res_http_websocket.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 2012, Digium, Inc.
 *
 * Joshua Colp <jcolp@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*! \file
 *
 * \brief WebSocket support for the Asterisk internal HTTP server
 *
 * \author Joshua Colp <jcolp@digium.com>
 */

/*** MODULEINFO
   <support_level>extended</support_level>
 ***/

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 417310 $")

#include "asterisk/module.h"
#include "asterisk/http.h"
#include "asterisk/astobj2.h"
#include "asterisk/strings.h"
#include "asterisk/file.h"
#include "asterisk/unaligned.h"

#define AST_API_MODULE
#include "asterisk/http_websocket.h"

/*! \brief GUID used to compute the accept key, defined in the specifications */
#define WEBSOCKET_GUID "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"

/*! \brief Number of buckets for registered protocols */
#define MAX_PROTOCOL_BUCKETS 7

/*! \brief Size of the pre-determined buffer for WebSocket frames */
#define MAXIMUM_FRAME_SIZE 8192

/*! \brief Default reconstruction size for multi-frame payload reconstruction. If exceeded the next frame will start a
 *         payload.
 */
#define DEFAULT_RECONSTRUCTION_CEILING 16384

/*! \brief Maximum reconstruction size for multi-frame payload reconstruction. */
#define MAXIMUM_RECONSTRUCTION_CEILING 16384

/*! \brief Maximum size of a websocket frame header
 * 1 byte flags and opcode
 * 1 byte mask flag + payload len
 * 8 bytes max extended length
 * 4 bytes optional masking key
 * ... payload follows ...
 * */
#define MAX_WS_HDR_SZ 14
#define MIN_WS_HDR_SZ 2

/*! \brief Structure definition for session */
struct ast_websocket {
   FILE *f;                          /*!< Pointer to the file instance used for writing and reading */
   int fd;                           /*!< File descriptor for the session, only used for polling */
   struct ast_sockaddr address;      /*!< Address of the remote client */
   enum ast_websocket_opcode opcode; /*!< Cached opcode for multi-frame messages */
   size_t payload_len;               /*!< Length of the payload */
   char *payload;                    /*!< Pointer to the payload */
   size_t reconstruct;               /*!< Number of bytes before a reconstructed payload will be returned and a new one started */
   int timeout;                      /*!< The timeout for operations on the socket */
   unsigned int secure:1;            /*!< Bit to indicate that the transport is secure */
   unsigned int closing:1;           /*!< Bit to indicate that the session is in the process of being closed */
   unsigned int close_sent:1;        /*!< Bit to indicate that the session close opcode has been sent and no further data will be sent */
};

/*! \brief Structure definition for protocols */
struct websocket_protocol {
   char *name;                      /*!< Name of the protocol */
   ast_websocket_callback callback; /*!< Callback called when a new session is established */
};

/*! \brief Container for registered protocols */
static struct ao2_container *protocols;

/*! \brief Hashing function for protocols */
static int protocol_hash_fn(const void *obj, const int flags)
{
   const struct websocket_protocol *protocol = obj;
   const char *name = obj;

   return ast_str_case_hash(flags & OBJ_KEY ? name : protocol->name);
}

/*! \brief Comparison function for protocols */
static int protocol_cmp_fn(void *obj, void *arg, int flags)
{
   const struct websocket_protocol *protocol1 = obj, *protocol2 = arg;
   const char *protocol = arg;

   return !strcasecmp(protocol1->name, flags & OBJ_KEY ? protocol : protocol2->name) ? CMP_MATCH | CMP_STOP : 0;
}

/*! \brief Destructor function for protocols */
static void protocol_destroy_fn(void *obj)
{
   struct websocket_protocol *protocol = obj;
   ast_free(protocol->name);
}

/*! \brief Destructor function for sessions */
static void session_destroy_fn(void *obj)
{
   struct ast_websocket *session = obj;

   ast_websocket_close(session, 0);

   if (session->f) {
      fclose(session->f);
      ast_verb(2, "WebSocket connection from '%s' closed\n", ast_sockaddr_stringify(&session->address));
   }

   ast_free(session->payload);
}

int AST_OPTIONAL_API_NAME(ast_websocket_add_protocol)(const char *name, ast_websocket_callback callback)
{
   struct websocket_protocol *protocol;

   ao2_lock(protocols);

