terminal: add systemd-subterm example

The systemd-subterm example is a stacked terminal that shows how to
use sd-term. Instead of rendering images and displaying it via X11/etc.,
it uses its parent terminal to display the page (terminal-emulator inside
a terminal-emulator) (like GNU-screen and friends do).

This is only for testing and not installed system-wide!

1 files changed, 991 insertions, 0 deletions

diff --git a/src/libsystemd-terminal/subterm.c b/src/libsystemd-terminal/subterm.c
new file mode 100644
index 0000000000..72ce2f6f6e
--- /dev/null
+++ b/src/libsystemd-terminal/subterm.c
@@ -0,0 +1,991 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+/***
+  This file is part of systemd.
+
+  Copyright (C) 2014 David Herrmann <dh.herrmann@gmail.com>
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+/*
+ * Stacked Terminal-Emulator
+ * This is an interactive test of the term_screen implementation. It runs a
+ * fully-fletched terminal-emulator inside of a parent TTY. That is, instead of
+ * rendering the terminal as X11-window, it renders it as sub-window in the
+ * parent TTY. Think of this like what "GNU-screen" does.
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <termios.h>
+#include "macro.h"
+#include "pty.h"
+#include "ring.h"
+#include "sd-event.h"
+#include "term-internal.h"
+#include "util.h"
+
+typedef struct Output Output;
+typedef struct Terminal Terminal;
+
+struct Output {
+        int fd;
+        unsigned int width;
+        unsigned int height;
+        unsigned int in_width;
+        unsigned int in_height;
+        unsigned int cursor_x;
+        unsigned int cursor_y;
+
+        char obuf[4096];
+        size_t n_obuf;
+
+        bool resized : 1;
+        bool in_menu : 1;
+};
+
+struct Terminal {
+        sd_event *event;
+        sd_event_source *frame_timer;
+        Output *output;
+        term_utf8 utf8;
+        term_parser *parser;
+        term_screen *screen;
+
+        int in_fd;
+        int out_fd;
+        struct termios saved_in_attr;
+        struct termios saved_out_attr;
+
+        Pty *pty;
+        Ring out_ring;
+
+        bool is_scheduled : 1;
+        bool is_dirty : 1;
+        bool is_menu : 1;
+};
+
+/*
+ * Output Handling
+ */
+
+#define BORDER_HORIZ            "\xe2\x94\x81"
+#define BORDER_VERT             "\xe2\x94\x83"
+#define BORDER_VERT_RIGHT       "\xe2\x94\xa3"
+#define BORDER_VERT_LEFT        "\xe2\x94\xab"
+#define BORDER_DOWN_RIGHT       "\xe2\x94\x8f"
+#define BORDER_DOWN_LEFT        "\xe2\x94\x93"
+#define BORDER_UP_RIGHT         "\xe2\x94\x97"
+#define BORDER_UP_LEFT          "\xe2\x94\x9b"
+
+static int output_winch(Output *o) {
+        struct winsize wsz = { };
+        int r;
+
+        assert_return(o, -EINVAL);
+
+        r = ioctl(o->fd, TIOCGWINSZ, &wsz);
+        if (r < 0) {
+                log_error("error: cannot read window-size: %m");
+                return -errno;
+        }
+
+        if (wsz.ws_col != o->width || wsz.ws_row != o->height) {
+                o->width = wsz.ws_col;
+                o->height = wsz.ws_row;
+                o->in_width = MAX(o->width, 2U) - 2;
+                o->in_height = MAX(o->height, 6U) - 6;
+                o->resized = true;
+        }
+
+        return 0;
+}
+
+static int output_flush(Output *o) {
+        ssize_t len;
+
+        if (o->n_obuf < 1)
+                return 0;
+
+        len = loop_write(o->fd, o->obuf, o->n_obuf, false);
+        if (len < 0) {
+                log_error("error: cannot write to TTY (%zd): %s", len, strerror(-len));
+                return len;
+        }
+
+        o->n_obuf = 0;
+
+        return 0;
+}
+
+static int output_write(Output *o, const void *buf, size_t size) {
+        ssize_t len;
+        int r;
+
+        assert_return(o, -EINVAL);
+        assert_return(buf || size < 1, -EINVAL);
+
+        if (size < 1)
+                return 0;
+
+        if (o->n_obuf + size > o->n_obuf && o->n_obuf + size <= sizeof(o->obuf)) {
+                memcpy(o->obuf + o->n_obuf, buf, size);
+                o->n_obuf += size;
