/* 定义在ssl.h头文件中 */ struct ssl_ctx_st {   SSL_METHOD *method; unsigned long options;      unsigned long mode;     STACK_OF(SSL_CIPHER) *cipher_list;  /* same as above but sorted for lookup */   STACK_OF(SSL_CIPHER) *cipher_list_by_id;        struct x509_store_st /* X509_STORE */ *cert_store;  struct lhash_st /* LHASH */ *sessions;  /* a set of SSL_SESSIONs */ /* Most session-ids that will be cached, default is  * SSL_SESSION_CACHE_MAX_SIZE_DEFAULT. 0 is unlimited. */   unsigned long session_cache_size;   struct ssl_session_st *session_cache_head;  struct ssl_session_st *session_cache_tail;      /* This can have one of 2 values, ored together,     * SSL_SESS_CACHE_CLIENT,    * SSL_SESS_CACHE_SERVER,    * Default is SSL_SESSION_CACHE_SERVER, which means only     * SSL_accept which cache SSL_SESSIONS. */      int session_cache_mode;         /* If timeout is not 0, it is the default timeout value set  * when SSL_new() is called.  This has been put in to make   * life easier to set things up */      long session_timeout;   /* If this callback is not null, it will be called each      * time a session id is added to the cache.  If this function        * returns 1, it means that the callback will do a   * SSL_SESSION_free() when it has finished using it.  Otherwise,     * on 0, it means the callback has finished with it.         * If remove_session_cb is not null, it will be called when  * a session-id is removed from the cache.  After the call,  * OpenSSL will SSL_SESSION_free() it. */ int (*new_session_cb)(struct ssl_st *ssl,SSL_SESSION *sess);        void (*remove_session_cb)(struct ssl_ctx_st *ctx,SSL_SESSION *sess);        SSL_SESSION *(*get_session_cb)(struct ssl_st *ssl,          unsigned char *data,int len,int *copy);     struct      {           int sess_connect;       /* SSL new conn - started */                int sess_connect_renegotiate;/* SSL reneg - requested */            int sess_connect_good;  /* SSL new conne/reneg - finished */                int sess_accept;        /* SSL new accept - started */              int sess_accept_renegotiate;/* SSL reneg - requested */             int sess_accept_good;   /* SSL accept/reneg - finished */           int sess_miss;          /* session lookup misses  */                int sess_timeout;       /* reuse attempt on timeouted session */            int sess_cache_full;    /* session removed due to full cache */             int sess_hit;           /* session reuse actually done */           int sess_cb_hit;        /* session-id that was not                                       * in the cache was                                  * passed back via the callback.  This                                       * indicates that the application is                                         * supplying session-id's from other                                         * processes - spooky :-) */    } stats;        int references;         void (*info_callback)();        /* if defined, these override the X509_verify_cert() calls */   int (*app_verify_callback)();       char *app_verify_arg; /* never used; should be void * */        /* default values to use in SSL structures */   struct cert_st /* CERT */ *cert;    int read_ahead;     int verify_mode;    int verify_depth;   unsigned int sid_ctx_length;        unsigned char sid_ctx[SSL_MAX_SID_CTX_LENGTH];      int (*default_verify_callback)(int ok,X509_STORE_CTX *ctx);     int purpose;            /* Purpose setting */       int trust;              /* Trust setting */     /* Default password callback. */        pem_password_cb *default_passwd_callback;       /* Default password callback user data. */      void *default_passwd_callback_userdata;         /* get client cert callback */  int (*client_cert_cb)(/* SSL *ssl, X509 **x509, EVP_PKEY **pkey */);    /* what we put in client cert requests */       STACK_OF(X509_NAME) *client_CA;         int quiet_shutdown;     CRYPTO_EX_DATA ex_data;         const EVP_MD *rsa_md5;  /* For SSLv2 - name is 'ssl2-md5' */        const EVP_MD *md5;              /* For SSLv3/TLSv1 'ssl3-md5' */    const EVP_MD *sha1;             /* For SSLv3/TLSv1 'ssl3->sha1' */   STACK_OF(X509) *extra_certs;STACK_OF(SSL_COMP) *comp_methods; /* stack of SSL_COMP, SSLv3/TLSv1 */ };