Implement verification cache

[rosecodym]

Description:

This PR introduces a cache that allows the scanner to avoid emitting multiple requests to verify the same credential. In practice, it doesn't seem to reduce scan time at all, but it does seem to reduce the number of calls to FromData rather drastically.

The cache is implemented as an opt-out feature that can be disabled with a new CLI flag. If we don't like this, we can change it.

The metrics collection hopefully isn't too architecture-astronauty; I wanted to create something useful here that could also accommodate future Prometheus configuration without making the implementation all stupid.

Here's the result of scanning rails a few times, with and without caching:

with caching
{"chunks": 497160, "bytes": 198670727, "verified_secrets": 0, "unverified_secrets": 100, "scan_duration": "29.301196125s", "trufflehog_version": "dev", "verification_caching": {"Hits":50,"Misses":60,"HitsWasted":0,"AttemptsSaved":50,"VerificationTimeSpentMS":48020}}
{"chunks": 497160, "bytes": 198670727, "verified_secrets": 0, "unverified_secrets": 100, "scan_duration": "27.765202709s", "trufflehog_version": "dev", "verification_caching": {"Hits":50,"Misses":60,"HitsWasted":0,"AttemptsSaved":50,"VerificationTimeSpentMS":41405}}

without caching
{"chunks": 497160, "bytes": 198670727, "verified_secrets": 0, "unverified_secrets": 100, "scan_duration": "28.843573s", "trufflehog_version": "dev", "verification_caching": {"Hits":0,"Misses":0,"HitsWasted":0,"AttemptsSaved":0,"VerificationTimeSpentMS":56733}}
{"chunks": 497160, "bytes": 198670727, "verified_secrets": 0, "unverified_secrets": 100, "scan_duration": "27.674744458s", "trufflehog_version": "dev", "verification_caching": {"Hits":0,"Misses":0,"HitsWasted":0,"AttemptsSaved":0,"VerificationTimeSpentMS":53908}}

The caching doesn't speed the scans up, which is expected, because scans aren't generally bottlenecked by verification. However, it does reduce the number of verification requests, which is good for avoiding account lockouts and stuff like that.

Cached results get this cool new text:

Checklist:

• Tests passing (make test-community)?
• Lint passing (make lint this requires golangci-lint)?
• Double-check names and comments and suchlike
• Put some metrics in this PR description

[ankushgoel27]

i understand it doesnt verify the same credential but I hope it does report it as verified(if verified) in the output.

[rosecodym]

i understand it doesnt verify the same credential but I hope it does report it as verified(if verified) in the output.

Yep, that's the idea! If the credential is cached as verified, then the output will report it as verified:

[zricethezav]

Question: @rosecodym any reason we need this to be an interface? I'm seeing InMemoryMetrics as the only struct that implements this interface.

[rosecodym]

Oh, good question. The plan is to use this seam to plug in a Prometheus-based reporter in enterprise. Rather than drape those metrics all over the OSS codebase I opted to create this interface, which looks silly on its own (as you've pointed out) but I hope will save some headaches in the long run.

[zricethezav]

lgtm, just one non-blocking question