IPK project 1 - HTTP domain names resolver

Dávid Špavor
xspavo00

Simple server programmed in .NET core which supports GET and POST requests. Server is running on localhost. Make sure internet connection is available which is needed for translation of IP or host name, otherwise application won't work as expected! Server can listen to maximum of 10 clients.

Usage:

• make build

• make run PORT=1234

PORT number is between 0 - 65535.

• CTRL+C for terminating server

Implementation:

Project is implemented in one file Resolver.cs, which contain various methods:

• public static int Main(String[] args)
  • Main method.
  • Arguments checking.
• public static void StartListening(int port)
  • Contains socket handling and while(true) statement, where server is running.
  • Argument port specifies port, where server is listening.
  • On connection received, received data are evaluated and parsed. Based on evaluation requested method is handled.
  • Incoming data are evaluated by Regular Expressions and switch statements.
  • On success, result data with HTTP header are sent back to client and connection will be closed.
  • On failure, correct error HTTP header is returned to client.
• private static Socket ResolveHostName(Socket handler, string url)
  • Tries to resolve incoming host name to ip address.
  • On failure, 404 Not Found header is returned to client.
• private static Socket ResolveIP(Socket handler, Match match, string url)
  • Tries to resolve incoming ip address to host name.
  • On failure, 404 Not Found header is returned to client.
• private static IPAddress GetIPV4Address(string url)
  • Return resolved IPv4 address, because IPAddress type contains array of IPv4 or IPv6 addresses .
• public static string GetDataFromSocket(ref Socket handler)
  • Decode received data encoded in Bytes to string and return them in correct format, which is needed for further parsing.
• public static void SendMsgToClient(ref Socket handler, string msg)
  • Method for sending messages to client.

Format of requests and Testing

Format of requests

GET /resolve?name=apple.com&type=A HTTP/1.1
POST /dns-query HTTP/1.1

Testing

Application was tested by utility curl.
Example:

curl localhost:5353/resolve?name=www.fit.vutbr.cz\&type=A

Response:

www.fit.vutbr.cz:A=147.229.9.23  

POST:

curl --data-binary @queries.txt -X POST http://localhost:5353/dns-query

Where queries.txt contains:

www.fit.vutbr.cz:A  
www.google.com:A  
www.seznam.cz:A  
147.229.14.131:PTR  
ihned.cz:A  

Response:

www.fit.vutbr.cz:A=147.229.9.23
www.google.com:A=216.58.201.68
www.seznam.cz:A=77.75.74.176
147.229.14.131:PTR=dhcpz131.fit.vutbr.cz
ihned.cz:A=46.255.231.42

Important notes:

Post method

Please wait for "Waiting for connection.." statement on server console. Only when this statement is showed, requests can be sent!

File, which is required for sending data with POST method, is handled as follows:

• Empty lines are ignored.
• If at least one translation of query is successful, 200 OK is always returned despite others errors in file, so wrong lines are skipped.
• If empty file is received, 400 Bad Request is returned.
• If all queries are wrong, correct error header is returned.

Reference:

Socket programming Microsoft Documentation

Contacts:

[email protected]