/*
 * Handle connections.
 *
 * Copyright (C) 2011  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 "connection.h"

/* close() */
#include <unistd.h>
/* getaddrinfo() */
#include <netdb.h>
/* poll() */
#include <poll.h>
/* errno */
#include <errno.h>
/* va_*() */
#include <stdarg.h>
/* pthread_*() */
#include <pthread.h>


/* Maximum line of a HTTP request line. Longer request lines are aborted with
 * an error. The standard doesn't specify a maximum line length but this
 * should be a good limit to make processing simpler. */
#define MAX_REQUEST_LINE 4096

/* Helper macro for LOG/LOG_PERROR. Print file/line number if compiled with
 * debug output. */
#ifdef DEBUG
#define LOG_PRINT_LOCATION fprintf(stdout, "%s:%-3d ", __FILE__, __LINE__);
#else
#define LOG_PRINT_LOCATION
#endif
/* Call log_message() and print current file and line number. */
#define LOG \
    LOG_PRINT_LOCATION \
    log_message
/* perror() replacement with debug level support. */
#define LOG_PERROR(level, message) \
    LOG_PRINT_LOCATION \
    log_message(level, "%s: %s", message, strerror(errno))


static int read_http_request(FILE *client_fd, char *request, size_t length);
static void send_bad_request(FILE *client_fd);
static void send_forwarding_failure(FILE *client_fd);

static void transfer_data(int client, int server);
static int read_from_write_to(int from, int to);

static int connect_to_host(const char *hostname, const char *port);

static int parse_request(const char *buffer, char *host, char *port,
                                             int *version_minor);

static void log_message(int level, const char *format, ...);


void handle_connection(int client_socket) {
    int server_socket;
    FILE *client_fd, *server_fd;

    char buffer[MAX_REQUEST_LINE];
    char host[MAX_REQUEST_LINE];
    char port[5 + 1];

    int version_minor;
    int result;

    LOG(LOG_DEBUG, "new connection");

    server_socket = -1;
    client_fd = NULL;
    server_fd = NULL;

    client_fd = fdopen(client_socket, "a+");
    if (NULL == client_fd) {
        LOG_PERROR(LOG_WARNING, "fdopen(): client failed");
        goto out;
    }

    /* Read request line (CONNECT ..) and headers (they are discarded). */
    result = read_http_request(client_fd, buffer, sizeof(buffer));
    if (-1 == result) {
        /* Read error. */
        LOG(LOG_WARNING, "read_http_request(): client read error");
        goto out;
    } else if (-2 == result) {
        /* EOF */
        LOG(LOG_WARNING, "read_http_request(): client EOF");
        send_bad_request(client_fd);
        goto out;
    }

    if (0 != parse_request(buffer, host, port, &version_minor)) {
        LOG(LOG_WARNING, "bad request: %s", buffer);
        send_bad_request(client_fd);
        goto out;
    }

    LOG(LOG_DEBUG, "target: %s:%s (HTTP 1.%d)", host, port, version_minor);

    /* Connect to proxy server or directly to server. */
    if (NULL != global_proxy_host && NULL != global_proxy_port) {
        LOG(LOG_DEBUG, "connecting to %s:%s", global_proxy_host,
                                              global_proxy_port);
        server_socket = connect_to_host(global_proxy_host, global_proxy_port);
    } else {
        LOG(LOG_DEBUG, "connecting to %s:%s", host, port);
        server_socket = connect_to_host(host, port);
    }

    if (-1 == server_socket) {
        LOG(LOG_WARNING, "failed to connect to server");
        send_forwarding_failure(client_fd);
        goto out;
    }
    server_fd = fdopen(server_socket, "a+");
    if (NULL == server_fd) {
        LOG_PERROR(LOG_WARNING, "fdopen(): server failed");
        send_forwarding_failure(client_fd);
        goto out;
    }

    /* Connect to proxy if requested (command line option). */
    if (NULL != global_proxy_host && NULL != global_proxy_port) {
        fprintf(server_fd, "CONNECT %s:%s HTTP/1.0\r\n", host, port);
        fprintf(server_fd, "\r\n");

