OnHeaderInfo event

Applies to

acHTTP component.

Declaration

type

TacHTTPHeaderInfoEvent = procedure(Sender: TObject; ErrorCode: Integer;

const RawHeadersCRLF, ContentType, ContentLanguage, ContentEncoding, Location: String;

ContentLength: Integer; Date, LastModified, Expires: TDateTime;

var ContinueDownload: Boolean) of object;

property OnHeaderInfo: TacHTTPHeaderInfo;

Description

The OnHeaderInfo event returns the headers the response from the HTTP server, before downloading the document content.

You can write this event handler to receive all response headers and to decide whether you want to download the document. If you decided to NOT download it, simply set ContinueDownload parameter to False in the event handler.

The acHTTP passes to the OnHeaderInfo event handler following parameters:

Parameters

Meaning

ErrorCode

the status code of HTTP request (see the list of possible status codes);

RawHeadersCRLF

contains ALL the headers reseived from the HTTP server in response to request, as plain text string, separated by CRLF characters (0D0A);

ContentType

contains the identifier of MIME-type of requested document. For more information about Internet media types, please read RFC 2045, 2046, 2047, 2048, and 2077. Check out also the Internet media type registry at ftp://ftp.iana.org/in-notes/iana/assignments/media-types;

ContentLanguage

identifies a language of document content (if provided), or contains empty string if the language is not provided or not applicable for the type requested document;

ContentEncoding

identifies the encoding method of requested document;

ContentLength

determinates the size of document, if the document is binary file. Unfortunately most servers does not provide the content length for ASCII documents with "text/*" MIME-type, since their content can be generated dynamically by CGI programs;

Location

determines the location from where the content is about to be downloaded (use this parameter to get the actual location of document in case if connection has been redirected by server to another location);

Date

shows the date and time at which the HTTP response was originated;

LastModified

the date and time at which the server belives the resource was last modified;

Expires

the date and time after which the resource should be considered outdated;

ContinueDownload

used to interrupt the download process. If you don't want to continue download the requested file — set it to False.

Notes

All date/time values that passed to the OnHeaderInfo even handler, is already converted from the server's time to local time, taking in account the time zone and daylight bias. (The acHTTP uses InternetTimeToDateTime function to convert the string representation of date/time to TDateTime value.) To get unmodified string parameters — parse the raw headers provided by RawHeadersCRLF parameter

See also

OnDone and OnRedirected events;

Abort method;

HTTP status codes.