docs » hs.network.ping.echoRequest

Provides lower-level access to the ICMP Echo Request infrastructure used by the hs.network.ping module. In general, you should not need to use this module directly unless you have specific requirements not met by the hs.network.ping module and the hs.network.ping object methods.

This module is based heavily on Apple's SimplePing sample project which can be found at https://developer.apple.com/library/content/samplecode/SimplePing/Introduction/Intro.html.

When a callback function argument is specified as an ICMP table, the Lua table returned will contain the following key-value pairs:

In cases where the callback receives a "receivedUnexpectedPacket" message because the packet is corrupted or truncated, this table may only contain the _raw field.

API Overview

API Documentation

Constructors

echoRequest
Signature hs.network.ping.echoRequest.echoRequest(server) -> echoRequestObject
Type Constructor
Description

Creates a new ICMP Echo Request object for the server specified.

Parameters:

  • server - a string containing the hostname or ip address of the server to communicate with. Both IPv4 and IPv6 style addresses are supported.

Returns:

  • an echoRequest object

Notes:

  • This constructor returns a lower-level object than the hs.network.ping.ping constructor and is more difficult to use. It is recommended that you use this constructor only if hs.network.ping.ping is not sufficient for your needs.

  • For convenience, you can call this constructor as hs.network.ping.echoRequest(server)

Methods

acceptAddressFamily
Signature hs.network.ping.echoRequest:acceptAddressFamily([family]) -> echoRequestObject | current value
Type Method
Description

Get or set the address family the echoRequestObject should communicate with.

Parameters:

  • family - an optional string, default "any", which specifies the address family used by this object. Valid values are "any", "IPv4", and "IPv6".

Returns:

  • if an argument is provided, returns the echoRequestObject, otherwise returns the current value.

Notes:

  • Setting this value to "IPv6" or "IPv4" will cause the echoRequestObject to attempt to resolve the server's name into an IPv6 address or an IPv4 address and communicate via ICMPv6 or ICMP(v4) when the hs.network.ping.echoRequest:start method is invoked. A callback with the message "didFail" will occur if the server could not be resolved to an address in the specified family.
  • If this value is set to "any", then the first address which is discovered for the server's name will determine whether ICMPv6 or ICMP(v4) is used, based upon the family of the address.

  • Setting a value with this method will have no immediate effect on an echoRequestObject which has already been started with hs.network.ping.echoRequest:start. You must first stop and then restart the object for any change to have an effect.

hostAddress
Signature hs.network.ping.echoRequest:hostAddress() -> string | false | nil
Type Method
Description

Returns a string representation for the server's IP address, or a boolean if address resolution has not completed yet.

Parameters:

  • None

Returns:

  • If the object has been started and address resolution has completed, then the string representation of the server's IP address is returned.
  • If the object has been started, but resolution is still pending, returns a boolean value of false.
  • If the object has not been started, returns nil.
hostAddressFamily
Signature hs.network.ping.echoRequest:hostAddressFamily() -> string
Type Method
Description

Returns the host address family currently in use by this echoRequestObject.

Parameters:

  • None

Returns:

  • a string indicating the IP address family currently used by this echoRequestObject. It will be one of the following values:
    • "IPv4" - indicates that ICMP(v4) packets are being sent and listened for.
    • "IPv6" - indicates that ICMPv6 packets are being sent and listened for.
    • "unresolved" - indicates that the echoRequestObject has not been started or that address resolution is still in progress.
hostName
Signature hs.network.ping.echoRequest:hostName() -> string
Type Method
Description

Returns the name of the target host as provided to the echoRequestObject's constructor

Parameters:

  • None

Returns:

  • a string containing the hostname as specified when the object was created.
identifier
Signature hs.network.ping.echoRequest:identifier() -> integer
Type Method
Description

Returns the identifier number for the echoRequestObject.

Parameters:

  • None

Returns:

  • an integer specifying the identifier which is embedded in the ICMP packets this object sends.

Notes:

  • ICMP Echo Replies which include this identifier will generate a "receivedPacket" message to the object callback, while replies which include a different identifier will generate a "receivedUnexpectedPacket" message.
isRunning
Signature hs.network.ping.echoRequest:isRunning() -> boolean
Type Method
Description

Returns a boolean indicating whether or not this echoRequestObject is currently listening for ICMP Echo Replies.

Parameters:

  • None

Returns:

  • true if the object is currently listening for ICMP Echo Replies, or false if it is not.
nextSequenceNumber
Signature hs.network.ping.echoRequest:nextSequenceNumber() -> integer
Type Method
Description

The sequence number that will be used for the next ICMP packet sent by this object.

Parameters:

  • None

Returns:

Notes:

  • ICMP Echo Replies which are expected by this object should always be less than this number, with the caveat that this number is a 16-bit integer which will wrap around to 0 after sending a packet with the sequence number 65535.
  • Because of this wrap around effect, this module will generate a "receivedPacket" message to the object callback whenever the received packet has a sequence number that is within the last 120 sequence numbers we've sent and a "receivedUnexpectedPacket" otherwise.
    • Per the comments in Apple's SimplePing.m file: Why 120? Well, if we send one ping per second, 120 is 2 minutes, which is the standard "max time a packet can bounce around the Internet" value.
seeAllUnexpectedPackets
Signature hs.network.ping.echoRequest:seeAllUnexpectedPackets([state]) -> boolean | echoRequestObject
Type Method
Description

Get or set whether or not the callback should receive all unexpected packets or only those which carry our identifier.

