Recent Changes - Search:

edit SideBar


This page contains discussion and notes about using the Node Package Manager (npm) with Accessors. See npm for links to other pages about npm.

Current Design

The idea is to use the Node Package Manager (npm) to manage the modules and accessors. npm supports dependencies and versioning.

If we don't use npm, then we will end up creating something very similar to npm.

The Node community is very large and is where our work could likely have the most impact.

The more we follow the Node/npm way, the more likely it is that people will use our work.

For smaller platforms, we want to be able to easily deploy swarmlets that include the required accessors, which would be a subset of all the accessors and all the hosts.

npm supports scopes, which are names that start with @.

We should have the following scopes:

  • @accessors - the npm scope for accessors themselves
  • @accessors-modules - the npm scope for modules required by accessors.
  • @accessors-hosts - for the hosts

Currently, we are optionally downloading accessor definitions from the accessors website. In practice, we almost never do this because we are running accessors in a development environment. Also, versioning of the accessors is not supported. Dependency management is hacked in, for example under Node, the serial accessor will attempt to npm install the serialport module if it is not present. This does not work very well.

We could define a npm module that defines a swarmlet. The package.json would list which accessors and which versions of the accessors are required. The accessor in the @accessors npm scope would in turn define which modules in the @accessors-modules scope are required and which versions. The package.json file would also refer to the .js file that defines the accessor itself.

Open questions:

  • How would other hosts work? Non-Node hosts could get the npm swarmlet and process the package.json file. Maybe the host-specific modules in @accessors-modules would be elsewhere in npm, such as @accessors-modules-cordova. Marten and Christopher are discussing this.
  • Possibly hosts themselves could be as npm modules so that we can version them.

We don't have to implement the npm accessors feature now, but if we keep the @accessors-modules scope, then we can implement the @accessors scope in the future.

(Details below here are somewhat obsolete)


Module Naming

NPM requires that package names be lower case:

  • "Some rules"
    • "New packages must not have uppercase letters in the name."
  • "Some tips:"
    • "Don't put "js" or "node" in the name. It's assumed that it's js, since you're writing a package.json file, and you can specify the engine using the "engines" field. (See below.)"


  • The accessors required some modules with mixed case names, which were changed to hyphenated names.
  • In Cape Code, some modules have Java classes. In Java, package names cannot have hyphens or @ signs.
    • So @accessors-modules becomes modules.
    • Hyphenated names like http-client are converted to camelCase: httpClient.
    • These conversions are done in $PTII/ptolemy/actor/lib/jjs/require.js.

How much of the npm module system should we use?

We have two npm packages

  • @terraswarm/accessors
  • @terraswarm/gdp

For the Node accessor host, we have these modules

  • ./hosts/hosts/node/node_modules/@accessors-modules/http-client/http-client.js: * @module @accessors-modules/http-client
  • ./hosts/hosts/node/node_modules/@accessors-modules/udp-socket/udpSocket.js: * @module @accessors-modules/udp-socket
  • ./hosts/hosts/node/node_modules/@accessors-modules/web-socket-client/web-socket-client.js: * @module @accessors-modules/web-socket-client
  • ./hosts/hosts/node/node_modules/@accessors-modules/web-socket-server/web-socket-server.js: * @module @accessors-modules/web-socket-server

We also have

  • ./hosts/common/commonHost.js: * @module @accessors-hosts/commonHost
  • ./hosts/node/nodeHost.js: * @module @accessors-hosts/node
  • ./hosts/node/nodeHostInvoke.js: * @module @accessors-hosts/nodeHostInvoke
  • ./hosts/node/nodeHostShell.js: * @module @accessors-hosts/nodeHostShell

One idea would be to break up the current accessor modules in the repository into separate modules.

Below are some upsides:

  • Using modules is the npm way. What we have now is a bit of hack.
    • Previously, in node_modules, we had both modules we have written and modules that are required. Having the modules we have written be regular npm modules and could help with management of the code.
  • This would improve dependency management because it would be possible to only include the modules required for a Composite Accessor.
  • We could use semantic versioning for module versions.
  • The accessors package.json could have certain modules, such as commonHost as dependencies

Moving the accessors

Currently, the accessors/web/ directory contains directories that define accessors along with other directories.

Accessor_1.dtd                  gdp                             package.json                       geodesy                         reports
accessors-license.htm           hosts                           robotics
audio                           image                           services
audioIo                         index.html                      signals
build.xml                       index.json                      styles
cameras                                 svn.html
contextAware                    jsdoc                           test
copyright.txt                   library                         toc.htm
coverage                        localization                    trusted
demo                            mutable                         tutorial
deterministicTemporalSemantics  net                             updateIndex
devices                         node_modules                    utilities
doc                             obsolete                        wiki

Perhaps the directories that define accessors should be moved in to a lib subdirectory?

