text: // Copyright 2017-2018 Espressif Systems (Shanghai) PTE LTD
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  #ifndef _TLS_H_
  #define _TLS_H_
  
  #if defined(CONFIG_USING_TLS)
  #include <stdbool.h>
  #include <unistd.h>
  #include <sys/socket.h>
  #include "mbedtls/platform.h"
  #include "mbedtls/net_sockets.h"
  #include "mbedtls/ssl.h"
  #include "mbedtls/certs.h"
  #include "mbedtls/x509_crt.h"
  #include "tperrors.h"
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  /**
   *  @brief TLS Connection State
   */
  typedef enum tls_conn_state {
      TLS_INIT = 0,
      TLS_CONNECTING,
      TLS_HANDSHAKE,
      TLS_FAIL,
      TLS_DONE,
  } tls_conn_state_t;
  
  /**
   * @brief      TLS configuration parameters 
   */ 
  typedef struct tls_cfg {
      const char **alpn_protos;               /*!< Application protocols required for HTTP2.
                                                   If HTTP2/ALPN support is required, a list
                                                   of protocols that should be negotiated.
                                                   The format is length followed by protocol
                                                   name.
                                                   For the most common cases the following is ok:
                                                   "\x02h2"
                                                   - where the first '2' is the length of the protocol and
                                                   - the subsequent 'h2' is the protocol name */
   
      const unsigned char *cacert_pem_buf;    /*!< Certificate Authority's certificate in a buffer */
   
      unsigned int cacert_pem_bytes;          /*!< Size of Certificate Authority certificate
                                                   pointed to by cacert_pem_buf */
  
      const unsigned char *clientcert_pem_buf;/*!< Client certificate in a buffer */
   
      unsigned int clientcert_pem_bytes;      /*!< Size of client certificate pointed to by
                                                   clientcert_pem_buf */
  
      const unsigned char *clientkey_pem_buf; /*!< Client key in a buffer */
  
      unsigned int clientkey_pem_bytes;       /*!< Size of client key pointed to by
                                                   clientkey_pem_buf */
  
      const unsigned char *clientkey_password;/*!< Client key decryption password string */
  
      unsigned int clientkey_password_len;    /*!< String length of the password pointed to by
                                                   clientkey_password */
  
      bool non_block;                         /*!< Configure non-blocking mode. If set to true the 
                                                   underneath socket will be configured in non 
                                                   blocking mode after tls session is established */
  
      int timeout_ms;                         /*!< Network timeout in milliseconds */
  
      bool use_global_ca_store;               /*!< Use a global ca_store for all the connections in which
                                                   this bool is set. */
  } tls_cfg_t;
  
  /**
   * @brief      TLS Connection Handle 
   */
  typedef struct tls {
      mbedtls_ssl_context ssl;                                                    /*!< TLS/SSL context */
   
      // mbedtls_entropy_context entropy;                                            /*!< mbedTLS entropy context structure */
   
      // mbedtls_ctr_drbg_context ctr_drbg;                                          /*!< mbedTLS ctr drbg context structure.
      //                                                                                  CTR_DRBG is deterministic random
      //                                                                                  bit generation based on AES-256 */
   
      mbedtls_ssl_config conf;                                                    /*!< TLS/SSL configuration to be shared 
                                                                                       between mbedtls_ssl_context 
                                                                                       structures */
   
      mbedtls_net_context server_fd;                                              /*!< mbedTLS wrapper type for sockets */
   
      mbedtls_x509_crt cacert;                                                    /*!< Container for the X.509 CA certificate */
  
      mbedtls_x509_crt *cacert_ptr;                                               /*!< Pointer to the cacert being used. */
  
      mbedtls_x509_crt clientcert;                                                /*!< Container for the X.509 client certificate */
  
      mbedtls_pk_context clientkey;                                               /*!< Container for the private key of the client
                                                                                       certificate */
  
      int sockfd;                                                                 /*!< Underlying socket file descriptor. */
   
      ssize_t (*read)(struct tls  *tls, char *data, size_t datalen, uint32_t timeout_ms);          /*!< Callback function for reading data from TLS/SSL
                                                                                       connection. */
   
      ssize_t (*write)(struct tls *tls, const char *data, size_t datalen);    /*!< Callback function for writing data to TLS/SSL
                                                                                       connection. */
  
      tls_conn_state_t  conn_state;                                           /*!< TLS Connection state */
  
      fd_set rset;                                                                /*!< read file descriptors */
  
      fd_set wset;                                                                /*!< write file descriptors */
  
      bool is_tls;                                                                /*!< indicates connection type (TLS or NON-TLS) */
  } tls_t;
  
  /**
   * @brief      Create a new blocking TLS/SSL connection
   *
   * This function establishes a TLS/SSL connection with the specified host in blocking manner.
   * 
   * @param[in]  hostname  Hostname of the host.
   * @param[in]  hostlen   Length of hostname.
   * @param[in]  port      Port number of the host.
   * @param[in]  cfg       TLS configuration as tls_cfg_t. If you wish to open
   *                       non-TLS connection, keep this NULL. For TLS connection,
   *                       a pass pointer to tls_cfg_t. At a minimum, this
   *                       structure should be zero-initialized.
   * @return pointer to tls_t, or NULL if connection couldn't be opened.
   */
  tls_t *tls_conn_new(const char *hostname, int hostlen, int port, const tls_cfg_t *cfg);
  
