# The Error Class

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

The Error class provides an easy API for registering errors ocurring while libwww serves a request. All errors are registered in an "error stack" in the Request object which allows for nested errors. The Error class is both natural language independent and application independent in that it uses enumerations in order to refer to specific errors. It is for the application to provide an error presentation module which interprets the errors associated with a request. An eample of such an implementation can be found in the HTDialog module.

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

    #ifndef HTERROR_H
    #define HTERROR_H

    typedef struct _HTError HTError;

    typedef enum _HTSeverity {
        ERR_UNKNOWN		  = 0x0,
        ERR_FATAL		  = 0x1,
        ERR_NON_FATAL	  = 0x2,
        ERR_WARN	 	  = 0x4,
        ERR_INFO	 	  = 0x8
    } HTSeverity;

    #include "HTReq.h"

## Error Codes and Messages

Note: All non-HTTP error codes have (`index number > HTERR_HTTP_CODES`), and they will not be shown in the error-message generated.

### The Error Message Object

An error consists of a messsage code, a short, natural language specific message, and a URI which can point to more information. This module also provides a default set of error objects with English text. Errors are registered together with a severity and you can also set the mode for what class of error severities should be shown and which should be ignored.

    typedef struct _HTErrorMessage {
        int  	code;           	/* Error number */
        char *	msg;          		/* Short explanation */
        char *	url;			/* Explaning URL */
    } HTErrorMessage;

### Error Message Index

Error codes are registered in an array where the following enumerations serve as an index. They must not be replaced!

    typedef enum _HTErrorElement {
    	HTERR_CONTINUE = 0,					/* 100 */
    	HTERR_SWITCHING,					/* 101 */
    	HTERR_OK,						/* 200 */
    	HTERR_CREATED,						/* 201 */
    	HTERR_ACCEPTED,						/* 202 */
    	HTERR_NON_AUTHORITATIVE,				/* 203 */
    	HTERR_NO_CONTENT,					/* 204 */
    	HTERR_RESET,						/* 205 */
    	HTERR_PARTIAL,						/* 206 */
    	HTERR_PARTIAL_OK,					/* 207 */
    	HTERR_MULTIPLE,						/* 300 */
    	HTERR_MOVED,						/* 301 */
    	HTERR_FOUND,						/* 302 */
    	HTERR_METHOD,						/* 303 */
    	HTERR_NOT_MODIFIED,					/* 304 */
    	HTERR_USE_PROXY,					/* 305 */
    	HTERR_PROXY_REDIRECT,					/* 306 */
    	HTERR_TEMP_REDIRECT,					/* 307 */
    	HTERR_BAD_REQUEST,					/* 400 */
    	HTERR_UNAUTHORIZED,					/* 401 */
    	HTERR_PAYMENT_REQUIRED,					/* 402 */
    	HTERR_FORBIDDEN,					/* 403 */
    	HTERR_NOT_FOUND,					/* 404 */
    	HTERR_NOT_ALLOWED,					/* 405 */
    	HTERR_NONE_ACCEPTABLE,					/* 406 */
    	HTERR_PROXY_UNAUTHORIZED,				/* 407 */
    	HTERR_TIMEOUT,						/* 408 */
    	HTERR_CONFLICT,						/* 409 */
    	HTERR_GONE,						/* 410 */
    	HTERR_LENGTH_REQUIRED,					/* 411 */
    	HTERR_PRECON_FAILED,					/* 412 */
    	HTERR_TOO_BIG,						/* 413 */
    	HTERR_URI_TOO_BIG,					/* 414 */
    	HTERR_UNSUPPORTED,					/* 415 */
    	HTERR_BAD_RANGE,					/* 416 */
    	HTERR_EXPECTATION_FAILED,				/* 417 */
    	HTERR_REAUTH,				                /* 418 */
    	HTERR_PROXY_REAUTH,				        /* 419 */
    	HTERR_INTERNAL,						/* 500 */
    	HTERR_NOT_IMPLEMENTED,					/* 501 */
    	HTERR_BAD_GATE,						/* 502 */
    	HTERR_DOWN,						/* 503 */
    	HTERR_GATE_TIMEOUT,					/* 504 */
    	HTERR_BAD_VERSION,					/* 505 */
    	HTERR_NO_PARTIAL_UPDATE,				/* 506 */

