0.14.0 --- the keystrokes this kernel keeps for itself are a position now

README.md

@@ -5,10 +5,10 @@ for Linux, written on the kernel's own system-call interface.
 
 ```toml
 [dependencies]
-openkal = "0.13.0"
+openkal = "0.14.0"
 
 [target.'cfg(os = "linux")'.dependencies]
-openkal-linux = "0.13.0"
+openkal-linux = "0.14.0"
 ```
 
 ## Why it does not use a C library

mcpp.toml

@@ -1,7 +1,7 @@
 [package]
 namespace   = "mcpplibs"
 name        = "openkal-linux"
-version     = "0.13.0"
+version     = "0.14.0"
 description = "The reference implementation of openkal for Linux, written on the kernel's own system-call interface so that it can be placed beneath a C library as well as above one."
 license     = "Apache-2.0"
 
@@ -18,7 +18,7 @@ authors     = ["mcpplibs"]
 repo        = "https://github.com/mcpplibs/openkal-linux"
 
 [dependencies]
-openkal = "0.13.0"
+openkal = "0.14.0"
 
 # The package contributes definitions and no modules. The interface it
 # implements is declared by the specification package, which this package

src/sys.h

@@ -506,9 +506,22 @@ enum : okl_long {
     tcgets = 0x5401, tcsets = 0x5402, tiocgwinsz = 0x5413,
 };
 
-// Positions within ktermios::lflag. Named here for the same reason the numbers
-// above are: they belong to the kernel and not to any library.
-enum : okl_u32 { t_icanon = 0000002u, t_echo = 0000010u };
+// Positions within ktermios::lflag and ktermios::iflag, and the two entries of
+// ktermios::cc that decide how long a read waits. Named here for the same
+// reason the numbers above are: they belong to the kernel and not to any
+// library.
+//
+// `t_isig', `t_ixon' and `t_iexten' are the three mechanisms by which this
+// kernel keeps a keystroke for itself --- the interrupt and its neighbours, the
+// pair that stops and starts output, and the one that takes the next keystroke
+// literally. KAL_TERM_PASS_CONTROL is the whole of them, because a program that
+// asked for every keystroke and was given two mechanisms out of three would
+// find one key missing and nothing to ask about it with.
+enum : okl_u32 {
+    t_isig = 0000001u, t_icanon = 0000002u, t_echo = 0000010u, t_iexten = 0100000u,
+};
+enum : okl_u32 { t_ixon = 0002000u };
+enum { v_time = 5, v_min = 6 };
 
 // --- openkal.net and openkal.datagram --------------------------------------
 //

src/terminal.cpp

@@ -16,10 +16,21 @@ namespace {
 // positions in this interface because a program that wants a password prompt
 // turns off one and leaves the other, and a backend that conflated them would
 // make that program's intent inexpressible.
+//
+// KAL_TERM_PASS_CONTROL IS READ FROM THREE FLAGS AND NOT FROM ISIG. The
+// position states that the environment reserves NO keystroke, so it is set only
+// where every mechanism by which this kernel reserves one is off: ISIG for the
+// interrupt and its neighbours, IXON for the pair that stops and starts output,
+// IEXTEN for the one that takes the next keystroke literally. A terminal upon
+// which some of them had been released reads as clear and is restored to the
+// set this kernel ordinarily reserves, which is the cost the specification
+// records beside the position.
 kal_uintptr mode_of(const okl::ktermios& t) {
     kal_uintptr m = 0;
     if ((t.lflag & okl::t_icanon) != 0) m |= KAL_TERM_LINE_EDIT;
     if ((t.lflag & okl::t_echo)   != 0) m |= KAL_TERM_ECHO;
+    if ((t.lflag & (okl::t_isig | okl::t_iexten)) == 0 &&
+        (t.iflag & okl::t_ixon) == 0)   m |= KAL_TERM_PASS_CONTROL;
     return m;
 }
 
@@ -59,12 +70,41 @@ int kal_terminal_set_mode(kal_stream s, kal_uintptr mode) {
     okl::ktermios t{};
     const int rc = get_termios(s, t);
     if (rc != kal_ok) return rc;
+    const kal_uintptr in_effect = mode_of(t);
 
     if ((mode & KAL_TERM_LINE_EDIT) != 0) t.lflag |=  okl::t_icanon;
     else                                  t.lflag &= ~okl::t_icanon;
     if ((mode & KAL_TERM_ECHO) != 0)      t.lflag |=  okl::t_echo;
     else                                  t.lflag &= ~okl::t_echo;
 
+    // A POSITION WHOSE REQUESTED VALUE IS THE ONE IN EFFECT IS NOT WRITTEN, and
+    // this position is why the specification states the rule: it stands for
+    // three of the kernel's flags, so establishing it again would settle two
+    // mechanisms the caller never asked about. A user who had released the
+    // keystroke that stops output keeps it released while a program turns the
+    // echo off and back on.
+    if (((mode ^ in_effect) & KAL_TERM_PASS_CONTROL) != 0) {
+        if ((mode & KAL_TERM_PASS_CONTROL) != 0) {
+            t.lflag &= ~(okl::t_isig | okl::t_iexten);
+            t.iflag &= ~okl::t_ixon;
+        } else {
+            t.lflag |=  (okl::t_isig | okl::t_iexten);
+            t.iflag |=   okl::t_ixon;
+        }
+    }
+
+    // AND A MODE IS NOT A WAY TO END THE INPUT. With line assembly off, how
+    // long a read waits is decided by VMIN and VTIME rather than by a newline,
+    // and a terminal left at VMIN=0 by whatever ran before makes
+    // `kal_stream_read' report zero --- which clause 7.4 says denotes the end
+    // of the input. The least count is therefore established together with the
+    // mode that needs it; a caller that wants a read which gives up asks
+    // `kal_timeout_read' for one.
+    if ((mode & KAL_TERM_LINE_EDIT) == 0) {
+        t.cc[okl::v_min]  = 1;
+        t.cc[okl::v_time] = 0;
+    }
+
     // A position this implementation does not distinguish is ignored rather
     // than refused, which is what clause 6.2 requires of a word: a program
     // compiled against a later revision sets a position this build has never

tests/conformance_v08.cpp

@@ -56,6 +56,24 @@ void terminal_section() {
         check(m.e == kal_ok, "an interactive stream reports its mode");
         check(kal::terminal::set_mode(out, m.m) == kal_ok,
               "the mode that was read can be set back");
+
+        // THE POSITION VERSION 0.14 ADDED, UPON A TERMINAL THAT EXISTS. This
+        // implementation distinguishes it, so the answer here is the stronger
+        // of the two clause 6.2 permits: what was asked for is what is read
+        // back. Whether the keystroke then arrives as a byte is a question for
+        // something that can type, which is the pty probe a C environment above
+        // this implementation runs; what is established here is that the
+        // position reaches the kernel and that the terminal survives it.
+        using kal::terminal::pass_control;
+        const auto wanted = m.m | pass_control;
+        check(kal::terminal::set_mode(out, wanted) == kal_ok,
+              "every keystroke can be asked for");
+        const auto after = kal::terminal::get_mode(out);
+        check(after.e == kal_ok && after.m.has(pass_control),
+              "the position asked for is the position read back");
+        check(kal::terminal::set_mode(out, m.m) == kal_ok &&
+              kal::terminal::get_mode(out).m.bits == m.m.bits,
+              "the mode found is the mode left behind");
     } else {
         check(m.e == kal_err_not_supported,
               "a stream that is not interactive refuses get_mode");