        /* Read response line from proxy server. */
        result = read_http_request(server_fd, buffer, sizeof(buffer));
        if (-1 == result) {
            /* Read error. */
            LOG(LOG_WARNING, "read_http_request(): proxy read error");
            send_forwarding_failure(client_fd);
            goto out;
        } else if (-2 == result) {
            /* EOF */
            LOG(LOG_WARNING, "read_http_request(): proxy EOF");
            send_forwarding_failure(client_fd);
            goto out;
        }

        /* Check response of proxy server. */
        if (0 != strncmp(buffer, "HTTP/1.0 200", 12)) {
            LOG(LOG_WARNING, "bad proxy response: %s", buffer);
            send_forwarding_failure(client_fd);
            goto out;
        }
    }

    LOG(LOG_DEBUG, "connection to server established");

    /* We've established a connection, tell the client. */
    fprintf(client_fd, "HTTP/1.0 200 Connection established\r\n");
    fprintf(client_fd, "\r\n");
    fflush(client_fd);

    /* And transfer all data between client and server transparently. */
    transfer_data(client_socket, server_socket);

out:
    /* Close connection to server/proxy. */
    if (NULL != server_fd) {
        fclose(server_fd);
    } else if (-1 != server_socket) {
        close(server_socket);
    }
    LOG(LOG_DEBUG, "connection to server closed");
    /* Close connection to client. */
    if (NULL != client_fd) {
        fclose(client_fd);
    } else {
        close(client_socket);
    }
    LOG(LOG_DEBUG, "connection to client closed");

    LOG(LOG_DEBUG, "connection finished");
}

/* Read HTTP request line and headers (ignored).
 *
 * On success 0 is returned, -1 on client error, -2 on unexpected EOF.
 */
static int read_http_request(FILE *client_fd, char *request, size_t length) {
    char buffer[MAX_REQUEST_LINE];

    if (NULL == fgets(request, (int)length, client_fd)) {
        if (ferror(client_fd)) {
            LOG_PERROR(LOG_WARNING, "read_http_request(): fgets()");
            return -1;
        }

        return -2;
    }

    while (NULL != fgets(buffer, MAX_REQUEST_LINE, client_fd)) {
        /* End of header. */
        if (0 == strcmp(buffer, "\n") || 0 == strcmp(buffer, "\r\n")) {
            break;
        }
    }
    if (ferror(client_fd)) {
        LOG_PERROR(LOG_WARNING, "read_http_request(): fgets()");
        return -1;
    }

    return 0;
}

static void send_bad_request(FILE *client_fd) {
    fprintf(client_fd, "HTTP/1.0 400 Bad Request\r\n");
    fprintf(client_fd, "\r\n");
}
static void send_forwarding_failure(FILE *client_fd) {
    fprintf(client_fd, "HTTP/1.0 503 Forwarding failure\r\n");
    fprintf(client_fd, "\r\n");
}


/* Transfer data between client and server sockets until one closes the
 * connection. */
static void transfer_data(int client, int server) {
    struct pollfd fds[2];
    fds[0].fd      = client;
    fds[0].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
    fds[0].revents = 0;
    fds[1].fd      = server;
    fds[1].events  = POLLIN | POLLPRI | POLLHUP | POLLERR;
    fds[1].revents = 0;

    for (;;) {
        int result = poll(fds, 2, -1 /* no timeout */);
        if (result < 0) {
            LOG_PERROR(LOG_ERROR, "transfer_data(): poll()");
            return;
        }

        /* Data available from client. */
        if (fds[0].revents & POLLIN || fds[0].revents & POLLPRI) {
            if (0 != read_from_write_to(client, server)) {
                /* EOF (or other error) */
                break;
            }
        }
        /* Data available from server. */
        if (fds[1].revents & POLLIN || fds[1].revents & POLLPRI) {
            if (0 != read_from_write_to(server, client)) {
                /* EOF (or other error) */
                break;
            }
        }

        /* Client closed connection. */
        if (fds[0].revents & POLLERR || fds[0].revents & POLLHUP) {
            break;
        }
        /* Server closed connection. */
        if (fds[1].revents & POLLERR || fds[1].revents & POLLHUP) {
            break;
        }
    }
}

