add support for setting protocol handlers with {.raises.} annotation (#1064)

Author: etan-status

examples/helloworld.nim

@@ -20,7 +20,7 @@ proc new(T: typedesc[TestProto]): T =
     # We must close the connections ourselves when we're done with it
     await conn.close()
 
-  return T(codecs: @[TestCodec], handler: handle)
+  return T.new(codecs = @[TestCodec], handler = handle)
 
 ##
 # Helper to create a switch/node

libp2p/multistream.nim

@@ -246,10 +246,14 @@ proc addHandler*(m: MultistreamSelect,
                  matcher: Matcher = nil) =
   addHandler(m, @[codec], protocol, matcher)
 
-proc addHandler*(m: MultistreamSelect,
-                 codec: string,
-                 handler: LPProtoHandler,
-                 matcher: Matcher = nil) =
+proc addHandler*[E](
+    m: MultistreamSelect,
+    codec: string,
+    handler: LPProtoHandler |
+      proc (
+        conn: Connection,
+        proto: string): InternalRaisesFuture[void, E],
+    matcher: Matcher = nil) =
   ## helper to allow registering pure handlers
   trace "registering proto handler", proto = codec
   let protocol = new LPProtocol

libp2p/protocols/protocol.nim

@@ -19,14 +19,12 @@ const
 
 type
   LPProtoHandler* = proc (
-    conn: Connection,
-    proto: string):
-    Future[void]
-    {.gcsafe, raises: [].}
+      conn: Connection,
+      proto: string): Future[void] {.async.}
 
   LPProtocol* = ref object of RootObj
     codecs*: seq[string]
-    handler*: LPProtoHandler ## this handler gets invoked by the protocol negotiator
+    handlerImpl: LPProtoHandler  ## invoked by the protocol negotiator
     started*: bool
     maxIncomingStreams: Opt[int]
 
@@ -52,23 +50,59 @@ proc `maxIncomingStreams=`*(p: LPProtocol, val: int) =
   p.maxIncomingStreams = Opt.some(val)
 
 func codec*(p: LPProtocol): string =
-  assert(p.codecs.len > 0, "Codecs sequence was empty!")
+  doAssert(p.codecs.len > 0, "Codecs sequence was empty!")
   p.codecs[0]
 
 func `codec=`*(p: LPProtocol, codec: string) =
   # always insert as first codec
   # if we use this abstraction
   p.codecs.insert(codec, 0)
 
+template `handler`*(p: LPProtocol): LPProtoHandler =
+  p.handlerImpl
+
+template `handler`*(
+    p: LPProtocol, conn: Connection, proto: string): Future[void] =
+  p.handlerImpl(conn, proto)
+
+func `handler=`*(p: LPProtocol, handler: LPProtoHandler) =
+  p.handlerImpl = handler
+
+# Callbacks that are annotated with `{.async: (raises).}` explicitly
+# document the types of errors that they may raise, but are not compatible
+# with `LPProtoHandler` and need to use a custom `proc` type.
+# They are internally wrapped into a `LPProtoHandler`, but still allow the
+# compiler to check that their `{.async: (raises).}` annotation is correct.
+# https://github.com/nim-lang/Nim/issues/23432
+func `handler=`*[E](
+    p: LPProtocol,
+    handler: proc (
+      conn: Connection,
+      proto: string): InternalRaisesFuture[void, E]) =
+  proc wrap(conn: Connection, proto: string): Future[void] {.async.} =
+    await handler(conn, proto)
+  p.handlerImpl = wrap
+
 proc new*(
-  T: type LPProtocol,
-  codecs: seq[string],
-  handler: LPProtoHandler,
-  maxIncomingStreams: Opt[int] | int = Opt.none(int)): T =
+    T: type LPProtocol,
+    codecs: seq[string],
+    handler: LPProtoHandler,
+    maxIncomingStreams: Opt[int] | int = Opt.none(int)): T =
   T(
     codecs: codecs,
-    handler: handler,
+    handlerImpl: handler,
     maxIncomingStreams:
       when maxIncomingStreams is int: Opt.some(maxIncomingStreams)
       else: maxIncomingStreams
   )
+
+proc new*[E](
+    T: type LPProtocol,
+    codecs: seq[string],
+    handler: proc (
+      conn: Connection,
+      proto: string): InternalRaisesFuture[void, E],
+    maxIncomingStreams: Opt[int] | int = Opt.none(int)): T =
+  proc wrap(conn: Connection, proto: string): Future[void] {.async.} =
+    await handler(conn, proto)
+  T.new(codec, wrap, maxIncomingStreams)

tests/errorhelpers.nim

@@ -24,6 +24,6 @@ proc allFuturesThrowing*(args: varargs[FutureBase]): Future[void] =
 proc allFuturesThrowing*[T](futs: varargs[Future[T]]): Future[void] =
   allFuturesThrowing(futs.mapIt(FutureBase(it)))
 
-proc allFuturesThrowing*[T, E](
+proc allFuturesThrowing*[T, E](  # https://github.com/nim-lang/Nim/issues/23432
     futs: varargs[InternalRaisesFuture[T, E]]): Future[void] =
   allFuturesThrowing(futs.mapIt(FutureBase(it)))

tests/testtortransport.nim

@@ -1,7 +1,7 @@
 {.used.}
 
 # Nim-Libp2p
-# Copyright (c) 2023 Status Research & Development GmbH
+# Copyright (c) 2023-2024 Status Research & Development GmbH
 # Licensed under either of
 #  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
 #  * MIT license ([LICENSE-MIT](LICENSE-MIT))
@@ -88,7 +88,6 @@ suite "Tor transport":
 
       # every incoming connections will be in handled in this closure
       proc handle(conn: Connection, proto: string) {.async.} =
-
         var resp: array[6, byte]
         await conn.readExactly(addr resp, 6)
         check string.fromBytes(resp) == "client"
@@ -97,7 +96,7 @@ suite "Tor transport":
         # We must close the connections ourselves when we're done with it
         await conn.close()
 
-      return T(codecs: @[TestCodec], handler: handle)
+      return T.new(codecs = @[TestCodec], handler = handle)
 
     let rng = newRng()