mongoose.c

// Copyright (c) 2004-2013 Sergey Lyubka <valenok@gmail.com>
// Copyright (c) 2013 Cesanta Software Limited
// All rights reserved
//
// This library is dual-licensed: you can redistribute it and/or modify
// it under the terms of the GNU General Public License version 2 as
// published by the Free Software Foundation. For the terms of this
// license, see <http://www.gnu.org/licenses/>.
//
// You are free to use this library under the terms of the GNU General
// Public License, 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.
//
// Alternatively, you can license this library under a commercial
// license, as set out in <http://cesanta.com/products.html>.

#undef _UNICODE                 // Use multibyte encoding on Windows
#define _MBCS                   // Use multibyte encoding on Windows
#define _INTEGRAL_MAX_BITS 64   // Enable _stati64() on Windows
#define _CRT_SECURE_NO_WARNINGS // Disable deprecation warning in VS2005+
#undef WIN32_LEAN_AND_MEAN      // Let windows.h always include winsock2.h
#define _XOPEN_SOURCE 600       // For flockfile() on Linux
#define __STDC_FORMAT_MACROS    // <inttypes.h> wants this for C++
#define __STDC_LIMIT_MACROS     // C++ wants that for INT64_MAX
#define _LARGEFILE_SOURCE       // Enable fseeko() and ftello() functions
#define _FILE_OFFSET_BITS 64    // Enable 64-bit file offsets

#ifdef _MSC_VER
#pragma warning (disable : 4127)  // FD_SET() emits warning, disable it
#pragma warning (disable : 4204)  // missing c99 support
#endif

#include <sys/types.h>
#include <sys/stat.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <assert.h>
#include <errno.h>
#include <time.h>
#include <ctype.h>
#include <stdarg.h>

#ifdef _WIN32
#include <windows.h>
#include <process.h>    // For _beginthread
#include <io.h>         // For _lseeki64
#include <direct.h>     // For _mkdir
typedef int socklen_t;
typedef int pid_t;
typedef SOCKET sock_t;
typedef unsigned char uint8_t;
typedef unsigned int uint32_t;
typedef unsigned short uint16_t;
typedef unsigned __int64 uint64_t;
typedef __int64   int64_t;
typedef CRITICAL_SECTION mutex_t;
typedef struct _stati64 file_stat_t;
#pragma comment(lib, "ws2_32.lib")
#define snprintf _snprintf
#define vsnprintf _vsnprintf
#define INT64_FMT  "I64d"
#define mutex_init(x) InitializeCriticalSection(x)
#define mutex_destroy(x) DeleteCriticalSection(x)
#define mutex_lock(x) EnterCriticalSection(x)
#define mutex_unlock(x) LeaveCriticalSection(x)
#define S_ISDIR(x) ((x) & _S_IFDIR)
#define sleep(x) Sleep((x) * 1000)
#define stat(x, y) _stati64((x), (y))
#define lseek(x, y, z) _lseeki64((x), (y), (z))
#define mkdir(x, y) _mkdir(x)
#define to64(x) _atoi64(x)
#define flockfile(x)
#define funlockfile(x)
#ifndef va_copy
#define va_copy(x,y) x = y
#endif // MINGW #defines va_copy
#ifndef __func__
#define STRX(x) #x
#define STR(x) STRX(x)
#define __func__ __FILE__ ":" STR(__LINE__)
#endif
#else
#include <dirent.h>
#include <inttypes.h>
#include <pthread.h>
#include <pwd.h>
#include <signal.h>
#include <unistd.h>
#include <arpa/inet.h>  // For inet_pton() when USE_IPV6 is defined
#include <netinet/in.h>
#include <sys/socket.h>
#include <sys/select.h>
#define closesocket(x) close(x)
typedef int sock_t;
typedef pthread_mutex_t mutex_t;
typedef struct stat file_stat_t;
#define mutex_init(x) pthread_mutex_init(x, NULL)
#define mutex_destroy(x) pthread_mutex_destroy(x)
#define mutex_lock(x) pthread_mutex_lock(x)
#define mutex_unlock(x) pthread_mutex_unlock(x)
#define INVALID_SOCKET ((sock_t) -1)
#define INT64_FMT PRId64
#define to64(x) strtoll(x, NULL, 10)
#define __cdecl
#define O_BINARY 0
#endif

#ifdef USE_SSL
// Following define gets rid of openssl deprecation messages
#define MAC_OS_X_VERSION_MIN_REQUIRED MAC_OS_X_VERSION_10_6
#include <openssl/ssl.h>
#endif

