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Asynchronous Web Server

Description

A web server that uses the following advanced I/O operations:

  • Asynchronous operations on files
  • Non-blocking operations on sockets
  • Zero-copying
  • Multiplexing I/O operations

The server implements a limited functionality of the HTTP protocol: passing files to clients.

The web server will use the multiplexing API to wait for connections from clients - epoll. On the established connections, requests from clients will be received and then responses will be distributed to them.

The server will serve files from the AWS_DOCUMENT_ROOT directory' header. Files are only found in subdirectories AWS_DOCUMENT_ROOT/static/ and AWS_DOCUMENT_ROOT/dynamic/. The corresponding request paths will be, for example, AWS_DOCUMENT_ROOT/static/test.dat and AWS_DOCUMENT_ROOT/dynamic/test.dat. The file processing will be:

  • The files in the AWS_DOCUMENT_ROOT/static/ directory are static files that will be transmitted to clients using the zero-copying API - sendfile]
  • Files in the AWS_DOCUMENT_ROOT/dynamic/ directory are files that are supposed to require a server-side post-processing phase. These files will be read from disk using the asynchronous API and then pushed to the clients. Streaming will use non-blocking sockets (Linux)
  • An HTTP 404 message will be sent for invalid request paths

After transmitting a file, according to the HTTP protocol, the connection is closed.

Details of the implementation

  • Implementing the server requires having a state machine for each connection, which is periodically queried and updated as the transfer proceeds. Check the connection_state data structure defined in the aws header.
  • The connection data structure defined in the aws header is used to keep track of an open connection.
  • Definitions of other useful macros and data structures can be found in the aws header.
  • HTTP responses will have the code 200 for existing files and 404 for not existing files.
    • A valid response consists of the HTTP header, containing the related directives, two newlines (\r\n\r\n), followed by the actual content (the file).
    • Sample answers can be found in the parser test file or in the provided sample.
    • The Content-Length directive must specify the size of the HTTP content (actual data) in bytes.
    • The Connection directive must be initialized to close.
  • The port on which the web server listens for connections is defined within the aws header: the AWS_LISTEN_PORT macro.
  • The root directory relative to which the resources/files are searched is defined within the aws header as the AWS_DOCUMENT_ROOT macro.

Resources