HTTP 1.0 vs 1.1
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 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. It's mostly used for Cross Origin Resource Sharing in web applications.
Caching:
HTTP 1.0 had support for caching via the header: If-Modified-Since.
HTTP 1.1 expands on the caching 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 are 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.
HTTP 1.0 (1994)
- It is still in use
- Can be used by a client that cannot deal with chunked (or compressed) server replies
HTTP 1.1 (1996- 2015)
- Formalizes many extensions to version 1.0
- Supports persistent and pipelined connections
- Supports chunked transfers, compression/decompression
- Supports virtual hosting (a server with a single IP Address hosting multiple domains)
- Supports multiple languages
- Supports byte-range transfers; useful for resuming interrupted data transfers
HTTP 1.1 is an enhancement of HTTP 1.0. The following lists the four major improvements:
Efficient use of IP addresses, by allowing multiple domains to be served from a single IP address.
Faster response, by allowing a web browser to send multiple requests over a single persistent connection.
- Faster response for dynamically-generated pages, by support for chunked encoding, which allows a response to be sent before its total length is known.
- Faster response and great bandwidth savings, by adding cache support.
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.
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.