TTY: Implement Canonical mode and basic echoing.

The TTY driver now respects the ICANON flag, enabling basic line
editing like VKILL, VERASE, VEOF and VWERASE. Additionally,
ICANON is now set by default.

Basic echoing has can now be enabled via the ECHO flag, though
more complicated echoing like ECHOCTL or ECHONL has not been
implemented.

Kernel/TTY/SlavePTY.cpp

@@ -30,6 +30,13 @@ StringView SlavePTY::tty_name() const
     return m_tty_name;
 }
 
+void SlavePTY::echo(u8 ch)
+{
+    if (should_echo_input()) {
+        m_master->on_slave_write(&ch, 1);
+    }
+}
+
 void SlavePTY::on_master_write(const u8* buffer, ssize_t size)
 {
     for (ssize_t i = 0; i < size; ++i)

Kernel/TTY/SlavePTY.h

@@ -16,6 +16,7 @@ private:
     // ^TTY
     virtual StringView tty_name() const override;
     virtual ssize_t on_tty_write(const u8*, ssize_t) override;
+    virtual void echo(u8) override;
 
     // ^CharacterDevice
     virtual bool can_read(FileDescription&) const override;

Kernel/TTY/TTY.cpp

@@ -19,8 +19,8 @@ TTY::~TTY()
 void TTY::set_default_termios()
 {
     memset(&m_termios, 0, sizeof(m_termios));
-    m_termios.c_lflag |= ISIG | ECHO;
-    static const char default_cc[32] = "\003\034\177\025\004\0\1\0\021\023\032\0\022\017\027\026\0";
+    m_termios.c_lflag |= ISIG | ECHO | ICANON;
+    static const char default_cc[32] = "\003\034\010\025\004\0\1\0\021\023\032\0\022\017\027\026\0";
     memcpy(m_termios.c_cc, default_cc, sizeof(default_cc));
 }
 
@@ -29,6 +29,26 @@ ssize_t TTY::read(FileDescription&, u8* buffer, ssize_t size)
     if (m_input_buffer.size() < size)
         size = m_input_buffer.size();
 
+    if (in_canonical_mode()) {
+        int i = 0;
+        for (; i < size; i++) {
+            u8 ch = m_input_buffer.dequeue();
+            if (ch == '\0') {
+                //Here we handle a ^D line, so we don't add the
+                //character to the output.
+                m_available_lines--;
+                break;
+            } else if (ch == '\n' || is_eol(ch)) {
+                buffer[i] = ch;
+                i++;
+                m_available_lines--;
+                break;
+            }
+            buffer[i] = ch;
+        }
+        return i;
+    }
+
     for (int i = 0; i < size; i++)
         buffer[i] = m_input_buffer.dequeue();
 
@@ -50,6 +70,9 @@ ssize_t TTY::write(FileDescription&, const u8* buffer, ssize_t size)
 
 bool TTY::can_read(FileDescription&) const
 {
+    if (in_canonical_mode()) {
+        return m_available_lines > 0;
+    }
     return !m_input_buffer.is_empty();
 }
 
@@ -58,6 +81,31 @@ bool TTY::can_write(FileDescription&) const
     return true;
 }
 
