Create a SOAP endpoint

author

fjf2002

PostgREST supports Media Type Handlers. With a bit of work, SOAP endpoints become possible.

Minimal Example

This example will simply return the request body, inside a tag therequestbodywas.

Add the following function to your PostgreSQL database:

create domain "text/xml" as pg_catalog.xml;

CREATE OR REPLACE FUNCTION my_soap_endpoint(xml) RETURNS "text/xml" AS $$
DECLARE
  nsarray CONSTANT text[][] := ARRAY[
    ARRAY['soapenv', 'http://schemas.xmlsoap.org/soap/envelope/']
  ];
BEGIN
  RETURN xmlelement(
    NAME "soapenv:Envelope",
    XMLATTRIBUTES('http://schemas.xmlsoap.org/soap/envelope/' AS "xmlns:soapenv"),
    xmlelement(NAME "soapenv:Header"),
    xmlelement(
      NAME "soapenv:Body",
      xmlelement(
        NAME theRequestBodyWas,
        (xpath('/soapenv:Envelope/soapenv:Body', $1, nsarray))[1]
      )
    )
 );
END;
$$ LANGUAGE plpgsql;

Do not forget to refresh the PostgREST schema cache.

Use curl for a first test:

curl http://localhost:3000/rpc/my_soap_endpoint \
    --header 'Content-Type: text/xml' \
    --header 'Accept: text/xml' \
    --data-binary @- <<XML
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
  <soapenv:Header/>
  <soapenv:Body>
    <mySOAPContent>
      My SOAP Content
    </mySOAPContent>
  </soapenv:Body>
</soapenv:Envelope>
XML

The output should contain the original request body within the therequestbodywas entity, and should roughly look like:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
  <soapenv:Header/>
  <soapenv:Body>
    <therequestbodywas>
      <soapenv:Body xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
        <mySOAPContent>
          My SOAP Content
        </mySOAPContent>
      </soapenv:Body>
    </therequestbodywas>
  </soapenv:Body>
</soapenv:Envelope>

A more elaborate example

Here we have a SOAP service that converts a fraction to a decimal value, with pass-through of PostgreSQL errors to the SOAP response. Please note that in production you probably should not pass through plain database errors potentially disclosing internals to the client, but instead handle the errors directly.

-- helper function
CREATE OR REPLACE FUNCTION _soap_envelope(body xml)
 RETURNS xml
 LANGUAGE sql
AS $function$
  SELECT xmlelement(
    NAME "soapenv:Envelope",
    XMLATTRIBUTES('http://schemas.xmlsoap.org/soap/envelope/' AS "xmlns:soapenv"),
    xmlelement(NAME "soapenv:Header"),
    xmlelement(NAME "soapenv:Body", body)
  );
$function$;

-- helper function
CREATE OR REPLACE FUNCTION _soap_exception(
  faultcode text,
  faultstring text
)
 RETURNS xml
 LANGUAGE sql
AS $function$
  SELECT _soap_envelope(
    xmlelement(NAME "soapenv:Fault",
      xmlelement(NAME "faultcode", faultcode),
      xmlelement(NAME "faultstring", faultstring)
    )
  );
$function$;

CREATE OR REPLACE FUNCTION fraction_to_decimal(xml)
 RETURNS "text/xml"
 LANGUAGE plpgsql
AS $function$
DECLARE
  nsarray CONSTANT text[][] := ARRAY[
    ARRAY['soapenv', 'http://schemas.xmlsoap.org/soap/envelope/']
  ];
  exc_msg text;
  exc_detail text;
  exc_hint text;
  exc_sqlstate text;
BEGIN
  -- simulating a statement that results in an exception:
  RETURN _soap_envelope(xmlelement(
    NAME "decimalValue",
    (
      (xpath('/soapenv:Envelope/soapenv:Body/fraction/numerator/text()', $1, nsarray))[1]::text::int
      /
      (xpath('/soapenv:Envelope/soapenv:Body/fraction/denominator/text()', $1, nsarray))[1]::text::int
    )::text::xml
  ));
EXCEPTION WHEN OTHERS THEN
  GET STACKED DIAGNOSTICS
    exc_msg := MESSAGE_TEXT,
    exc_detail := PG_EXCEPTION_DETAIL,
    exc_hint := PG_EXCEPTION_HINT,
    exc_sqlstate := RETURNED_SQLSTATE;
  RAISE WARNING USING
    MESSAGE = exc_msg,
    DETAIL = exc_detail,
    HINT = exc_hint;
  RETURN _soap_exception(faultcode => exc_sqlstate, faultstring => concat(exc_msg, ', DETAIL: ', exc_detail, ', HINT: ', exc_hint));
END
$function$;

Let’s test the fraction_to_decimal service with illegal values:

curl http://localhost:3000/rpc/fraction_to_decimal \
  --header 'Content-Type: text/xml' \
  --header 'Accept: text/xml' \
  --data-binary @- <<XML
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
  <soapenv:Header/>
  <soapenv:Body>
    <fraction>
      <numerator>42</numerator>
      <denominator>0</denominator>
    </fraction>
  </soapenv:Body>
</soapenv:Envelope>
XML

The output should roughly look like:

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
  <soapenv:Header/>
  <soapenv:Body>
    <soapenv:Fault>
      <faultcode>22012</faultcode>
      <faultstring>division by zero, DETAIL: , HINT: </faultstring>
    </soapenv:Fault>
  </soapenv:Body>
</soapenv:Envelope>

References

For more information concerning PostgREST, cf.

For SOAP reference, visit