lws-ws-ext.h

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/*
 * libwebsockets - small server side websockets and web server implementation
 *
 * Copyright (C) 2010 - 2019 Andy Green <andy@warmcat.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */
 
/*! \defgroup extensions Extension related functions
 * ##Extension releated functions
 *
 *  Ws defines optional extensions, lws provides the ability to implement these
 *  in user code if so desired.
 *
 *  We provide one extensions permessage-deflate.
 */
///@{
 
/*
 * NOTE: These public enums are part of the abi.  If you want to add one,
 * add it at where specified so existing users are unaffected.
 */
enum lws_extension_callback_reasons {
        LWS_EXT_CB_CONSTRUCT                            =  4,
        LWS_EXT_CB_CLIENT_CONSTRUCT                     =  5,
        LWS_EXT_CB_DESTROY                              =  8,
        LWS_EXT_CB_PACKET_TX_PRESEND                    = 12,
        LWS_EXT_CB_PAYLOAD_TX                           = 21,
        LWS_EXT_CB_PAYLOAD_RX                           = 22,
        LWS_EXT_CB_OPTION_DEFAULT                       = 23,
        LWS_EXT_CB_OPTION_SET                           = 24,
        LWS_EXT_CB_OPTION_CONFIRM                       = 25,
        LWS_EXT_CB_NAMED_OPTION_SET                     = 26,
 
        /****** add new things just above ---^ ******/
};
 
/** enum lws_ext_options_types */
enum lws_ext_options_types {
        EXTARG_NONE, /**< does not take an argument */
        EXTARG_DEC,  /**< requires a decimal argument */
        EXTARG_OPT_DEC /**< may have an optional decimal argument */
 
        /* Add new things just above here ---^
         * This is part of the ABI, don't needlessly break compatibility */
};
 
/** struct lws_ext_options -    Option arguments to the extension.  These are
 *                              used in the negotiation at ws upgrade time.
 *                              The helper function lws_ext_parse_options()
 *                              uses these to generate callbacks */
struct lws_ext_options {
        const char *name; /**< Option name, eg, "server_no_context_takeover" */
        enum lws_ext_options_types type; /**< What kind of args the option can take */
 
        /* Add new things just above here ---^
         * This is part of the ABI, don't needlessly break compatibility */
};
 
/** struct lws_ext_option_arg */
struct lws_ext_option_arg {
        const char *option_name; /**< may be NULL, option_index used then */
        int option_index; /**< argument ordinal to use if option_name missing */
        const char *start; /**< value */
        int len; /**< length of value */
};
 
/**
 * typedef lws_extension_callback_function() - Hooks to allow extensions to operate
 * \param context:      Websockets context
 * \param ext:  This extension
 * \param wsi:  Opaque websocket instance pointer
 * \param reason:       The reason for the call
 * \param user: Pointer to ptr to per-session user data allocated by library
 * \param in:           Pointer used for some callback reasons
 * \param len:  Length set for some callback reasons
 *
 *      Each extension that is active on a particular connection receives
 *      callbacks during the connection lifetime to allow the extension to
 *      operate on websocket data and manage itself.
 *
 *      Libwebsockets takes care of allocating and freeing "user" memory for
 *      each active extension on each connection.  That is what is pointed to
 *      by the user parameter.
 *
 *      LWS_EXT_CB_CONSTRUCT:  called when the server has decided to
 *              select this extension from the list provided by the client,
 *              just before the server will send back the handshake accepting
 *              the connection with this extension active.  This gives the
 *              extension a chance to initialize its connection context found
 *              in user.
 *
 *      LWS_EXT_CB_CLIENT_CONSTRUCT: same as LWS_EXT_CB_CONSTRUCT
 *              but called when client is instantiating this extension.  Some
 *              extensions will work the same on client and server side and then
 *              you can just merge handlers for both CONSTRUCTS.
 *
 *      LWS_EXT_CB_DESTROY:  called when the connection the extension was
 *              being used on is about to be closed and deallocated.  It's the
 *              last chance for the extension to deallocate anything it has
 *              allocated in the user data (pointed to by user) before the
 *              user data is deleted.  This same callback is used whether you
 *              are in client or server instantiation context.
 *
 *      LWS_EXT_CB_PACKET_TX_PRESEND: this works the same way as
 *              LWS_EXT_CB_PACKET_RX_PREPARSE above, except it gives the
 *              extension a chance to change websocket data just before it will
 *              be sent out.  Using the same lws_token pointer scheme in in,
 *              the extension can change the buffer and the length to be
 *              transmitted how it likes.  Again if it wants to grow the
 *              buffer safely, it should copy the data into its own buffer and
 *              set the lws_tokens token pointer to it.
 *
 *      LWS_EXT_CB_ARGS_VALIDATE:
 */
typedef int
lws_extension_callback_function(struct lws_context *context,
                              const struct lws_extension *ext, struct lws *wsi,
                              enum lws_extension_callback_reasons reason,
                              void *user, void *in, size_t len);
 
/** struct lws_extension -      An extension we support */
struct lws_extension {
        const char *name; /**< Formal extension name, eg, "permessage-deflate" */
        lws_extension_callback_function *callback; /**< Service callback */
        const char *client_offer; /**< String containing exts and options client offers */
 
        /* Add new things just above here ---^
         * This is part of the ABI, don't needlessly break compatibility */
};
 
/**
 * lws_set_extension_option(): set extension option if possible
 *
 * \param wsi:  websocket connection
 * \param ext_name:     name of ext, like "permessage-deflate"
 * \param opt_name:     name of option, like "rx_buf_size"
 * \param opt_val:      value to set option to
 */
LWS_VISIBLE LWS_EXTERN int
lws_set_extension_option(struct lws *wsi, const char *ext_name,
                         const char *opt_name, const char *opt_val);
 
/**
 * lws_ext_parse_options() - deal with parsing negotiated extension options
 *
 * \param ext: related extension struct
 * \param wsi:  websocket connection
 * \param ext_user: per-connection extension private data
 * \param opts: list of supported options
 * \param o: option string to parse
 * \param len: length
 */
LWS_VISIBLE LWS_EXTERN int LWS_WARN_UNUSED_RESULT
lws_ext_parse_options(const struct lws_extension *ext, struct lws *wsi,
                      void *ext_user, const struct lws_ext_options *opts,
                      const char *o, int len);
 
/** lws_extension_callback_pm_deflate() - extension for RFC7692
 *
 * \param context:      lws context
 * \param ext:  related lws_extension struct
 * \param wsi:  websocket connection
 * \param reason:       incoming callback reason
 * \param user: per-connection extension private data
 * \param in:   pointer parameter
 * \param len:  length parameter
 *
 * Built-in callback implementing RFC7692 permessage-deflate
 */
LWS_EXTERN int
lws_extension_callback_pm_deflate(struct lws_context *context,
                                  const struct lws_extension *ext,
                                  struct lws *wsi,
                                  enum lws_extension_callback_reasons reason,
                                  void *user, void *in, size_t len);
 
/*
 * The internal exts are part of the public abi
 * If we add more extensions, publish the callback here  ------v
 */
///@}