   /* Ensure a second protocol handler is not registered for the same protocol */
   if ((protocol = ao2_find(protocols, name, OBJ_KEY | OBJ_NOLOCK))) {
      ao2_ref(protocol, -1);
      ao2_unlock(protocols);
      return -1;
   }

   if (!(protocol = ao2_alloc(sizeof(*protocol), protocol_destroy_fn))) {
      ao2_unlock(protocols);
      return -1;
   }

   if (!(protocol->name = ast_strdup(name))) {
      ao2_ref(protocol, -1);
      ao2_unlock(protocols);
      return -1;
   }

   protocol->callback = callback;

   ao2_link_flags(protocols, protocol, OBJ_NOLOCK);
   ao2_unlock(protocols);
   ao2_ref(protocol, -1);

   ast_verb(2, "WebSocket registered sub-protocol '%s'\n", name);

   return 0;
}

int AST_OPTIONAL_API_NAME(ast_websocket_remove_protocol)(const char *name, ast_websocket_callback callback)
{
   struct websocket_protocol *protocol;

   if (!(protocol = ao2_find(protocols, name, OBJ_KEY))) {
      return -1;
   }

   if (protocol->callback != callback) {
      ao2_ref(protocol, -1);
      return -1;
   }

   ao2_unlink(protocols, protocol);
   ao2_ref(protocol, -1);

   ast_verb(2, "WebSocket unregistered sub-protocol '%s'\n", name);

   return 0;
}

/*! \brief Close function for websocket session */
int AST_OPTIONAL_API_NAME(ast_websocket_close)(struct ast_websocket *session, uint16_t reason)
{
   char frame[4] = { 0, }; /* The header is 2 bytes and the reason code takes up another 2 bytes */
   int res;

   if (session->close_sent) {
      return 0;
   }

   frame[0] = AST_WEBSOCKET_OPCODE_CLOSE | 0x80;
   frame[1] = 2; /* The reason code is always 2 bytes */

   /* If no reason has been specified assume 1000 which is normal closure */
   put_unaligned_uint16(&frame[2], htons(reason ? reason : 1000));

   session->closing = 1;
   session->close_sent = 1;

   ao2_lock(session);
   res = ast_careful_fwrite(session->f, session->fd, frame, 4, session->timeout);
   ao2_unlock(session);

   return res;
}


/*! \brief Write function for websocket traffic */
int AST_OPTIONAL_API_NAME(ast_websocket_write)(struct ast_websocket *session, enum ast_websocket_opcode opcode, char *payload, uint64_t actual_length)
{
   size_t header_size = 2; /* The minimum size of a websocket frame is 2 bytes */
   char *frame;
   uint64_t length = 0;

   if (actual_length < 126) {
      length = actual_length;
   } else if (actual_length < (1 << 16)) {
      length = 126;
      /* We need an additional 2 bytes to store the extended length */
      header_size += 2;
   } else {
      length = 127;
      /* We need an additional 8 bytes to store the really really extended length */
      header_size += 8;
   }

   frame = ast_alloca(header_size);
   memset(frame, 0, sizeof(*frame));

   frame[0] = opcode | 0x80;
   frame[1] = length;

   /* Use the additional available bytes to store the length */
   if (length == 126) {
      put_unaligned_uint16(&frame[2], htons(actual_length));
   } else if (length == 127) {
      put_unaligned_uint64(&frame[2], htonl(actual_length));
   }

   ao2_lock(session);
   if (session->closing) {
      ao2_unlock(session);
      return -1;
   }

   if (ast_careful_fwrite(session->f, session->fd, frame, header_size, session->timeout)) {
      ao2_unlock(session);
      return -1;
   }

   if (ast_careful_fwrite(session->f, session->fd, payload, actual_length, session->timeout)) {
      ao2_unlock(session);
      return -1;
   }
   fflush(session->f);
   ao2_unlock(session);

   return 0;
}

void AST_OPTIONAL_API_NAME(ast_websocket_reconstruct_enable)(struct ast_websocket *session, size_t bytes)
{
   session->reconstruct = MIN(bytes, MAXIMUM_RECONSTRUCTION_CEILING);
}

