/*
 * tlsproxy is a TLS proxy for HTTPS which intercepts the connections and
 * ensures the server certificate doesn't change. Normally this isn't detected
 * if a trusted CA for the new server certificate is installed.
 *
 * Copyright (C) 2011-2014  Simon Ruderich
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "tlsproxy.h"
#include "sem.h"
#include "connection.h"

#include <arpa/inet.h>
#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <netinet/in.h>
#include <pthread.h>
#include <signal.h>
#include <stdint.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>

#if GNUTLS_VERSION_NUMBER <= 0x020b00
/* Necessary for GnuTLS when used with threads. */
#include <gcrypt.h>
GCRY_THREAD_OPTION_PTHREAD_IMPL;
#endif


/* Size of ringbuffer. */
#define RINGBUFFER_SIZE 10


/* For gnutls_*() functions. */
#define GNUTLS_ERROR_EXIT(error, message) \
    if (error != GNUTLS_E_SUCCESS) { \
        fprintf(stderr, "%s: %s\n", message, gnutls_strerror(error)); \
        exit(EXIT_FAILURE); \
    }


/* Server should shut down. Set by SIGINT handler. */
static volatile int done; /* = 0 */

/* Number of threads. */
static size_t thread_count;

/* Synchronized ring buffer storing accept()ed client sockets. */
static int ringbuffer[RINGBUFFER_SIZE];
static int ringbuffer_read;
static int ringbuffer_write;
static SEM *ringbuffer_full; /* At least one element in the buffer? */
static SEM *ringbuffer_free; /* Space for another element in the buffer? */
static SEM *ringbuffer_lock; /* Read lock. */


#ifdef DEBUG
static void sigint_handler(int signal);
#endif

static void parse_arguments(int argc, char **argv);
static void print_usage(const char *argv);
static char *slurp_text_file(const char *path);

static void initialize_gnutls(void);
static void deinitialize_gnutls(void);

static void *worker_thread(void *unused);


int main(int argc, char **argv) {
    int port;
    int client_socket, server_socket;
#ifdef USE_IPV4_ONLY
    struct sockaddr_in server_in;
#else
    struct sockaddr_in6 server_in;
#endif

    size_t i;
    pthread_t *threads;

    struct sigaction action;

    /* Required in a few places. */
    ct_assert(sizeof(size_t) >= sizeof(int));
    ct_assert(sizeof(size_t) >= sizeof(ssize_t));

    parse_arguments(argc, argv);

    port = atoi(argv[argc - 1]);
    if (port <= 0 || port > 0xffff ) {
        fprintf(stderr, "invalid port: '%s'\n", argv[argc - 1]);
        return EXIT_FAILURE;
    }

    memset(&action, 0, sizeof(action));
    sigemptyset(&action.sa_mask);
#ifdef DEBUG
    /* Setup our SIGINT signal handler which allows a "normal" termination of
     * the server in DEBUG mode. */
    action.sa_handler = sigint_handler;
    sigaction(SIGINT, &action, NULL);
#endif
    /* Ignore SIGPIPEs. */
    action.sa_handler = SIG_IGN;
    sigaction(SIGPIPE, &action, NULL);

    /* Initialize ring buffer. */
    ringbuffer_read  = 0;
    ringbuffer_write = 0;
    ringbuffer_full  = sem_init(0);
    ringbuffer_free  = sem_init(RINGBUFFER_SIZE);
    ringbuffer_lock  = sem_init(1);
    if (NULL == ringbuffer_full
            || NULL == ringbuffer_free
            || NULL == ringbuffer_lock) {
        perror("sem_init()");
        return EXIT_FAILURE;
    }

    initialize_gnutls();

    /* Spawn worker threads to handle requests. */
    threads = malloc(thread_count * sizeof(*threads));
    if (threads == NULL) {
        perror("thread malloc failed");
        return EXIT_FAILURE;
    }
    for (i = 0; i < thread_count; i++) {
        errno = pthread_create(threads + i, NULL, &worker_thread, NULL);
        if (errno != 0) {
            perror("failed to create worker thread");
            return EXIT_FAILURE;
        }
    }

