#ifndef CONNECT___HTTP_CONNECTOR__H
#define CONNECT___HTTP_CONNECTOR__H

/* $Id: ncbi_http_connector.h 598971 2019-12-17 18:49:26Z lavr $
 * ===========================================================================
 *
 *                            PUBLIC DOMAIN NOTICE
 *               National Center for Biotechnology Information
 *
 *  This software/database is a "United States Government Work" under the
 *  terms of the United States Copyright Act.  It was written as part of
 *  the author's official duties as a United States Government employee and
 *  thus cannot be copyrighted.  This software/database is freely available
 *  to the public for use. The National Library of Medicine and the U.S.
 *  Government have not placed any restriction on its use or reproduction.
 *
 *  Although all reasonable efforts have been taken to ensure the accuracy
 *  and reliability of the software and data, the NLM and the U.S.
 *  Government do not and cannot warrant the performance or results that
 *  may be obtained by using this software or data. The NLM and the U.S.
 *  Government disclaim all warranties, express or implied, including
 *  warranties of performance, merchantability or fitness for any particular
 *  purpose.
 *
 *  Please cite the author in any work or product based on this material.
 *
 * ===========================================================================
 *
 * Author:  Denis Vakatov
 *
 * File Description:
 *   Implement CONNECTOR for the HTTP-based network connection
 *
 *   See in "ncbi_connector.h" for the detailed specification of the underlying
 *   connector ("CONNECTOR", "SConnectorTag") methods and structures.
 *
 */

#include <connect/ncbi_connutil.h>

#ifndef NCBI_DEPRECATED
#  define NCBI_HTTP_CONNECTOR_DEPRECATED
#else
#  define NCBI_HTTP_CONNECTOR_DEPRECATED NCBI_DEPRECATED
#endif