void AST_OPTIONAL_API_NAME(ast_websocket_reconstruct_disable)(struct ast_websocket *session)
{
   session->reconstruct = 0;
}

void AST_OPTIONAL_API_NAME(ast_websocket_ref)(struct ast_websocket *session)
{
   ao2_ref(session, +1);
}

void AST_OPTIONAL_API_NAME(ast_websocket_unref)(struct ast_websocket *session)
{
   ao2_ref(session, -1);
}

int AST_OPTIONAL_API_NAME(ast_websocket_fd)(struct ast_websocket *session)
{
   return session->closing ? -1 : session->fd;
}

struct ast_sockaddr * AST_OPTIONAL_API_NAME(ast_websocket_remote_address)(struct ast_websocket *session)
{
   return &session->address;
}

int AST_OPTIONAL_API_NAME(ast_websocket_is_secure)(struct ast_websocket *session)
{
   return session->secure;
}

int AST_OPTIONAL_API_NAME(ast_websocket_set_nonblock)(struct ast_websocket *session)
{
   int flags;

   if ((flags = fcntl(session->fd, F_GETFL)) == -1) {
      return -1;
   }

   flags |= O_NONBLOCK;

   if ((flags = fcntl(session->fd, F_SETFL, flags)) == -1) {
      return -1;
   }

   return 0;
}

int AST_OPTIONAL_API_NAME(ast_websocket_set_timeout)(struct ast_websocket *session, int timeout)
{
   session->timeout = timeout;

   return 0;
}

/* MAINTENANCE WARNING on ast_websocket_read()!
 *
 * We have to keep in mind during this function that the fact that session->fd seems ready
 * (via poll) does not necessarily mean we have application data ready, because in the case
 * of an SSL socket, there is some encryption data overhead that needs to be read from the
 * TCP socket, so poll() may say there are bytes to be read, but whether it is just 1 byte
 * or N bytes we do not know that, and we do not know how many of those bytes (if any) are
 * for application data (for us) and not just for the SSL protocol consumption
 *
 * There used to be a couple of nasty bugs here that were fixed in last refactoring but I
 * want to document them so the constraints are clear and we do not re-introduce them:
 *
 * - This function would incorrectly assume that fread() would necessarily return more than
 *   1 byte of data, just because a websocket frame is always >= 2 bytes, but the thing
 *   is we're dealing with a TCP bitstream here, we could read just one byte and that's normal.
 *   The problem before was that if just one byte was read, the function bailed out and returned
 *   an error, effectively dropping the first byte of a websocket frame header!
 *
 * - Another subtle bug was that it would just read up to MAX_WS_HDR_SZ (14 bytes) via fread()
 *   then assume that executing poll() would tell you if there is more to read, but since
 *   we're dealing with a buffered stream (session->f is a FILE*), poll would say there is
 *   nothing else to read (in the real tcp socket session->fd) and we would get stuck here
 *   without processing the rest of the data in session->f internal buffers until another packet
 *   came on the network to unblock us!
 *
 * Note during the header parsing stage we try to read in small chunks just what we need, this
 * is buffered data anyways, no expensive syscall required most of the time ...
 */
static inline int ws_safe_read(struct ast_websocket *session, char *buf, int len, enum ast_websocket_opcode *opcode)
{
   int sanity;
   size_t rlen;
   int xlen = len;
   char *rbuf = buf;
   for (sanity = 10; sanity; sanity--) {
      clearerr(session->f);
      rlen = fread(rbuf, 1, xlen, session->f);
      if (0 == rlen && ferror(session->f) && errno != EAGAIN) {
         ast_log(LOG_ERROR, "Error reading from web socket: %s\n", strerror(errno));
         (*opcode) = AST_WEBSOCKET_OPCODE_CLOSE;
         session->closing = 1;
         return -1;
      }
      xlen = (xlen - rlen);
      rbuf = rbuf + rlen;
      if (0 == xlen) {
         break;
      }
      if (ast_wait_for_input(session->fd, 1000) < 0) {
         ast_log(LOG_ERROR, "ast_wait_for_input returned err: %s\n", strerror(errno));
         (*opcode) = AST_WEBSOCKET_OPCODE_CLOSE;
         session->closing = 1;
         return -1;
      }
   }
   if (!sanity) {
      ast_log(LOG_WARNING, "Websocket seems unresponsive, disconnecting ...\n");
      (*opcode) = AST_WEBSOCKET_OPCODE_CLOSE;
      session->closing = 1;
      return -1;
   }
   return 0;
}

