HTTP 1.0 vs 1.1

Question

Could somebody give me a brief overview of the differences between HTTP 1.0 and HTTP 1.1? I've spent some time with both of the RFCs, but haven't been able to pull out a lot of difference between them. Wikipedia says this:

HTTP/1.1 (1997-1999)

Current version; persistent connections enabled by default and works well with proxies. Also supports request pipelining, allowing multiple requests to be sent at the same time, allowing the server to prepare for the workload and potentially transfer the requested resources more quickly to the client.

But that doesn't mean a lot to me. I realize this is a somewhat complicated subject, so I'm not expecting a full answer, but can someone give me a brief overview of the differences at a bit lower level? By this I mean that I'm looking for the info I would need to know to implement either an HTTP server or application.

I realize that this can be a somewhat complicated subject (based on what I know about HTTP as of right now), so I'm not necessarily looking for a full answer. I'm really more looking for a nudge in the right direction so that I can figure it out on my own.

Answer 1

One of the first differences that I can recall from top of my head are multiple domains running in the same server, partial resource retrieval, this allows you to retrieve and speed up the download of a resource (it's what almost every download accelerator does).

If you want to develop an application like a website or similar, you don't need to worry too much about the differences but you should know the difference between GET and POST verbs at least.

Now if you want to develop a browser then yes, you will have to know the complete protocol as well as if you are trying to develop a HTTP server.

If you are only interested in knowing the HTTP protocol I would recommend you starting with HTTP/1.1 instead of 1.0.

Answer 2

This is quite a good summary of the key differences:

http://www.research.att.com/~bala/papers/h0vh1.html

Answer 3

For trivial applications (e.g. sporadically retrieving a temperature value from a web-enabled thermometer) HTTP 1.0 is fine for both a client and a server. You can write a bare-bones socket-based HTTP 1.0 client or server in about 20 lines of code.

For more complicated scenarios HTTP 1.1 is the way to go. Expect a 3 to 5-fold increase in code size for dealing with the intricacies of the more complex HTTP 1.1 protocol. The complexity mainly comes, because in HTTP 1.1 you will need to create, parse, and respond to various headers. You can shield your application from this complexity by having a client use an HTTP library, or server use a web application server.

Answer 4

Proxy support and the Host field:

HTTP 1.1 has a required Host header by spec.

HTTP 1.0 does not officially require a Host header, but it doesn't hurt to add one, and many applications (proxies) expect to see the Host header regardless of the protocol version.

Example:

GET / HTTP/1.1
Host: www.blahblahblahblah.com

This header is useful because it allows you to route a message through proxy servers, and also because your a web server can distinguish between different sites on the same server.

So this means if you have blahblahlbah.com and helohelohelo.com both pointing to the same IP. Your web server can use the Host field to distinguish which site the client machine wants.

Persistent connections:

HTTP 1.1 also allows you to have persistent connections which means that you can have more than one request/response on the same HTTP connection.

In HTTP 1.0 you had to open a new connection for each request/response pair. And after each response the connection would be closed. This lead to some big efficiency problems because of TCP Slow Start.

OPTIONS method:

HTTP/1.1 introduces the OPTIONS method. An HTTP client can use this method to determine the abilities of the HTTP server. Although it is not very much used today, most of this information is passed on server responses.

Caching:

HTTP 1.0 had support for caching via the header: If-Modified-Since.

HTTP 1.1 expands on the cachine support a lot by using something called 'entity tag'. If 2 resources are the same, then they will have the same entity tags.

HTTP 1.1 also adds the If-Unmodified-Since, If-Match, If-None-Match conditional headers.

There is also further additions relating to caching like the Cache-Control header.

100 Continue status:

There is a new return code in HTTP/1.1 100 Continue. This is to prevent a client from sending a large request when that client is not even sure if the server can process the request, or is authorized to process the request. In this case the client sends only the headers, and the server will tell the client 100 Continue, go ahead with the body.

Much more:

• Digest authentication and proxy authentication
• Extra new status codes
• Chunked transfer encoding
• Connection header
• Enhanced compression support
• Much much more.

Answer 5

A key compatibility issue is support for persistent connections. I recently worked on a server that "supported" HTTP/1.1, yet failed to close the connection when a client sent an HTTP/1.0 request. When writing a server that supports HTTP/1.1, be sure it also works well with HTTP/1.0-only clients.