#include "mongoose.h"

struct linked_list_link { struct linked_list_link *prev, *next; };
#define LINKED_LIST_INIT(N)  ((N)->next = (N)->prev = (N))
#define LINKED_LIST_DECLARE_AND_INIT(H)  struct linked_list_link H = { &H, &H }
#define LINKED_LIST_ENTRY(P,T,N)  ((T *)((char *)(P) - offsetof(T, N)))
#define LINKED_LIST_IS_EMPTY(N)  ((N)->next == (N))
#define LINKED_LIST_FOREACH(H,N,T) \
  for (N = (H)->next, T = (N)->next; N != (H); N = (T), T = (N)->next)
#define LINKED_LIST_ADD_TO_FRONT(H,N) do { ((H)->next)->prev = (N); \
  (N)->next = ((H)->next);  (N)->prev = (H); (H)->next = (N); } while (0)
#define LINKED_LIST_ADD_TO_TAIL(H,N) do { ((H)->prev)->next = (N); \
  (N)->prev = ((H)->prev); (N)->next = (H); (H)->prev = (N); } while (0)
#define LINKED_LIST_REMOVE(N) do { ((N)->next)->prev = ((N)->prev); \
  ((N)->prev)->next = ((N)->next); LINKED_LIST_INIT(N); } while (0)

#define ARRAY_SIZE(array) (sizeof(array) / sizeof(array[0]))
#define MAX_REQUEST_SIZE 16384
#define IOBUF_SIZE 8192
#define MAX_PATH_SIZE 8192
#define LUA_SCRIPT_PATTERN "**.mg.lua$"
#define CGI_ENVIRONMENT_SIZE 4096
#define MAX_CGI_ENVIR_VARS 64
#define ENV_EXPORT_TO_CGI "MONGOOSE_CGI"
#define PASSWORDS_FILE_NAME ".htpasswd"

#ifndef WEBSOCKET_PING_INTERVAL_SECONDS
#define WEBSOCKET_PING_INTERVAL_SECONDS 5
#endif

// Extra HTTP headers to send in every static file reply
#if !defined(EXTRA_HTTP_HEADERS)
#define EXTRA_HTTP_HEADERS ""
#endif

#ifdef ENABLE_DBG
#define DBG(x) do { printf("%-20s ", __func__); printf x; putchar('\n'); \
  fflush(stdout); } while(0)
#else
#define DBG(x)
#endif

union socket_address {
  struct sockaddr sa;
  struct sockaddr_in sin;
#ifdef USE_IPV6
  struct sockaddr_in6 sin6;
#endif
};

struct vec {
  const char *ptr;
  int len;
};

struct uri_handler {
  struct linked_list_link link;
  char *uri;
  mg_handler_t handler;
};

// For directory listing and WevDAV support
struct dir_entry {
  struct connection *conn;
  char *file_name;
  file_stat_t st;
};

// NOTE(lsm): this enum shoulds be in sync with the config_options.
enum {
  ACCESS_CONTROL_LIST, ACCESS_LOG_FILE, AUTH_DOMAIN, CGI_INTERPRETER,
  CGI_PATTERN, DOCUMENT_ROOT, ENABLE_DIRECTORY_LISTING, ERROR_LOG_FILE,
  EXTRA_MIME_TYPES, GLOBAL_AUTH_FILE, HIDE_FILES_PATTERN, IDLE_TIMEOUT_MS,
  INDEX_FILES, LISTENING_PORT, DAV_AUTH_FILE,
  RUN_AS_USER, SSL_CERTIFICATE, URL_REWRITES, NUM_OPTIONS
};

struct mg_server {
  sock_t listening_sock;
  union socket_address lsa;   // Listening socket address
  struct linked_list_link active_connections;
  struct linked_list_link uri_handlers;
  char *config_options[NUM_OPTIONS];
  void *server_data;
  void *ssl_ctx;    // SSL context
  sock_t ctl[2];    // Control socketpair. Used to wake up from select() call
};

// Expandable IO buffer
struct iobuf {
  char *buf;    // Buffer that holds the data
  int size;     // Buffer size
  int len;      // Number of bytes currently in a buffer
};

// Local endpoint representation
union endpoint {
  int fd;                   // Opened regular local file
  sock_t cgi_sock;          // CGI socket
  void *ssl;                // SSL descriptor
  struct uri_handler *uh;   // URI handler user function
};

enum endpoint_type { EP_NONE, EP_FILE, EP_CGI, EP_USER, EP_PUT };
enum connection_flags {
  CONN_CLOSE = 1, CONN_SPOOL_DONE = 2, CONN_SSL_HANDS_SHAKEN = 4
};

struct connection {
  struct mg_connection mg_conn;   // XXX: Must be first
  struct linked_list_link link;   // Linkage to server->active_connections
  struct mg_server *server;
  sock_t client_sock;             // Connected client
  struct iobuf local_iobuf;
  struct iobuf remote_iobuf;
  union endpoint endpoint;
  enum endpoint_type endpoint_type;
  time_t birth_time;
  time_t last_activity_time;
  char *path_info;
  char *request;
  int64_t num_bytes_sent; // Total number of bytes sent
  int64_t cl;             // Reply content length, for Range support
  int request_len;  // Request length, including last \r\n after last header
  int flags;        // CONN_* flags: CONN_CLOSE, CONN_SPOOL_DONE, etc
  mutex_t mutex;    // Guards concurrent mg_write() calls
  void *ssl;        // SSL descriptor
};