+                return 0;
+        }
+
+        r = output_flush(o);
+        if (r < 0)
+                return r;
+
+        len = loop_write(o->fd, buf, size, false);
+        if (len < 0) {
+                log_error("error: cannot write to TTY (%zd): %s", len, strerror(-len));
+                return len;
+        }
+
+        return 0;
+}
+
+static int output_vnprintf(Output *o, size_t max, const char *format, va_list args) {
+        char buf[4096];
+        int r;
+
+        assert_return(o, -EINVAL);
+        assert_return(format, -EINVAL);
+        assert_return(max <= sizeof(buf), -EINVAL);
+
+        r = vsnprintf(buf, max, format, args);
+        if (r > (ssize_t)max)
+                r = max;
+
+        return output_write(o, buf, r);
+}
+
+static int output_nprintf(Output *o, size_t max, const char *format, ...) {
+        va_list args;
+        int r;
+
+        va_start(args, format);
+        r = output_vnprintf(o, max, format, args);
+        va_end(args);
+
+        return r;
+}
+
+static int output_vprintf(Output *o, const char *format, va_list args) {
+        char buf[4096];
+        int r;
+
+        assert_return(o, -EINVAL);
+        assert_return(format, -EINVAL);
+
+        r = vsnprintf(buf, sizeof(buf), format, args);
+
+        assert_return(r < (ssize_t)sizeof(buf), -ENOBUFS);
+
+        return output_write(o, buf, r);
+}
+
+static int output_printf(Output *o, const char *format, ...) {
+        va_list args;
+        int r;
+
+        va_start(args, format);
+        r = output_vprintf(o, format, args);
+        va_end(args);
+
+        return r;
+}
+
+static int output_move_to(Output *o, unsigned int x, unsigned int y) {
+        int r;
+
+        assert_return(o, -EINVAL);
+
+        /* force the \e[H code as o->cursor_x/y might be out-of-date */
+
+        r = output_printf(o, "\e[%u;%uH", y + 1, x + 1);
+        if (r < 0)
+                return r;
+
+        o->cursor_x = x;
+        o->cursor_y = y;
+        return 0;
+}
+
+static int output_print_line(Output *o, size_t len) {
+        const char line[] =
+                BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ
+                BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ
+                BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ
+                BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ
+                BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ
+                BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ
+                BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ BORDER_HORIZ;
+        const size_t max = (sizeof(line) - 1) / (sizeof(BORDER_HORIZ) - 1);
+        size_t i;
+        int r = 0;
+
+        assert_return(o, -EINVAL);
+
+        for ( ; len > 0; len -= i) {
+                i = (len > max) ? max : len;
+                r = output_write(o, line, i * (sizeof(BORDER_HORIZ) - 1));
+                if (r < 0)
+                        break;
+        }
+
+        return r;
+}
+
+static int output_frame_printl(Output *o, const char *format, ...) {
+        va_list args;
+        int r;
+
+        assert(o);
+        assert(format);
+
+        /* out of frame? */
+        if (o->cursor_y < 3 || o->cursor_y >= o->height - 3)
+                return 0;
+
+        va_start(args, format);
+        r = output_vnprintf(o, o->width - 2, format, args);
+        va_end(args);
+
+        if (r < 0)
+                return r;
+
+        return output_move_to(o, 1, o->cursor_y + 1);
+}
+
+static Output *output_free(Output *o) {
+        if (!o)
+                return NULL;
+
+        /* disable alternate screen buffer */
+        output_printf(o, "\e[?1049l");
+        output_flush(o);
+
+        /* o->fd is owned by the caller */
+        free(o);
+
+        return NULL;
+}
+
+static int output_new(Output **out, int fd) {
+        Output *o;
+        int r;
+
+        assert_return(out, -EINVAL);
+
+        o = new0(Output, 1);
+        if (!o)
+                return log_oom();
+
+        o->fd = fd;
