Add a max TTL for cached entries #12
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Thank you for the PR!
We usually use the Options pattern to configure services. To see how this looks in practice, have a look at https://github.com/libp2p/go-tcp-transport/blob/c0bf21d689afb213896072e52f225f9126d2ba67/tcp.go#L90-L103.
In this case, we should probably have a func WithMaxTTL(time.Duration) Option option passed to the constructor (func NewResolver(url string, ...Option) *Resolver).
By default, we shouldn't limit the TTL (you can use the zero value of r.maxCacheTTL to mean that we're not applying any limit).
marten-seemann
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Thanks @marten-seemann. I have updated the PR accordingly. Indeed, the option pattern looks better. It does not require an update of the existing tests. |
resolver.go
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| @@ -81,6 +102,10 @@ func (r *Resolver) LookupIPAddr(ctx context.Context, domain string) (result []ne | |||
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| if r.maxCacheTTL != NoMaxCacheTTL { | |||
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Given that we add entries to the cache even if ttl == 0, can we just maxCacheTTL == 0 to mean that we're not applying any max TTL?
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A value of zero means cache is not used by default. If we override 0 meaning to be a special case, users won't be able to define a resolver that revalidates the cache on each query (effectively not using it).
I updated the code to useMaxUint32 as a default. This way, it does not interfere with the possible values for the TTL.
resolver.go
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| func NewResolver(url string) *Resolver { | ||
| type Option func(*Resolver) error | ||
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| var NoMaxCacheTTL = -1 |
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This could be a const, and should not be exported. And with my comment below, we could get rid of it altogether.
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This value has now been removed.
resolver.go
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| func NewResolver(url string) *Resolver { | ||
| type Option func(*Resolver) error | ||
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| func WithMaxCacheTTL(maxCacheTTL uint32) Option { |
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Docs needed here to indicate the units (IIRC seconds). Adding a shoutout for 0 meaning disabled isn't strictly necessary, but might be nice too
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We don't handle 0 correctly at the moment. We insert every value into the cache. That's something we can fix, but I don't think we have to do it in this PR.
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Yep, I'm mostly saying the semantics might want to be called out. To some extent it's reasonable to assume users will figure out that a max TTL of 0 means you'll always do a lookup but might be worth specifying.
Waiting until the fix comes in to update the comment is fine too if you're concerned about bugs involving things like Windows thinking the time difference between two events is 0 when it's just small.
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A value of 0 is handled properly by cacheTXT and cacheIPAddr.
The first line of both method is
if ttl == 0 {
return
}
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Ah sorry, I missed that!
If I understand @aschmahmann correctly, he was suggesting was introducing a DisableCache option, which internally would just set the max TTL to 0. I think that would be a good idea.
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I also added a comment on WithMaxCacheTTL function. It describes the normal behaviour, has well as the behaviour of 0.
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Get it. I have added a new option WithCacheDisabled
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I wasn't saying that specifically just asking for docs, but that's a reasonable idea/approach @marten-seemann 😁
resolver.go
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| func NewResolver(url string) *Resolver { | ||
| type Option func(*Resolver) error | ||
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| func WithMaxCacheTTL(maxCacheTTL uint32) Option { |
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This should be a time.Duration.
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Agree. This makes the library easier to use.
resolver_test.go
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| } | ||
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| func TestLookupCache(t *testing.T) { | ||
| cacheTTL := time.Duration(1) * time.Second |
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| cacheTTL := time.Duration(1) * time.Second | |
| const cacheTTL = time.Second |
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I just merged #13. Would you mind rebasing? |
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There are also a few failures in the |
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@marten-seemann I rebased the code (especially since the interface of the constructor changed). |
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Thank you!
@codecov again. This tool has been causing us so many problems.... |
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Tests are passing now. |
Fixes #10.