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Working with HTTP headers

Headers in HTTP requests can be obtained using a combination of the NEXT_HTTP_HEADER and HTTP_HEADER functions. The NEXT_HTTP_HEADER function iterates through the HTTP headers included within a request and returns the next HTTP header name. Calling it with NULL causes it to return the name of the first header. Subsequent headers are retrieved by passing the function the name of the previous header. This function returns NULL when called with the name of the last header.

Calling this function repeatedly returns all the header fields exactly once, but not necessarily in the order that they appear in the HTTP request.

The HTTP_HEADER function returns the value of the named HTTP header field, or NULL if not called from an HTTP service. It is used when processing an HTTP request via a web service. If a header for the given field name does not exist, the return value is NULL.

Here is a table of some typical HTTP headers and values.

To get the value of each header, use the NEXT_HTTP_HEADER function to get the name of the header and then use the HTTP_HEADER function to get its value. The following example illustrates how to do this.

CREATE PROCEDURE HTTPHeaderExample()
RESULT ( html_string LONG VARCHAR )
BEGIN
    declare header_name long varchar;
    declare header_value long varchar;
    declare table_rows XML;

    set header_name  = NULL;
    set table_rows = NULL;
header_loop:        
    LOOP
        SET header_name = NEXT_HTTP_HEADER( header_name );
        IF header_name IS NULL THEN 
            LEAVE header_loop 
        END IF;
        SET header_value = HTTP_HEADER( header_name );
        -- Format header name and value into an HTML table row
        SET table_rows = table_rows || 
            XMLELEMENT( name "tr", 
                XMLATTRIBUTES( 'left' AS "align", 
                                'top' AS "valign" ),
                XMLELEMENT( name "td", header_name ),
                XMLELEMENT( name "td", header_value ) );
                        
    END LOOP;
    SELECT XMLELEMENT( name "table",
                XMLATTRIBUTES( '' AS "BORDER", 
                             '10' AS "CELLPADDING", 
                              '0' AS "CELLSPACING" ),
                XMLELEMENT( name "th", 
                    XMLATTRIBUTES( 'left' AS "align", 
                                   'top'  AS "valign" ),
                                   'Header Name' ), 
                XMLELEMENT( name "th", 
                    XMLATTRIBUTES( 'left' AS "align", 
                                   'top'  AS "valign" ),
                                   'Header Value' ),
                table_rows );
END;

This example formats the header names and values into an HTML table. The following service can be defined to show how this sample procedure works.

CREATE SERVICE ShowHTTPHeaders
TYPE 'RAW'
AUTHORIZATION OFF 
USER DBA
AS CALL HTTPHeaderExample();

To test the service, open a web browser and supply the following URL:

 http://localhost:80/demo/ShowHTTPHeaders

For more information on header processing, see HTTP and SOAP functions.