+
+        r = output_winch(o);
+        if (r < 0)
+                goto error;
+
+        /* enable alternate screen buffer */
+        r = output_printf(o, "\e[?1049h");
+        if (r < 0)
+                goto error;
+
+        r = output_flush(o);
+        if (r < 0)
+                goto error;
+
+        *out = o;
+        return 0;
+
+error:
+        output_free(o);
+        return r;
+}
+
+static void output_draw_frame(Output *o) {
+        unsigned int i;
+
+        assert(o);
+
+        /* print header-frame */
+
+        output_printf(o, BORDER_DOWN_RIGHT);
+        output_print_line(o, o->width - 2);
+        output_printf(o, BORDER_DOWN_LEFT
+                         "\r\n"
+                         BORDER_VERT
+                         "\e[2;%uH"    /* cursor-position: 2/x */
+                         BORDER_VERT
+                         "\r\n"
+                         BORDER_VERT_RIGHT,
+                      o->width);
+        output_print_line(o, o->width - 2);
+        output_printf(o, BORDER_VERT_LEFT
+                         "\r\n");
+
+        /* print body-frame */
+
+        for (i = 0; i < o->in_height; ++i) {
+                output_printf(o, BORDER_VERT
+                                 "\e[%u;%uH"    /* cursor-position: 2/x */
+                                 BORDER_VERT
+                                 "\r\n",
+                              i + 4, o->width);
+        }
+
+        /* print footer-frame */
+
+        output_printf(o, BORDER_VERT_RIGHT);
+        output_print_line(o, o->width - 2);
+        output_printf(o, BORDER_VERT_LEFT
+                         "\r\n"
+                         BORDER_VERT
+                         "\e[%u;%uH"    /* cursor-position: 2/x */
+                         BORDER_VERT
+                         "\r\n"
+                         BORDER_UP_RIGHT,
+                      o->height - 1, o->width);
+        output_print_line(o, o->width - 2);
+        output_printf(o, BORDER_UP_LEFT);
+
+        /* print header/footer text */
+
+        output_printf(o, "\e[2;3H");
+        output_nprintf(o, o->width - 4, "systemd - embedded terminal emulator");
+        output_printf(o, "\e[%u;3H", o->height - 1);
+        output_nprintf(o, o->width - 4, "press ^C to enter menu");
+}
+
+static void output_draw_menu(Output *o) {
+        assert(o);
+
+        output_frame_printl(o, "");
+        output_frame_printl(o, "    Menu: (the following keys are recognized)");
+        output_frame_printl(o, "      q: quit");
+        output_frame_printl(o, "     ^C: send ^C to the PTY");
+}
+
+static void output_draw_screen(Output *o, term_screen *s) {
+        unsigned int i, j;
+        bool first = true;
+
+        assert(o);
+        assert(s);
+
+        for (j = 0; j < s->page->height && j < o->in_height; ++j) {
+                if (!first)
+                        output_printf(o, "\e[m\r\n" BORDER_VERT);
+                first = false;
+
+                for (i = 0; i < s->page->width && i < o->in_width; ++i) {
+                        term_charbuf_t buf;
+                        term_cell *cell = &s->page->lines[j]->cells[i];
+                        size_t k, len, ulen;
+                        const uint32_t *str;
+                        char utf8[4];
+
+                        switch (cell->attr.fg.ccode) {
+                        case TERM_CCODE_DEFAULT:
+                                output_printf(o, "\e[39m");
+                                break;
+                        case TERM_CCODE_256:
+                                output_printf(o, "\e[38;5;%um", cell->attr.fg.c256);
+                                break;
+                        case TERM_CCODE_RGB:
+                                output_printf(o, "\e[38;2;%u;%u;%um", cell->attr.fg.red, cell->attr.fg.green, cell->attr.fg.blue);
+                                break;
+                        case TERM_CCODE_BLACK ... TERM_CCODE_WHITE:
+                                if (cell->attr.bold)
