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Asynchronous DNS for Icicle

This library is a component for Icicle, providing an asynchronous DNS query executor, resolver, and client connector. An asynchronous DNS server is currently under development and will be added to this component in the future. Like other Icicle components, this library uses Generators to make writing asynchronous code more like writing synchronous code.

Requirements

• PHP 5.5+ for v0.6.x branch (current stable) and v1.x branch (mirrors current stable)
• PHP 7 for v2.0 branch (under development) supporting generator delegation and return expressions

Installation

The recommended way to install is with the Composer package manager. (See the Composer installation guide for information on installing and using Composer.)

Run the following command to use this library in your project:

You can also manually edit composer.json to add this library as a project requirement.

Example

The example below uses the Icicle\Dns\resolver() function to asynchronously find the IP address for the domain icicle.io.

Documentation

• Executors - Executes a DNS query.
  • Creating an Executor
  • execute() function
  • Using an Executor
  • MultiExecutor
• Resolver - Resolves the IP address for a domain name.
  • resolve() function
• Connector - Connects to a host and port.
  • connect() function

Methods returning a Generator can be used to create a Coroutine (e.g., new Coroutine($executor->execute(...))) or yielded within another Coroutine (use yield from in PHP 7 for better performance).

This library uses LibDNS to create and parse DNS messages. Unfortunately the documentation for this library is currently limited to DocComments in the source code. If only using resolvers and connectors in this library, there is no need to worry about how LibDNS works. Executors returns coroutines that are resolved with LibDNS\Messages\Message instances, representing the response from the DNS server. Using these objects is simple and will be described in the executor section below.

Function prototypes

Prototypes for object instance methods are described below using the following syntax:

Executors

Executors are the foundation of the DNS component, performing any DNS query and returning the full results of that query. Resolvers and connectors depend on executors to perform the DNS query required for their operation.

Each executor implements Icicle\Dns\Executor\Executor that defines a single method, execute().

An executor will retry a query a number of times if it doesn't receive a response within timeout seconds. The number of times a query will be retried before failing is defined by retries, with timeout seconds elapsing between each query attempt.

execute() Function

The simplest way to perform a DNS query is to use the Icicle\Dns\execute() function. This function uses an Icicle\Dns\Executor\Executor object that can be set or retrieved using the Icicle\Dns\executor() function.

Example using the execute() function to find the A record for a domain:

Creating an Executor

The simplest executor is Icicle\Dns\Executor\BasicExecutor, created by providing the constructor with the IP address of a DNS server to use to perform queries. It is recommended to use a DNS server closest to you, such as the local router. If this is not possible, Google operates two DNS server that also can be used at 8.8.8.8 and 8.8.4.4.

The Icicle\Dns\Executor\BasicExecutor constructor also accepts an instance of Icicle\Socket\Connector\Connector as the second argument if custom behavior is desired when connecting to the name server. If no instance is given, the default global connector is used (see Icicle\Socket\connector()).

Using an Executor

Once created, an executor is used by calling the execute() method with the domain and type of DNS query to be performed. The type may be a case-insensitive string naming a record type (e.g., 'A', 'MX', 'NS', 'PTR', 'AAAA') or the integer value corresponding to a record type (LibDNS\Records\ResourceQTypes defines constants corresponding to a the integer value of a type). execute() returns a coroutine fulfilled with an instance of LibDNS\Messages\Message that represents the response from the name server. LibDNS\Messages\Message objects have several methods that will need to be used to fetch the data in the response.

• getAnswerRecords(): Returns an instance of LibDNS\Records\RecordCollection, a traversable collection of LibDNS\Record\Resource objects containing the response answer records.
• getAuthorityRecords(): Returns an instance of LibDNS\Records\RecordCollection containing the response authority records.
• getAdditionalRecords(): Returns an instance of LibDNS\Records\RecordCollection containing the response additional records.
• getAuthorityRecords(): Returns an instance of LibDNS\Records\RecordCollection containing the response authority records.
• isAuthoritative(): Determines if the response is authoritative for the records returned.

DNS records in the traversable LibDNS\Records\RecordCollection objects are represented as instances of LibDNS\Records\Resource. These objects have several methods to access the data associated with the record.

• getType(): Returns the record type as an integer.
• getName(): Gets the domain name associated with the record as a string.
• getData(): Returns an LibDNS\Records\RData instance representing the records data. This object may be cast to a string or each field can be accessed with the LibDNS\Records\RData::getField(int $index) method. The number of fields in a resource depends on the type of resource (e.g., MX records contain two fields, a priority and a host name).
• getTTL(): Gets the TTL (time-to-live) as an integer.

Below is an example of how an executor can be used to find the NS records for a domain.

MultiExecutor

The Icicle\Dns\Executor\MultiExecutor class can be used to combine multiple executors to send queries to several name servers so queries can be resolved even if some name servers stop responding.

Queries using the above executor will automatically send requests to the second name server if the first does not respond. Subsequent queries are initially sent to the last server that successfully responded to a query.

Resolver

A resolver finds the IP addresses for a given domain. Icicle\Dns\Resolver\BasicResolver implements Icicle\Dns\Resolver\Resolver, which defines a single method, resolve(). A resolver is essentially a specialized executor that performs only A queries, fulfilling the coroutine returned from resolve() with an array of IP addresses (even if only one or zero IP addresses is found, the coroutine is still resolved with an array).

resolve() Function

The simplest way find the IP address for a domain is to use the Icicle\Dns\resolve() function. This function uses an Icicle\Dns\Resolver\Resolver object that can be set or retrieved using the Icicle\Dns\resolver() function.

Example using the resolve() function to resolve the IP address of a domain:

Like executors, a resolver will retry a query retries times if the name server does not respond within timeout seconds.

The Icicle\Resolver\BasicResolver class is constructed by passing an Icicle\Executor\Executor instance that is used to execute queries to resolve domains. If no executor is given, one will be created by default, using 8.8.8.8 and 8.8.4.4 as DNS servers for the executor.

Example

Connector

The connector component connects to a server by first resolving the hostname provided, then making the connection and resolving the returned coroutine with an instance of Icicle\Socket\Socket.

Icicle\Dns\Connector\Connector defines a single method, connect() that should resolve a host name and connect to one of the resolved servers, resolving the coroutine with the connected client.

connect() Function

The simplest way to resolve a domain name and connect to a port on the resolved host is with the Icicle\Dns\connect() function. This function uses an Icicle\Dns\Connector\Connector object that can be set or retrieved using the Icicle\Dns\connector() function.

Example using the connect() function to resolve the IP address of a domain and connect to port 443:

Icicle\Dns\Connector\DefaultConnector will attempt to connect to one of the IP addresses found for a given host name. If the server at that IP is unresponsive, the connector will attempt to establish a connection to the next IP in the list until a server accepts the connection. Only if the connector is unable to connect to all of the IPs will it reject the coroutine returned from connect(). The constructor also optionally accepts an instance of Icicle\Socket\Connector\Connector if custom behavior is desired when connecting to the resolved host.

Additionally, all the other options available to Icicle\Socket\Connector\Connector::connect() may also be used.

Example