Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

Enjoy The TCP/IP Guide? Get the complete PDF!
The TCP/IP Guide

Custom Search







Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
                9  TCP/IP World Wide Web (WWW, "The Web") and the Hypertext Transfer Protocol (HTTP)
                     9  TCP/IP Hypertext Transfer Protocol (HTTP)
                          9  HTTP Messages, Message Formats, Methods and Status Codes

Previous Topic/Section
HTTP Methods
Previous Page
Pages in Current Topic/Section
123
4
Next Page
HTTP Message Headers
Next Topic/Section

HTTP Status Code Format, Status Codes and Reason Phrases
(Page 4 of 4)

The 100 (Continue) Preliminary Reply

Phew. Now, let's go back to the top, status code 100. Normally, a client sends a complete request to the server, and waits for a response to it (while optionally pipelining additional requests). In certain circumstances, however, the client might wish to check in advance if the server is willing to accept the request before it bothers sending the whole message. This is not a common occurrence, because most requests are quite small, which makes it not worth the bother. However, in cases where a user wants to submit a very large amount of data to an online program, or use PUT to store a large file, for example, checking with the server first can be a useful optimization.

In this situation, the client sends a request containing the special header “Expect: 100-continue”. Assuming that the server supports the feature, it will process the request's headers and immediately send back the “100 Continue” preliminary reply. This tells the client to continue sending the rest of the request. The server then processes it and responds normally. If the server doesn't send the 100 response after a certain amount of time, the client will typically just send the rest of the request anyway.

Note: In some cases, servers send these preliminary replies even when they are not supposed to, so clients must be prepared to deal with them (they are simply discarded, since they contain no information).


 


Previous Topic/Section
HTTP Methods
Previous Page
Pages in Current Topic/Section
123
4
Next Page
HTTP Message Headers
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.