win32: emulate SIGPIPE

The code to check whether a write error is due to a broken pipe
can now either:

- return with error EPIPE;
- cause the process to exit with code 128+SIGPIPE.

The default is the latter but the behaviour can be changed by issuing
signal(SIGPIPE, SIG_IGN) and signal(SIGPIPE, SIG_DFL) calls.

No actual signal is involved so kill can't send SIGPIPE and handlers
other than SIG_IGN and SIG_DFL aren't supported.

This does, however, avoid unsightly 'broken pipe' errors from commands
like the example in GitHub issue #99:

  dd if=/dev/urandom | tr -dc _A-Z-a-z-0-9 | head -c${1:-32};echo;

1 files changed, 23 insertions, 3 deletions

diff --git a/win32/winansi.c b/win32/winansi.c
index a8f5dba79..167b4b0b1 100644
--- a/win32/winansi.c
+++ b/win32/winansi.c
@@ -475,12 +475,32 @@ int winansi_puts(const char *s)
         return (winansi_fputs(s, stdout) == EOF || putchar('\n') == EOF) ? EOF : 0;
 }
 
+static sighandler_t sigpipe_handler = SIG_DFL;
+
+#undef signal
+sighandler_t winansi_signal(int signum, sighandler_t handler)
+{
+        sighandler_t old;
+
+        if (signum == SIGPIPE) {
+                old = sigpipe_handler;
+                sigpipe_handler = handler;
+                return old;
+        }
+        return signal(signum, handler);
+}
+
 static void check_pipe_fd(int fd)
 {
-        if (GetLastError() == ERROR_NO_DATA) {
-                if (GetFileType((HANDLE)_get_osfhandle(fd)) == FILE_TYPE_PIPE) {
+        int error = GetLastError();
+
+        if ((error == ERROR_NO_DATA &&
+                        GetFileType((HANDLE)_get_osfhandle(fd)) == FILE_TYPE_PIPE) ||
+                        error == ERROR_BROKEN_PIPE) {
+                if (sigpipe_handler == SIG_DFL)
+                        exit(128+SIGPIPE);
+                else /* SIG_IGN */
                         errno = EPIPE;
-                }
         }
 }