/* Read available data from socket from and write it to socket to. At maximum
 * 4096 bytes are read/written. */
static int read_from_write_to(int from, int to) {
    ssize_t size_read;
    ssize_t size_written;
    char buffer[4096];

    size_read = read(from, buffer, sizeof(buffer));
    if (0 > size_read) {
        LOG_PERROR(LOG_WARNING, "read_from_write_to(): read()");
        return -1;
    }
    /* EOF */
    if (0 == size_read) {
        return -1;
    }

    size_written = write(to, buffer, (size_t)size_read);
    if (0 > size_written) {
        LOG_PERROR(LOG_WARNING, "read_from_write_to(): write()");
        return -1;
    }
    if (size_read != size_written) {
        LOG(LOG_ERROR, "read_from_write_to(): only written %ld of %ld bytes!",
                       (long int)size_written, (long int)size_read);
        return -1;
    }

    return 0;
}


static int connect_to_host(const char *hostname, const char *port) {
    struct addrinfo gai_hints;
    struct addrinfo *gai_result;
    int gai_return;

    int server_socket;
    struct addrinfo *server;

    if (NULL == hostname || NULL == port) {
        return -1;
    }

    /* Get IP of hostname server. */
    memset(&gai_hints, 0, sizeof(gai_hints));
    gai_hints.ai_family   = AF_UNSPEC;
    gai_hints.ai_socktype = SOCK_STREAM;
    gai_hints.ai_protocol = 0;
    gai_hints.ai_flags    = AI_NUMERICSERV /* given port is numeric */
                          | AI_ADDRCONFIG  /* supported by this computer */
                          | AI_V4MAPPED;   /* support IPv4 through IPv6 */
    gai_return = getaddrinfo(hostname, port, &gai_hints, &gai_result);
    if (0 != gai_return) {
        LOG_PERROR(LOG_WARNING, "connect_to_host(): getaddrinfo()");
        return -1;
    }

    /* Now try to connect to each server returned by getaddrinfo(), use the
     * first successful connect. */
    for (server = gai_result; NULL != server; server = server->ai_next) {
        server_socket = socket(server->ai_family,
                               server->ai_socktype,
                               server->ai_protocol);
        if (-1 == server_socket) {
            LOG_PERROR(LOG_DEBUG, "connect_to_host(): socket(), trying next");
            continue;
        }

        if (-1 != connect(server_socket, server->ai_addr,
                                         server->ai_addrlen)) {
            break;
        }
        LOG_PERROR(LOG_DEBUG, "connect_to_host(): connect(), trying next");

        close(server_socket);
    }
    /* Make sure we free the result from getaddrinfo(). */
    freeaddrinfo(gai_result);

    if (NULL == server) {
        LOG_PERROR(LOG_WARNING, "connect_to_host(): no server found, abort");
        return -1;
    }

    return server_socket;
}


/* Parse HTTP CONNECT request string and save its parameters.
 *
 * The following format is expected: "CONNECT host:port HTTP/1.x".
 *
 * request and host must have the same size! port must be at least 6 bytes
 * long (5 + '\0').
 */
static int parse_request(const char *request, char *host, char *port,
                                              int *version_minor) {
    int port_unused; /* just used to verify the port is numeric */
    char *position;

    /* scanf() doesn't check spaces. */
    if (0 != strncmp(request, "CONNECT ", 8)) {
        return -1;
    }
    /* Check request and extract data, "host:port" is not yet separated. */
    if (2 != sscanf(request, "CONNECT %s HTTP/1.%d",
                             host, version_minor)) {
        return -1;
    }
    /* Make sure ":port" is there. */
    if (NULL == (position = strchr(host, ':'))) {
        return -1;
    }
    /* Make sure port is numeric. */
    if (1 != sscanf(position + 1, "%d", &port_unused)) {
        return -1;
    }
    /* Store it in *port. */
    strncpy(port, position + 1, 5);
    port[5] = '\0';
    /* And remove port from host. */
    *position = '\0';

    return 0;
}


static void log_message(int level, const char *format, ...) {
    va_list ap;
    const char *level_string;

    if (global_log_level < level) {
        return;
    }

    switch (level) {
        case LOG_ERROR:   level_string = "ERROR";   break;
        case LOG_WARNING: level_string = "WARNING"; break;
        case LOG_DEBUG:   level_string = "DEBUG";   break;
        default:          level_string = "UNKNOWN";
    }

    va_start(ap, format);
    fprintf(stdout, "[%s] [%d] ", level_string, (int)pthread_self());
    vfprintf(stdout, format, ap);
    fprintf(stdout, "\n");
    va_end(ap);
}