int AST_OPTIONAL_API_NAME(ast_websocket_read)(struct ast_websocket *session, char **payload, uint64_t *payload_len, enum ast_websocket_opcode *opcode, int *fragmented)
{
   char buf[MAXIMUM_FRAME_SIZE] = "";
   int fin = 0;
   int mask_present = 0;
   char *mask = NULL, *new_payload = NULL;
   size_t options_len = 0, frame_size = 0;

   *payload = NULL;
   *payload_len = 0;
   *fragmented = 0;

   if (ws_safe_read(session, &buf[0], MIN_WS_HDR_SZ, opcode)) {
      return 0;
   }
   frame_size += MIN_WS_HDR_SZ;

   /* ok, now we have the first 2 bytes, so we know some flags, opcode and payload length (or whether payload length extension will be required) */
   *opcode = buf[0] & 0xf;
   *payload_len = buf[1] & 0x7f;
   if (*opcode == AST_WEBSOCKET_OPCODE_TEXT || *opcode == AST_WEBSOCKET_OPCODE_BINARY || *opcode == AST_WEBSOCKET_OPCODE_CONTINUATION ||
       *opcode == AST_WEBSOCKET_OPCODE_PING || *opcode == AST_WEBSOCKET_OPCODE_PONG) {
      fin = (buf[0] >> 7) & 1;
      mask_present = (buf[1] >> 7) & 1;

      /* Based on the mask flag and payload length, determine how much more we need to read before start parsing the rest of the header */
      options_len += mask_present ? 4 : 0;
      options_len += (*payload_len == 126) ? 2 : (*payload_len == 127) ? 8 : 0;
      if (options_len) {
         /* read the rest of the header options */
         if (ws_safe_read(session, &buf[frame_size], options_len, opcode)) {
            return 0;
         }
         frame_size += options_len;
      }

      if (*payload_len == 126) {
         /* Grab the 2-byte payload length  */
         *payload_len = ntohs(get_unaligned_uint16(&buf[2]));
         mask = &buf[4];
      } else if (*payload_len == 127) {
         /* Grab the 8-byte payload length  */
         *payload_len = ntohl(get_unaligned_uint64(&buf[2]));
         mask = &buf[10];
      } else {
         /* Just set the mask after the small 2-byte header */
         mask = &buf[2];
      }

      /* Now read the rest of the payload */
      *payload = &buf[frame_size]; /* payload will start here, at the end of the options, if any */
      frame_size = frame_size + (*payload_len); /* final frame size is header + optional headers + payload data */
      if (frame_size > MAXIMUM_FRAME_SIZE) {
         ast_log(LOG_WARNING, "Cannot fit huge websocket frame of %zu bytes\n", frame_size);
         /* The frame won't fit :-( */
         ast_websocket_close(session, 1009);
         return -1;
      }

      if (ws_safe_read(session, (*payload), (*payload_len), opcode)) {
         return 0;
      }

      /* If a mask is present unmask the payload */
      if (mask_present) {
         unsigned int pos;
         for (pos = 0; pos < *payload_len; pos++) {
            (*payload)[pos] ^= mask[pos % 4];
         }
      }

      if (!(new_payload = ast_realloc(session->payload, (session->payload_len + *payload_len)))) {
         ast_log(LOG_WARNING, "Failed allocation: %p, %zu, %"PRIu64"\n",
            session->payload, session->payload_len, *payload_len);
         *payload_len = 0;
         ast_websocket_close(session, 1009);
         return 0;
      }