static void close_local_endpoint(struct connection *conn);

static const struct {
  const char *extension;
  size_t ext_len;
  const char *mime_type;
} static_builtin_mime_types[] = {
  {".html", 5, "text/html"},
  {".htm", 4, "text/html"},
  {".shtm", 5, "text/html"},
  {".shtml", 6, "text/html"},
  {".css", 4, "text/css"},
  {".js",  3, "application/x-javascript"},
  {".ico", 4, "image/x-icon"},
  {".gif", 4, "image/gif"},
  {".jpg", 4, "image/jpeg"},
  {".jpeg", 5, "image/jpeg"},
  {".png", 4, "image/png"},
  {".svg", 4, "image/svg+xml"},
  {".txt", 4, "text/plain"},
  {".torrent", 8, "application/x-bittorrent"},
  {".wav", 4, "audio/x-wav"},
  {".mp3", 4, "audio/x-mp3"},
  {".mid", 4, "audio/mid"},
  {".m3u", 4, "audio/x-mpegurl"},
  {".ogg", 4, "application/ogg"},
  {".ram", 4, "audio/x-pn-realaudio"},
  {".xml", 4, "text/xml"},
  {".json",  5, "text/json"},
  {".xslt", 5, "application/xml"},
  {".xsl", 4, "application/xml"},
  {".ra",  3, "audio/x-pn-realaudio"},
  {".doc", 4, "application/msword"},
  {".exe", 4, "application/octet-stream"},
  {".zip", 4, "application/x-zip-compressed"},
  {".xls", 4, "application/excel"},
  {".tgz", 4, "application/x-tar-gz"},
  {".tar", 4, "application/x-tar"},
  {".gz",  3, "application/x-gunzip"},
  {".arj", 4, "application/x-arj-compressed"},
  {".rar", 4, "application/x-arj-compressed"},
  {".rtf", 4, "application/rtf"},
  {".pdf", 4, "application/pdf"},
  {".swf", 4, "application/x-shockwave-flash"},
  {".mpg", 4, "video/mpeg"},
  {".webm", 5, "video/webm"},
  {".mpeg", 5, "video/mpeg"},
  {".mov", 4, "video/quicktime"},
  {".mp4", 4, "video/mp4"},
  {".m4v", 4, "video/x-m4v"},
  {".asf", 4, "video/x-ms-asf"},
  {".avi", 4, "video/x-msvideo"},
  {".bmp", 4, "image/bmp"},
  {".ttf", 4, "application/x-font-ttf"},
  {NULL,  0, NULL}
};

static const char *static_config_options[] = {
  "access_control_list", NULL,
  "access_log_file", NULL,
  "auth_domain", "mydomain.com",
  "cgi_interpreter", NULL,
  "cgi_pattern", "**.cgi$|**.pl$|**.php$",
  "document_root",  NULL,
  "enable_directory_listing", "yes",
  "error_log_file", NULL,
  "extra_mime_types", NULL,
  "global_auth_file", NULL,
  "hide_files_patterns", NULL,
  "idle_timeout_ms", "30000",
  "index_files","index.html,index.htm,index.cgi,index.shtml,index.php,index.lp",
  "listening_port", NULL,
  "dav_auth_file", NULL,
  "run_as_user", NULL,
  "ssl_certificate", NULL,
  "url_rewrites", NULL,
  NULL
};

static const char *static_month_names[] = {
  "Jan", "Feb", "Mar", "Apr", "May", "Jun",
  "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};

void *mg_start_thread(void *(*f)(void *), void *p) {
#ifdef _WIN32
  return (void *) _beginthread((void (__cdecl *)(void *)) f, 0, p);
#else
  pthread_t thread_id = (pthread_t) 0;
  pthread_attr_t attr;

  (void) pthread_attr_init(&attr);
  (void) pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

#if USE_STACK_SIZE > 1
  // Compile-time option to control stack size, e.g. -DUSE_STACK_SIZE=16384
  (void) pthread_attr_setstacksize(&attr, USE_STACK_SIZE);
#endif

  pthread_create(&thread_id, &attr, f, p);
  pthread_attr_destroy(&attr);

  return (void *) thread_id;
#endif
}

static void set_close_on_exec(int fd) {
#ifdef _WIN32
  (void) SetHandleInformation((HANDLE) fd, HANDLE_FLAG_INHERIT, 0);
#else
  fcntl(fd, F_SETFD, FD_CLOEXEC);
#endif
}