#ifdef USE_IPV4_ONLY
    server_socket = socket(AF_INET, SOCK_STREAM, 0);
#else
    server_socket = socket(AF_INET6, SOCK_STREAM, 0);
#endif
    if (server_socket < 0) {
        perror("socket()");
        return EXIT_FAILURE;
    }

    /* Fast rebinding for debug mode, could cause invalid packets. */
    if (global_log_level >= LOG_DEBUG1_LEVEL) {
        int socket_option = 1;
        setsockopt(server_socket, SOL_SOCKET, SO_REUSEADDR,
                   &socket_option, sizeof(socket_option));
    }

    /* Bind to the listen socket. */
    memset(&server_in, 0, sizeof(server_in));
#ifdef USE_IPV4_ONLY
    server_in.sin_family      = AF_INET;               /* IPv4 only */
    server_in.sin_addr.s_addr = htonl(INADDR_ANY);     /* bind to any address */
    server_in.sin_port        = htons((uint16_t)port); /* port to bind to */
#else
    server_in.sin6_family = AF_INET6;              /* IPv6 (and IPv4) */
    server_in.sin6_addr   = in6addr_any;           /* bind to any address */
    server_in.sin6_port   = htons((uint16_t)port); /* port to bind to */
#endif
    if (bind(server_socket, (struct sockaddr *)&server_in,
                            sizeof(server_in)) != 0) {
        perror("bind()");
        return EXIT_FAILURE;
    }
    /* And accept connections. */
    if (listen(server_socket, 5) != 0) {
        perror("listen()");
        return EXIT_FAILURE;
    }

    if (global_log_level >= LOG_DEBUG1_LEVEL) {
        printf("tlsproxy %s\n", VERSION);
        printf("Listening for connections on port %d.\n", port);
        printf("Priority string: %s.\n", PROXY_TLS_PRIORITIES);

        if (global_proxy_host != NULL && global_proxy_port != NULL) {
            printf("Using proxy: %s:%s.\n", global_proxy_host,
                                            global_proxy_port);
        }
    }

    while (!done) {
        /* Accept new connection. */
        client_socket = accept(server_socket, NULL, NULL);
        if (client_socket < 0) {
            perror("accept()");
            break;
        }

        /* No lock necessary, we only have one producer! */
        P(ringbuffer_free);
        ringbuffer[ringbuffer_write] = client_socket;
        ringbuffer_write = (ringbuffer_write + 1) % RINGBUFFER_SIZE;
        V(ringbuffer_full);
    }

    close(server_socket);

    /* Poison all threads and shut them down. */
    for (i = 0; i < thread_count; i++) {
        P(ringbuffer_free);
        ringbuffer[ringbuffer_write] = -1; /* poison */
        ringbuffer_write = (ringbuffer_write + 1) % RINGBUFFER_SIZE;
        V(ringbuffer_full);
    }
    for (i = 0; i < thread_count; i++) {
        errno = pthread_join(threads[i], NULL);
        if (errno != 0) {
            perror("pthread_join()");
        }
    }

    sem_del(ringbuffer_full);
    sem_del(ringbuffer_free);
    sem_del(ringbuffer_lock);

    free(threads);

    deinitialize_gnutls();

    free(global_proxy_host);
    free(global_proxy_port);
    free(global_http_digest_authorization);

    return EXIT_FAILURE;
}

#ifdef DEBUG
static void sigint_handler(int signal_number) {
    (void)signal_number;

    done = 1;
}
#endif

static void parse_arguments(int argc, char **argv) {
    int option;