/** @addtogroup Connectors
 *
 * @{
 */


#ifdef __cplusplus
extern "C" {
#endif


/** HTTP connector flags.
 *
 * @var fHTTP_Flushable
 *
 *    HTTP/1.0 or when fHTTP_WriteThru is not set:
 *       by default all data written to the connection are kept until read
 *       begins (even though CONN_Flush() might have been called in between the
 *       writes);  with this flag set, CONN_Flush() will result the data to be
 *       actually sent to the server side, so the following write will form a
 *       new request, and not get added to the previous one;  also this flag
 *       assures that the connector sends at least an HTTP header on "CLOSE"
 *       and re-"CONNECT", even if no data for HTTP body have been written.
 *
 *    HTTP/1.1 and when fHTTP_WriteThru is set:
 *       CONN_Flush() attempts to send all pending data down to server.
 *
 * @var fHTTP_KeepHeader
 *       Do not strip HTTP header (i.e. everything up to the first "\r\n\r\n",
 *       including the "\r\n\r\n") from the incomning HTTP response (including
 *       any server error, which then is made available for reading as well).
 *       *NOTE* this flag disables automatic authorization and redirection.
 *
 * @var fHCC_UrlDecodeInput
 *       Assume the response body as single-part, URL-encoded;  perform the
 *       URL-decoding on read, and deliver decoded data to the user.  Obsolete!
 *
 * @var fHTTP_PushAuth
 *       Present credentials to the server if they are set in the connection
 *       parameters when sending 1st request.  Normally, the credentials are
 *       only presented on a retry when the server rejects the initial request
 *       with 401 / 407.  This saves a hit, but is only honored with HTTP/1.1.
 *
 * @var fHTTP_WriteThru
 *       Valid only with HTTP/1.1:  Connection to the server is made upon a
 *       first CONN_Write(), or CONN_Flush() if fHTTP_Flushable is set, or
 *       CONN_Wait(eIO_Write), and each CONN_Write() forms a chunk of HTTP
 *       data to be sent to the server.  Reading / waiting for read from the
 *       connector finalizes the body and, if reading, fetches the response.
 *
 * @var fHTTP_NoUpread
 *       Do *not* do internal reading into temporary buffer while sending data
 *       to HTTP server;  by default any send operation tries to fetch data as
 *       they are coming back from the server in order to prevent stalling due
 *       to data clogging the connection.
 *
 * @var fHTTP_DropUnread
 *       Do not collect incoming data in "Read" mode before switching into
 *       "Write" mode for preparing next request;  by default all data sent by
 *       the server get stored even if not all of it have been requested prior
 *       to a "Write" that followed data reading (stream emulation).
 *
 * @var fHTTP_NoAutoRetry
 *       Do not attempt any auto-retries in case of failing connections
 *       (this flag effectively overrides SConnNetInfo::max_try with 1).
 *
 * @var fHTTP_UnsafeRedirects
 *       For security reasons the following redirects comprise security risk,
 *       and thus, are prohibited:  switching from https to http, and/or
 *       re-POSTing data (regardless of the transport, either http or https);
 *       this flag allows such redirects (when encountered) to be honored.
 *
 * @note
 *  URL encoding/decoding (in the "fHCC_Url*" cases and "net_info->args")
 *  is performed by URL_Encode() and URL_Decode() -- see "ncbi_connutil.[ch]".
 *
 * @sa
 *  SConnNetInfo, ConnNetInfo_OverrideUserHeader, URL_Encode, URL_Decode
 */
enum EHTTP_Flag {
    fHTTP_AutoReconnect   = 0x1,  /**< See HTTP_CreateConnectorEx()          */
    fHTTP_Flushable       = 0x2,  /**< Connector will really flush on Flush()*/
    fHTTP_KeepHeader      = 0x4,  /**< Keep HTTP header (see limitations)    */
  /*fHCC_UrlEncodeArgs    = 0x8,       URL-encode "info->args" (w/o fragment)*/
  /*fHCC_UrlDecodeInput   = 0x10,      URL-decode response body              */
  /*fHCC_UrlEncodeOutput  = 0x20,      URL-encode all output data            */
  /*fHCC_UrlCodec         = 0x30,      fHTTP_UrlDecodeInput | ...EncodeOutput*/
    fHTTP_PushAuth        = 0x10, /**< HTTP/1.1 pushes out auth if present   */
    fHTTP_WriteThru       = 0x20, /**< HTTP/1.1 writes through (chunked)     */
    fHTTP_NoUpread        = 0x40, /**< Do not use SOCK_SetReadOnWrite()      */
    fHTTP_DropUnread      = 0x80, /**< Each microsession drops unread data   */
    fHTTP_NoAutoRetry     = 0x100,/**< No auto-retries allowed               */
    fHTTP_NoAutomagicSID  = 0x200,/**< Do not add NCBI SID automagically     */
    fHTTP_UnsafeRedirects = 0x400,/**< Any redirect will be honored          */
    fHTTP_AdjustOnRedirect= 0x800,/**< Call adjust routine for redirects, too*/
    fHTTP_SuppressMessages= 0x1000/**< Most annoying ones reduced to traces  */
};
typedef unsigned int THTTP_Flags; /**< Bitwise OR of EHTTP_Flag              */
NCBI_HTTP_CONNECTOR_DEPRECATED
/** DEPRECATED, do not use! */
typedef enum {
  /*fHCC_AutoReconnect    = fHTTP_AutoReconnect,                             */
  /*fHCC_Flushable        = fHTTP_Flushable,                                 */
  /*fHCC_SureFlush        = fHTTP_Flushable,                                 */
  /*fHCC_KeepHeader       = fHTTP_KeepHeader,                                */
    fHCC_UrlEncodeArgs    = 0x8,  /**< NB: Error-prone semantics, do not use!*/
    fHCC_UrlDecodeInput   = 0x10, /**< Obsolete, may not work, do not use!   */
    fHCC_UrlEncodeOutput  = 0x20, /**< Obsolete, may not work, do not use!   */
    fHCC_UrlCodec         = 0x30  /**< fHCC_UrlDecodeInput | ...EncodeOutput */
  /*fHCC_NoUpread         = fHTTP_NoUpread,                                  */
  /*fHCC_DropUnread       = fHTTP_DropUnread,                                */
  /*fHCC_NoAutoRetry      = fHTTP_NoAutoRetry                                */
} EHCC_Flag;
NCBI_HTTP_CONNECTOR_DEPRECATED
typedef unsigned int THCC_Flags;  /**< bitwise OR of EHCC_Flag, deprecated   */


