HTTP Transport

This document covers the sending and receiving of SOAP messages with Axis2 using HTTP as the transport mechanism.

Contents

CommonsHTTPTransportSender

CommonsHTTPTransportSender is the transport sender that is used by default in both the Server and Client APIs. As its name implies, it is based on commons-httpclient-3.1. For maximum flexibility, this sender supports both the HTTP GET and POST interfaces. (REST in Axis2 also supports both interfaces.)

Axis2 uses a single HTTPClient instance per ConfigurationContext (which usually means per instance of ServiceClient). This pattern allows for HTTP 1.1 to automatically reuse TCP connections - in earlier versions of Axis2 the REUSE_HTTP_CLIENT configuration property was necessary to enable this functionality, but as of 1.5 this is no longer necessary.

Commons HttpClient also provides HTTP 1.1, Chunking and KeepAlive support for Axis2.

The <transportSender/> element defines transport senders in the axis2.xml configuration file as follows:

<transportSender name="http" class="org.apache.axis2.transport.http.CommonsHTTPTransportSender">
   <parameter name="PROTOCOL">HTTP/1.1</parameter>
   <parameter name="Transfer-Encoding">chunked</parameter>
</transportSender>

The above code snippet shows the simplest configuration of a transport sender for common use. The <parameter/> element is used to specify additional constraints that the sender should comply with. The HTTP PROTOCOL parameter should be set as HTTP/1.0 or HTTP/1.1. The default version is HTTP/1.1. Note that chunking support is available only for HTTP/1.1. Thus, even if "chunked" is specified as a parameter, if the HTTP version is 1.0, this setting will be ignored by the transport framework. Also, KeepAlive is enabled by default in HTTP/1.1.

If you use HTTP1.1 for its Keep-Alive ability, but you need to disable chunking at runtime (some servers don't allow chunked requests to prevent denial of service), you can do so in the Stub: 

options.setProperty(HTTPConstants.CHUNKED, "false");

Some absolute properties are provided at runtime instead. For example, character encoding style (UTF-8, UTF-16, etc.) is provided via MessageContext.

HTTPS support

CommonsHTTPTransportSender can be also used to communicate over https. 
   <transportSender name="https" class="org.apache.axis2.transport.http.CommonsHTTPTransportSender">
      <parameter name="PROTOCOL">HTTP/1.1</parameter>
      <parameter name="Transfer-Encoding">chunked</parameter>
   </transportSender>

Please note that by default HTTPS works only when the server does not expect to authenticate the clients (1-way SSL only) and where the server has the clients' public keys in its trust store. If you want to perform SSL client authentication (2-way SSL), you may use the Protocol.registerProtocol feature of HttpClient. You can overwrite the "https" protocol, or use a different protocol for your SSL client authentication communications if you don't want to mess with regular https. Find more information at http://jakarta.apache.org/commons/httpclient/sslguide.html

Timeout Configuration

Two timeout instances exist in the transport level, Socket timeout and Connection timeout. These can be configured either at deployment or run time. If configuring at deployment time, the user has to add the following lines in axis2.xml.

For Socket timeout:

<parameter name="SO_TIMEOUT">some_integer_value</parameter>

For Connection timeout:

 <parameter name="CONNECTION_TIMEOUT">some_integer_value</parameter>

For runtime configuration, it can be set as follows within the client stub: 
...
Options options = new Options();
options.setProperty(HTTPConstants.SO_TIMEOUT, new Integer(timeOutInMilliSeconds));
options.setProperty(HTTPConstants.CONNECTION_TIMEOUT, new Integer(timeOutInMilliSeconds));

// or
options.setTimeOutInMilliSeconds(timeOutInMilliSeconds);
...

HTTP Version Configuration

The default HTTP version is 1.1. There are two methods in which the user can change the HTTP version to 1.0

  • By defining the version in axis2.xml as shown below. 
     <parameter name="PROTOCOL">HTTP/1.0</parameter>
  • By changing the version at runtime by using code similar to the following: 
    ...
options.setProperty(org.apache.axis2.context.MessageContextConstants.HTTP_PROTOCOL_VERSION,
   org.apache.axis2.transport.http.HTTPConstants.HEADER_PROTOCOL_10);
...

Proxy Authentication

The Commons-http client has built-in support for proxy authentication. Axis2 uses deployment time and runtime mechanisms to authenticate proxies. At deployment time, the user has to change the axis2.xml as follows. This authentication is available for both HTTP and HTTPS.

<transportSender name="http" class="org.apache.axis2.transport.http.CommonsHTTPTransportSender">
   <parameter name="PROTOCOL">HTTP/1.1</parameter>
   <parameter name="PROXY" proxy_host="proxy_host_name" proxy_port="proxy_host_port">userName:domain:passWord</parameter>
</transportSender>

For a particular proxy, if authentication is not available, enter the "userName:domain:passWord" as "anonymous:anonymous:anonymous".

Prior shown configuration has been deprecated after Axis2 1.2 release and we strongly recommend using the new proxy configuration as below.

New proxy configuration would require the user to add a TOP level parameter in the axis2.xml named "Proxy". 

<parameter name="Proxy">
    <Configuration>
        <ProxyHost>example.org</ProxyHost>
        <ProxyPort>5678</ProxyPort>
        <ProxyUser>EXAMPLE\saminda</ProxyUser>
        <ProxyPassword>ppp</ProxyPassword>
    </Configuration>
</parameter>

Thus, if its a open proxy, user can ignore ProxyUser and ProxyPassword elements.

