Tcl library for redis access

Installation:

'make install' will install the library into what it detects is your library location for tcl. It does this detection through the entirely simple method of using the tclsh in your path to check the output of 'info library' command. The method of detection should be expanded in the future to play more nicely with alternate tcl installations.

'package require redis' will get you started.

The 'redis' command creates a redis connection that can then be passed normal redis commands. For example, the following creates a redis connection, and runs the redis time command (it ignores the output however, that part is up to you!):

    package require redis
    
    set redis [redis $host $port]
    
    $redis time
    $redis set abc 123
    $redis get abc

There is chance that you want to send redis commands in pipeline mode, and read all the result back in a batch.

So we have the $redis pipeline command for this.

    $redis pipeline {
        $redis set abc 321
        $redis -key abc get abc

        $redis set def 789
        $redis -key def -- get def
    }

One problem here is when complex logic are inserted between each redis command. The brace will be very large. And it's not good for clear reading.

We noticed that the key here is defer reading of the results. So we introce -defer for it.

    $redis -defer set abc 123
    $redis -defer -key abc get abc
    
    # use "--" to separate redis command. This make code easy to read.
    
    $redis -defer -- set def 456
    $redis -defer -key def -- get def
    
    set result [$redis collect]

    # Output: 0 OK abc 123 2 OK def 456

• Use -defer option to send commands to redis server first.
• But defer the reasult reading to later stage.
• Use $redis collect to get all the results back.
• Option -key is used to provide the key in the returned dict
• When -key option is missing, a sequence number is used.

It is possible to use this client for basic pub/sub operations with redis. To subscribe to a channel you must first set a callback and then subscribe as below:

    $redis setcallback procname

    $redis subscribe x y taters

Once a specific connection is set for a subscription it CANNOT be used for other redis communications. At this time it is only possible to bulk unsubscribe from all channels through:

    $redis unsubscribe

This will also reset callback to empty. To get the callback before unsubscribe:

    set callback [$redis getcallback]

An example of callback may looks like:

    proc onPublish {channels redis type reply} {
      if {[llength $reply]==1 && $reply>0} {
        # OK subscribe $reply
        return
      }

      lassign $reply kind channel data
      # kind = enum { subscribe unsubscribe message }
    }