/** Same as HTTP_CreateConnector(net_info, flags, 0, 0, 0, 0)
 * with the passed "user_header" overriding the value provided in
 * "net_info->http_user_header".
 * @sa
 *  HTTP_CreateConnectorEx, ConnNetInfo_OverrideUserHeader
 */
extern NCBI_XCONNECT_EXPORT CONNECTOR HTTP_CreateConnector
(const SConnNetInfo* net_info,
 const char*         user_header,
 THTTP_Flags         flags
 );


/** The extended version HTTP_CreateConnectorEx() is able to track the HTTP
 * response chain and also change the URL of the server "on-the-fly":
 * - FHTTP_ParseHeader() gets called every time a new HTTP response header is
 *   received from the server, and only if fHTTP_KeepHeader is NOT set.
 *   Return code from the parser adjusts the existing server error condition
 *   (if any) as the following:
 *
 *   + eHTTP_HeaderError:    unconditionally flag a server error;
 *   + eHTTP_HeaderSuccess:  header parse successful, retain existing condition
 *                           (note that in case of an already existing server
 *                           error condition the response body can be logged
 *                           but will not be made available for the user code
 *                           to read, and eIO_Unknown will result on read);
 *   + eHTTP_HeaderContinue: if there was already a server error condition,
 *                           the response body will be made available for the
 *                           user code to read (but only if HTTP connector
 *                           cannot post-process the request such as for
 *                           redirects, authorization etc);  otherwise, this
 *                           code has the same effect as eHTTP_HeaderSuccess;
 *   + eHTTP_HeaderComplete: flag this request as processed completely, and do
 *                           not do any post-processing (such as redirects,
 *                           authorization etc), yet make the response body (if
 *                           any, and regardless of whether there was a server
 *                           error or not) available for reading.
 *
 * - FHTTP_Adjust() gets invoked every time before starting a new "HTTP
 *   micro-session" to make a hit when a previous hit has failed;  it is passed
 *   "net_info" as stored within the connector, and the number of previously
 *   unsuccessful consecutive attempts (in the least significant word) since
 *   the connector was opened;  it is passed 0 in that parameter if calling for
 *   a redirect (when fHTTP_AdjustOnRedirect was set).  A zero (false) return
 *   value ends the retries;  a non-zero continues with the request:  an
 *   advisory value of greater than 0 means an adjustment was made, and a
 *   negative value indicates no changes.
 *   This very same callback is also invoked when a new request is about to be
 *   made for solicitaiton of new URL for the hit -- in this case return 1 if
 *   the SConnNetInfo was updated with a new parameters;  or -1 of no changes
 *   were made;  or 0 to stop the request with an error.
 *
 * - FHTTP_Cleanup() gets called when the connector is about to be destroyed;
 *   "user_data" is guaranteed not to be referenced anymore (so this is a good
 *   place to clean up "user_data" if necessary).
 *
 * @sa
 *   SConnNetInfo::max_try
 */
typedef enum {
    eHTTP_HeaderError    = 0,  /**< Parse failed, treat as a server error */
    eHTTP_HeaderSuccess  = 1,  /**< Parse succeeded, retain server status */
    eHTTP_HeaderContinue = 2,  /**< Parse succeeded, continue with body   */
    eHTTP_HeaderComplete = 3   /**< Parse succeeded, no more processing   */
} EHTTP_HeaderParse;
typedef EHTTP_HeaderParse (*FHTTP_ParseHeader)
(const char*         http_header,   /**< HTTP header to parse                */
 void*               user_data,     /**< supplemental user data              */
 int                 server_error   /**< != 0 if HTTP error (NOT 2xx code)   */
 );