static void set_non_blocking_mode(sock_t sock) {
#ifdef _WIN32
  unsigned long on = 1;
  ioctlsocket(sock, FIONBIO, &on);
#else
  int flags = fcntl(sock, F_GETFL, 0);
  fcntl(sock, F_SETFL, flags | O_NONBLOCK);
#endif
}

static int should_keep_alive(const struct mg_connection *conn) {
  const char *method = conn->request_method;
  const char *http_version = conn->http_version;
  const char *header = mg_get_header(conn, "Connection");
  return method != NULL && !strcmp(method, "GET") &&
    ((header != NULL && !strcmp(header, "keep-alive")) ||
     (header == NULL && http_version && !strcmp(http_version, "1.1")));
}

static const char *suggest_connection_header(const struct mg_connection *conn) {
  return should_keep_alive(conn) ? "keep-alive" : "close";
}

static void mg_strlcpy(register char *dst, register const char *src, size_t n) {
  for (; *src != '\0' && n > 1; n--) {
    *dst++ = *src++;
  }
  *dst = '\0';
}

static int spool(struct iobuf *io, const void *buf, int len) {
  static const double mult = 1.2;
  char *p = NULL;
  int new_len = 0;

  assert(io->len >= 0);
  assert(io->len <= io->size);

  //DBG(("1. %d %d %d", len, io->len, io->size));
  if (len <= 0) {
  } else if ((new_len = io->len + len) < io->size) {
    memcpy(io->buf + io->len, buf, len);
    io->len = new_len;
  } else if ((p = (char *) realloc(io->buf, (int) (new_len * mult))) != NULL) {
    io->buf = p;
    memcpy(io->buf + io->len, buf, len);
    io->len = new_len;
    io->size = (int) (new_len * mult);
  } else {
    len = 0;
  }
  //DBG(("%d %d %d", len, io->len, io->size));

  return len;
}

// Like snprintf(), but never returns negative value, or a value
// that is larger than a supplied buffer.
static int mg_vsnprintf(char *buf, size_t buflen, const char *fmt, va_list ap) {
  int n;
  if (buflen < 1) return 0;
  n = vsnprintf(buf, buflen, fmt, ap);
  if (n < 0) {
    n = 0;
  } else if (n >= (int) buflen) {
    n = (int) buflen - 1;
  }
  buf[n] = '\0';
  return n;
}

static int mg_snprintf(char *buf, size_t buflen, const char *fmt, ...) {
  va_list ap;
  int n;
  va_start(ap, fmt);
  n = mg_vsnprintf(buf, buflen, fmt, ap);
  va_end(ap);
  return n;
}

static void send_http_error(struct connection *conn, int code) {
  const char *message;
  char headers[200], body[200];
  int body_len, headers_len;

  switch (code) {
    case 201: message = "Created";                  break;
    case 204: message = "No Content";               break;
    case 304: message = "Not Modified";             break;
    case 400: message = "Bad Request";              break;
    case 403: message = "Forbidden";                break;
    case 404: message = "Not Found";                break;
    case 405: message = "Method Not Allowed";       break;
    case 409: message = "Conflict";                 break;
    case 411: message = "Length Required";          break;
    case 413: message = "Request Entity Too Large"; break;
    case 415: message = "Unsupported Media Type";   break;
    case 423: message = "Locked";                   break;
    case 501: message = "Not Implemented";          break;
    default:  message = "Server Error";             break;
  }

  conn->mg_conn.status_code = code;
  body_len = mg_snprintf(body, sizeof(body), "%d %s\n", code, message);
  if (code >= 300 && code <= 399) {
    // 3xx errors do not have body
    body_len = 0;
  }
  headers_len = mg_snprintf(headers, sizeof(headers),
                            "HTTP/1.1 %d %s\r\nContent-Length: %d\r\n"
                            "Content-Type: text/plain\r\n\r\n",
                            code, message, body_len);
  spool(&conn->remote_iobuf, headers, headers_len);
  spool(&conn->remote_iobuf, body, body_len);
  close_local_endpoint(conn);  // This will write to the log file
}

static void mg_printf(struct connection *conn, const char *fmt, ...) {
  char buf[IOBUF_SIZE];
  va_list ap;
  int len;

  va_start(ap, fmt);
  len = vsnprintf(buf, sizeof(buf), fmt, ap);
  va_end(ap);

  spool(&conn->remote_iobuf, buf, len);
  close_local_endpoint(conn);  // Log the request
}

