Overhaul needed for Package scan requests and indexing

[JonoYang]

I've set up purldb and scancode.io locally, where I run make run_visit and make run_map to visit and map Maven packages. I then run make request_scans and make process_scans to get information on the Resources in the packages we visit and map. I've noticed that the scan requests we send off to scancode.io are for multiple versions of the same package. This causes a few problems:

• We cannot possibly scan every single package in the maven index to create our matching index
• In the case of the directory structure fingerprint, if there is little/no difference between the different versions of a package, then we are essentially scanning and indexing the same package repeatedly
• We can't populate our matching index with a single scancode.io instance, we need multiple instances so we can have multiple scans going at once

For the first two issues, we need to come up with a new way to group and index fingerprints. A starting idea would be to come up with a bit more general. Currently, we create directory fingerprints for every package we map. If two packages we index are the same package but different versions, then we may have the same fingerprints twice. We could do something along the lines of indexing fingerprints to a package in general, rather than to a specific package version.

For the second issue, we will have to flip the current scan queue request model. purldb will have a queue of packages that it wants scanned and it will be up to scancode.io to poll purldb to see what needs to be scanned. scancode.io would poll purldb, get the package that needs to be scanned, scan and fingerprint it, then send the results back to purldb. This issue is tracked at #14

[JonoYang]

There are my notes for an on-demand queue for requesting package information. This queue would take in a package URL, and the queue would figure out which handler works for the package url, and then look at the upstream repo for package information.

This is a queue that allows us to:

• Visit and map a package requested by the user
• Visit and map the other versions of the package requested by the user

How does (should) it work:

• Take a purl and create something similar to a ResourceURI
• Using the purl, look up in the right repo, then get pom info and map info as package
• Look up other versions of the package and map that package info

How should we start:

• Create ResourceURI-like model
• Create queue loop (we will add the ResourceURI in manually for now, in the future we will have an API or something that can take in requests)
• Queue loop only works on maven packages for now, in the future we will have that router thing like what we do with the visitors and mappers

https://repo1.maven.org/maven2/yom/yom/1.0-alpha-1/
https://repo1.maven.org/maven2/<namespace>/<name>/<version>/<name>-<version>-<classifier>.jar

We would first create a new Package in the packagedb with the initial information from maven, then we would download the sources jar of the package (if available), create a Package and index it. We would also have to do some sort of summarization (maybe use the license clarity score plugin?) on the scanned sources jar in order to get a copyright and license.

[DennisClark]

@JonoYang all this looks great! Question please: is the "ResourceURI" the same concept as the "Inferred URL" that we can see in scan results? or does it include other cases? (I guess I am asking for a somewhat precise definition of a ResourceURI.)

[JonoYang]

@DennisClark

ResourceURI is different than inferred URLs that are generated from purls.

ResourceURI is a model that represents a Resource from the internet you can download. The value of these URIs are usually the download URLs for a Package. In special cases, URIs could point to an upstream repo's index, like https://repo1.maven.org/maven2/.index/nexus-maven-repository-index.gz or https://replicate.npmjs.com/registry/_changes?include_docs=true&limit=1000&since=0. These are called seed URIs.

In purldb, we have visitors and mappers that work on these ResourceURIs. Visitors visit the seed URIs and create ResourceURIs for the packages it finds listed from the repo index. Mappers take the ResourceURIs created by visitors and creates new entries in the PackageDB for each ResourceURI.

[DennisClark]

@JonoYang thanks, that all makes sense!

[JonoYang]

We have updated the scan queue in #285