IPC::LDT 2.03

IPC::LDT is a Perl module that implements a length based IPC protocol.

Interprocess communication often uses line (or record) oriented protocols. FTP, for example, usually is such a protocol: a client sends a command (e.g. "LS") which is completed by a carriage return. This carriage return is included in the command which is sent to the server process (FTP deamon) which could implement its reading in a way like this:

while ($cmd= )
{
chomp($cmd);
performCommand($cmd);
}

Well, such record oriented, blocked protocols are very useful and simply to implement, but sometimes there is a need to transfer more complex data which has no trailing carriage return, or data which may include more carriage returns inside the message which should not cause the reciepient to think the message is already complete while it is really not. Even if you choose to replace carriage returns by some obscure delimiters, the same could happen again until you switch to a protocol which does not flag the end of a message by special strings.
On the other hand, if there is no final carriage return (or whatever flag string) within a message, the end of the message has to be marked another way to avoid blocking by endless waiting for more message parts. A simple way to provide this is to precede a message by a prefix which includes the length of the remaining (real) message. A reciepient reads this prefix, decodes the length information and continues reading until the announced number of bytes came in.

IPC::LDT provides a class to build objects which transparently perform such "length driven transfer". A user sends and receives messages by simple method calls, while the LDT objects perform the complete translation into and from LDT messages (with prefix) and all the necessary low level IO handling to transfer stream messages on non blocked handles.

IPC::LDT objects can be configured to transfer simle string messages as well as complex data structures. Additionally, they allow to delay the transfer of certain messages in a user defined way.