Dns

This document describes the Dns client available in the JavaScript environment for app serivices.

Table of content

Object	Dns
Functions	getHostByName
Object	DnsRequest
Functions	onresult
Object	DnsResult
Members	addr isIPv6
Examples	Getting an IP address for a host name Getting all IP addresses for a host name

Dns

getHostByName

Starts a DNS resolution of a given host name.

Parameters

string hostName	The hostname to be resolved.
bool all	Optional. If true, the result will be an array of all resolved addresses.
int timeout	Optional. The timeout for the request in milliseconds. If no timeout is specified, the default timeout of 5000ms will be used.

Return value

DnsRequest

An object representing the request.

Dns.getHostByName("www.example.com")
    .onresult(function(hostName, result) {
        log(hostName + ": " + (result ? result.addr : "not found"));
     });

Sets a callback function for processing the response from the DNS server. The callback must be set synchronously after calling Dns.getHostByName. Note that depending on the parameter all, the result will be

a single DnsResult or undefined
an array containing 0..n DnsResult objects

Parameters, if all is set to false

function callback(string hostName, DnsResult result)

A callback that will be called the DNS request is complete.

Parameters, if all is set to true

function callback(string hostName, [DnsResult])

A callback that will be called the DNS request is complete.

Return value

DnsRequest

A reference to the object itself. Useful for method chaining.

Dns.getHostByName("www.example.com")
    .onresult(function(hostName, result) {
        log(hostName + ": " + (result ? result.addr : "not found"));
     });

DnsResult

addr

A string containing the resolved address.

isIPv6

True, if addr represents an IPv6 address. Otherwise addr represents an IPv4 address.

Examples

Getting an IP address for a host name

In this example we do a DNS resolution of a host name and print the resolved address to the log.

Dns.getHostByName("www.example.com").onresult(function(hostName, result) {
    log("DNS resolution for " + hostName + ":");
    if (result) {
        log((result.isIPv6 ? "    IPv6: " : "    IPv4: ") + result.addr);
    }
    else {
        log("    host not found");
    }
});

Getting all IP addresses for a host name

In this example we do a DNS resolution of a host name and print all resolved addresses to the log.

Dns.getHostByName("www.example.com", true).onresult(function(hostName, result) {
    log("DNS resolution for " + hostName + ":");
    if (result.length) {
        result.forEach(function(r) {
            log((r.isIPv6 ? "    IPv6: " : "    IPv4: ") + r.addr);
        });
    }
    else {
        log("    host not found");
    }
});