// A helper function for traversing a comma separated list of values.
// It returns a list pointer shifted to the next value, or NULL if the end
// of the list found.
// Value is stored in val vector. If value has form "x=y", then eq_val
// vector is initialized to point to the "y" part, and val vector length
// is adjusted to point only to "x".
static const char *next_option(const char *list, struct vec *val,
                               struct vec *eq_val) {
  if (list == NULL || *list == '\0') {
    // End of the list
    list = NULL;
  } else {
    val->ptr = list;
    if ((list = strchr(val->ptr, ',')) != NULL) {
      // Comma found. Store length and shift the list ptr
      val->len = list - val->ptr;
      list++;
    } else {
      // This value is the last one
      list = val->ptr + strlen(val->ptr);
      val->len = list - val->ptr;
    }

    if (eq_val != NULL) {
      // Value has form "x=y", adjust pointers and lengths
      // so that val points to "x", and eq_val points to "y".
      eq_val->len = 0;
      eq_val->ptr = (const char *) memchr(val->ptr, '=', val->len);
      if (eq_val->ptr != NULL) {
        eq_val->ptr++;  // Skip over '=' character
        eq_val->len = val->ptr + val->len - eq_val->ptr;
        val->len = (eq_val->ptr - val->ptr) - 1;
      }
    }
  }

  return list;
}

static int mg_socketpair(sock_t sp[2]) {
  struct sockaddr_in sa;
  sock_t sock, ret = -1;
  socklen_t len = sizeof(sa);

  sp[0] = sp[1] = INVALID_SOCKET;

  (void) memset(&sa, 0, sizeof(sa));
  sa.sin_family = AF_INET;
  sa.sin_port = htons(0);
  sa.sin_addr.s_addr = htonl(0x7f000001);

  if ((sock = socket(AF_INET, SOCK_STREAM, 0)) != INVALID_SOCKET &&
      !bind(sock, (struct sockaddr *) &sa, len) &&
      !listen(sock, 1) &&
      !getsockname(sock, (struct sockaddr *) &sa, &len) &&
      (sp[0] = socket(AF_INET, SOCK_STREAM, 6)) != -1 &&
      !connect(sp[0], (struct sockaddr *) &sa, len) &&
      (sp[1] = accept(sock,(struct sockaddr *) &sa, &len)) != INVALID_SOCKET) {
    set_close_on_exec(sp[0]);
    set_close_on_exec(sp[1]);
    ret = 0;
  } else {
    if (sp[0] != INVALID_SOCKET) closesocket(sp[0]);
    if (sp[1] != INVALID_SOCKET) closesocket(sp[1]);
    sp[0] = sp[1] = INVALID_SOCKET;
  }
  closesocket(sock);

  return ret;
}

#ifndef NO_CGI
#ifdef _WIN32
static pid_t start_process(char *interp, const char *cmd, const char *env,
                           const char *envp[], const char *dir, sock_t sock) {
  STARTUPINFOA si = {0};
  PROCESS_INFORMATION pi = {0};
  HANDLE hs = (HANDLE) sock, me = GetCurrentProcess();
  char cmdline[MAX_PATH_SIZE], full_dir[MAX_PATH_SIZE], buf[MAX_PATH_SIZE], *p;
  FILE *fp;

  si.cb = sizeof(si);
  si.dwFlags = STARTF_USESTDHANDLES | STARTF_USESHOWWINDOW;
  si.wShowWindow = SW_HIDE;

  DuplicateHandle(me, hs, me, &si.hStdInput, 0, TRUE, DUPLICATE_SAME_ACCESS);
  DuplicateHandle(me, hs, me, &si.hStdOutput, 0, TRUE, DUPLICATE_SAME_ACCESS);
  si.hStdError = GetStdHandle(STD_ERROR_HANDLE);
  closesocket(sock);

  if (interp == NULL && (fp = fopen(cmd, "r")) != NULL) {
    buf[0] = buf[1] = '\0';
    fgets(buf, sizeof(buf), fp);
    buf[sizeof(buf) - 1] = '\0';
    if (buf[0] == '#' && buf[1] == '!') {
      interp = buf + 2;
      for (p = interp + strlen(interp);
           isspace(* (uint8_t *) p) && p > interp; p--) *p = '\0';
    }
    fclose(fp);
  }

  if (interp != NULL) {
    GetFullPathNameA(interp, sizeof(buf), buf, NULL);
    interp = buf;
  }
  GetFullPathNameA(dir, sizeof(full_dir), full_dir, NULL);
  mg_snprintf(cmdline, sizeof(cmdline), "%s%s\"%s\"",
              interp ? interp : "", interp ? " " : "", cmd);

  DBG(("Starting commad: [%s]", cmdline));
  CreateProcess(NULL, cmdline, NULL, NULL, TRUE,
                CREATE_NEW_PROCESS_GROUP, (void *) env, full_dir, &si, &pi);

  CloseHandle(si.hStdOutput);
  CloseHandle(si.hStdInput);
  CloseHandle(pi.hThread);

  return (pid_t) pi.hProcess;
}
#else
static pid_t start_process(const char *interp, const char *cmd, const char *env,
                           const char *envp[], const char *dir, sock_t sock) {
  pid_t pid = fork();
  (void) env;

  if (pid == 0) {
    chdir(dir);
    dup2(sock, 0);
    dup2(sock, 1);
    closesocket(sock);

