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, 1 insertions, 5 deletions

diff --git a/shell/ash.c b/shell/ash.c
index 22dedc1b6..2e3b22850 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -4410,11 +4410,7 @@ sprint_status48(char *s, int status, int sigonly)
 #endif
                         st = WTERMSIG(status);
                 if (sigonly) {
-#ifdef SIGPIPE
                         if (st == SIGINT || st == SIGPIPE)
-#else
-                        if (st == SIGINT)
-#endif
                                 goto out;
 #if JOBS
                         if (WIFSTOPPED(status))
@@ -14951,7 +14947,7 @@ forkshell_openhere(struct forkshell *fs)
         ignoresig(SIGQUIT); //signal(SIGQUIT, SIG_IGN);
         ignoresig(SIGHUP);  //signal(SIGHUP, SIG_IGN);
         ignoresig(SIGTSTP); //signal(SIGTSTP, SIG_IGN);
-        //signal(SIGPIPE, SIG_DFL);
+        signal(SIGPIPE, SIG_DFL);
         if (redir->type == NHERE) {
                 size_t len = strlen(redir->nhere.doc->narg.text);
                 full_write(pip[1], redir->nhere.doc->narg.text, len);