httpGet

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Module

urn:org:ten60:netkernel:ext:http:client

The httpGet accessor is exported by the urn:org:ten60:netkernel:ext:http:client module. Import this module to gain access to the accessor.

Syntax

URI

active:httpGet

Argument	Rules	Description
url	Mandatory	the URL to issue the request to.
config	Optional	an optional config resource
state	Optional	an optional state resource

Example Usage

DPML

<instr>
  <type>httpGet</type>
  <url>http://www.1060research.com</url>
  <state>var:mystate</state>
  <target>this:response</target>
</instr>

NetKernel Foundation API

req=context.createSubRequest("active:httpGet");
req.addArgument("url", [resource representation, aspect, or URI] );
result=context.issueSubRequest(req);

Purpose

Issues an HTTP GET request for the given url and returns the resource.

The optional state argument is used to store client-side state information.

Client-Side State

Interactions with the remote server are stateless unless a resource is provided as the optional state argument. Please refer to the httpState guide for details.

Header field interpretation

If the HTTP response code is not OK (200) then a HTTPResponseCodeAspect is returned containing the response code and the response body - if necessary this can be passed to the httpResponseCodeFilter which can be used to raise a NetKernel Exception.

The MIME type of from the HTTP header is passed through into the response from this accessor.

The EXPIRES header is used to determine the expiry of the response from this accessor. If on expires field is specified the result is assumed expired. Heuristic determination of expiry as specified in RFC 2616 section 13.2.2 is not implemented and pessimistic behaviour is followed.

Config

Configuration information is provided as the config argument. If this is missing the service will request configuration information from the address ffcpl:/etc/HTTPClientConfig.xml. If this is missing the following default is used:

<config>
  <proxyHost>proxy.mydomain.com</proxyHost>
  <proxyPort>80</proxyPort>
  <followRedirects>true</followRedirects>
  <retryAttempts>3</retryAttempts>
  <maxConnectionsPerHost>4</maxConnectionsPerHost>
  <maxTotalConnections>10</maxTotalConnections>
  <maxAcceptableContentLength>-1</maxAcceptableContentLength>
  <stateExpirationTime>600</stateExpirationTime>
  <connectTimeout>2000</connectTimeout>
  <timeout>5000</timeout>
</config>

Each configuration element is optional, if not specified the default values (above) will be used. The parameters are as follows:

proxyHost	hostname of proxy server
proxyPort	port of proxy server
followRedirects	follow HTTP redirect response codes
retryAttempts	number of attempts to make connection before failing
maxConnectionsPerHost	maximum simultaneous connections to make to a single host
maxTotalConneciton	max total connections
maxAcceptableConentLength	largest resource to handle in response, -1 indicates accept any size.
stateExpirationTime	time for client side state to be valid.
connectTimeout	time to allow for a connection to be established with server before failing
timeout	time to allow an established connection to remain idle before failing

Proxy settings will be taken from the global system proxy settings if they are not specified in the config.

Requesting an HTTPResponseCode

If the accessor is requested to return an HTTPResponseCodeAspect aspect (see NKFRequest) then the accessor will always return a HTTPResponseCodeAspect containing the HTTP code and body response - this can be valuable for testing purposes.

Example

Passing Query Parameters in the GET url request

<instr>
  <type>httpGet</type>
  <url>http://localhost:8081/test-http-client/server/echo.idoc?query1=hello&amp;query2=world</url>
  <target>this:response</target>
</instr>