    // After exec, all signal handlers are restored to their default values,
    // with one exception of SIGCHLD. According to POSIX.1-2001 and Linux's
    // implementation, SIGCHLD's handler will leave unchanged after exec
    // if it was set to be ignored. Restore it to default action.
    signal(SIGCHLD, SIG_DFL);

    if (interp == NULL) {
      execle(cmd, cmd, NULL, envp);
    } else {
      execle(interp, interp, cmd, NULL, envp);
    }
    exit(EXIT_FAILURE);  // exec call failed
  }

  return pid;
}
#endif  // _WIN32

// This structure helps to create an environment for the spawned CGI program.
// Environment is an array of "VARIABLE=VALUE\0" ASCIIZ strings,
// last element must be NULL.
// However, on Windows there is a requirement that all these VARIABLE=VALUE\0
// strings must reside in a contiguous buffer. The end of the buffer is
// marked by two '\0' characters.
// We satisfy both worlds: we create an envp array (which is vars), all
// entries are actually pointers inside buf.
struct cgi_env_block {
  struct mg_connection *conn;
  char buf[CGI_ENVIRONMENT_SIZE];       // Environment buffer
  const char *vars[MAX_CGI_ENVIR_VARS]; // char *envp[]
  int len;                              // Space taken
  int nvars;                            // Number of variables in envp[]
};

// Append VARIABLE=VALUE\0 string to the buffer, and add a respective
// pointer into the vars array.
static char *addenv(struct cgi_env_block *block, const char *fmt, ...) {
  int n, space;
  char *added;
  va_list ap;

  // Calculate how much space is left in the buffer
  space = sizeof(block->buf) - block->len - 2;
  assert(space >= 0);

  // Make a pointer to the free space int the buffer
  added = block->buf + block->len;

  // Copy VARIABLE=VALUE\0 string into the free space
  va_start(ap, fmt);
  n = mg_vsnprintf(added, (size_t) space, fmt, ap);
  va_end(ap);

  // Make sure we do not overflow buffer and the envp array
  if (n > 0 && n + 1 < space &&
      block->nvars < (int) ARRAY_SIZE(block->vars) - 2) {
    // Append a pointer to the added string into the envp array
    block->vars[block->nvars++] = added;
    // Bump up used length counter. Include \0 terminator
    block->len += n + 1;
  }

  return added;
}

static void addenv2(struct cgi_env_block *blk, const char *name) {
  const char *s;
  if ((s = getenv(name)) != NULL) addenv(blk, "%s=%s", name, s);
}

static void prepare_cgi_environment(struct connection *conn,
                                    const char *prog,
                                    struct cgi_env_block *blk) {
  struct mg_connection *ri = &conn->mg_conn;
  const char *s, *slash;
  char *p, **opts = conn->server->config_options;
  int  i;

  blk->len = blk->nvars = 0;
  blk->conn = ri;

  addenv(blk, "SERVER_NAME=%s", opts[AUTH_DOMAIN]);
  addenv(blk, "SERVER_ROOT=%s", opts[DOCUMENT_ROOT]);
  addenv(blk, "DOCUMENT_ROOT=%s", opts[DOCUMENT_ROOT]);
  addenv(blk, "SERVER_SOFTWARE=%s/%s", "Mongoose", MONGOOSE_VERSION);

  // Prepare the environment block
  addenv(blk, "%s", "GATEWAY_INTERFACE=CGI/1.1");
  addenv(blk, "%s", "SERVER_PROTOCOL=HTTP/1.1");
  addenv(blk, "%s", "REDIRECT_STATUS=200"); // For PHP

  // TODO(lsm): fix this for IPv6 case
  addenv(blk, "SERVER_PORT=%d", ri->remote_port);

  addenv(blk, "REQUEST_METHOD=%s", ri->request_method);
  addenv(blk, "REMOTE_ADDR=%s", ri->remote_ip);
  addenv(blk, "REMOTE_PORT=%d", ri->remote_port);
  addenv(blk, "REQUEST_URI=%s%s%s", ri->uri,
         ri->query_string == NULL ? "" : "?",
         ri->query_string == NULL ? "" : ri->query_string);

  // SCRIPT_NAME
  if (conn->path_info != NULL) {
    addenv(blk, "SCRIPT_NAME=%.*s",
           (int) (strlen(ri->uri) - strlen(conn->path_info)), ri->uri);
    addenv(blk, "PATH_INFO=%s", conn->path_info);
  } else {
    s = strrchr(prog, '/');
    slash = strrchr(ri->uri, '/');
    addenv(blk, "SCRIPT_NAME=%.*s%s",
           slash == NULL ? 0 : (int) (slash - ri->uri), ri->uri,
           s == NULL ? prog : s);
  }

  addenv(blk, "SCRIPT_FILENAME=%s", prog);
  addenv(blk, "PATH_TRANSLATED=%s", prog);
  addenv(blk, "HTTPS=%s", conn->ssl != NULL ? "on" : "off");

  if ((s = mg_get_header(ri, "Content-Type")) != NULL)
    addenv(blk, "CONTENT_TYPE=%s", s);

  if (ri->query_string != NULL)
    addenv(blk, "QUERY_STRING=%s", ri->query_string);

  if ((s = mg_get_header(ri, "Content-Length")) != NULL)
    addenv(blk, "CONTENT_LENGTH=%s", s);

  addenv2(blk, "PATH");
  addenv2(blk, "PERLLIB");
  addenv2(blk, ENV_EXPORT_TO_CGI);