/* Called with failure_count == 0 for redirects; and with failure_count == -1
 * for a new URL before starting new successive request(s).  Return value 0
 * means an error, and stops processing;  return value 1 means changes were
 * made, and request should proceed;  and return value -1 means no changes.
 */
typedef int/*bool*/ (*FHTTP_Adjust)
(SConnNetInfo*       net_info,      /**< net_info to adjust (in place)       */
 void*               user_data,     /**< supplemental user data              */
 unsigned int        failure_count  /**< low word: # of failures since open  */
 );

typedef void        (*FHTTP_Cleanup)
(void*               user_data      /**< supplemental user data              */
 );


/** Create new CONNECTOR structure to hit the specified URL using HTTP with
 * either POST / GET (or ANY) method.  Use the configuration values stored in
 * "net_info".  If "net_info" is NULL, then use the default info as created by
 * ConnNetInfo_Create(0).
 *
 * If "net_info" does not explicitly specify an HTTP request method (i.e. it
 * has it as "eReqMethod_Any"), then the actual method sent to the HTTP server
 * depends on whether any data has been written to the connection with
 * CONN_Write():  the presence of pending data will cause a POST request (with
 * a "Content-Length:" tag supplied automatically and reflecting the total
 * pending data size), and GET request method will result in the absence of any
 * data.  An explicit value for the request method will cause the specified
 * request to be used regardless of pending data, and will flag an error if any
 * data will have to be sent with a GET (per the standard).
 *
 * When not using HTTP/1.1's fHTTP_WriteThru mode, in order to work around
 * some HTTP communication features, this code does:
 *
 *  1. Accumulate all output data in an internal memory buffer until the
 *     first CONN_Read() (including peek) or CONN_Wait(on read) is attempted
 *     (also see fHTTP_Flushable flag below).
 *  2. On the first CONN_Read() or CONN_Wait(on read), compose and send the
 *     whole HTTP request as:
 *        @verbatim
 *        METHOD <net_info->path>?<net_info->args> HTTP/1.0\r\n
 *        <user_header\r\n>
 *        Content-Length: <accumulated_data_length>\r\n
 *        \r\n
 *        <accumulated_data>
 *        @endverbatim
 *     @note
 *       If <user_header> is neither a NULL pointer nor an empty string, then:
 *       - it must NOT contain any "empty lines":  "\r\n\r\n";
 *       - multiple tags must be separated by "\r\n" (*not* just "\n");
 *       - it should be terminated by a single "\r\n" (will be added, if not);
 *       - it gets inserted to the HTTP header "as is", without any automatic
 *         checking and / or encoding (except for the trailing "\r\n");
 *       - the "user_header" specified in the arguments overrides any user
 *         header that can be provided via the "net_info" argument, see
 *         ConnNetInfo_OverrideUserHeader() from <connect/ncbi_connutil.h>.
 *     @note
 *       Data may depart to the server side earlier if CONN_Flush()'ed in a
 *       fHTTP_Flushable connector, see "flags".
 *  3. After the request has been sent, then the response data from the peer
 *     (usually, a CGI program) can be actually read out.
 *  4. On a CONN_Write() operation, which follows data reading, the connection
 *     to the peer is read out until EOF (the data stored internally) then
 *     forcedly closed (the peer CGI process will presumably die if it has not
 *     done so yet on its own), and data to be written again get stored in the
 *     buffer until next "Read" etc, see item 1).  The subsequent read will
 *     first see the leftovers (if any) of data stored previously, then the
 *     new data generated in response to the latest request.  The behavior can
 *     be changed by the fHTTP_DropUnread flag.
 *
 *  When fHTTP_WriteThru is set with HTTP/1.1, writing to the connector begins
 *  upon any write operations, and reading from the connector causes the
 *  request body to finalize and response to be fetched from the server.
 *  Request method must be explicitly specified with fHTTP_WriteThru, "ANY"
 *  does not get accepted (the eIO_NotSupported error returned).
 *
 *  @note
 *     If "fHTTP_AutoReconnect" is set in "flags", then the connector makes an
 *     automatic reconnect to the same URL with just the same parameters for
 *     each micro-session steps (1,2,3) repeated.
 *  @note
 *     If "fHTTP_AutoReconnect" is not set then only a single
 *     "Write ... Write Read ... Read" micro-session is allowed, and any
 *     following write attempt fails with "eIO_Closed".
 *
 * @sa
 *  EHTTP_Flag
 */
extern NCBI_XCONNECT_EXPORT CONNECTOR HTTP_CreateConnectorEx
(const SConnNetInfo* net_info,
 THTTP_Flags         flags,
 FHTTP_ParseHeader   parse_header,  /**< may be NULL, then no addtl. parsing */
 void*               user_data,     /**< user data for HTTP CBs (callbacks)  */
 FHTTP_Adjust        adjust,        /**< may be NULL                         */
 FHTTP_Cleanup       cleanup        /**< may be NULL                         */
 );