      /* Per the RFC for PING we need to send back an opcode with the application data as received */
      if ((*opcode == AST_WEBSOCKET_OPCODE_PING) && (ast_websocket_write(session, AST_WEBSOCKET_OPCODE_PONG, *payload, *payload_len))) {
         *payload_len = 0;
         ast_websocket_close(session, 1009);
         return 0;
      }

      session->payload = new_payload;
      memcpy((session->payload + session->payload_len), (*payload), (*payload_len));
      session->payload_len += *payload_len;

      if (!fin && session->reconstruct && (session->payload_len < session->reconstruct)) {
         /* If this is not a final message we need to defer returning it until later */
         if (*opcode != AST_WEBSOCKET_OPCODE_CONTINUATION) {
            session->opcode = *opcode;
         }
         *opcode = AST_WEBSOCKET_OPCODE_CONTINUATION;
         *payload_len = 0;
         *payload = NULL;
      } else {
         if (*opcode == AST_WEBSOCKET_OPCODE_CONTINUATION) {
            if (!fin) {
               /* If this was not actually the final message tell the user it is fragmented so they can deal with it accordingly */
               *fragmented = 1;
            } else {
               /* Final frame in multi-frame so push up the actual opcode */
               *opcode = session->opcode;
            }
         }
         *payload_len = session->payload_len;
         *payload = session->payload;
         session->payload_len = 0;
      }
   } else if (*opcode == AST_WEBSOCKET_OPCODE_CLOSE) {
      /* Make the payload available so the user can look at the reason code if they so desire */
      if ((*payload_len) && (new_payload = ast_realloc(session->payload, *payload_len))) {
         if (ws_safe_read(session, &buf[frame_size], (*payload_len), opcode)) {
            return 0;
         }
         session->payload = new_payload;
         memcpy(session->payload, &buf[frame_size], *payload_len);
         *payload = session->payload;
         frame_size += (*payload_len);
      }

      session->closing = 1;
   } else {
      ast_log(LOG_WARNING, "WebSocket unknown opcode %u\n", *opcode);
      /* We received an opcode that we don't understand, the RFC states that 1003 is for a type of data that can't be accepted... opcodes
       * fit that, I think. */
      ast_websocket_close(session, 1003);
   }

   return 0;
}

/*! \brief Callback that is executed everytime an HTTP request is received by this module */
static int websocket_callback(struct ast_tcptls_session_instance *ser, const struct ast_http_uri *urih, const char *uri, enum ast_http_method method, struct ast_variable *get_vars, struct ast_variable *headers)
{
   struct ast_variable *v;
   char *upgrade = NULL, *key = NULL, *key1 = NULL, *key2 = NULL, *protos = NULL, *requested_protocols = NULL, *protocol = NULL;
   int version = 0, flags = 1;
   struct websocket_protocol *protocol_handler = NULL;
   struct ast_websocket *session;

   /* Upgrade requests are only permitted on GET methods */
   if (method != AST_HTTP_GET) {
      ast_http_error(ser, 501, "Not Implemented", "Attempt to use unimplemented / unsupported method");
      return -1;
   }

   /* Get the minimum headers required to satisfy our needs */
   for (v = headers; v; v = v->next) {
      if (!strcasecmp(v->name, "Upgrade")) {
         upgrade = ast_strip(ast_strdupa(v->value));
      } else if (!strcasecmp(v->name, "Sec-WebSocket-Key")) {
         key = ast_strip(ast_strdupa(v->value));
      } else if (!strcasecmp(v->name, "Sec-WebSocket-Key1")) {
         key1 = ast_strip(ast_strdupa(v->value));
      } else if (!strcasecmp(v->name, "Sec-WebSocket-Key2")) {
         key2 = ast_strip(ast_strdupa(v->value));
      } else if (!strcasecmp(v->name, "Sec-WebSocket-Protocol")) {
         requested_protocols = ast_strip(ast_strdupa(v->value));
         protos = ast_strdupa(requested_protocols);
      } else if (!strcasecmp(v->name, "Sec-WebSocket-Version")) {
         if (sscanf(v->value, "%30d", &version) != 1) {
            version = 0;
         }
      }
   }

