feat!: switch RPIT to more TAIT-like interface#138
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nyonson merged 1 commit intorust-bitcoin:mainfrom Jul 16, 2025
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The Protocol type is generic over Read/AsyncRead, but after the handshake completes, we need to store a different reader type that accounts for any leftover bytes read during handshake processing when searching for the garbage terminator. This creates a type mismatch: Protocol<R> performs a handshake with reader type R, but afterwards needs to store a chained reader that first drains leftover bytes. The actual reader type becomes Chain<Cursor<Vec<u8>>, R>, (for the blocking implementation) not the original R. This implemenation detail was initially hidden from the caller using a RPIT (impl Read/AsyncRead) for the Protocol. However, this isn't a great use case for RPIT because the Protocol is generally long-lived and callers want to store it in structs/enums. But RPITs currently can't be named, so callers can't store and reference them. The ideal language feature for this woult be a TAIT. It keeps the implementation details hidden, but allows for the callers to store and reference the returned Protocol. But TAITs are still only supported on the nightly toolchain. So in the mean time, a ProtocolSessionReader type is used to give the caller a concrete type to name. It matches the interface of a TAIT, so hopefully can be easily swapped out when that feature is stablized.
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Got a little too excited with that RPIT stuff, rolling back to the newtype pattern.
The Protocol type is generic over Read/AsyncRead, but after the handshake completes, we need to store a different reader type that accounts for any leftover bytes read during handshake processing when searching for the garbage terminator.
This creates a type mismatch: Protocol performs a handshake with reader type R, but afterwards needs to store a chained reader that first drains leftover bytes. The actual reader type becomes Chain<Cursor<Vec>, R>, (for the blocking implementation) not the original R.
This implemenation detail was initially hidden from the caller using a RPIT (impl Read/AsyncRead) for the Protocol. However, this isn't a great use case for RPIT because the Protocol is generally long-lived and callers want to store it in structs/enums. But RPITs currently can't be named, so callers can't store and reference them.
The ideal language feature for this woult be a TAIT. It keeps the implementation details hidden, but allows for the callers to store and reference the returned Protocol. But TAITs are still only supported on the nightly toolchain. So in the mean time, a ProtocolSessionReader type is used to give the caller a concrete type to name. It matches the interface of a TAIT, so hopefully can be easily swapped out when that feature is stablized.