
          in the git mailing list.  */
       const unsigned char *p = buffer;
-      const unsigned chunk = 30 * 1024 * 1024;
+      const bool is_pipe = (fd < MAXDESC
+                            && ((fd_info[fd].flags & (FILE_PIPE | FILE_NDELAY))
+                                == (FILE_PIPE | FILE_NDELAY)));
+      /* Some programs, notably Node.js's node.exe, seem to never
+         completely empty the pipe, so writing more than the size of
+         the pipe's buffer always returns ENOSPC, and we loop forever
+         between send_process and here.  As a workaround, write no
+         more than the pipe's buffer can hold.  */
+      DWORD pipe_buffer_size;
+      if (is_pipe)
+        {
+          if (!GetNamedPipeInfo ((HANDLE)_get_osfhandle (fd),
+                                NULL, &pipe_buffer_size, NULL, NULL))
+            {
+              DebPrint (("GetNamedPipeInfo: error %u\n", GetLastError ()));
+              pipe_buffer_size = 4096;
+            }
+        }
+      const unsigned chunk = is_pipe ? pipe_buffer_size : 30 * 1024 * 1024;
 
       nchars = 0;
+      errno = 0;
       while (count > 0)
         {
           unsigned this_chunk = count < chunk ? count : chunk;
           int n = _write (fd, p, this_chunk);
 
-          nchars += n;
+          if (n > 0)
+            nchars += n;
           if (n < 0)
             {
               /* When there's no buffer space in a pipe that is in the
@@ -8654,12 +8679,10 @@ sys_write (int fd, const void * buffer, unsigned int count)
                  avoiding deadlock whereby each side of the pipe is
                  blocked on write, waiting for the other party to read
                  its end of the pipe.  */
-              if (errno == ENOSPC
-                  && fd < MAXDESC
-                  && ((fd_info[fd].flags & (FILE_PIPE | FILE_NDELAY))
-                      == (FILE_PIPE | FILE_NDELAY)))
+              if (errno == ENOSPC && is_pipe)
                 errno = EAGAIN;
-              nchars = n;
+              if (nchars == 0)
+                nchars = -1;
               break;
             }
           else if (n < this_chunk)
diff --git a/src/w32proc.c b/src/w32proc.c
index a65f085fb3d..a89a9850466 100644
--- a/src/w32proc.c
+++ b/src/w32proc.c
@@ -3702,6 +3702,13 @@ of time slices to wait (effectively boosting the priority of the child
 process temporarily).  A value of zero disables waiting entirely.  */);
   w32_pipe_read_delay = 50;
 
+  DEFVAR_INT ("w32-pipe-buffer-size", w32_pipe_buffer_size,
+              doc: /* Size of buffer for pipes created to communicate with subprocesses.
+The size is in bytes, and must be non-negative.  The default is zero,
+which lets the OS use its default size, usually 4KB (4096 bytes).
+Any negative value means to use the default value of zero.  */);
+  w32_pipe_buffer_size = 0;
+
   DEFVAR_LISP ("w32-downcase-file-names", Vw32_downcase_file_names,
                doc: /* Non-nil means convert all-upper case file names to lower case.
 This applies when performing completions and file name expansion.