Include checksum of dependency in dub.selections.json

[no-longer-on-githu-b]

The selections file only contains version numbers. However, a malicious library author could repoint a tag to a different version, wreaking havoc amongst users.

For example:

1. I add a new dependency on foo 1.0 to dub.json.
2. I run a DUB command that causes the dependency to be downloaded, and dub.selections.json to be created.
3. The library author includes malware in a new commit, and changes the 1.0 tag to this new commit.
4. I clear the DUB cache and run the DUB command again, which will again download the dependency.
5. I now have different code than I had before.

By verifying the checksum as part of the second download, this issue is mitigated: the library user needs to audit the dependency only the first time they download it.

[nordlow]

I would like to see this work for dependencies to all kinds of files including pre-built libraries (lib ...).

Then all dependencies could be queried using their content hash rather name and have them be renamed if needed.

[nordlow]

When should the selections file be tagged with the hash and should it be automatic or hidden behind a flag? I'm thinking short term behind a flag and long term automatic.

[Geod24]

No switch. It needs to be transparent for users across versions.

[nordlow]

No switch. It needs to be transparent for users across versions.

Ok, great. So the dub.selections.json file will be changed automatically for every dependency upon initial build?

[Geod24]

No only in the project being built. We can't change dependencies selections. We might want to consider an explicit upgrade otherwise we'll have to blindly accept the checksum I think (?).

[nordlow]

How should the dub.selections.json be modified? What about

{
	"fileVersion": 1,
	"versions": {
		"concepts": "0.0.8"
	}
}

to

{
	"fileVersion": 1,
	"versions": {
		"concepts": {"version": "0.0.8", "sha256": "$INITIAL_FILE_CONTENT_SHA256_DIGEST"}
	}
}

?

For comparison note that we currently have, for instance

"windows-headers": {"repository":"git+https://github.com/kinke/windows-headers.git","version":"4922dbdf2057ed239c21c4b3161accb7a0695e01"},

[Geod24]

fileVersion needs to be bumped to 2.
And instead of the hash function itself I was thinking of using checksum as field name. Bear in mind we can already have objects instead of the version string, e.g. for path dependencies.

[Geod24]

Actually perhaps none. Since we already accept objects we can make the checksum optionals.

[nordlow]

Actually perhaps none. Since we already accept objects we can make the checksum optionals.

1. What do you mean by "accept objects"? Accept dependencies to object files? I can find any reference to objects in https://dub.pm/package-format-sdl.
2. Ok. Can you elaborate with the contents of an example dub.selections.json?

[Geod24]

This is valid:

{
	"fileVersion": 1,
	"versions": {
		"bitblob": {"path":"submodules/bitblob/"},
		"vibe-d": {"version":"v0.9.5"},
	}
}

So the field type of an entry in versions can be an object, it doesn't have to be a string.
Since, until the last release, we are pretty lax about the format, adding a field means older versions will not care, newer versions will take it into account.

[nordlow]

So for the hashing shall we use something like

{
	"fileVersion": 1,
	"versions": {
		"bitblob": {"path":"submodules/bitblob/", "checksum":"..."},
		"vibe-d": {"version":"v0.9.5", "checksum":"..."},
	}
}

or

{
	"fileVersion": 1,
	"versions": {
		"bitblob": {"path":"submodules/bitblob/", "sha256":"..."},
		"vibe-d": {"version":"v0.9.5", "sha256":"..."},
	}
}

? Do you prefer "checksum" or "sha256", @kinke @s-ludwig ?

[Geod24]

diff --git a/source/dub/recipe/selection.d b/source/dub/recipe/selection.d
index 097f735b..bfa50a11 100644
--- a/source/dub/recipe/selection.d
+++ b/source/dub/recipe/selection.d
@@ -26,6 +26,7 @@ private struct SelectedDependency
     @Optional @Name("version") string version_;
     @Optional string path;
     @Optional string repository;
+    @Optional string checksum;
 
     public void validate () const scope @safe pure
     {

That would be enough to ensure future-proofness.