+                                        output_printf(o, "\e[%um", cell->attr.fg.ccode - TERM_CCODE_BLACK + 90);
+                                else
+                                        output_printf(o, "\e[%um", cell->attr.fg.ccode - TERM_CCODE_BLACK + 30);
+                                break;
+                        case TERM_CCODE_LIGHT_BLACK ... TERM_CCODE_LIGHT_WHITE:
+                                output_printf(o, "\e[%um", cell->attr.fg.ccode - TERM_CCODE_LIGHT_BLACK + 90);
+                                break;
+                        }
+
+                        switch (cell->attr.bg.ccode) {
+                        case TERM_CCODE_DEFAULT:
+                                output_printf(o, "\e[49m");
+                                break;
+                        case TERM_CCODE_256:
+                                output_printf(o, "\e[48;5;%um", cell->attr.bg.c256);
+                                break;
+                        case TERM_CCODE_RGB:
+                                output_printf(o, "\e[48;2;%u;%u;%um", cell->attr.bg.red, cell->attr.bg.green, cell->attr.bg.blue);
+                                break;
+                        case TERM_CCODE_BLACK ... TERM_CCODE_WHITE:
+                                output_printf(o, "\e[%um", cell->attr.bg.ccode - TERM_CCODE_BLACK + 40);
+                                break;
+                        case TERM_CCODE_LIGHT_BLACK ... TERM_CCODE_LIGHT_WHITE:
+                                output_printf(o, "\e[%um", cell->attr.bg.ccode - TERM_CCODE_LIGHT_BLACK + 100);
+                                break;
+                        }
+
+                        output_printf(o, "\e[%u;%u;%u;%u;%u;%um",
+                                      cell->attr.bold ? 1 : 22,
+                                      cell->attr.italic ? 3 : 23,
+                                      cell->attr.underline ? 4 : 24,
+                                      cell->attr.inverse ? 7 : 27,
+                                      cell->attr.blink ? 5 : 25,
+                                      cell->attr.hidden ? 8 : 28);
+
+                        str = term_char_resolve(cell->ch, &len, &buf);
+
+                        if (len < 1) {
+                                output_printf(o, " ");
+                        } else {
+                                for (k = 0; k < len; ++k) {
+                                        ulen = term_utf8_encode(utf8, str[k]);
+                                        output_write(o, utf8, ulen);
+                                }
+                        }
+                }
+        }
+
+        output_move_to(o, s->cursor_x + 1, s->cursor_y + 3);
+        output_printf(o, "\e[m");
+}
+
+static void output_draw(Output *o, bool menu, term_screen *screen) {
+        assert(o);
+
+        /*
+         * This renders the contenst of the terminal. The layout contains a
+         * header, the main body and a footer. Around all areas we draw a
+         * border. It looks something like this:
+         *
+         *     +----------------------------------------------------+
+         *     |                      Header                        |
+         *     +----------------------------------------------------+
+         *     |                                                    |
+         *     |                                                    |
+         *     |                                                    |
+         *     |                       Body                         |
+         *     |                                                    |
+         *     |                                                    |
+         *     ~                                                    ~
+         *     ~                                                    ~
+         *     +----------------------------------------------------+
+         *     |                      Footer                        |
+         *     +----------------------------------------------------+
+         *
+         * The body is the part that grows vertically.
