Kernel: Perform output processing on echo

Previously, we would echo characters back just as they were passed to
us, even in canonical mode. This caused newlines to not work correctly
in some programs.

Fixes #7802

Kernel/TTY/TTY.cpp

@@ -90,22 +90,17 @@ KResultOr<size_t> TTY::write(FileDescription&, u64, const UserOrKernelBuffer& bu
     constexpr size_t num_chars = 256;
     return buffer.read_buffered<num_chars>(size, [&](u8 const* data, size_t buffer_bytes) {
         u8 modified_data[num_chars * 2];
-        size_t extra_chars = 0;
+        size_t modified_data_size = 0;
         for (size_t i = 0; i < buffer_bytes; ++i) {
-            auto ch = data[i];
-            if (m_termios.c_oflag & OPOST) {
-                if (ch == '\n' && (m_termios.c_oflag & ONLCR)) {
-                    modified_data[i + extra_chars] = '\r';
-                    extra_chars++;
-                }
-            }
-            modified_data[i + extra_chars] = ch;
+            process_output(data[i], [this, &modified_data, &modified_data_size](u8 out_ch) {
+                modified_data[modified_data_size++] = out_ch;
+            });
         }
-        ssize_t bytes_written = on_tty_write(UserOrKernelBuffer::for_kernel_buffer(modified_data), buffer_bytes + extra_chars);
+        ssize_t bytes_written = on_tty_write(UserOrKernelBuffer::for_kernel_buffer(modified_data), modified_data_size);
         VERIFY(bytes_written != 0);
         if (bytes_written < 0 || !(m_termios.c_oflag & OPOST) || !(m_termios.c_oflag & ONLCR))
             return bytes_written;
-        if ((size_t)bytes_written == buffer_bytes + extra_chars)
+        if ((size_t)bytes_written == modified_data_size)
             return (ssize_t)buffer_bytes;
 
         // Degenerate case where we converted some newlines and encountered a partial write
@@ -127,6 +122,23 @@ KResultOr<size_t> TTY::write(FileDescription&, u64, const UserOrKernelBuffer& bu
     });
 }
 
+void TTY::echo_with_processing(u8 ch)
+{
+    process_output(ch, [this](u8 out_ch) { echo(out_ch); });
+}
+
+template<typename Functor>
+void TTY::process_output(u8 ch, Functor put_char)
+{
+    if (m_termios.c_oflag & OPOST) {
+        if (ch == '\n' && (m_termios.c_oflag & ONLCR))
+            put_char('\r');
+        put_char(ch);
+    } else {
+        put_char(ch);
+    }
+}
+
 bool TTY::can_read(const FileDescription&, size_t) const
 {
     if (in_canonical_mode()) {
@@ -239,7 +251,8 @@ void TTY::emit(u8 ch, bool do_evaluate_block_conditions)
 
         if (ch == '\n') {
             if (m_termios.c_lflag & ECHO || m_termios.c_lflag & ECHONL)
-                echo('\n');
+                echo_with_processing('\n');
+
             set_special_bit();
             m_input_buffer.enqueue('\n');
             m_available_lines++;
@@ -254,7 +267,7 @@ void TTY::emit(u8 ch, bool do_evaluate_block_conditions)
 
     m_input_buffer.enqueue(ch);
     if (m_termios.c_lflag & ECHO)
-        echo(ch);
+        echo_with_processing(ch);
 }
 
 bool TTY::can_do_backspace() const
@@ -271,6 +284,7 @@ void TTY::do_backspace()
 {
     if (can_do_backspace()) {
         m_input_buffer.dequeue_end();
+        // We deliberately don't process the output here.
         echo(8);
         echo(' ');
         echo(8);
@@ -318,6 +332,7 @@ void TTY::kill_line()
 
 void TTY::erase_character()
 {
+    // We deliberately don't process the output here.
     echo(m_termios.c_cc[VERASE]);
     echo(' ');
     echo(m_termios.c_cc[VERASE]);

Kernel/TTY/TTY.h

@@ -80,6 +80,10 @@ protected:
 private:
     // ^CharacterDevice
     virtual bool is_tty() const final override { return true; }
+    inline void echo_with_processing(u8);
+
+    template<typename Functor>
+    void process_output(u8, Functor put_char);
 
     CircularDeque<u8, TTY_BUFFER_SIZE> m_input_buffer;
     // FIXME: use something like AK::Bitmap but which takes a size template parameter