+bool TTY::is_eol(u8 ch) const
+{
+    return ch == m_termios.c_cc[VEOL];
+}
+
+bool TTY::is_eof(u8 ch) const
+{
+    return ch == m_termios.c_cc[VEOF];
+}
+
+bool TTY::is_kill(u8 ch) const
+{
+    return ch == m_termios.c_cc[VKILL];
+}
+
+bool TTY::is_erase(u8 ch) const
+{
+    return ch == m_termios.c_cc[VERASE];
+}
+
+bool TTY::is_werase(u8 ch) const
+{
+    return ch == m_termios.c_cc[VWERASE];
+}
+
 void TTY::emit(u8 ch)
 {
     if (should_generate_signals()) {
@@ -77,7 +125,80 @@ void TTY::emit(u8 ch)
             return;
         }
     }
+
+    if (in_canonical_mode()) {
+        if (is_eof(ch)) {
+            m_available_lines++;
+            //We use '\0' to delimit the end
+            //of a line.
+            m_input_buffer.enqueue('\0');
+            return;
+        }
+        if (is_kill(ch)) {
+            kill_line();
+            return;
+        }
+        if (is_erase(ch)) {
+            do_backspace();
+            return;
+        }
+        if (is_werase(ch)) {
+            erase_word();
+            return;
+        }
+        if (ch == '\n' || is_eol(ch)) {
+            m_available_lines++;
+        }
+    }
     m_input_buffer.enqueue(ch);
+    echo(ch);
+}
+
+bool TTY::can_do_backspace() const
+{
+    //can't do back space if we're empty. Plus, we don't want to
+    //removing any lines "commited" by newlines or ^D.
+    if (!m_input_buffer.is_empty() && !is_eol(m_input_buffer.last()) && m_input_buffer.last() != '\0') {
+        return true;
+    }
+    return false;
+}
+
+void TTY::do_backspace()
+{
+    if (can_do_backspace()) {
+        m_input_buffer.dequeue_end();
+        echo(m_termios.c_cc[VERASE]);
+    }
+}
+
+// TODO: Currently, both erase_word() and kill_line work by sending
+// a lot of VERASE characters; this is done because Terminal.cpp
+// doesn't currently support VWERASE and VKILL. When these are
+// implemented we could just send a VKILL or VWERASE.
+
+void TTY::erase_word()
+{
+    //Note: if we have leading whitespace before the word
+    //we want to delete we have to also delete that.
+    bool first_char = false;
+    while (can_do_backspace()) {
+        u8 ch = m_input_buffer.last();
+        if (ch == ' ' && first_char)
+            break;
+        if (ch != ' ')
+            first_char = true;
+        m_input_buffer.dequeue_end();
+        echo(m_termios.c_cc[VERASE]);
+    }
+}
+
+void TTY::kill_line()
+{
+    while (can_do_backspace()) {
+        m_input_buffer.dequeue_end();
+        echo(m_termios.c_cc[VERASE]);
+    }
 }
 
 void TTY::generate_signal(int signal)

Kernel/TTY/TTY.h

@@ -1,7 +1,7 @@
 #pragma once
 
 #include "DoubleBuffer.h"
-#include <AK/CircularQueue.h>
+#include <AK/CircularDeque.h>
 #include <Kernel/Devices/CharacterDevice.h>
 #include <Kernel/UnixTypes.h>
 
@@ -40,14 +40,28 @@ protected:
 
     TTY(unsigned major, unsigned minor);
     void emit(u8);
+    virtual void echo(u8) = 0;
+
+    bool can_do_backspace() const;
+    void do_backspace();
+    void erase_word();
+    void kill_line();
+
+    bool is_eol(u8) const;
+    bool is_eof(u8) const;
+    bool is_kill(u8) const;
+    bool is_erase(u8) const;
+    bool is_werase(u8) const;
 
     void generate_signal(int signal);
 
+    int m_available_lines { 0 };
+
 private:
     // ^CharacterDevice
     virtual bool is_tty() const final override { return true; }
 
-    CircularQueue<u8, 1024> m_input_buffer;
+    CircularDeque<u8, 1024> m_input_buffer;
     pid_t m_pgid { 0 };
     termios m_termios;
     unsigned short m_rows { 0 };

Kernel/TTY/VirtualConsole.h

@@ -33,6 +33,7 @@ private:
     // ^TTY
     virtual ssize_t on_tty_write(const u8*, ssize_t) override;
     virtual StringView tty_name() const override;
+    virtual void echo(u8) override { return; }
 
     // ^CharacterDevice
     virtual const char* class_name() const override { return "VirtualConsole"; }