Parameters:

  • state - an optional boolean, default false, specifying whether or not all unexpected packets or only those which carry our identifier should generate a "receivedUnexpectedPacket" callback message.

Returns:

  • if an argument is provided, returns the echoRequestObject; otherwise returns the current value

Notes:

  • The nature of ICMP packet reception is such that all listeners receive all ICMP packets, even those which belong to another process or echoRequestObject.
    • By default, a valid packet (i.e. with a valid checksum) which does not contain our identifier is ignored since it was not intended for our receiver. Only corrupt or packets with our identifier but that were otherwise unexpected will generate a "receivedUnexpectedPacket" callback message.
    • This method optionally allows the echoRequestObject to receive all incoming packets, even ones which are expected by another process or echoRequestObject.
  • If you wish to examine ICMPv6 router advertisement and neighbor discovery packets, you should set this property to true. Note that this module does not provide the necessary tools to decode these packets at present, so you will have to decode them yourself if you wish to examine their contents.
sendPayload
Signature hs.network.ping.echoRequest:sendPayload([payload]) -> echoRequestObject | false | nil
Type Method
Description

Sends a single ICMP Echo Request packet.

Parameters:

  • payload - an optional string containing the data to include in the ICMP Echo Request as the packet payload.

Returns:

  • If the object has been started and address resolution has completed, then the ICMP Echo Packet is sent and this method returns the echoRequestObject
  • If the object has been started, but resolution is still pending, the packet is not sent and this method returns a boolean value of false.
  • If the object has not been started, the packet is not sent and this method returns nil.

Notes:

  • By convention, unless you are trying to test for specific network fragmentation or congestion problems, ICMP Echo Requests are generally 64 bytes in length (this includes the 8 byte header, giving 56 bytes of payload data). If you do not specify a payload, a default payload which will result in a packet size of 64 bytes is constructed.
setCallback
Signature hs.network.ping.echoRequest:setCallback(fn | nil) -> echoRequestObject
Type Method
Description

Set or remove the object callback function

Parameters:

  • fn - a function to set as the callback function for this object, or nil if you wish to remove any existing callback function.

Returns:

  • the echoRequestObject

Notes:

  • The callback function should expect between 3 and 5 arguments and return none. The possible arguments which are sent will be one of the following:

    • "didStart" - indicates that the object has resolved the address of the server and is ready to begin sending and receiving ICMP Echo packets.

      • object - the echoRequestObject itself
      • message - the message to the callback, in this case "didStart"
      • address - a string representation of the IPv4 or IPv6 address of the server specified to the constructor.
    • "didFail" - indicates that the object has failed, either because the address could not be resolved or a network error has occurred.

      • object - the echoRequestObject itself
      • message - the message to the callback, in this case "didFail"
      • error - a string describing the error that occurred.
    • Notes:

    • "sendPacket" - indicates that the object has sent an ICMP Echo Request packet.

      • object - the echoRequestObject itself
      • message - the message to the callback, in this case "sendPacket"
      • icmp - an ICMP packet table representing the packet which has been sent as described in the header of this module's documentation.
      • seq - the sequence number for this packet. Sequence numbers always start at 0 and increase by 1 every time the hs.network.ping.echoRequest:sendPayload method is called.
    • "sendPacketFailed" - indicates that the object failed to send the ICMP Echo Request packet.

      • object - the echoRequestObject itself
      • message - the message to the callback, in this case "sendPacketFailed"
      • icmp - an ICMP packet table representing the packet which was to be sent.
      • seq - the sequence number for this packet.
      • error - a string describing the error that occurred.
    • Notes:

      • Unlike "didFail", the echoRequestObject is not stopped when this message occurs; you can try to send another payload if you wish without restarting the object first.
    • "receivedPacket" - indicates that an expected ICMP Echo Reply packet has been received by the object.

      • object - the echoRequestObject itself
      • message - the message to the callback, in this case "receivedPacket"
      • icmp - an ICMP packet table representing the packet received.
      • seq - the sequence number for this packet.
    • "receivedUnexpectedPacket" - indicates that an unexpected ICMP packet was received

      • object - the echoRequestObject itself
      • message - the message to the callback, in this case "receivedUnexpectedPacket"
      • icmp - an ICMP packet table representing the packet received.
    • Notes:
      • This message can occur for a variety of reasons, the most common being:
        • the ICMP packet is corrupt or truncated and cannot be parsed
      • the ICMP Identifier does not match ours and the sequence number is not one we have sent
      • the ICMP type does not match an ICMP Echo Reply
      • When using IPv6, this is especially common because IPv6 uses ICMP for network management functions like Router Advertisement and Neighbor Discovery.
      • In general, it is reasonably safe to ignore these messages, unless you are having problems receiving anything else, in which case it could indicate problems on your network that need addressing.
start
Signature hs.network.ping.echoRequest:start() -> echoRequestObject
Type Method
Description

Start the echoRequestObject by resolving the server's address and start listening for ICMP Echo Reply packets.

Parameters:

  • None

Returns:

  • the echoRequestObject
stop
Signature hs.network.ping.echoRequest:stop() -> echoRequestObject
Type Method
Description

Start listening for ICMP Echo Reply packets with this object.

Parameters:

  • None

Returns:

  • the echoRequestObject