In addition to this, if you don't want to go through writing the above parameter you could use Java Networking Properties for open proxies, -Dhttp.proxyHost=10.150.112.254 -Dhttp.proxyPort=8080

At runtime, the user can override the PROXY settings using the HttpTransportProperties.ProxyProperties object. Within your client stub, create an instance of this object, configure proxy values for it, and then set it to the MessageContext's property bag via options.setProperty(). For example:

...
Options options = new Options();
...

HttpTransportProperties.ProxyProperties proxyProperties = new HttpTransportProperties.new ProxyProperties();
proxyProperties.setProxyHostName(....);
proxyProperties.setProxyPort(...);
...
options.setProperty(HttpConstants.PROXY, proxyProperties);
...

The above code will override the deployment proxy configuration settings.

Basic, Digest and NTLM Authentication

HttpClient supports three different types of HTTP authentication schemes: Basic, Digest and NTLM. Based on the challenge provided by the server, HttpClient automatically selects the authentication scheme with which the request should be authenticated. The most secure method is NTLM and the Basic is the least secure.

NTLM is the most complex of the authentication protocols supported by HttpClient. It requires an instance of NTCredentials to be available for the domain name of the server or the default credentials. Note that since NTLM does not use the notion of realms, HttpClient uses the domain name of the server as the name of the realm. Also note that the username provided to the NTCredentials should not be prefixed with the domain - ie: "axis2" is correct whereas "DOMAIN\axis2" is not correct.

There are some significant differences in the way that NTLM works compared with basic and digest authentication. These differences are generally handled by HttpClient, however having an understanding of these differences can help avoid problems when using NTLM authentication.

  1. NTLM authentication works almost exactly the same way as any other form of authentication in terms of the HttpClient API. The only difference is that you need to supply 'NTCredentials' instead of 'UsernamePasswordCredentials' (NTCredentials actually extends UsernamePasswordCredentials so you can use NTCredentials right throughout your application if need be).
  2. The realm for NTLM authentication is the domain name of the computer to which you are being connected. This can become troublesome as servers often have multiple domain names that refer to them. Only the domain name that the HttpClient connects to (as specified by the HostConfiguration) is used to look up the credentials. It is generally advised that while initially testing NTLM authentication, you pass the realm as null, which is its default value.
  3. NTLM authenticates a connection and not a request. So you need to authenticate every time a new connection is made, and keeping the connection open during authentication is vital. Because of this, NTLM cannot be used to authenticate with both a proxy and the server, nor can NTLM be used with HTTP 1.0 connections or servers that do not support HTTP keep-alives.

Axis2 also allows adding a custom Authentication Scheme to HttpClient.

The static inner bean Authenticator of HttpTransportProperties will hold the state of the server to be authenticated with. Once filled, it has to be set to the Options's property bag with the key as HTTPConstants.AUTHENTICATE. The following code snippet shows how to configure the transport framework to use Basic Authentication:

...
Options options = new Options();
 
HttpTransportProperties.Authenticator
   auth = new HttpTransportProperties.Authenticator();
auth.setUsername("username");
auth.setPassword("password");
// set if realm or domain is known

options.setProperty(org.apache.axis2.transport.http.HTTPConstants.AUTHENTICATE, auth);
...

Reusing the httpclient object

By default, a new httpclient object is created for each send. It may be worthwhile to reuse the same httpclient object to take advantage of HTTP1.1 Keep-Alive, especially in HTTPS environment, where the SSL handshake may not be of negligible cost. To reuse the same httpclient object, you can set the relevant property in the Stub: 

options.setProperty(HTTPConstants.REUSE_HTTP_CLIENT, "true");

Setting the cached httpclient object

To control the max connections per host attempted in parallel by a reused httpclient (this can be worthwhile as the default value is 2 connections per host), or any other advanced parameters, you need to set the cached httpclient object when your application starts up (before any actual axis request). You can set the relevant property in the Stub: 
MultiThreadedHttpConnectionManager conmgr = new MultiThreadedHttpConnectionManager();
conmgr.getParams().setDefaultMaxConnectionsPerHost(10);
HttpClient client = new HttpClient(conmgr);
configurationContext.setProperty(HTTPConstants.CACHED_HTTP_CLIENT, client);

Setting the cached httpstate object

HttpState object can be set as property to the options of a given Axis2 client. HttpState keeps HTTP attributes that may persist from request to request, such as cookies and authentication credentials. So, it is possible to re-use one and the same HttpState object if appropriate. The idea is to provide the capability to specify/associate a separate HttpState with every client and still reuse one and the same HttpClient. So, this make sense only when CACHED_HTTP_CLIENT is re-used between different clients from different threads which may invoke different hosts with different credentials and cookies. This is really complicated scenario, but is absolutely possible one. If you re-use a common HttpClient between different clients then the clients will re-use, the internal for the HttpClient, HttpState object. Doing so authentication credentials are exposed to all clients sharing one and the same HttpClient. This is definitely not a good idea. The problem with Cookies is different. The problem here is that if two distinct clients invoke one and the same service at a specific host then the session established with a given cookie by one of the clients can wrongly be shared among them, too, if it has not expired. This will cause problems since the two client may need different sessions, which is the more probable scenario. Sample configuration: 
HttpState myHttpState = new HttpState();
options.setProperty(WSClientConstants.CACHED_HTTP_STATE, myHttpState);
Doing so the HttpState is attached to the client. Respectively this is automatically propagated to all MessageContext objects used by the client. Underneath this just instructs Axis2 that the CACHED_HTTP_STATE set should be passed as a parameter when HttpClient#executeMethod is invoked.