ensure dlsource is not dropped when other attribution data fails validation

[bhearsum]

The new dlsource key that we added in #162 is somewhat different than existing data: it's meant to convey that a download was initiated through Bedrock, and override the dlsource value that already exists in our installers on archive.mozilla.org. Because of this, we should be a bit more liberal with how it's applied. For example, even if we fail the referer check for RTAMO, we should still attribute with dlsource (but not with other attribution data). There may be other cases like this as well - but that's the obvious one that stands out.

[willdurand]

I have been thinking about RTAMO specifically, and I am wondering: instead of dropping all the attribution data, maybe we could only delete the content parameter (which contains the rta: prefix and the GUID of the add-on to be installed on first startup)?

[bhearsum]

I have been thinking about RTAMO specifically, and I am wondering: instead of dropping all the attribution data, maybe we could only delete the content parameter (which contains the rta: prefix and the GUID of the add-on to be installed on first startup)?

Just to be clear: it sounds like you're suggesting that we make this a bit more general, and only drop the RTAMO specific data when the referer check fails (leaving dlsource, campaign, and anything else that happens to be present available). If so, I think that makes a lot of sense.

The only thing I'd add is that in other cases where validation fails we may want to only preserve dlsource. For example, if source is not in the source whitelist we certainly need to drop it (and maybe other UTM parameters?), but I think we should keep dlsource.

[willdurand]

Just to be clear: it sounds like you're suggesting that we make this a bit more general, and only drop the RTAMO specific data when the referer check fails (leaving dlsource, campaign, and anything else that happens to be present available). If so, I think that makes a lot of sense.

This, indeed.

The only thing I'd add is that in other cases where validation fails we may want to only preserve dlsource. For example, if source is not in the source whitelist we certainly need to drop it (and maybe other UTM parameters?), but I think we should keep dlsource.

When source is not allowed, I think we use a fallback value, we probably don't drop the attribution data so that should still work?

I think other cases are actual errors, e.g. signature mismatch or no attribution code.

[bhearsum]

Err, right, yes. This all sounds sensible to me in that case.