I found the apache xfire has add one head parameter in its post header:
POST /testservice/services/TestService1.1 HTTP/1.1
SOAPAction: "testAPI" Content-Type: text/xml; charset=UTF-8
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; XFire Client +http://xfire.codehaus.org)
Host: 192.168.10.111:9082
Expect: 100-continue
Will this Expect: 100-continue make the roundtrip call between the xfire client and its endpoint server a little bit waste because it will use one more handshake for the origin server to return the "willing to accept request"?
This just my guess.
Vance
I know this is old question but as I was just researching the subject, here is my answer. You don't really need to use "Expect: 100-continue" and it indeed does introduce extra roundtrip. The purpose of this header is to indicate to the server that you want your request to be validated before posting the data. This also means that if it is set, you are committed to waiting (within your own timeout period - not indefinitely!) for server response (either 100 or HTTP failure) before sending your form or data. Although it seems like extra expense, it is meant to improve performance in failure cases, by allowing the server to make you know not to send the data (since the request has failed).
If the header is not set by the client, this means you are not awaiting for 100 code from the server and should send your data in the request body. Here is relevant standard: http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html (jump to section 8.2.3).
Hint for .NET 4 users: this header can be disabled using static property "Expect100Continue"
Hint for libcurl users: there was a bug in old version 7.15 when disabling this header wasn't working; fixed in newer versions (more here: http://curl.haxx.se/mail/lib-2006-08/0061.html)