This would take some work, but now is better than later.

Another idea is to create to separate node organizations:

  • @accessors - for the non-host-specific Accessor definitions
    • Each of the hosts would need to be able to understand this syntax
    • We need to be able to support development.
      • Where do these go
    • Do we have a repo per module?
  1. @accessors-node or @accessors/node - for the node-specific implementations

Restructuring Proposal

To check out the work in progress:

  svn co accessors-npm

The npm system includes support for dependencies and versioning, so we will use it.

We can use npm for the accessors definitions themselves and the modules required by the accessors.

First, we will try it with the Node host, then try other hosts.

One point of discussion is that accessors are not modules. However accessors require a bunch of features that modules have such as versioning, dependency management, being downloaded from a central location. We can either use this nice, somewhat sane npm module system to support these features for accessors, or we can spend time reimplementing it all. I say that we should use npm.


npm supports scoping ( I'd like to create two scopes: @accessors and @accessors-impl

1) @accessors would define the accessors definitions, for example, we would have @accessors/net/TCPSocketClient which would define the TCPSocketClient accessor as a npm module.

(I'm not sure if we can have three deep directories like @accessors/net/TCPSocket. If we can't then we could go with @accessors-net/TCPSocket or some other idea)

@accessors/common would define the common host module.

2) @accessors-modules (not sure about the name) would include the implementations of the modules required by the accessors. For example the TCPSocketClient accessor currently requires a socket module, which would be renamed to @accessors-impl/socket.

Accessor hosts would provide host-specific implementations of these modules.

For Cape Code, we could consider moving actor/lib/jjs/modules to actor/lib/jjs/@accessor-impl, or we could just have the Cape Code-specific require() function map @accessor-impl to modules. So require('@accessor-impl/') would find actor/lib/jjs/modules/socket/package.json, which already exists.

One open question is: what would the development tree look like? Probably we would have directories that would contain the definitions of the modules.

So, we would have


which would describe the TCPSocketClient accessor and include dependency and version information. The code itself would be in


The node host would have:


which would describe the socket implementation (including version info).

An alternative would be to create separate repos for each module. This would make configuration and set up more difficult, but would be more in the npm spirit. We might as well bite the bullet and create git repos.

In the near term, I'm proposing that not go with separate repos, but consider the possibility of supporting that in the future.

Design Decisions

Use dash-separated module names as opposed to camelCase
So that we can follow the npm style
There are two types of npm modules - ones we write and ones that get loaded by other modules. Ideally, we would like to keep these separate
accessors/web/node_modules could be for modules we write so that we can find them and accessors/node_modules would be for modules that are required by the modules we write.
There should be a @accessors-hosts namespace
For common, node and other hosts
The node host should have a separate node_modules directory for the implementation of the modules required by the accessors
Other hosts could have a similar structure. The modules would be in the @accessor-modules scope. So, we would have accessors/web/node_modules/@accessors-hosts/node/node_modules/@accessors-modules/@accessors-modules
Getting require to work with accessors themselves seems tricky
Part of the issue is that we need to be able to read the code of the accessor. We could use the npm module.filename to get the filename. However, finding the code seems tricky
Push down accessor definitions
It would be good if the accessor definitions themselves were pushed down a level from accessors/web/cameras to accessors/web/accessors/cameras or accessors/node_modules/@accessors/cameras.
There is this tension between developing accessors and using npm to get the definitions
We need to be able to support both
We need a way to upload the npm modules programmatically
Note that the version number in package.json needs to be incremented for each upload.

Cape Code Host NPM Design Decisions

To find the modules, we will map require('@accessors-modules/cameras') to actor/lib/jjs/modules/cameras
In Java, @accessor-modules is not a legitmate package name, it should be mapped to _accessor_modules, which means that we would have actor/lib/jjs/_accessor_modules/cameras. It seems easier to just stick with what we have with actor/lib/jjs/modules/cameras. To implement this, in actor/lib/jjs/external/require.js, resolveModuleToFile() gets a one line addition:
           moduleName = moduleName.replace(/@accessors-modules/, 'modules');


npm 5 it not backward compatibile, so it gets its open npm5 page.

See Also

Edit - History - Print - Recent Changes - Search
Page last modified on October 06, 2017, at 03:29 PM