    /* Default values. */
    thread_count = 10;
#ifdef DEBUG
    global_log_level = LOG_DEBUG2_LEVEL;
#else
    global_log_level = LOG_WARNING_LEVEL;
#endif
    global_passthrough_unknown = 0;

    while ((option = getopt(argc, argv, "a:d:p:t:uh?")) != -1) {
        switch (option) {
            case 'a': {
                global_http_digest_authorization = slurp_text_file(optarg);
                if (global_http_digest_authorization == NULL) {
                    fprintf(stderr, "failed to open authorization file '%s': ",
                                    optarg);
                    perror("");
                    exit(EXIT_FAILURE);
                } else if (strlen(global_http_digest_authorization) == 0) {
                    fprintf(stderr, "empty authorization file '%s'\n",
                                    optarg);
                    exit(EXIT_FAILURE);
                }

                /* Just in case the file has a trailing newline. */
                strtok(global_http_digest_authorization, "\r\n");

                break;
            }
            case 'd': {
                global_log_level = atoi(optarg);
                if (global_log_level < 0) {
                    fprintf(stderr, "-d positive number required: '%s'\n",
                                    optarg);
                    exit(EXIT_FAILURE);
                }
                break;
            }
            case 'p': {
                char *position;

                /* -p must have the format host:port. */
                if ((position = strchr(optarg, ':')) == NULL
                        || optarg == position
                        || strlen(position + 1) == 0
                        || atoi(position + 1) <= 0
                        || atoi(position + 1) > 0xffff) {
                    fprintf(stderr, "invalid -p: '%s', format host:port\n",
                                    optarg);
                    exit(EXIT_FAILURE);
                }

                global_proxy_host = malloc((size_t)(position - optarg) + 1);
                if (global_proxy_host == NULL) {
                    perror("malloc()");
                    exit(EXIT_FAILURE);
                }
                memcpy(global_proxy_host, optarg, (size_t)(position - optarg));
                global_proxy_host[position - optarg] = '\0';

                global_proxy_host = strdup(position + 1);
                if (global_proxy_port == NULL) {
                    perror("strdup()");
                    exit(EXIT_FAILURE);
                }

                break;
            }
            case 't': {
                if (atoi(optarg) <= 0) {
                    fprintf(stderr, "-t positive number required: '%s'\n",
                                    optarg);
                    exit(EXIT_FAILURE);
                }
                thread_count = (size_t)atoi(optarg);
                break;
            }
            case 'u': {
                global_passthrough_unknown = 1;
                break;
            }
            case 'h':
            default: /* '?' */
                print_usage(argv[0]);
                exit(EXIT_FAILURE);
        }
    }

    if (optind >= argc) {
        fprintf(stderr, "port missing\n");
        exit(EXIT_FAILURE);
    }
}
static void print_usage(const char *argv) {
    fprintf(stderr, "tlsproxy %s, a certificate checking TLS proxy\n",
                    VERSION);
    fprintf(stderr, "Usage: %s [-a file] [-d level] [-p host:port] [-t count] [-u] port\n",
                    argv);
    fprintf(stderr, "\n");
    fprintf(stderr, "-a digest authentication file [default: none]\n");
    fprintf(stderr, "-d debug level: 0=errors only, 2=debug, 3=more debug [default: 1]\n");
    fprintf(stderr, "-p proxy hostname and port\n");
    fprintf(stderr, "-t number of threads [default: 10]\n");
    fprintf(stderr, "-u passthrough connection if no certificate is stored \
[default: error]\n");
    fprintf(stderr, "   WARNING: might be a security problem!\n");
}

#if 0
static void log_function_gnutls(int level, const char *string) {
    (void)level;
    fprintf(stderr, "    => %s", string);
}
#endif

static void initialize_gnutls(void) {
    int result;
    char *dh_parameters;
    gnutls_datum_t dh_parameters_datum;

/* Recent versions of GnuTLS automatically initialize the cryptography layer
 * in gnutls_global_init(), including a thread-safe setup. */
#if GNUTLS_VERSION_NUMBER <= 0x020b00
    gcry_error_t error;