+         *
+         * We need at least 6 vertical lines to render the screen. This would
+         * leave 0 lines for the body. Therefore, we require 7 lines so there's
+         * at least one body line. Similarly, we need 2 horizontal cells for the
+         * frame, so we require 3.
+         * If the window is too small, we print an error message instead.
+         */
+
+        if (o->in_width < 1 || o->in_height < 1) {
+                output_printf(o, "\e[2J"         /* erase-in-display: whole screen */
+                                 "\e[H");        /* cursor-position: home */
+                output_printf(o, "error: screen too small, need at least 3x7 cells");
+                output_flush(o);
+                return;
+        }
+
+        /* hide cursor */
+        output_printf(o, "\e[?25l");
+
+        /* frame-content is contant; only resizes can change it */
+        if (o->resized || o->in_menu != menu) {
+                output_printf(o, "\e[2J"         /* erase-in-display: whole screen */
+                                 "\e[H");        /* cursor-position: home */
+                output_draw_frame(o);
+                o->resized = false;
+                o->in_menu = menu;
+        }
+
+        /* move cursor to child's position */
+        output_move_to(o, 1, 3);
+
+        if (menu)
+                output_draw_menu(o);
+        else
+                output_draw_screen(o, screen);
+
+        /* show cursor */
+        if (!(screen->flags & TERM_FLAG_HIDE_CURSOR))
+                output_printf(o, "\e[?25h");
+
+        /*
+         * Hack: sd-term was not written to support TTY as output-objects, thus
+         * expects callers to use term_screen_feed_keyboard(). However, we
+         * forward TTY input directly. Hence, we're not notified about keypad
+         * changes. Update the related modes djring redraw to keep them at least
+         * in sync.
+         */
+        if (screen->flags & TERM_FLAG_CURSOR_KEYS)
+                output_printf(o, "\e[?1h");
+        else
+                output_printf(o, "\e[?1l");
+
+        if (screen->flags & TERM_FLAG_KEYPAD_MODE)
+                output_printf(o, "\e=");
+        else
+                output_printf(o, "\e>");
+
+        output_flush(o);
+}
+
+/*
+ * Terminal Handling
+ */
+
+static void terminal_dirty(Terminal *t) {
+        uint64_t usec;
+        int r;
+
+        assert(t);
+
+        if (t->is_scheduled) {
+                t->is_dirty = true;
+                return;
+        }
+
+        /* 16ms timer */
+        r = sd_event_now(t->event, CLOCK_MONOTONIC, &usec);
+        assert(r >= 0);
+
+        usec += 16 * USEC_PER_MSEC;
+        r = sd_event_source_set_time(t->frame_timer, usec);
+        if (r >= 0) {
+                r = sd_event_source_set_enabled(t->frame_timer, SD_EVENT_ONESHOT);
+                if (r >= 0)
+                        t->is_scheduled = true;
+        }
+
+        t->is_dirty = false;
+        output_draw(t->output, t->is_menu, t->screen);
+}
+
+static int terminal_frame_timer_fn(sd_event_source *source, uint64_t usec, void *userdata) {
+        Terminal *t = userdata;
+
+        t->is_scheduled = false;
+        if (t->is_dirty)
+                terminal_dirty(t);
+
+        return 0;
+}
+
+static int terminal_winch_fn(sd_event_source *source, const struct signalfd_siginfo *ssi, void *userdata) {
+        Terminal *t = userdata;
+        int r;
+
+        output_winch(t->output);
+
+        if (t->pty) {
+                r = pty_resize(t->pty, t->output->in_width, t->output->in_height);
+                if (r < 0)
+                        log_error("error: pty_resize() (%d): %s", r, strerror(-r));
+        }
+
+        r = term_screen_resize(t->screen, t->output->in_width, t->output->in_height);
