Design and Implementation of an HTTP Server

Design and Implementation of an HTTP Server
A Simple Network Application in Java

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Hypertext Transfer Protocol

Some Properties:
- Simple
- Stateless
For Our Current Purposes:
- An easy way to "GET" text content from a host computer

The Process

The client opens a connection
The client sends a request (GET, HEAD, or POST)
The client waits for a response
The server processes the request
The server sends a response
The connection is closed

Handling Special Characters

Encoding:
- URLEncoder
Decoding:
- URLDecoder

Uniform Resource Identifiers

Defined:
- A means for identifying a resource
- Details are discussed in RFC 2396 and RFC 2732
HTTP URIs:
- http://Host[:Port]/Path[?QueryString]
- where the QueryString consists of name=value pairs delimited by the '&' character (i.e., name=value[&...])

A Sequence Diagram

HTTP 1.0 GET/HEAD Requests without Headers

GET Without Headers (a.k.a., Simple-Request):
- GET URI HTTP/1.0 CRLF
  CRLF
HEAD:
- HEAD URI HTTP/1.0 CRLF
  CRLF

HTTP 1.0 GET without Headers (cont.)

Ignoring the Query String

javaexamples/http/v0/HttpRequest.java

HTTP 1.0 Responses without Headers

HTTP/1.0 ResponseCode ResponseText CRLF
CRLF
Content-Length:length CRLF
Content-Type:type CRLF
CRLF
Data

javaexamples/http/v0/HttpResponse.java

Name=Value Pairs

Use:
- The Query String uses name=value pairs
- Headers use name=value pairs
- Content Types are often represented as name=value pairs
An Observation:
- We could use a Map but they really have more funtionality than we need (making them unsafe)
- We sometimes need thread safety
- We sometimes needs speed (and not thread safety)

A NameValueMap Class

Options for Limiting the Functionality:
- Delegate to a Map but don't support the entire interface (as you would with the decorator)
- Specialize a Map but override the unnecessary methods
The Better Option in this Case:
- Since we want to support two versions (one that is thread-safe and one that is not) -- use a Factory and delegation

A NameValueMap Class (cont.)

javaexamples/http/v1/NameValueMap.java

HTTP 1.0 GET Requests with Headers

GET URI HTTP/1.0 CRLF
Name1: Value1 CRLF
Name2: Value2 CRLF
.
.
.
NameN: ValueN CRLF
CRLF

HTTP 1.0 GET with Headers (cont.)

javaexamples/http/v1/HttpRequest.java

HTTP 1.0 Responses with Headers

HTTP/1.0 ResponseCode ResponseText CRLF
Name1: Value1 CRLF
Name2: Value2 CRLF
.
.
.
NameN: ValueN CRLF
CRLF
Data

javaexamples/http/v1/HttpResponse.java

A Shortcoming of the Current Design

Code Duplication:
- In the HttpRequest and HttpResponse classes
An Improvement:
- Have an abstract common parent

An Improved Design

javaexamples/http/v2/HttpMessage.java

An Improved Design (cont.)

javaexamples/http/v2/HttpRequest.java

An Improved Design (cont.)

javaexamples/http/v2/HttpResponse.java

Content Types

Specification:
- Use the Multipurpose Internet Mail Extensions (MIME) descibed in RFC 1521
Designing a MIMETyper Class:
- Needs to read MIME types from a file into a NameValueMap so we don't want to construct a new one every time it is needed (hence, should use the Singleton pattern)
- Each connection will need to use it so it needs to be thread safe

A MIMETyper Class

javaexamples/http/v2/MIMETyper.java

An HTTP Connection Handler

javaexamples/http/v2/HttpConnectionHandler.java

An HTTP Server

Using Multiple Threads:
- Each connection can be handled in its own independent thread of execution
Using a Thread Pool:
- Use of a fixed thread pool allows the server to degrade gracefully (i.e., the system won't stop responding when capacity is exceeded, it will service them as fast as it can)

An HTTP Server

javaexamples/http/v2/HttpServer.java

HTTP 1.0 POST Requests

POST URI HTTP/1.0 CRLF
Content-type: Type CRLF
Content-length: Bytes CRLF
CRLF
Data

There's Always More to Learn