Sun ONE Web Server 6.1 NSAPI Programmer's Guide |
Chapter 12
Hypertext Transfer ProtocolThe Hypertext Transfer Protocol (HTTP) is a protocol (a set of rules that describes how information is exchanged) that allows a client (such as a web browser) and a web server to communicate with each other.
HTTP is based on a request-response model. The browser opens a connection to the server and sends a request to the server. The server processes the request and generates a response, which it sends to the browser. The server then closes the connection.
This chapter provides a short introduction to a few HTTP basics. For more information on HTTP, see the IETF home page at:
This chapter has the following sections:
ComplianceSun ONE Web Server 6.1 supports HTTP/1.1. Previous versions of the server supported HTTP/1.0. The server is conditionally compliant with the HTTP/1.1 proposed standard, as approved by the Internet Engineering Steering Group (IESG), and the Internet Engineering Task Force (IETF) HTTP working group.
For more information on the criteria for being conditionally compliant, see the Hypertext Transfer Protocol -- HTTP/1.1 specification (RFC 2068) at:
http://www.ietf.org/rfc/rfc2068.txt?number=2068
RequestsA request from a browser to a server includes the following information:
Request Method, URI, and Protocol Version
A browser can request information using a number of methods. The commonly used methods include the following:
- GET -- Requests the specified resource (such as a document or image)
- HEAD -- Requests only the header information for the document
- POST -- Requests that the server accept some data from the browser, such as form input for a CGI program
- PUT -- Replaces the contents of a server’s document with data from the browser
Request Headers
The browser can send headers to the server. Most are optional.
The following table lists some of the commonly used request headers.
Request Data
If the browser has made a POST or PUT request, it sends data after the blank line following the request headers. If the browser sends a GET or HEAD request, there is no data to send.
ResponsesThe server’s response includes the following:
HTTP Protocol Version, Status Code, and Reason Phrase
The server sends back a status code, which is a three-digit numeric code. The five categories of status codes are:
The following table lists some common status codes.
Response Headers
The response headers contain information about the server and the response data.
The following table lists some common response headers.
Response Data
The server sends a blank line after the last header. It then sends the response data such as an image or an HTML page.
Buffered StreamsBuffered streams improve the efficiency of network I/O (for example, the exchange of HTTP requests and responses), especially for dynamic content generation. Buffered streams are implemented as transparent NSPR I/O layers, which means even existing NSAPI modules can use them without any change.
The buffered streams layer adds the following features to the Sun ONE Web Server:
- Enhanced keep-alive support: When the response is smaller than the buffer size, the buffering layer generates the Content-Length header so that the client can detect the end of the response and reuse the connection for subsequent requests.
- Response length determination: If the buffering layer cannot determine the length of the response, it uses HTTP/1.1 chunked encoding instead of the Content-Length header to convey the delineation information. If the client only understands HTTP/1.0, the server must close the connection to indicate the end of the response.
- Deferred header writing: Response headers are written out as late as possible to give the servlets a chance to generate their own headers (for example, the session management header set-cookie).
- Ability to understand request entity bodies with chunked encoding: Though popular clients do not use chunked encoding for sending POST request data, this feature is mandatory for HTTP/1.1 compliance.
The improved connection handling and response length header generation provided by buffered streams also addresses the HTTP/1.1 protocol compliance issues, where absence of the response length headers is regarded as a category 1 failure. In previous Enterprise Server versions, it was the responsibility of the dynamic content generation programs to send the length headers. If a CGI script did not generate the Content-Length header, the server had to close the connection to indicate the end of the response, breaking the keep-alive mechanism. However, it is often very inconvenient to keep track of response length in CGI scripts or servlets, and as an application platform provider, the web server is expected to handle such low-level protocol issues.
Output buffering has been built in to the functions that transmit data, such as net_write (see "NSAPI Function Reference"). You can specify the following Service SAF parameters that affect stream buffering, which are described in detail in the chapter “Syntax and Use of magnus.conf” in the Sun ONE Web Server 6.1 Administrator’s Configuration File Reference.
The UseOutputStreamSize, ChunkedRequestBufferSize, and ChunkedRequestTimeout parameters also have equivalent magnus.conf directives; see “Chunked Encoding” in the chapter “Syntax and Use of magnus.conf” in the Sun ONE Web Server 6.1 Administrator’s Configuration File Reference. The obj.conf parameters override the magnus.conf directives.
Note
The UseOutputStreamSize parameter can be set to zero (0) in the obj.conf file to disable output stream buffering. For the magnus.conf file, setting UseOutputStreamSize to zero has no effect.
To override the default behavior when invoking an SAF that uses one of the functions net_read or netbuf_grab, you can specify the value of the parameter in obj.conf, for example:
Service fn="my-service-saf" type=perf UseOutputStreamSize=8192