# The Alert Class

    /*
    **	(c) COPYRIGHT MIT 1995.
    **	Please first read the full copyright statement in the file COPYRIGH.
    */

The Alert class defines a set of methods to be used by libwww to be used for passing prompts and message to a user. In order to maintain the Library core application independent and natural language independent, libwww does not know how to communicate with a user. Note here that a user is a somewhat abstract notion for something that can receive a message or prompt from the Library. This can for example be a person, but is may also be handled automatically by a robot or a client receiving a response from a HTTP server.

Libwww has a set of opcodes that classifies the nature of the message, for example that it is a question that must be confirmed in order to continue a request or simply a progress notification. The application can register a method for any number of the defined opcodes - in case the Library has a message for an opcode that does not have a method associated, the message is ignored. You can also globally disable any message send from the Library.

Note: The library core does not define any message or dialog methods - they are all considered part of the application. The library comes with a default set of methods which can be initiated using the function `HTAlertInit()` in HTInit module

This module is implemented by HTAlert.c, and it is a part of the W3C Sample Code Library.

    #ifndef HTALERT_H
    #define HTALERT_H

    #include "HTReq.h"

## Message Opcodes and Messages

The callback functions are defined as a generic callback where the caller can pass a set of input parameters and the callee can return a set of outptu parameters. Also note that all the `*_PROG_*` opcodes are a subset of `HT_A_PROGRESS`. This means that you easily can register a callback for all progress reports.

    typedef enum _HTAlertOpcode {
        HT_PROG_DNS		= 0x1,		/* Doing DNS resolution */
        HT_PROG_CONNECT	= 0x2,		/* Connecting Active */
        HT_PROG_ACCEPT	= 0x4,		/* Connecting Passive */
        HT_PROG_READ	= 0x8,		/* Read data */
        HT_PROG_WRITE	= 0x10,		/* Write data */
        HT_PROG_DONE	= 0x20,		/* Request finished */
        HT_PROG_INTERRUPT   = 0x40,         /* Request interrupted */
        HT_PROG_OTHER       = 0x80,         /* Other progress notes */
        HT_PROG_TIMEOUT     = 0x100,        /* Request timed out */
        HT_PROG_LOGIN	= 0x200,	/* Automatic login notifications */
        HT_A_PROGRESS	= 0xFFFF,	/* Get all progress reports - no reply */

        /* First word are reserved for progresss notifications */

        HT_A_MESSAGE	= 0x1<<16, /* Send a message - no reply */
        HT_A_CONFIRM	= 0x2<<16, /* Want YES or NO back */
        HT_A_PROMPT		= 0x4<<16, /* Want full dialog */
        HT_A_SECRET		= 0x8<<16, /* Secret dialog (e.g. password) */
        HT_A_USER_PW	= 0x10<<16 /* Atomic userid and password */
    } HTAlertOpcode;

    typedef struct _HTAlertPar HTAlertPar;

    typedef BOOL HTAlertCallback   (HTRequest * request, HTAlertOpcode op,
    				int msgnum, const char * dfault, void * input,
    				HTAlertPar * reply);

If you don't expect any return values then `reply` can be NULL. The return value of the callback function can be used to indicate confirmation on a prompt (Yes or No).

## User Prompts and Questions

This is an enumerated list of messages that can be converted into a string table etc. See the HTDialog module for default initialization of these strings.

    typedef enum _HTAlertMsg {
        HT_MSG_NULL = -1,
        HT_MSG_UID = 0,
        HT_MSG_PROXY_UID,
        HT_MSG_FTP_UID,
        HT_MSG_PW,
        HT_MSG_FILENAME,
        HT_MSG_ACCOUNT,
        HT_MSG_METHOD,
        HT_MSG_MOVED,
        HT_MSG_RULES,
        HT_MSG_FILE_REPLACE,
        HT_MSG_RETRY_AUTHENTICATION,
        HT_MSG_RETRY_PROXY_AUTH,
        HT_MSG_REDO,
        HT_MSG_BIG_PUT,
        HT_MSG_SOURCE_MOVED,
        HT_MSG_DESTINATION_MOVED,
        HT_MSG_REDIRECTION,
        HT_MSG_PROXY,
        HT_MSG_CACHE_LOCK,
        HT_MSG_ACCEPT_COOKIE,
        HT_MSG_ELEMENTS		            /* This MUST be the last element */
    } HTAlertMsg;