+        if (r < 0)
+                log_error("error: term_screen_resize() (%d): %s", r, strerror(-r));
+
+        terminal_dirty(t);
+
+        return 0;
+}
+
+static int terminal_push_tmp(Terminal *t, uint32_t ucs4) {
+        char buf[4];
+        size_t len;
+        int r;
+
+        assert(t);
+
+        len = term_utf8_encode(buf, ucs4);
+        if (len < 1)
+                return 0;
+
+        r = ring_push(&t->out_ring, buf, len);
+        if (r < 0)
+                log_oom();
+
+        return r;
+}
+
+static int terminal_write_tmp(Terminal *t) {
+        struct iovec vec[2];
+        size_t num, i;
+        int r;
+
+        assert(t);
+
+        num = ring_peek(&t->out_ring, vec);
+        if (num < 1)
+                return 0;
+
+        if (t->pty) {
+                for (i = 0; i < num; ++i) {
+                        r = pty_write(t->pty, vec[i].iov_base, vec[i].iov_len);
+                        if (r < 0) {
+                                log_error("error: cannot write to PTY (%d): %s", r, strerror(-r));
+                                return r;
+                        }
+                }
+        }
+
+        ring_flush(&t->out_ring);
+        return 0;
+}
+
+static void terminal_discard_tmp(Terminal *t) {
+        assert(t);
+
+        ring_flush(&t->out_ring);
+}
+
+static int terminal_menu(Terminal *t, const term_seq *seq) {
+        switch (seq->type) {
+        case TERM_SEQ_IGNORE:
+                break;
+        case TERM_SEQ_GRAPHIC:
+                switch (seq->terminator) {
+                case 'q':
+                        sd_event_exit(t->event, 0);
+                        return 0;
+                }
+
+                break;
+        case TERM_SEQ_CONTROL:
+                switch (seq->terminator) {
+                case 0x03:
+                        terminal_push_tmp(t, 0x03);
+                        terminal_write_tmp(t);
+                        break;
+                }
+
+                break;
+        }
+
+        t->is_menu = false;
+        terminal_dirty(t);
+
+        return 0;
+}
+
+static int terminal_io_fn(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
+        Terminal *t = userdata;
+        char buf[4096];
+        ssize_t len, i;
+        int r, type;
+
+        len = read(fd, buf, sizeof(buf));
+        if (len < 0) {
+                if (errno == EAGAIN || errno == EINTR)
+                        return 0;
+
+                log_error("error: cannot read from TTY (%d): %m", -errno);
+                return -errno;
+        }
+
+        for (i = 0; i < len; ++i) {
+                const term_seq *seq;
+                const uint32_t *str;
+                size_t n_str, j;
+
+                str = term_utf8_decode(&t->utf8, &n_str, buf[i]);
+                for (j = 0; j < n_str; ++j) {
+                        type = term_parser_feed(t->parser, &seq, str[j]);
+                        if (type < 0) {
+                                log_error("error: term_parser_feed() (%d): %s", type, strerror(-type));
+                                return type;
+                        }
+
+                        if (!t->is_menu) {
+                                r = terminal_push_tmp(t, str[j]);
+                                if (r < 0)
+                                        return r;
+                        }
+
+                        if (type == TERM_SEQ_NONE) {
+                                /* We only intercept one-char sequences, so in
+                                 * case term_parser_feed() couldn't parse a
+                                 * sequence, it is waiting for more data. We
+                                 * know it can never be a one-char sequence
+                                 * then, so we can safely forward the data.