    	/* Cache warnings */
    	HTERR_STALE,						/* 10 */
    	HTERR_REVALIDATION_FAILED,				/* 11 */
    	HTERR_DISCONNECTED_CACHE,				/* 12 */
    	HTERR_HEURISTIC_EXPIRATION,				/* 13 */
    	HTERR_TRANSFORMED,					/* 14 */
    	HTERR_CACHE,						/* 99 */

    	/* Put all non-HTTP status codes after this */
    	HTERR_NO_REMOTE_HOST,
    	HTERR_NO_HOST,
    	HTERR_NO_FILE,
    	HTERR_FTP_SERVER,
    	HTERR_FTP_NO_RESPONSE,
            HTERR_FTP_LOGIN_FAILURE,
    	HTERR_TIME_OUT,
    	HTERR_GOPHER_SERVER,
    	HTERR_INTERRUPTED,
    	HTERR_CON_INTR,
    	HTERR_CSO_SERVER,
    	HTERR_HTTP09,
    	HTERR_BAD_REPLY,
    	HTERR_UNKNOWN_AA,
    	HTERR_NEWS_SERVER,
    	HTERR_FILE_TO_FTP,
    	HTERR_AUTO_REDIRECT,
    	HTERR_MAX_REDIRECT,
    	HTERR_EOF,
    	HTERR_WAIS_OVERFLOW,
    	HTERR_WAIS_MODULE,
    	HTERR_WAIS_NO_CONNECT,
    	HTERR_SYSTEM,
    	HTERR_CLASS,
    	HTERR_ACCESS,
    	HTERR_LOGIN,
            HTERR_CACHE_EXPIRED,
            HTERR_NO_AUTO_RULES,
            HTERR_NO_AUTO_PROXY,
    	HTERR_ELEMENTS		            /* This MUST be the last element */
    } HTErrorElement;

### Default English Language Messages

Default set of error messages arranged in an array into which the index codes serve as index. These error objects can of course be initialized as you like.