#if defined(_WIN32)
  addenv2(blk, "COMSPEC");
  addenv2(blk, "SYSTEMROOT");
  addenv2(blk, "SystemDrive");
  addenv2(blk, "ProgramFiles");
  addenv2(blk, "ProgramFiles(x86)");
  addenv2(blk, "CommonProgramFiles(x86)");
#else
  addenv2(blk, "LD_LIBRARY_PATH");
#endif // _WIN32

  // Add all headers as HTTP_* variables
  for (i = 0; i < ri->num_headers; i++) {
    p = addenv(blk, "HTTP_%s=%s",
        ri->http_headers[i].name, ri->http_headers[i].value);

    // Convert variable name into uppercase, and change - to _
    for (; *p != '=' && *p != '\0'; p++) {
      if (*p == '-')
        *p = '_';
      *p = (char) toupper(* (unsigned char *) p);
    }
  }

  blk->vars[blk->nvars++] = NULL;
  blk->buf[blk->len++] = '\0';

  assert(blk->nvars < (int) ARRAY_SIZE(blk->vars));
  assert(blk->len > 0);
  assert(blk->len < (int) sizeof(blk->buf));
}

static void open_cgi_endpoint(struct connection *conn, const char *prog) {
  struct cgi_env_block blk;
  char dir[MAX_PATH_SIZE], *p = NULL;
  sock_t fds[2];

  prepare_cgi_environment(conn, prog, &blk);
  // CGI must be executed in its own directory. 'dir' must point to the
  // directory containing executable program, 'p' must point to the
  // executable program name relative to 'dir'.
  mg_snprintf(dir, sizeof(dir), "%s", prog);
  if ((p = strrchr(dir, '/')) != NULL) {
    *p++ = '\0';
  } else {
    dir[0] = '.', dir[1] = '\0';
    p = (char *) prog;
  }

  // Try to create socketpair in a loop until success. mg_socketpair()
  // can be interrupted by a signal and fail.
  // TODO(lsm): use sigaction to restart interrupted syscall
  do {
    mg_socketpair(fds);
  } while (fds[0] < 0);

  if (start_process(conn->server->config_options[CGI_INTERPRETER],
                    prog, blk.buf, blk.vars, dir, fds[1]) > 0) {
    conn->endpoint_type = EP_CGI;
    conn->endpoint.cgi_sock = fds[0];
  } else {
    closesocket(fds[0]);
    send_http_error(conn, 500);
  }

  closesocket(fds[1]);
}
#endif  // !NO_CGI

// 'sa' must be an initialized address to bind to
static sock_t open_listening_socket(union socket_address *sa) {
  sock_t on = 1, sock = INVALID_SOCKET;

  if ((sock = socket(sa->sa.sa_family, SOCK_STREAM, 6)) == INVALID_SOCKET ||
      setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, (void *) &on, sizeof(on)) ||
      bind(sock, &sa->sa, sa->sa.sa_family == AF_INET ?
           sizeof(sa->sin) : sizeof(sa->sa)) != 0 ||
      listen(sock, SOMAXCONN) != 0) {
    closesocket(sock);
    sock = INVALID_SOCKET;
  }

  return sock;
}

static char *mg_strdup(const char *str) {
  char *copy = (char *) malloc(strlen(str) + 1);
  if (copy != NULL) {
    strcpy(copy, str);
  }
  return copy;
}

static int isbyte(int n) {
  return n >= 0 && n <= 255;
}

static int parse_net(const char *spec, uint32_t *net, uint32_t *mask) {
  int n, a, b, c, d, slash = 32, len = 0;

  if ((sscanf(spec, "%d.%d.%d.%d/%d%n", &a, &b, &c, &d, &slash, &n) == 5 ||
      sscanf(spec, "%d.%d.%d.%d%n", &a, &b, &c, &d, &n) == 4) &&
      isbyte(a) && isbyte(b) && isbyte(c) && isbyte(d) &&
      slash >= 0 && slash < 33) {
    len = n;
    *net = ((uint32_t)a << 24) | ((uint32_t)b << 16) | ((uint32_t)c << 8) | d;
    *mask = slash ? 0xffffffffU << (32 - slash) : 0;
  }

  return len;
}

// Verify given socket address against the ACL.
// Return -1 if ACL is malformed, 0 if address is disallowed, 1 if allowed.
static int check_acl(const char *acl, uint32_t remote_ip) {
  int allowed, flag;
  uint32_t net, mask;
  struct vec vec;