   /* If this is not a websocket upgrade abort */
   if (!upgrade || strcasecmp(upgrade, "websocket")) {
      ast_log(LOG_WARNING, "WebSocket connection from '%s' could not be accepted - did not request WebSocket\n",
         ast_sockaddr_stringify(&ser->remote_address));
      ast_http_error(ser, 426, "Upgrade Required", NULL);
      return -1;
   } else if (ast_strlen_zero(requested_protocols)) {
      ast_log(LOG_WARNING, "WebSocket connection from '%s' could not be accepted - no protocols requested\n",
         ast_sockaddr_stringify(&ser->remote_address));
      fputs("HTTP/1.1 400 Bad Request\r\n"
            "Sec-WebSocket-Version: 7, 8, 13\r\n\r\n", ser->f);
      return -1;
   } else if (key1 && key2) {
      /* Specification defined in http://tools.ietf.org/html/draft-hixie-thewebsocketprotocol-76 and
       * http://tools.ietf.org/html/draft-ietf-hybi-thewebsocketprotocol-00 -- not currently supported*/
      ast_log(LOG_WARNING, "WebSocket connection from '%s' could not be accepted - unsupported version '00/76' chosen\n",
         ast_sockaddr_stringify(&ser->remote_address));
      fputs("HTTP/1.1 400 Bad Request\r\n"
            "Sec-WebSocket-Version: 7, 8, 13\r\n\r\n", ser->f);
      return 0;
   }

   /* Iterate through the requested protocols trying to find one that we have a handler for */
   while ((protocol = strsep(&requested_protocols, ","))) {
      if ((protocol_handler = ao2_find(protocols, ast_strip(protocol), OBJ_KEY))) {
         break;
      }
   }

   /* If no protocol handler exists bump this back to the requester */
   if (!protocol_handler) {
      ast_log(LOG_WARNING, "WebSocket connection from '%s' could not be accepted - no protocols out of '%s' supported\n",
         ast_sockaddr_stringify(&ser->remote_address), protos);
      fputs("HTTP/1.1 400 Bad Request\r\n"
            "Sec-WebSocket-Version: 7, 8, 13\r\n\r\n", ser->f);
      return 0;
   }

   /* Determine how to respond depending on the version */
   if (version == 7 || version == 8 || version == 13) {
      /* Version 7 defined in specification http://tools.ietf.org/html/draft-ietf-hybi-thewebsocketprotocol-07 */
      /* Version 8 defined in specification http://tools.ietf.org/html/draft-ietf-hybi-thewebsocketprotocol-10 */
      /* Version 13 defined in specification http://tools.ietf.org/html/rfc6455 */
      char *combined, base64[64];
      unsigned combined_length;
      uint8_t sha[20];

      combined_length = (key ? strlen(key) : 0) + strlen(WEBSOCKET_GUID) + 1;
      if (!key || combined_length > 8192) { /* no stack overflows please */
         fputs("HTTP/1.1 400 Bad Request\r\n"
               "Sec-WebSocket-Version: 7, 8, 13\r\n\r\n", ser->f);
         ao2_ref(protocol_handler, -1);
         return 0;
      }

      if (!(session = ao2_alloc(sizeof(*session), session_destroy_fn))) {
         ast_log(LOG_WARNING, "WebSocket connection from '%s' could not be accepted\n",
            ast_sockaddr_stringify(&ser->remote_address));
         fputs("HTTP/1.1 400 Bad Request\r\n"
               "Sec-WebSocket-Version: 7, 8, 13\r\n\r\n", ser->f);
         ao2_ref(protocol_handler, -1);
         return 0;
      }
      session->timeout = AST_DEFAULT_WEBSOCKET_WRITE_TIMEOUT;

      combined = ast_alloca(combined_length);
      snprintf(combined, combined_length, "%s%s", key, WEBSOCKET_GUID);
      ast_sha1_hash_uint(sha, combined);
      ast_base64encode(base64, (const unsigned char*)sha, 20, sizeof(base64));

      fprintf(ser->f, "HTTP/1.1 101 Switching Protocols\r\n"
         "Upgrade: %s\r\n"
         "Connection: Upgrade\r\n"
         "Sec-WebSocket-Accept: %s\r\n"
         "Sec-WebSocket-Protocol: %s\r\n\r\n",
         upgrade,
         base64,
         protocol);
      fflush(ser->f);
   } else {

      /* Specification defined in http://tools.ietf.org/html/draft-hixie-thewebsocketprotocol-75 or completely unknown */
      ast_log(LOG_WARNING, "WebSocket connection from '%s' could not be accepted - unsupported version '%d' chosen\n",
         ast_sockaddr_stringify(&ser->remote_address), version ? version : 75);
      fputs("HTTP/1.1 400 Bad Request\r\n"
            "Sec-WebSocket-Version: 7, 8, 13\r\n\r\n", ser->f);
      ao2_ref(protocol_handler, -1);
      return 0;
   }

