chat.c

/*
 *  Copyright (c) 2014, Facebook, Inc.
 *  All rights reserved.
 *
 *  This source code is licensed under the BSD-style license found in
 *  the LICENSE file in the root directory of this source tree. An
 *  additional grant of patent rights can be found in the PATENTS file
 *  in the same directory.
 *
 */
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include "util.h"
#include "chat.h"
#include "fs.h"

__attribute__((noreturn))
static void chat_die(void)
{
    die(ECOMM, "lost connection to child");
}


struct chat*
chat_new(int to, int from)
{
    struct chat* cc = xcalloc(sizeof (*cc));
    cc->to = xfdopen(to, "w");
    cc->from = xfdopen(from, "r");
    return cc;
}

char
chat_getc(struct chat* cc)
{
    int c = getc(cc->from);
    if (c == EOF)
        chat_die();

    return c;
}

void
chat_expect(struct chat* cc, char expected)
{
    int c = chat_getc(cc);
    if ((char)c != expected) {
        die(ECOMM,
            "[child] expected 0x%02x %c, found 0x%02x %c",
            expected,
            isprint(expected) ? expected : '.',
            (char) c,
            isprint(c) ? c : '.');
    }
}

bool
chat_expect_maybe(struct chat* cc, char expected)
{
    char c = chat_getc(cc);
    if (c != expected) {
        ungetc(c, cc->from);
        return false;
    }
    return true;
}

static void
chat_swallow_prompt(struct chat* cc)
{
    SCOPED_RESLIST(rl);

    /* 100% reliable prompt detection */
    unsigned csi_arg = 0;
    enum { S_NORMAL, S_AFTER_ESC, S_AFTER_CSI } state = S_NORMAL;
    struct growable_string pre_prompt = {};

    for (;;) {
        int char_read = getc(cc->from);
        if (char_read == EOF) {
            growable_string_trim_trailing_whitespace(&pre_prompt);
            if (pre_prompt.strlen == 0)
                chat_die();
            die(ECOMM, "%s", growable_string_c_str(&pre_prompt));
        }
        char c = char_read;
        if (c == '#' || c == '$')
            break;

        // Some systems run resize(1), part of busybox, when an
        // interactive shell connects.  The state machine below looks
        // for status queries from this program and replies with a
        // fake answer.  Ignoring the query leads to busybox waiting
        // three seconds for an answer before giving up.

        // For details of the control codes, see
        // http://invisible-island.net/xterm/ctlseqs/ctlseqs.html

        switch (state) {
            default:
            case S_NORMAL:
                if (c == '\033')
                    state = S_AFTER_ESC;
                else
                    growable_string_append_c(&pre_prompt, c);
                break;

            case S_AFTER_ESC:
                if (c == '[') {
                    state = S_AFTER_CSI;
                    csi_arg = 0;
                } else {
                    state = S_NORMAL;
                }

                break;

            case S_AFTER_CSI:
                if ('0' <= c && c <= '9') {
                    csi_arg = 10 * csi_arg + c-'0';
                } else if (c == 'n') {
                    if (csi_arg == 5) {
                        if (fputs("\033[0n", cc->to) == EOF)
                            chat_die();
                    } else if (csi_arg == 6) {
                        if (fputs("\033[25;80R", cc->to) == EOF)
                            chat_die();
                    }
                    if (fflush(cc->to) == EOF)
                        chat_die();

                    state = S_NORMAL;
                } else {
                    state = S_NORMAL;
                }

                break;
        }
    }

    chat_expect(cc, ' ');
}

void
chat_talk_at(struct chat* cc, const char* what, int flags)
{
    if (flags & CHAT_SWALLOW_PROMPT)
        chat_swallow_prompt(cc);

    if (fputs(what, cc->to) == EOF)
        chat_die();

    if (putc('\n', cc->to) == EOF)
        chat_die();

    if (fflush(cc->to) == EOF)
        chat_die();

    /* When busybox is built with FEATURE_EDITING_ASK_TERMINAL, it may
     * send us ESC"[6n" immediately after the prompt if its input
     * buffer is empty.  There is no need to respond; busybox just
     * sleeps for 20ms and then continues. */
    if ((flags & CHAT_SWALLOW_PROMPT) && *what &&
        !chat_expect_maybe(cc, *what++))
    {
        what--;
        if (chat_expect_maybe(cc, '\033')) {
            chat_expect(cc, '[');
            chat_expect(cc, '6');
            chat_expect(cc, 'n');
        }
    }

    /* We expect the child to echo us, so read back the echoed
     * characters.  */
    while (*what)
        chat_expect(cc, *what++);

    /* Yes, this is really what comes back after a \n.  */
    chat_expect(cc, '\r');
    chat_expect_maybe(cc, '\r');
    chat_expect(cc, '\n');
}

char*
chat_read_line(struct chat* cc)
{
    size_t linesz;
    char* line = slurp_line(cc->from, &linesz);
    if (line == NULL)
        die(ECOMM, "lost connection to child");
    rtrim(line, &linesz, "\r\n");
    return line;
}