Implement chunked write to the cmdfd.

This is needed so big input like a paste of several megabyte does not clog our
I/O.

1 files changed, 51 insertions, 2 deletions

diff --git a/st.c b/st.c
index 17e0a65..e65e981 100644
--- a/st.c
+++ b/st.c
@@ -1478,8 +1478,57 @@ ttyread(void)
 void
 ttywrite(const char *s, size_t n)
 {
-        if (xwrite(cmdfd, s, n) == -1)
-                die("write error on tty: %s\n", strerror(errno));
+        fd_set wfd;
+        struct timespec tv;
+        ssize_t r;
+
+        /*
+         * Remember that we are using a pty, which might be a modem line.
+         * Writing too much will clog the line. That's why we are doing this
+         * dance.
+         * FIXME: Migrate the world to Plan 9.
+         */
+        while (n > 0) {
+                FD_ZERO(&wfd);
+                FD_SET(cmdfd, &wfd);
+                tv.tv_sec = 0;
+                tv.tv_nsec = 0;
+
+                /* Check if we can write. */
+                if (pselect(cmdfd+1, NULL, &wfd, NULL, &tv, NULL) < 0) {
+                        if (errno == EINTR)
+                                continue;
+                        die("select failed: %s\n", strerror(errno));
+                }
+                if(!FD_ISSET(cmdfd, &wfd)) {
+                        /* No, then free some buffer space. */
+                        ttyread();
+                } else {
+                        /*
+                         * Only write 256 bytes at maximum. This seems to be a
+                         * reasonable value for a serial line. Bigger values
+                         * might clog the I/O.
+                         */
+                        r = write(cmdfd, s, (n < 256)? n : 256);
+                        if (r < 0) {
+                                die("write error on tty: %s\n",
+                                                strerror(errno));
+                        }
+                        if (r < n) {
+                                /*
+                                 * We weren't able to write out everything.
+                                 * This means the buffer is getting full
+                                 * again. Empty it.
+                                 */
+                                ttyread();
+                                n -= r;
+                                s += r;
+                        } else {
+                                /* All bytes have been written. */
+                                break;
+                        }
+                }
+        }
 }
 
 void