zig-dns

Experimental DNS library implemented in zig.

So far implements RFC 1035 plus some updates.

The library itself has no dependencies, the CLI example uses zig-network to send and receive packets over the network.

• Library: src/dns.zig
• CLI test: src/main.zig

Features

• Streaming interface
• Parse DNS packets
• Generate DNS packets
• Print packet contents
• Label compression

Currently supported record types

• A - A host address
• NS - An authoritative name server
• MD - A mail destination (Obsolete)
• MF - A mail forwarder (Obsolete)
• CNAME - The canonical name for an alias
• SOA - Marks the start of a zone of authority
• MB - A mailbox domain name (Experimental)
• MG - A mail group member (Experimental)
• MR - A mail rename domain name (Experimental)
• NULL - A byte array (Experimental)
• WKS - A well known service description
• PTR - A domain name pointer
• HINFO - Host information
• MINFO - Mailbox or mail list information
• MX - Mail exchange
• TXT - Text strings
• RP - Responsible Person RFC 1183
• AAAA - An IPv6 host address RFC 3596
• LOC - Location information RFC 1876
• SRV - Service locator RFC 2782
• SSHFP - SSH Fingerprint RFC 4255, RFC 6594
• URI - Uniform Resource Identifier RFC 7553

Interactive

For testing and development purposes you can call the library interactively from the command line.

Usage: zig-dns <dns-server> <domain> <query-type>

Interactive Example

$ zig-dns 1.1.1.1 www.lambda.cx A
Sending bytes: { 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 3, 119, 119, 119, 6, 108, 97, 109, 98, 100, 97, 2, 99, 120, 0, 0, 1, 0, 1 }
Query:
 Message {
  Header {
    ID: 1
    Response: false
    OpCode: query
    Authoritative Answer: false
    Truncation: false
    Recursion Desired: true
    Recursion Available: false
    Z: 0
    Response Code: no_error
  }
  Questions {
    Question {
      Name: www.lambda.cx.
      QType: A
      QClass: IN
    }
  }
  Ansewrs {
  }
  Authorities {
  }
  Additional {
  }
}
Recv: { 0, 1, 129, 128, 0, 1, 0, 2, 0, 0, 0, 0, 3, 119, 119, 119, 6, 108, 97, 109, 98, 100, 97, 2, 99, 120, 0, 0, 1, 0, 1, 192, 12, 0, 5, 0, 1, 0, 0, 7, 8, 0, 2, 192, 16, 192, 16, 0, 1, 0, 1, 0, 0, 7, 8, 0, 4, 155, 138, 137, 134 }
Response:
Message {
  Header {
    ID: 1
    Response: true
    OpCode: query
    Authoritative Answer: false
    Truncation: false
    Recursion Desired: true
    Recursion Available: true
    Z: 0
    Response Code: no_error
  }
  Questions {
    Question {
      Name: www.lambda.cx.
      QType: A
      QClass: IN
    }
  }
  Ansewrs {
    Resource Record {
      Name: www.lambda.cx.
      Type: CNAME
      Class: IN
      TTL: 1800
      Resource Data Length: 2
      Resource Data: lambda.cx.
    }
    Resource Record {
      Name: lambda.cx.
      Type: A
      Class: IN
      TTL: 1800
      Resource Data Length: 4
      Resource Data: 155.138.137.134
    }
  }
  Authorities {
  }
  Additional {
  }
}

Example Code

const std = @import("std");
const io = std.io;
const network = @import("network");
const dns = @import("zig-dns/src/dns.zig");

// [...] Main function, allocator, etc.

try network.init();
defer network.deinit();
const sock = try network.connectToHost(allocator, "8.8.8.8", 53, .udp);
defer sock.close();
const writer = sock.writer();

const message = try dns.createQuery(allocator, "lambda.cx", .A);
defer message.deinit();

var message_bytes = try message.to_bytes();
try writer.writeAll(message_bytes);

var recv = [_]u8{0} ** 1024;
const recv_size = try sock.receive(&recv);

const response = try dns.Message.from_bytes(allocator, recv[0..recv_size]);
defer response.deinit();

std.debug.print("Response:\n{any}\n", .{ response });

Output:

Response:
Message {
  Header {
    ID: 1
    Response: true
    OpCode: query
    Authoritative Answer: false
    Truncation: false
    Recursion Desired: true
    Recursion Available: true
    Z: 0
    Response Code: no_error
  }
  Questions {
    Question {
      Name: www.lambda.cx.
      QType: A
      QClass: IN
    }
  }
  Ansewrs {
    Resource Record {
      Name: www.lambda.cx.
      Type: CNAME
      Class: IN
      TTL: 1800
      Resource Data Length: 2
      Resource Data: lambda.cx.
    }
    Resource Record {
      Name: lambda.cx.
      Type: A
      Class: IN
      TTL: 1800
      Resource Data Length: 4
      Resource Data: 155.138.137.134
    }
  }
  Authorities {
  }
  Additional {
  }
}

Iterative Example

See iterative.zig as an example for how to use this library iteratively.