    /*    CODE  ERROR MESSAGE				ERROR URL */
    #define HTERR_ENGLISH_INITIALIZER \
        { 100, "Continue", 					"information" }, \
        { 101, "Switching Protocols",			"information" }, \
        { 200, "OK", 					"success" }, \
        { 201, "Created", 					"success" }, \
        { 202, "Accepted", 					"success" }, \
        { 203, "Non-authoritative Information",		"success" }, \
        { 204, "Document Updated",				"success" }, \
        { 205, "Reset Content",				"success" }, \
        { 206, "Partial Content",				"success" }, \
        { 207, "Partial Update OK",				"success" }, \
        { 300, "Multiple Choices",				"redirection" }, \
        { 301, "Moved Permanently",				"redirection" }, \
        { 302, "Found",  			                "redirection" }, \
        { 303, "See Other",					"redirection" }, \
        { 304, "Not Modified",       			"redirection" }, \
        { 305, "Use Proxy",					"redirection" }, \
        { 306, "Proxy Redirect",				"redirection" }, \
        { 307, "Temporary Redirect",			"redirection" }, \
        { 400, "Bad Request", 				"client_error" }, \
        { 401, "Unauthorized",				"client_error" }, \
        { 402, "Payment Required", 				"client_error" }, \
        { 403, "Forbidden", 				"client_error" }, \
        { 404, "Not Found",		       			"client_error" }, \
        { 405, "Method Not Allowed",	 		"client_error" }, \
        { 406, "Not Acceptable",		 		"client_error" }, \
        { 407, "Proxy Authentication Required", 		"client_error" }, \
        { 408, "Request Timeout",		 		"client_error" }, \
        { 409, "Conflict",			 		"client_error" }, \
        { 410, "Gone",			 		"client_error" }, \
        { 411, "Length Required",		 		"client_error" }, \
        { 412, "Precondition Failed",	 		"client_error" }, \
        { 413, "Request Entity Too Large",	 		"client_error" }, \
        { 414, "Request-URI Too Large",	 		"client_error" }, \
        { 415, "Unsupported Media Type",	 		"client_error" }, \
        { 416, "Range Not Satisfiable",	 		"client_error" }, \
        { 417, "Expectation Failed",	 		"client_error" }, \
        { 418, "Reauthentication Required",	 		"client_error" }, \
        { 419, "Proxy Reauthentication Reuired", 		"client_error" }, \
        { 500, "Internal Server Error",			"server_error" }, \
        { 501, "Not Implemented", 				"server_error" }, \
        { 502, "Bad Gateway", 				"server_error" }, \
        { 503, "Service Unavailable",			"server_error" }, \
        { 504, "Gateway Timeout", 				"server_error" }, \
        { 505, "HTTP Version not supported",		"server_error" }, \
        { 506, "Partial update Not Implemented",		"server_error" }, \
     \
        /* Cache Warnings */ \
        { 10,  "Response is Stale",				"cache" }, \
        { 11,  "Revalidation Failed",			"cache" }, \
        { 12,  "Disconnected Opeartion",			"cache" }, \
        { 13,  "Heuristic Expiration",			"cache" }, \
        { 14,  "Transformation Applied",			"cache" }, \
        { 99,  "Cache warning", 				"cache" }, \
     \
        /* Non-HTTP Error codes and warnings */ \
        { 0,   "Can't locate remote host", 			"internal" }, \
        { 0,   "No host name found", 			"internal" }, \
        { 0,   "No file name found or file not accessible", "internal" }, \
        { 0,   "FTP server replies", 			"internal" }, \
        { 0,   "FTP server doesn't reply", 			"internal" }, \
        { 0,   "FTP login failure", 			"internal" }, \
        { 0,   "Server timed out", 				"internal" }, \
        { 0,   "Gopher-server replies", 			"internal" }, \
        { 0,   "Data transfer interrupted", 		"internal" }, \
        { 0,   "Connection establishment interrupted", 	"internal" }, \
        { 0,   "CSO-server replies", 			"internal" }, \
        { 0,   "This is probably a HTTP server 0.9 or less","internal" }, \
        { 0,   "Bad, Incomplete, or Unknown Response",	"internal" }, \
        { 0,   "Unknown access authentication scheme",	"internal" }, \
        { 0,   "News-server replies",			"internal" }, \
        { 0,   "Trying `ftp://' instead of `file://'",	"internal" }, \
        { 0,   "Too many redirections",			"internal" }, \
        { 0,   "Method not suited for automatic redirection","internal" }, \
        { 0,   "Premature End Of File",			"internal" }, \
        { 0,   "Response from WAIS Server too Large - Extra lines \
    ignored","internal"}, \
        { 0,   "WAIS-server doesn't return any data", 	"internal" }, \
        { 0,   "Can't connect to WAIS-server",		"internal" }, \
        { 0,   "operation failed",				"internal" }, \
        { 0,   "Wrong or unknown access scheme",		"internal" }, \
        { 0,   "Access scheme not allowed in this context",	"internal" }, \
        { 0,   "When you are connected, you can log in",	"internal" }, \
        { 0,   "This version has expired and will be automatically reloaded", "internal" }, \
        { 0,   "Loading new rules must be explicitly acknowledged", "internal" }, \
        { 0,   "Automatic proxy redirection must be explicitly acknowledged", "internal" }

## What Errors should be Ignored or Passed Through?

This variable dictates which errors should be put out when generating the message to the user. The first four enumerations make it possible to see `everything as bad or worse than' this level, e.g. `HT_ERR_SHOW_NON_FATAL` shows messages of type `HT_ERR_SHOW_NON_FATAL` and `HT_ERR_SHOW_FATAL`.