+                                 * This avoids withholding ESC or other values
+                                 * that may be one-shot depending on the
+                                 * application. */
+                                r = terminal_write_tmp(t);
+                                if (r < 0)
+                                        return r;
+                        } else if (t->is_menu) {
+                                r = terminal_menu(t, seq);
+                                if (r < 0)
+                                        return r;
+                        } else if (seq->type == TERM_SEQ_CONTROL && seq->terminator == 0x03) { /* ^C opens the menu */
+                                terminal_discard_tmp(t);
+                                t->is_menu = true;
+                                terminal_dirty(t);
+                        } else {
+                                r = terminal_write_tmp(t);
+                                if (r < 0)
+                                        return r;
+                        }
+                }
+        }
+
+        return 0;
+}
+
+static int terminal_pty_fn(Pty *pty, void *userdata, unsigned int event, const void *ptr, size_t size) {
+        Terminal *t = userdata;
+        int r;
+
+        switch (event) {
+        case PTY_CHILD:
+                sd_event_exit(t->event, 0);
+                break;
+        case PTY_DATA:
+                r = term_screen_feed_text(t->screen, ptr, size);
+                if (r < 0) {
+                        log_error("error: term_screen_feed_text() (%d): %s", r, strerror(-r));
+                        return r;
+                }
+
+                terminal_dirty(t);
+                break;
+        }
+
+        return 0;
+}
+
+static int terminal_write_fn(term_screen *screen, void *userdata, const void *buf, size_t size) {
+        Terminal *t = userdata;
+        int r;
+
+        if (!t->pty)
+                return 0;
+
+        r = ring_push(&t->out_ring, buf, size);
+        if (r < 0)
+                log_oom();
+
+        return r;
+}
+
+static int terminal_cmd_fn(term_screen *screen, void *userdata, unsigned int cmd, const term_seq *seq) {
+        return 0;
+}
+
+static Terminal *terminal_free(Terminal *t) {
+        if (!t)
+                return NULL;
+
+        ring_clear(&t->out_ring);
+        term_screen_unref(t->screen);
+        term_parser_free(t->parser);
+        output_free(t->output);
+        sd_event_source_unref(t->frame_timer);
+        sd_event_unref(t->event);
+        tcsetattr(t->in_fd, TCSANOW, &t->saved_in_attr);
+        tcsetattr(t->out_fd, TCSANOW, &t->saved_out_attr);
+        free(t);
+
+        return NULL;
+}
+
+static int terminal_new(Terminal **out, int in_fd, int out_fd) {
+        struct termios in_attr, out_attr;
+        Terminal *t;
+        int r;
+
+        assert_return(out, -EINVAL);
+
+        r = tcgetattr(in_fd, &in_attr);
+        if (r < 0) {
+                log_error("error: tcgetattr() (%d): %m", -errno);
+                return -errno;
+        }
+
+        r = tcgetattr(out_fd, &out_attr);
+        if (r < 0) {
+                log_error("error: tcgetattr() (%d): %m", -errno);
+                return -errno;
+        }
+
+        t = new0(Terminal, 1);
+        if (!t)
+                return log_oom();
+
+        t->in_fd = in_fd;
+        t->out_fd = out_fd;
+        memcpy(&t->saved_in_attr, &in_attr, sizeof(in_attr));
+        memcpy(&t->saved_out_attr, &out_attr, sizeof(out_attr));
+
+        cfmakeraw(&in_attr);
+        cfmakeraw(&out_attr);
+
+        r = tcsetattr(t->in_fd, TCSANOW, &in_attr);
+        if (r < 0) {
+                log_error("error: tcsetattr() (%d): %s", r, strerror(-r));
+                goto error;
+        }
+
+        r = tcsetattr(t->out_fd, TCSANOW, &out_attr);
+        if (r < 0) {
+                log_error("error: tcsetattr() (%d): %s", r, strerror(-r));
+                goto error;
