is a product of Dropseed

Building collectors

Collectors are responsible for discovering what is installed and available, and reporting that information in this format:

    "dependencies": [
            "name": "coverage",
            "installed": {"version": "4.3.4"},
            "available": [
                {"version": "4.4"},
                {"version": "4.3"},
                {"version": "..."}
            "path": "requirements-dev.txt",
            "source": "pypi"

read more about our JSON schema

Collecting installed versions

The biggest challenge with a collector is determining which version of a package would be installed. Depending on the tool, there may be different ways to specify dependencies, using different files, and sometimes using “lock files”. The tools change over time and as such, their behavior can change. Because of these challenges, collectors usually go one of two ways.

1. Install the dependencies

This is the easiest, and the most CPU/memory intensive route. By using the native “install” command (e.g. npm install, pip install, etc.) you can let the tool itself resolve the dependencies and do exactly the same thing that a user would do. Once everything is installed, there is usually some command or way to parse out which version it ended up installing.

Pros: easy, less guess-work
Cons: slow, expensive

2. Avoid installing the dependencies

Sometimes it is possible to statically parse out what would be installed, without actually installing it (parsing lockfiles, resolving requirements manually, etc.). Actually, this should almost always be possible, but depending on the tool at-hand can take a lot of work. The best way to do this in our experience is to use the APIs that are a part of the package you’re using – most of the time these aren’t documented, stable, or very user friendly though.

Pros: fast! 🐢💨
Cons: difficult, less predictable, undocumented APIs

Finding available versions

Another important job of the collector is to figure out which versions are available. Again, some tools provide an easy way to do this (e.g. npm view react versions --json) and others don’t. Fortunately there is almost always some kind of JSON API behind these things which can be used in some way.


Take a look at the source code for our official collectors to see more implementation details.

Official collectors on GitHub