Note: The default value is made so that it only puts a message to stderr if a `real' error has occurred. If a separate widget is available for information and error messages then probably `HT_ERR_SHOW_DETAILED` would be more appropriate.

    typedef enum _HTErrorShow {
        HT_ERR_SHOW_FATAL     = 0x1,
        HT_ERR_SHOW_NON_FATAL = 0x3,
        HT_ERR_SHOW_WARNING   = 0x7,
        HT_ERR_SHOW_INFO 	  = 0xF,
        HT_ERR_SHOW_PARS	  = 0x10,
        HT_ERR_SHOW_LOCATION  = 0x20,
        HT_ERR_SHOW_IGNORE    = 0x40,
        HT_ERR_SHOW_FIRST     = 0x80,
        HT_ERR_SHOW_LINKS     = 0x100,
        HT_ERR_SHOW_DEFAULT	  = 0x13,
        HT_ERR_SHOW_DETAILED  = 0x1F,
        HT_ERR_SHOW_DEBUG	  = 0x7F
    } HTErrorShow;

    extern HTErrorShow HTError_show (void);
    extern BOOL HTError_setShow (HTErrorShow mask);

## Creation and Deletion Methods

### Add an Error

Add an error message to the error list. `par' and `where' might be set to NULL. If par is a string, it is sufficient to let length be unspecified, i.e., 0. If only a part of the string is wanted then specify a length inferior to strlen((char *) par). The string is '\0' terminated automaticly. See also HTError_addSystem for system errors. Returns YES if OK, else NO.

    extern BOOL HTError_add (HTList * 	list,
    			 HTSeverity	severity,
    			 BOOL		ignore,
    			 int		element,
    			 void *		par,
    			 unsigned int	length,
    			 char *		where);

### Add a System Error

Add a system error message to the error list. syscall is the name of the system call, e.g. "close". The message put to the list is that corresponds to the error number passed. See also HTError_add. Returns YES if OK, else NO.

    extern BOOL HTError_addSystem (HTList *		list,
    			       HTSeverity 	severity,
    			       int		errornumber,
    			       BOOL		ignore,
    			       char *		syscall);

### Delete an Entire Error Stack

Deletes all errors in a list.

    extern BOOL HTError_deleteAll (HTList * list);

### Deletes the Last Edded Entry

Deletes the last error entry added to the list. Return YES if OK, else NO

    extern BOOL HTError_deleteLast (HTList * list);

## Object Methods

### Show the Error Entry?

Should we show this entry in the list or just continue to the next one?

    extern BOOL HTError_doShow (HTError * info);

### Ignore last Added Error

Turns on the `ignore' flag for the most recent error entered the error list. Returns YES if OK else NO

    extern BOOL HTError_ignoreLast	(HTList * list);
    extern BOOL HTError_setIgnore	(HTError * info);

### Error Index Number

Each error object is assigned an index number as defined by the `HTErrorElement` above. The mapping from this index to an error code and a message must be done by the application. The Library provides a default implementation in the HTDialog module, but that can of course be changed depending on the application.

    extern int HTError_index		(HTError * info);

### Error Severity

This function returns the severity of the error object passed by the caller

    extern HTSeverity HTError_severity	(HTError * info);

You can ask whether a list of errors contains any error object with a severity level which is higher than the one specifed.

    extern BOOL HTError_hasSeverity 	(HTList * list, HTSeverity severity);

### Parameters Asscotiated with Error

    extern void * HTError_parameter		(HTError * info, int * length);

### Where did it happen?

    extern const char * HTError_location	(HTError * info);

    #endif