+        }
+
+        r = sd_event_default(&t->event);
+        if (r < 0) {
+                log_error("error: sd_event_default() (%d): %s", r, strerror(-r));
+                goto error;
+        }
+
+        r = sigprocmask_many(SIG_BLOCK, SIGINT, SIGQUIT, SIGTERM, SIGWINCH, SIGCHLD, -1);
+        if (r < 0) {
+                log_error("error: sigprocmask_many() (%d): %s", r, strerror(-r));
+                goto error;
+        }
+
+        r = sd_event_add_signal(t->event, NULL, SIGINT, NULL, NULL);
+        if (r < 0) {
+                log_error("error: sd_event_add_signal() (%d): %s", r, strerror(-r));
+                goto error;
+        }
+
+        r = sd_event_add_signal(t->event, NULL, SIGQUIT, NULL, NULL);
+        if (r < 0) {
+                log_error("error: sd_event_add_signal() (%d): %s", r, strerror(-r));
+                goto error;
+        }
+
+        r = sd_event_add_signal(t->event, NULL, SIGTERM, NULL, NULL);
+        if (r < 0) {
+                log_error("error: sd_event_add_signal() (%d): %s", r, strerror(-r));
+                goto error;
+        }
+
+        r = sd_event_add_signal(t->event, NULL, SIGWINCH, terminal_winch_fn, t);
+        if (r < 0) {
+                log_error("error: sd_event_add_signal() (%d): %s", r, strerror(-r));
+                goto error;
+        }
+
+        /* force initial redraw on event-loop enter */
+        t->is_dirty = true;
+        r = sd_event_add_time(t->event, &t->frame_timer, CLOCK_MONOTONIC, 0, 0, terminal_frame_timer_fn, t);
+        if (r < 0) {
+                log_error("error: sd_event_add_time() (%d): %s", r, strerror(-r));
+                goto error;
+        }
+
+        r = output_new(&t->output, out_fd);
+        if (r < 0)
+                goto error;
+
+        r = term_parser_new(&t->parser, true);
+        if (r < 0)
+                goto error;
+
+        r = term_screen_new(&t->screen, terminal_write_fn, t, terminal_cmd_fn, t);
+        if (r < 0)
+                goto error;
+
+        r = term_screen_set_answerback(t->screen, "systemd-subterm");
+        if (r < 0)
+                goto error;
+
+        r = term_screen_resize(t->screen, t->output->in_width, t->output->in_height);
+        if (r < 0) {
+                log_error("error: term_screen_resize() (%d): %s", r, strerror(-r));
+                goto error;
+        }
+
+        r = sd_event_add_io(t->event, NULL, in_fd, EPOLLIN, terminal_io_fn, t);
+        if (r < 0)
+                goto error;
+
+        *out = t;
+        return 0;
+
+error:
+        terminal_free(t);
+        return r;
+}
+
+static int terminal_run(Terminal *t) {
+        pid_t pid;
+
+        assert_return(t, -EINVAL);
+
+        pid = pty_fork(&t->pty, t->event, terminal_pty_fn, t, t->output->in_width, t->output->in_height);
+        if (pid < 0) {
+                log_error("error: cannot fork PTY (%d): %s", pid, strerror(-pid));
+                return pid;
+        } else if (pid == 0) {
+                /* child */
+
+                char **argv = (char*[]){
+                        (char*)getenv("SHELL") ? : (char*)_PATH_BSHELL,
+                        NULL
+                };
+
+                setenv("TERM", "xterm-256color", 1);
+                setenv("COLORTERM", "systemd-subterm", 1);
+
+                execve(argv[0], argv, environ);
+                log_error("error: cannot exec %s (%d): %m", argv[0], -errno);
+                _exit(1);
+        }
+
+        /* parent */
+
+        return sd_event_loop(t->event);
+}
+
+/*
+ * Context Handling
+ */
+
+int main(int argc, char *argv[]) {
+        Terminal *t = NULL;
+        int r;
+
+        r = terminal_new(&t, 0, 1);
+        if (r < 0)
+                goto out;
+
+        r = terminal_run(t);
+        if (r < 0)
+                goto out;
+
+out:
+        if (r < 0)
+                log_error("error: terminal failed (%d): %s", r, strerror(-r));
+        terminal_free(t);
+        return -r;
+}