  // If any ACL is set, deny by default
  allowed = acl == NULL ? '+' : '-';

  while ((acl = next_option(acl, &vec, NULL)) != NULL) {
    flag = vec.ptr[0];
    if ((flag != '+' && flag != '-') ||
        parse_net(&vec.ptr[1], &net, &mask) == 0) {
      return -1;
    }

    if (net == (remote_ip & mask)) {
      allowed = flag;
    }
  }

  return allowed == '+';
}

static struct connection *accept_new_connection(struct mg_server *server) {
  union socket_address sa;
  socklen_t len = sizeof(sa);
  sock_t sock = INVALID_SOCKET;
  struct connection *conn = NULL;

  // NOTE(lsm): on Windows, sock is always > FD_SETSIZE
  if ((sock = accept(server->listening_sock, &sa.sa, &len)) == INVALID_SOCKET) {
  } else if (!check_acl(server->config_options[ACCESS_CONTROL_LIST],
                        ntohl(* (uint32_t *) &sa.sin.sin_addr))) {
    // NOTE(lsm): check_acl doesn't work for IPv6
    closesocket(sock);
  } else if ((conn = (struct connection *) calloc(1, sizeof(*conn))) == NULL) {
    closesocket(sock);
#ifdef USE_SSL
  } else if (server->ssl_ctx != NULL &&
             ((conn->ssl = SSL_new(server->ssl_ctx)) == NULL ||
              SSL_set_fd(conn->ssl, sock) != 1)) {
    DBG(("SSL error"));
    closesocket(sock);
    free(conn);
    conn = NULL;
#endif
  } else {
    set_close_on_exec(sock);
    set_non_blocking_mode(sock);
    conn->server = server;
    conn->client_sock = sock;
    mutex_init(&conn->mutex);
    LINKED_LIST_ADD_TO_FRONT(&server->active_connections, &conn->link);
    DBG(("added conn %p", conn));
  }

  return conn;
}

static void close_conn(struct connection *conn) {
  DBG(("closing %p %d %d", conn, conn->flags, conn->endpoint_type));
  LINKED_LIST_REMOVE(&conn->link);
  closesocket(conn->client_sock);
  free(conn->request);            // It's OK to free(NULL), ditto below
  free(conn->path_info);
  free(conn->remote_iobuf.buf);
  free(conn->local_iobuf.buf);
#ifdef USE_SSL
  if (conn->ssl != NULL) SSL_free(conn->ssl);
#endif
  mutex_destroy(&conn->mutex);
  free(conn);
}

// Check whether full request is buffered. Return:
//   -1  if request is malformed
//    0  if request is not yet fully buffered
//   >0  actual request length, including last \r\n\r\n
static int get_request_len(const char *s, int buf_len) {
  const unsigned char *buf = (unsigned char *) s;
  int i;

  for (i = 0; i < buf_len; i++) {
    // Control characters are not allowed but >=128 are.
    // Abort scan as soon as one malformed character is found.
    if (!isprint(buf[i]) && buf[i] != '\r' && buf[i] != '\n' && buf[i] < 128) {
      return -1;
    } else if (buf[i] == '\n' && i + 1 < buf_len && buf[i + 1] == '\n') {
      return i + 2;
    } else if (buf[i] == '\n' && i + 2 < buf_len && buf[i + 1] == '\r' &&
               buf[i + 2] == '\n') {
      return i + 3;
    }
  }

  return 0;
}


// Skip the characters until one of the delimiters characters found.
// 0-terminate resulting word. Skip the rest of the delimiters if any.
// Advance pointer to buffer to the next word. Return found 0-terminated word.
static char *skip(char **buf, const char *delimiters) {
  char *p, *begin_word, *end_word, *end_delimiters;

  begin_word = *buf;
  end_word = begin_word + strcspn(begin_word, delimiters);
  end_delimiters = end_word + strspn(end_word, delimiters);

  for (p = end_word; p < end_delimiters; p++) {
    *p = '\0';
  }

  *buf = end_delimiters;

  return begin_word;
}

// Protect against directory disclosure attack by removing '..',
// excessive '/' and '\' characters
static void remove_double_dots_and_double_slashes(char *s) {
  char *p = s;

  while (*s != '\0') {
    *p++ = *s++;
    if (s[-1] == '/' || s[-1] == '\\') {
      // Skip all following slashes, backslashes and double-dots
      while (s[0] != '\0') {
        if (s[0] == '/' || s[0] == '\\') { s++; }
        else if (s[0] == '.' && s[1] == '.') { s += 2; }
        else { break; }
      }
    }