src/dns/dns-client.c

/* Copyright (c) 2010-2018 Dovecot authors, see the included COPYING file */

#include "lib.h"
#include "ioloop.h"
#include "istream.h"
#include "ostream.h"
#include "restrict-access.h"
#include "master-service.h"

#include <unistd.h>

struct dns_client {
    int fd;
    struct istream *input;
    struct ostream *output;
    struct io *io;
};

#define MAX_INBUF_SIZE 1024
#define MAX_OUTBUF_SIZE (1024*64)
#define INPUT_TIMEOUT_MSECS (1000*10)

static struct dns_client *dns_client = NULL;

static void dns_client_destroy(struct dns_client **client);

static int dns_client_input_line(struct dns_client *client, const char *line)
{
    struct ip_addr *ips, ip;
    const char *name;
    unsigned int i, ips_count;
    int ret;

    if (strncmp(line, "IP\t", 3) == 0) {
        ret = net_gethostbyname(line + 3, &ips, &ips_count);
        if (ret == 0 && ips_count == 0) {
            /* shouldn't happen, but fix it anyway.. */
            ret = EAI_NONAME;
        }
        if (ret != 0) {
            o_stream_nsend_str(client->output,
                t_strdup_printf("%d\n", ret));
        } else {
            o_stream_nsend_str(client->output,
                t_strdup_printf("0 %u\n", ips_count));
            for (i = 0; i < ips_count; i++) {
                o_stream_nsend_str(client->output, t_strconcat(
                    net_ip2addr(&ips[i]), "\n", NULL));
            }
        }
    } else if (strncmp(line, "NAME\t", 5) == 0) {
        if (net_addr2ip(line+5, &ip) < 0)
            o_stream_nsend_str(client->output, "-1\n");
        else if ((ret = net_gethostbyaddr(&ip, &name)) != 0) {
            o_stream_nsend_str(client->output,
                t_strdup_printf("%d\n", ret));
        } else {
            o_stream_nsend_str(client->output,
                t_strdup_printf("0 %s\n", name));
        }
    } else if (strcmp(line, "QUIT") == 0) {
        return -1;
    } else {
        o_stream_nsend_str(client->output, "Unknown command\n");
    }

    if (client->output->overflow)
        return -1;
    return 0;
}

static void dns_client_input(struct dns_client *client)
{
    const char *line;
    int ret = 0;

    o_stream_cork(client->output);
    while ((line = i_stream_read_next_line(client->input)) != NULL) {
        if (dns_client_input_line(client, line) < 0) {
            ret = -1;
            break;
        }
    }
    o_stream_uncork(client->output);

    if (client->input->eof || client->input->stream_errno != 0 || ret < 0)
        dns_client_destroy(&client);
}

static struct dns_client *dns_client_create(int fd)
{
    struct dns_client *client;

    client = i_new(struct dns_client, 1);
    client->fd = fd;
    client->input = i_stream_create_fd(fd, MAX_INBUF_SIZE);
    client->output = o_stream_create_fd(fd, MAX_OUTBUF_SIZE);
    o_stream_set_no_error_handling(client->output, TRUE);
    client->io = io_add(fd, IO_READ, dns_client_input, client);
    return client;
}

static void dns_client_destroy(struct dns_client **_client)
{
    struct dns_client *client = *_client;

    *_client = NULL;

    io_remove(&client->io);
    i_stream_destroy(&client->input);
    o_stream_destroy(&client->output);
    if (close(client->fd) < 0)
        i_error("close() failed: %m");
    i_free(client);

    dns_client = NULL;
    master_service_client_connection_destroyed(master_service);
}

static void client_connected(struct master_service_connection *conn)
{
    if (dns_client != NULL) {
        i_error("dns-client must be configured with client_limit=1");
        return;
    }

    master_service_client_connection_accept(conn);
    dns_client = dns_client_create(conn->fd);
}

int main(int argc, char *argv[])
{
    master_service = master_service_init("dns-client", 0, &argc, &argv, "");
    if (master_getopt(master_service) > 0)
        return FATAL_DEFAULT;

    master_service_init_log(master_service, "dns-client: ");
    restrict_access_by_env(RESTRICT_ACCESS_FLAG_ALLOW_ROOT, NULL);
    restrict_access_allow_coredumps(TRUE);

    master_service_init_finish(master_service);

    master_service_run(master_service, client_connected);
    if (dns_client != NULL)
        dns_client_destroy(&dns_client);

    master_service_deinit(&master_service);
        return 0;
}