/** Create a tunnel to "net_info->host:net_info->port" via an HTTP proxy server
 * located at "net_info->http_proxy_host:net_info->http_proxy_port".  Return
 * the tunnel as a socket via the last parameter.  For compatibility with
 * future API extensions, please make sure *sock is NULL when making the call.
 * The proxy gets contacted via HTTPS if "net_info->scheme == eURL_Https", and
 * the resultant socket is returned secure (with the SSL session still active).
 * @note
 *  "net_info" can be passed as NULL to be constructed from the environment.
 * @note
 *  "sock" parameter must be non-NULL but must point to a NULL SOCK (checked!).
 * @note
 *  Some HTTP proxies do not process "data" correctly (e.g. Squid 3) when sent
 *  along with the tunnel creation request (despite the standard specifically
 *  allows such use), so they may require separate SOCK I/O calls to write the
 *  data to the tunnel.
 * @return
 *  eIO_Success if the tunnel has been successfully created;
 *  otherwise, return an error code and set "*sock" to NULL upon return.
 * @sa
 *  THTTP_Flags, SOCK_CreateEx, SOCK_Close
 */
extern NCBI_XCONNECT_EXPORT EIO_Status HTTP_CreateTunnelEx
(const SConnNetInfo* net_info,
 THTTP_Flags         flags,
 const void*         init_data,  /**< initial data block to send via tunnel  */
 size_t              init_size,  /**< size of the initial data block         */
 void*               user_data,  /**< user data for the adjust callback      */
 FHTTP_Adjust        adjust,     /**< adjust callback, may be NULL           */
 SOCK*               sock        /**< return socket; must be non-NULL        */
 );


/** Same as HTTP_CreateTunnelEx(net_info, flags, 0, 0, 0, 0, sock) */
extern NCBI_XCONNECT_EXPORT EIO_Status HTTP_CreateTunnel
(const SConnNetInfo* net_info,
 THTTP_Flags         flags,
 SOCK*               sock
 );


typedef void (*FHTTP_NcbiMessageHook)(const char* message);

/** Set a message hook procedure for messages originating from NCBI via HTTP.
 *  Any hook will be called no more than once.  Until no hook is installed,
 *  and exactly one message is caught, a critical error will be generated in
 *  the standard log file upon acceptance of every message.  *Not MT-safe*.
 */
extern NCBI_XCONNECT_EXPORT void HTTP_SetNcbiMessageHook
(FHTTP_NcbiMessageHook  /**< New hook to be installed, NULL to reset */
 );


#ifdef __cplusplus
}  /* extern "C" */
#endif


/* @} */

#endif /* CONNECT___HTTP_CONNECTOR__H */
