filter: add get_ref, get_mut, and into_inner
#522
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This branch adds methods to access the inner service of a `Filter` or an `AsyncFilter`. These are identical to the similarly-named method provided by many other middleware services. Along with the changes in #521, this is also necessary to implement filtered versions of foreign traits in downstream code. I probably should've added this in that PR, but I wasn't thinking it through...
LucioFranco
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Jan 11, 2021
olix0r
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Jan 14, 2021
Tower provides a `tower::filter` utility for conditionally rejecting some requests and accepting others. Rather than using `tower`'s filter, we have a similar `linkerd_stack::request_filter`, due to two main issues with the filtering API in tower 0.3 and earlier: * `tower::filter`'s predicates returned futures, which we don't need --- all our filtering predicates are purely sunchronous * `tower::filter` didn't allow filters to return any error of their choosing --- they had to return a specific filter-rejected error. This doesn't work with other code where we downcast error types, like switch/fallback. However, Tower 0.4 includes a rewritten `Filter` API that no longer has these issues (tower-rs/tower#508). Therefore, we can switch to using the upstream implementation. This branch replaces `RequestFilter` with `tower::filter::Filter`. It was necessary to add an impl of `NewService` for `Filter`. This required an upstream change to expose access to the wrapped service, so that its `new_service` method can be called when it's a `NewService`, and to expose access to the `Predicate`. Therefore, this PR depends on tower-rs/tower#521 and tower-rs/tower#522, and introduces a Git dependency. The git dep can be removed when Tower 0.4.3 is released. Signed-off-by: Eliza Weisman <eliza@buoyant.io>
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This branch adds methods to access the inner service of a
Filteror anAsyncFilter. These are identical to the similarly-named methodprovided by many other middleware services.
Along with the changes in #521, this is also necessary to implement
filtered versions of foreign traits in downstream code. I probably
should've added this in that PR, but I wasn't thinking it through...