Kamaelia.File.ReadFileAdaptor

• component ReadFileAdaptor

• ReadFileAdaptor Component
  • Example Usage
  • How to use it
  • To do

ReadFileAdaptor Component

A simple component that reads data from a file, line by line, or in chunks of bytes, at a constant rate that you specify.

Example Usage

Read one line at a time from a text file every 0.2 seconds, outputting to standard output:

Pipeline( ReadFileAdaptor("myfile.text", readmode='line', readsize=1, steptime=0.2),
          ConsoleEchoer(),
        ).run()

Read from a file at 1 Kilobits per second, in chunks of 256 bytes and send it to a server over a TCP network socket:

Pipeline( ReadFileAdaptor("myfile.data", readmode='bitrate', readsize=1, bitrate=1024*10),
          TCPClient("remoteServer.provider.com", port=1500),
        ).run()

How to use it

This component takes input from the outside world, and makes it available on it's outbox. It can take input from the following data sources:

• A specific file
• The output of a command
• stdin

In all cases, it can make the data available in the following modes:

• On a line by line basis
• On a "block by block" basis.
• At an attempted (not guaranteed) bit rate.
• If at a bit rate, also a "frame rate". (eg if you want 1Mbit/s, do you want that as 1x1Mbit block, 4x250Kbit blocks, 25x 40Kbit blocks, or what, each second?
• A "step time" to define how often to read 0 == as often/fast as possible 0.1 == every 0.1 seconds, 0.5 = every 0.5 seconds, 2 = every 2 seconds etc.

Clearly some of these modes are mutually exclusive!

Once ReadFileAdaptor has finished reading from the file, it finishes by sending a producerFinished() message out of its "signal" outbox, then immediately terminates.

There is no way to tell ReadFileAdaptor to prematurely stop. It ignores all messages sent to its "control" inbox.

To do

The default standalone behaviour is to read in from stdin, and dump to stdout in a teletype fashion the data it recieves. It _may_ gain command line parsing at some point, which would be wacky. (And probably a good way of initialising components - useful standalone & externally)

XXX TODO: Signal EOF on an external output to allow clients to destroy us. XXX Implement the closeDown method - ideally add to the component XXX framework.

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Kamaelia.File.ReadFileAdaptor.ReadFileAdaptor

class ReadFileAdaptor(Axon.Component.component)

An instance of this class is a read file adaptor component. It's constructor arguments are all optional. If no arguments are provided, then the default is to read from stdin, one line at a time, as fast as possible. Note that this will cause the outbox to fill at the same rate as stdin can provide data. (Be wary of memory constraints this will cause!)

Arguments & meaning:

• filename="filename" - the name of the file to read. If you want stdin, do not provide a filename! If you want the output from a command, also leave this blank...

• command="command" - the name of the command you want the output from. Leave the filename blank if you use this!

• readmode - possible values:

  • "bitrate" - read at a specified bitrate.
  • "line" - read on a line by line basis
  • "block" - read the file on a block by block basis.

• If bitrate mode is set, you should set bitrate= to your desired bitrate (unless you want 64Kbit/s), and chunkrate= to your desired chunkrate (unless you want 24 fps). You are expected to be able to handle the bit rate you request!

• If block mode is set then you should set readsize (size of the block in bytes), and steptime (how often you want bytes). If steptime is set to zero, you will read blocks at the speed the source device can provide them. (be wary of memory constraints)

After setting the ReadFileAdaptor in motion, you can then hook it into your linkages like any other component.

Inboxes

• control : NOT USED
• inbox : NOT USED

Outboxes

• outbox : When data is read, it is made available here.
• signal : Shutdown signalling

Methods defined here

__init__(self[, filename][, command][, readmode][, readsize][, steptime][, bitrate][, chunkrate][, debug])

Standard constructor, see class docs for details

closeDownComponent(self)

#!!!! Called at component exit... Closes the file handle

getDataByteLen(self)

This method attempts to read data of a specific block size from the file handle. If null, the file is EOF. This method is never called directly. If the readmode is block or bitrate, then the attribute self.getData is set to this function, and then this function is called using self.getData(). The reason for this indirection is to make it so that the check for which readmode we are in is done once, and once only

getDataReadline(self)

This method attempts to read a line of data from the file handle. If null, the file is EOF. As with getDataByteLen, this method is never called directly. If the readmode is readline (or ""), then the attribute self.getData is set to this function, and then this function is called using self.getData(). Same reason for indirection as above.

initialiseComponent(self)

Opens the appropriate file handle

mainBody(self)

We check whether it's time to perform a new read, if it is, we read some data. If we get some data, we put it in out outbox "outbox", and to stdout (if debugging). If we had an error state (eg EOF), we return 0, stopping this component, otherwise we return 1 to live for another line/block.