terminal: drain PTY when client terminates

This is done by:

* Not limiting the number of times we try to read from the PTY when
  we’ve have POLLHUP
* Not requiring the entire the previous read to have filled our
  buffer.
* Not erroring out on EIO.

CHANGELOG.md

@@ -42,6 +42,7 @@
 * OSC-4/104 out-of-bounds accesses to the color table. This was the
   reason pywal turned foot windows transparent
   (https://codeberg.org/dnkl/foot/issues/434).
+* PTY not being drained when the client application terminates.
 
 
 ### Security

terminal.c

@@ -230,15 +230,20 @@ fdm_ptmx(struct fdm *fdm, int fd, int events, void *data)
     uint8_t buf[24 * 1024];
     ssize_t count = sizeof(buf);
 
-    const size_t max_iterations = 10;
+    const size_t max_iterations = !hup ? 10 : (size_t)-1ll;
 
-    for (size_t i = 0; i < max_iterations && pollin && count == sizeof(buf); i++) {
+    for (size_t i = 0; i < max_iterations && pollin; i++) {
         xassert(pollin);
         count = read(term->ptmx, buf, sizeof(buf));
 
         if (count < 0) {
-            if (errno == EAGAIN)
+            if (errno == EAGAIN || errno == EIO) {
-                return true;
+                /*
+                 * EAGAIN: no more to read - FDM will trigger us again
+                 * EIO: assume PTY was closed - we already have, or will get, a EPOLLHUP
+                 */
+                break;
+            }
 
             LOG_ERRNO("failed to read from pseudo terminal");
             return false;