  
  /**
   * @brief      Create a new non-blocking TLS/SSL connection
   *
   * This function initiates a non-blocking TLS/SSL connection with the specified host, but due to
   * its non-blocking nature, it doesn't wait for the connection to get established.
   *
   * @param[in]  hostname  Hostname of the host.
   * @param[in]  hostlen   Length of hostname.
   * @param[in]  port      Port number of the host.
   * @param[in]  cfg       TLS configuration as tls_cfg_t. `non_block` member of
   *                       this structure should be set to be true.
   * @param[in]  tls       pointer to tls as tls handle.
   *
   * @return
   *             - -1      If connection establishment fails.
   *             -  0      If connection establishment is in progress.
   *             -  1      If connection establishment is successful.
   */
  int tls_conn_new_async(const char *hostname, int hostlen, int port, const tls_cfg_t *cfg, tls_t *tls);
  
  
  
  /**
   * @brief      Write from buffer 'data' into specified tls connection.
   * 
   * @param[in]  tls      pointer to tls as tls handle.
   * @param[in]  data     Buffer from which data will be written.
   * @param[in]  datalen  Length of data buffer.
   * 
   * @return 
   *             - >0  if write operation was successful, the return value is the number 
   *                   of bytes actually written to the TLS/SSL connection.  
   *             -  0  if write operation was not successful. The underlying
   *                   connection was closed.
   *             - <0  if write operation was not successful, because either an 
   *                   error occured or an action must be taken by the calling process.   
   */
  static inline ssize_t tls_conn_write(tls_t *tls, const void *data, size_t datalen)
  {
      return tls->write(tls, (char *)data, datalen);
  }
  
  /**
   * @brief      Read from specified tls connection into the buffer 'data'.
   * 
   * @param[in]  tls      pointer to tls as tls handle.
   * @param[in]  data     Buffer to hold read data.
   * @param[in]  datalen  Length of data buffer. 
   *
   * @return
   *             - >0  if read operation was successful, the return value is the number
   *                   of bytes actually read from the TLS/SSL connection.
   *             -  0  if read operation was not successful. The underlying
   *                   connection was closed.
   *             - <0  if read operation was not successful, because either an
   *                   error occured or an action must be taken by the calling process.
   */
  static inline ssize_t tls_conn_read(tls_t *tls, void  *data, size_t datalen, uint32_t timeout_ms)
  {
      return tls->read(tls, (char *)data, datalen, timeout_ms);
  }
  
  /**
   * @brief      Close the TLS/SSL connection and free any allocated resources.
   * 
   * This function should be called to close each tls connection opened with tls_conn_new() or
   * tls_conn_http_new() APIs.
   *
   * @param[in]  tls  pointer to tls as tls handle.
   */
  void tls_conn_delete(tls_t *tls);
  
  /**
   * @brief      Return the number of application data bytes remaining to be
   *             read from the current record
   *
   * This API is a wrapper over mbedtls's mbedtls_ssl_get_bytes_avail() API.
   *
   * @param[in]  tls  pointer to tls as tls handle.
   *
   * @return
   *            - -1  in case of invalid arg
   *            - bytes available in the application data
   *              record read buffer
   */
  size_t tls_get_bytes_avail(tls_t *tls);
  
  /**
   * @brief      Create a global CA store, initially empty.
   *
   * This function should be called if the application wants to use the same CA store for multiple connections.
   * This function initialises the global CA store which can be then set by calling tls_set_global_ca_store().
   * To be effective, this function must be called before any call to tls_set_global_ca_store().
   *
   * @return
   *             - WEB_OK             if creating global CA store was successful.
   *             - WEB_ERR_NO_MEM     if an error occured when allocating the mbedTLS resources.
   */
  web_err_t tls_init_global_ca_store();
  
  /**
   * @brief      Set the global CA store with the buffer provided in pem format.
   *
   * This function should be called if the application wants to set the global CA store for
   * multiple connections i.e. to add the certificates in the provided buffer to the certificate chain.
   * This function implicitly calls tls_init_global_ca_store() if it has not already been called.
   * The application must call this function before calling tls_conn_new().
   *
   * @param[in]  cacert_pem_buf    Buffer which has certificates in pem format. This buffer
   *                               is used for creating a global CA store, which can be used
   *                               by other tls connections.
   * @param[in]  cacert_pem_bytes  Length of the buffer.
   *
   * @return
   *             - WEB_OK  if adding certificates was successful.
   *             - Other   if an error occured or an action must be taken by the calling process.
   */
  web_err_t tls_set_global_ca_store(const unsigned char *cacert_pem_buf, const unsigned int cacert_pem_bytes);
  
  /**
   * @brief      Get the pointer to the global CA store currently being used.
   *
   * The application must first call tls_set_global_ca_store(). Then the same
   * CA store could be used by the application for APIs other than tls.
   *
   * @note       Modifying the pointer might cause a failure in verifying the certificates.
   *
   * @return
   *             - Pointer to the global CA store currently being used    if successful.
   *             - NULL                                                   if there is no global CA store set.
   */
  mbedtls_x509_crt *tls_get_global_ca_store();
  
  /**
   * @brief      Free the global CA store currently being used.
   *
   * The memory being used by the global CA store to store all the parsed certificates is
   * freed up. The application can call this API if it no longer needs the global CA store.
   */
  void tls_free_global_ca_store();
  
  
  #ifdef __cplusplus
  }
  #endif
  
  #endif
  
  #endif /* ! _TLS_H_ */
  