   /* Enable keepalive on all sessions so the underlying user does not have to */
   if (setsockopt(ser->fd, SOL_SOCKET, SO_KEEPALIVE, &flags, sizeof(flags))) {
      ast_log(LOG_WARNING, "WebSocket connection from '%s' could not be accepted - failed to enable keepalive\n",
         ast_sockaddr_stringify(&ser->remote_address));
      fputs("HTTP/1.1 400 Bad Request\r\n"
            "Sec-WebSocket-Version: 7, 8, 13\r\n\r\n", ser->f);
      ao2_ref(session, -1);
      ao2_ref(protocol_handler, -1);
      return 0;
   }

   ast_verb(2, "WebSocket connection from '%s' for protocol '%s' accepted using version '%d'\n", ast_sockaddr_stringify(&ser->remote_address), protocol, version);

   /* Populate the session with all the needed details */
   session->f = ser->f;
   session->fd = ser->fd;
   ast_sockaddr_copy(&session->address, &ser->remote_address);
   session->opcode = -1;
   session->reconstruct = DEFAULT_RECONSTRUCTION_CEILING;
   session->secure = ser->ssl ? 1 : 0;

   /* Give up ownership of the socket and pass it to the protocol handler */
   protocol_handler->callback(session, get_vars, headers);
   ao2_ref(protocol_handler, -1);

   /*
    * By dropping the FILE* and fd from the session the connection
    * won't get closed when the HTTP server cleans up because we
    * passed the connection to the protocol handler.
    */
   ser->f = NULL;
   ser->fd = -1;

   return 0;
}

static struct ast_http_uri websocketuri = {
   .callback = websocket_callback,
   .description = "Asterisk HTTP WebSocket",
   .uri = "ws",
   .has_subtree = 0,
   .data = NULL,
   .key = __FILE__,
};

/*! \brief Simple echo implementation which echoes received text and binary frames */
static void websocket_echo_callback(struct ast_websocket *session, struct ast_variable *parameters, struct ast_variable *headers)
{
   int flags, res;

   ast_debug(1, "Entering WebSocket echo loop\n");

   if ((flags = fcntl(ast_websocket_fd(session), F_GETFL)) == -1) {
      goto end;
   }

   flags |= O_NONBLOCK;

   if (fcntl(ast_websocket_fd(session), F_SETFL, flags) == -1) {
      goto end;
   }

   while ((res = ast_wait_for_input(ast_websocket_fd(session), -1)) > 0) {
      char *payload;
      uint64_t payload_len;
      enum ast_websocket_opcode opcode;
      int fragmented;

      if (ast_websocket_read(session, &payload, &payload_len, &opcode, &fragmented)) {
         /* We err on the side of caution and terminate the session if any error occurs */
         ast_log(LOG_WARNING, "Read failure during WebSocket echo loop\n");
         break;
      }

      if (opcode == AST_WEBSOCKET_OPCODE_TEXT || opcode == AST_WEBSOCKET_OPCODE_BINARY) {
         ast_websocket_write(session, opcode, payload, payload_len);
      } else if (opcode == AST_WEBSOCKET_OPCODE_CLOSE) {
         break;
      } else {
         ast_debug(1, "Ignored WebSocket opcode %u\n", opcode);
      }
   }

end:
   ast_debug(1, "Exitting WebSocket echo loop\n");
   ast_websocket_unref(session);
}

static int load_module(void)
{
   protocols = ao2_container_alloc(MAX_PROTOCOL_BUCKETS, protocol_hash_fn, protocol_cmp_fn);
   ast_http_uri_link(&websocketuri);
   ast_websocket_add_protocol("echo", websocket_echo_callback);

   return 0;
}

static int unload_module(void)
{
   ast_websocket_remove_protocol("echo", websocket_echo_callback);
   ast_http_uri_unlink(&websocketuri);
   ao2_ref(protocols, -1);

   return 0;
}

AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS | AST_MODFLAG_LOAD_ORDER, "HTTP WebSocket Support",
      .load = load_module,
      .unload = unload_module,
      .load_pri = AST_MODPRI_CHANNEL_DEPEND,
   );