    /* Thread safe setup. Must be called before gnutls_global_init(). */
    error = gcry_control(GCRYCTL_SET_THREAD_CBS, &gcry_threads_pthread);
    if (error != 0) {
        fprintf(stderr, "gcry_control(): %s/%s\n", gcry_strsource(error),
                                                   gcry_strerror(error));
        exit(EXIT_FAILURE);
    }
    /* Prevent usage of blocking /dev/random. */
    error = gcry_control(GCRYCTL_ENABLE_QUICK_RANDOM, 0);
    if (error != 0) {
        fprintf(stderr, "gcry_control(): %s/%s\n", gcry_strsource(error),
                                                   gcry_strerror(error));
        exit(EXIT_FAILURE);
    }
#endif

    if (gnutls_check_version(GNUTLS_VERSION) == NULL) {
        fprintf(stderr, "gnutls_check_version(): version mismatch, "
                        "expected at least '" GNUTLS_VERSION "'\n");
        exit(EXIT_FAILURE);
    }

    /* Initialize GnuTLS. */
    result = gnutls_global_init();
    GNUTLS_ERROR_EXIT(result, "gnutls_global_init()");

#if 0
    gnutls_global_set_log_level(10);
    gnutls_global_set_log_function(log_function_gnutls);
#endif

    /* Setup GnuTLS cipher suites. */
    result = gnutls_priority_init(&global_tls_priority_cache,
                                  PROXY_TLS_PRIORITIES, NULL);
    GNUTLS_ERROR_EXIT(result, "gnutls_priority_init()");

    /* Read Diffie-Hellman parameters. */
    dh_parameters = slurp_text_file(PROXY_DH_PATH);
    if (dh_parameters == NULL) {
        fprintf(stderr, PROXY_DH_PATH " missing, "
                        "use `tlsproxy-setup` to create it\n");
        exit(EXIT_FAILURE);
    }
    dh_parameters_datum.data = (unsigned char *)dh_parameters;
    assert(strlen(dh_parameters) <= UINT_MAX);
    dh_parameters_datum.size = (unsigned int)(strlen(dh_parameters));

    result = gnutls_dh_params_init(&global_tls_dh_params);
    GNUTLS_ERROR_EXIT(result, "gnutls_dh_params_init()");
    result = gnutls_dh_params_import_pkcs3(global_tls_dh_params,
                                           &dh_parameters_datum,
                                           GNUTLS_X509_FMT_PEM);
    GNUTLS_ERROR_EXIT(result, "gnutls_dh_params_import_pkcs3()");

    free(dh_parameters);
}
static void deinitialize_gnutls(void) {
    gnutls_dh_params_deinit(global_tls_dh_params);
    gnutls_priority_deinit(global_tls_priority_cache);

    gnutls_global_deinit();
}

static void *worker_thread(void *unused) {
    int client_socket;

    (void)unused;

    for (;;) {
        /* Get next element from ring buffer. */
        P(ringbuffer_full);
        P(ringbuffer_lock);
        client_socket = ringbuffer[ringbuffer_read];
        ringbuffer_read = (ringbuffer_read + 1) % RINGBUFFER_SIZE;
        V(ringbuffer_lock);
        V(ringbuffer_free);

        /* Negative value indicates we should shut down our thread. */
        if (client_socket < 0) {
            break;
        }

        handle_connection(client_socket);
    }

    return NULL;
}

static char *slurp_text_file(const char *path) {
    struct stat stat;
    size_t size_read;
    char *content = NULL;

    FILE *file = fopen(path, "r");
    if (file == NULL) {
        return NULL;
    }

    ct_assert(sizeof(stat.st_size) <= sizeof(size_t));

    if (fstat(fileno(file), &stat) != 0) {
        goto out;
    }
    if (stat.st_size < 0) { /* just in case ... */
        abort();
    } else if ((size_t)stat.st_size >= SIZE_MAX - 1) {
        errno = 0;
        goto out;
    }

    content = malloc((size_t)stat.st_size + 1);
    if (content == NULL) {
        goto out;
    }

    errno = 0;
    size_read = fread(content, 1, (size_t)stat.st_size, file);
    if (size_read != (size_t)stat.st_size) {
        free(content);
        content = NULL;
        goto out;
    }
    content[size_read] = '\0';

out:
    fclose(file);

    return content;
}