## Enable or Disable Messages

If you really don't want the library to prompt for anything at all then enable this constant. The default value is Interactive.

    extern void HTAlert_setInteractive	(BOOL interative);
    extern BOOL HTAlert_interactive		(void);

## Creation and Deletion Methods

Message methods are registered in lists. By default a list is not enabled before you assign it as being active. This allows the application to maintain multiple lists of message handlers which can be swapped in and out as neeeded.

### Add a Callback Function

Register a call back function that is to be called when generating messages, dialog, prompts, progress reports etc. The opcode signifies which call back function to call depending of the type of the message. Opcode can be any combination of the bitflags defined by `HTAlertOpcode`. If you register one callback for `HT_A_PROGRESS` then this will get called on all progress notifications.

    extern BOOL HTAlertCall_add (HTList * list, HTAlertCallback * cbf,
    			     HTAlertOpcode opcode);

### Delete a Callback function

Unregister a call back function from a list

    extern BOOL HTAlertCall_delete (HTList * list, HTAlertCallback * cbf);

### Delete all Callbacks With this Opcode

Unregister all handlers registered for a given opcode.

    extern BOOL HTAlertCall_deleteOpcode (HTList * list, HTAlertOpcode opcode);

### Delete a list of Callback Functions

Unregisters all call back functions

    extern BOOL HTAlertCall_deleteAll (HTList * list);

### Find a Callback Function

Finds a callback function corresponding to the opcode. If none has been registered then NULL is returned.

    extern HTAlertCallback * HTAlertCall_find(HTList * list, HTAlertOpcode opcode);

## The Reply Object

The reply object is used for communicating input from the user back to the Library. This is only required to use when for example the user is prompted for a file name etc. You can find several examples on how to use this in the default message and dialog module provided together with the Library.

    extern HTAlertPar * HTAlert_newReply	(void);
    extern void HTAlert_deleteReply		(HTAlertPar * old);

### Handle the Reply Message

These methods provide the API for handling the reply message. There are two ways of assigning a message to the reply message - either by copying the buffer or by reusing the same buffer. In the latter case, the caller must make sure not to free the reply message before it has been used.

    extern BOOL HTAlert_setReplyMessage	(HTAlertPar * me, const char *message);
    extern BOOL HTAlert_assignReplyMessage	(HTAlertPar * me, char * message);

You can get the data back again by using this method:

    extern char * HTAlert_replyMessage	(HTAlertPar * me);

    extern char * HTAlert_replySecret	(HTAlertPar * me);
    extern BOOL HTAlert_setReplySecret	(HTAlertPar * me, const char * secret);

    extern void * HTAlert_replyOutput	(HTAlertPar * me);
    extern BOOL HTAlert_setReplyOutput	(HTAlertPar * me, void * output);

## Active set of Callback Functions

A list can be assigned as being active in which case it is visible for libwww by assigning the list as the global alert list. Libwww does not know about inactive lists of alert handlers.

    extern void HTAlert_setGlobal	(HTList * list);
    extern HTList * HTAlert_global	(void);

### Global Alert List Methods

You can assign a callback directly to the global list in which case it becomes immediately available to libwww. In this case you do not need to worry about creating the list - it will be created as well as deleted automatically.

#### Add an Alert Handler

    extern BOOL HTAlert_add	(HTAlertCallback * cbf, HTAlertOpcode opcode);

#### Delete an Alert Handler

You can either delete a handler by referring to its address or to the opcode that it has been registered for.

    extern BOOL HTAlert_delete (HTAlertCallback * cbf);
    extern BOOL HTAlert_deleteOpcode (HTAlertOpcode opcode);

#### Delete all Alert Handlers

    extern BOOL HTAlert_deleteAll (void);

#### Find an Alert Handler

    extern HTAlertCallback * HTAlert_find (HTAlertOpcode opcode);

    #endif