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Socket

This page contains random notes about the @accessors-modules/socket module. See The JSDoc page for user-level information.

Problems with the Node socket implementation.

TCPSocketServer is not receiving data events

'''This issue is solved, the notes are left here for future reference.

The port of the @accessors-modules/socket module to node is not working.

The TCPSocketServer in a composite accessor is not receiving data events.

Running this command:

  (cd $PTII/org/terraswarm/accessor/accessors/web/; node hosts/node/nodeHostInvoke.js hosts/node/node_modules/@accessors-modules/socket/test/auto/TCPSocketUnsignedShort.js)

causes an error because the test actor connected to the TCPSocketServer is not getting input

Details

Below are the files in question:

$PTII/ptolemy/actor/lib/jjs/modules/socket/SocketHelper.java

Cape Code Java Implementation

$PTII/ptolemy/actor/lib/jjs/modules/socket/socket.js

Cape Code socket module implementation that uses SocketHelper

$PTII/org/terraswarm/accessor/accessors/web/node_modules/@accessors-hosts/node/node_modules/@accessors-modules/socket/socket.js

Node socket module implementation

$PTII/org/terraswarm/accessor/test/auto/TCPSocketUnsignedShort.xml

The Cape Code model

$PTII/org/terraswarm/accessor/accessors/web/node_modules/@accessors-hosts/node/node_modules/@accessors-modules/socket/test/auto/TCPSocketUnsignedShort.js

The composite accessor to be run by node

A model was updated to include only accessors:

To run the model:

  $PTII/bin/capecode $PTII/org/terraswarm/accessor/test/auto/TCPSocketUnsignedShort.xml

The model works fine in Cape Code:

• TrainableTest, which is connected to the TCPSocketServer has correctValues of {65535, 0, 1, 65535, 0}
• TrainableTest2, which is connected to the TCPSocketClient has correctValues of {0, 1, 2, 0, 1}

The issue is that when we drag in a code generator and generate code, then the generated code fails because TrainableTest is not seeing any data.

To run the generated code:

  (cd $PTII/org/terraswarm/accessor/accessors/web/cg; node ../node_modules/@accessors-hosts/node/nodeHostInvoke.js cg/TCPSocketUnsignedShort)

The generated model with the stopTime increased slightly is checked in as PTII/org/terraswarm/accessor/accessors/web/hosts/node/node_modules/@accessors-modules/socket/test/auto/TCPSocketUnsignedShort.js

The checked in version may be run with:

  (cd $PTII/org/terraswarm/accessor/accessors/web/; node hosts/node/nodeHostInvoke.js hosts/node/node_modules/@accessors-modules/socket/test/auto/TCPSocketUnsignedShort.js)

TCPSocketServer.js and TCPSocketClient.js have had debugging statements temporarily added to them.

Comparing the output of the Cape Code run and the Node run indicates that the server is not getting socket data.

Below is the output of the Node version of the model, which was created with

  (cd $PTII/org/terraswarm/accessor/accessors/web/; node hosts/node/nodeHostInvoke.js hosts/node/node_modules/@accessors-modules/socket/test/auto/TCPSocketUnsignedShort.js)

and then the output hangs until the model times out and fails.

Below is the Cape Code output, created with:

  $PTII/bin/capecode $PTII/org/terraswarm/accessor/test/auto/TCPSocketUnsignedShort.xml

which works fine:

The two outputs are slightly different because of platform dependencies, below is a more detailed analysis of the above outputs.

The Node and Cape Code output match fairly closely until processBuffer().

The Node output calls emit

The difference is that the Cape Code output below shows that TCPSocketServer.js is getting data events, whereas the node output is not.

Looking at the source code is helpful.

In Cape Code, the way _processBuffer() gets invoked is that $PTII/ptolemy/actor/lib/jjs/modules/socket/SocketHelper.java has:

In Cape Code, _processBuffer() is defined as below.

The code above emits a data event on the _eventEmitter.

(BTW - To make it easier to track _eventEmitter, in socket.js, a field was added to SocketClient, SocketServer and Socket so that we can easily print out the name of the object. In both Cape Code and Node, we are calling emit on a Socket)

In Cape Code, when we run the above, we generate the following output

$PTII/org/terraswarm/accessor/accessors/web/net/TCPSocketServer.js contains the following:

Which, in Cape Code, correctly produces:

For the Node socket module, a SocketWrapper was added, which is a partial port of the SocketWrapper from the Cape Code SocketWrapper defined in SocketHelper.java

Looking at the socket module in node at $PTII/org/terraswarm/accessor/accessors/web/hosts/node/node_modules/@accessors-modules/socket/socket.js

In the Node host, the above generates

However, it seems that the data event that is emitted is never acted upon.

Solution to emit problem

In hosts/node/node_modules/@accessors-modules/socket/socket.js, one fix was to change:

       this.eventEmitter.emit("emit", "data", buffer.readUInt16BE(position));

to

       this.eventEmitter.emit('data', buffer.readUInt16BE(position));

Node: Downstream Actors Don't See Tokens.

To replicate:

  $PTII/bin/capecode $PTII/org/terraswarm/accessor/test/auto/TCPSocketUnsignedShortSimple.xml 

This model works fine under CapeCode.

Under Node, when we generate code, it fails because the TrainableTest actor sees a 2 instead of 65536.

This is because under Node, the TCPSocketServer produces 65535,0,1,65535,0,2 and the TrainableTest sees the last 2.

In the CapeCode output below, we can see that we are emitting the data and then the Test accessor is getting the inputs

In the node example, which was created from the Cape Code model and run with:

we can see that we are getting a 2 as the first data item instead of 65535: