Add third_party/pexpect

third_party/pexpect/tools/display-maxcanon.py

Index: third_party/pexpect/tools/display-maxcanon.py
diff --git a/third_party/pexpect/tools/display-maxcanon.py b/third_party/pexpect/tools/display-maxcanon.py
new file mode 100644
index 0000000000000000000000000000000000000000..cbd664ffec73c261ae58dcd0afe1eec2bcbd0d30
--- /dev/null
+++ b/third_party/pexpect/tools/display-maxcanon.py
@@ -0,0 +1,80 @@
+#!/usr/bin/env python
+"""
+This tool uses pexpect to test expected Canonical mode length.
+
+All systems use the value of MAX_CANON which can be found using
+fpathconf(3) value PC_MAX_CANON -- with the exception of Linux
+and FreeBSD.
+
+Linux, though defining a value of 255, actually honors the value
+of 4096 from linux kernel include file tty.h definition
+N_TTY_BUF_SIZE.
+
+Linux also does not honor IMAXBEL. termios(3) states, "Linux does not
+implement this bit, and acts as if it is always set." Although these
+tests ensure it is enabled, this is a non-op for Linux.
+
+FreeBSD supports neither, and instead uses a fraction (1/5) of the tty
+speed which is always 9600.  Therefor, the maximum limited input line
+length is 9600 / 5 = 1920.
+
+These tests only ensure the correctness of the behavior described by
+the sendline() docstring -- the values listed there, and above should
+be equal to the output of the given OS described, but no promises!
+"""
+# std import
+from __future__ import print_function
+import sys
+import os
+
+
+def detect_maxcanon():
+    import pexpect
+    bashrc = os.path.join(
+        # re-use pexpect/replwrap.py's bashrc file,
+        os.path.dirname(__file__), os.path.pardir, 'pexpect', 'bashrc.sh')
+
+    child = pexpect.spawn('bash', ['--rcfile', bashrc],
+                          echo=True, encoding='utf8', timeout=3)
+
+    child.sendline(u'echo -n READY_; echo GO')
+    child.expect_exact(u'READY_GO')
+
+    child.sendline(u'stty icanon imaxbel erase ^H; echo -n retval: $?')
+    child.expect_exact(u'retval: 0')
+
+    child.sendline(u'echo -n GO_; echo AGAIN')
+    child.expect_exact(u'GO_AGAIN')
+    child.sendline(u'cat')
+
+    child.delaybeforesend = 0
+
+    column, blocksize = 0, 64
+    ch_marker = u'_'
+
+    print('auto-detecting MAX_CANON: ', end='')
+    sys.stdout.flush()
+
+    while True:
+        child.send(ch_marker * blocksize)
+        result = child.expect([ch_marker * blocksize, u'\a'])
+        if result == 0:
+            # entire block fit without emitting bel
+            column += blocksize
+        elif result == 1:
+            # an '\a' was emitted, count the number of ch_markers
+            # found since last blocksize, determining our MAX_CANON
+            column += child.before.count(ch_marker)
+            break
+    print(column)
+
+if __name__ == '__main__':
+    try:
+        detect_maxcanon()
+    except ImportError:
+        # we'd like to use this with CI -- but until we integrate
+        # with tox, we can't determine a period in testing when
+        # the pexpect module has been installed 
+        print('warning: pexpect not in module path, MAX_CANON '
+              'could not be determined by systems test.',
+              file=sys.stderr)