import macros, options, std_shims/macros_shim, chronos type MessageKind* = enum msgHandshake msgNotification msgRequest msgResponse Message* = ref object id*: int ident*: NimNode kind*: MessageKind procDef*: NimNode timeoutParam*: NimNode recIdent*: NimNode recBody*: NimNode protocol*: P2PProtocol response*: Message userHandler*: NimNode initResponderCall*: NimNode Request* = ref object queries*: seq[Message] response*: Message SendProc* = object ## A `SendProc` is a proc used to send a single P2P message. ## If it's a Request, then the return type will be a Future ## of the respective Response type. All send procs also have ## an automatically inserted `timeout` parameter. msg*: Message ## The message being implemented def*: NimNode ## The definition of the proc peerParam*: NimNode ## Cached ident for the peer param msgParams*: seq[NimNode] ## Cached param ident for all values that must be written ## on the wire. The automatically inserted `timeout` is not ## included. timeoutParam*: NimNode ## Cached ident for the timeout parameter extraDefs*: NimNode ## The reponse procs have extra templates that must become ## part of the generated code P2PProtocol* = ref object # Settings name*: string version*: int timeouts*: int64 useRequestIds*: bool shortName*: string outgoingRequestDecorator*: NimNode incomingRequestDecorator*: NimNode incomingRequestThunkDecorator*: NimNode incomingResponseDecorator*: NimNode incomingResponseThunkDecorator*: NimNode PeerStateType*: NimNode NetworkStateType*: NimNode backend*: Backend # Cached properties nameIdent*: NimNode protocolInfoVar*: NimNode # All messages messages*: seq[Message] # Messages by type: handshake*: Message notifications*: seq[Message] requests*: seq[Request] # Output procs outSendProcs*: NimNode outRecvProcs*: NimNode outProcRegistrations*: NimNode # Event handlers onPeerConnected*: NimNode onPeerDisconnected*: NimNode Backend* = ref object # Code generators implementMsg*: proc (msg: Message) implementProtocolInit*: proc (protocol: P2PProtocol): NimNode afterProtocolInit*: proc (protocol: P2PProtocol) # Bound symbols to the back-end run-time types and procs PeerType*: NimNode NetworkType*: NimNode SerializationFormat*: NimNode ResponderType*: NimNode ReqIdType*: NimNode registerProtocol*: NimNode setEventHandlers*: NimNode BackendFactory* = proc (p: P2PProtocol): Backend P2PBackendError* = object of CatchableError InvalidMsgError* = object of P2PBackendError const defaultReqTimeout = 10.seconds tracingEnabled = defined(p2pdump) let # Variable names affecting the public interface of the library: reqIdVar* {.compileTime.} = ident "reqId" # XXX: Binding the int type causes instantiation failure for some reason ReqIdType* {.compileTime.} = ident "int" peerVar* {.compileTime.} = ident "peer" responseVar* {.compileTime.} = ident "response" perProtocolMsgIdVar* {.compileTime.} = ident "perProtocolMsgId" currentProtocolSym* {.compileTime.} = ident "CurrentProtocol" resultIdent* {.compileTime.} = ident "result" # Locally used symbols: Option {.compileTime.} = ident "Option" Future {.compileTime.} = ident "Future" Void {.compileTime.} = ident "void" template Opt(T): auto = newTree(nnkBracketExpr, Option, T) template Fut(T): auto = newTree(nnkBracketExpr, Future, T) proc initFuture*[T](loc: var Future[T]) = loc = newFuture[T]() template applyDecorator(p: NimNode, decorator: NimNode) = if decorator.kind != nnkNilLit: p.pragma.insert(0, decorator) when tracingEnabled: proc logSentMsgFields(peer: NimNode, protocolInfo: NimNode, msgName: string, fields: openarray[NimNode]): NimNode = ## This generates the tracing code inserted in the message sending procs ## `fields` contains all the params that were serialized in the message var tracer = ident("tracer") result = quote do: var `tracer` = init StringJsonWriter beginRecord(`tracer`) for f in fields: result.add newCall(bindSym"writeField", tracer, newLit($f), f) result.add quote do: endRecord(`tracer`) logMsgEventImpl("outgoing_msg", `peer`, `protocolInfo`, `msgName`, getOutput(`tracer`)) proc createPeerState[Peer, ProtocolState](peer: Peer): RootRef = var res = new ProtocolState mixin initProtocolState initProtocolState(res, peer) return cast[RootRef](res) proc createNetworkState[NetworkNode, NetworkState](network: NetworkNode): RootRef {.gcsafe.} = var res = new NetworkState mixin initProtocolState initProtocolState(res, network) return cast[RootRef](res) proc expectBlockWithProcs*(n: NimNode): seq[NimNode] = template helperName: auto = $n[0] if n.len != 2 or n[1].kind != nnkStmtList: error(helperName & " expects a block", n) for p in n[1]: if p.kind == nnkProcDef: result.add p elif p.kind == nnkCommentStmt: continue else: error(helperName & " expects a proc definition.", p) proc nameOrNil*(procDef: NimNode): NimNode = if procDef != nil: procDef.name else: newNilLit() proc chooseFieldType(n: NimNode): NimNode = ## Examines the parameter types used in the message signature ## and selects the corresponding field type for use in the ## message object type (i.e. `p2p.hello`). ## ## For now, only openarray types are remapped to sequences. result = n if n.kind == nnkBracketExpr and eqIdent(n[0], "openarray"): result = n.copyNimTree result[0] = ident("seq") proc verifyStateType(t: NimNode): NimNode = result = t[1] if result.kind == nnkSym and $result == "nil": return nil if result.kind != nnkBracketExpr or $result[0] != "ref": error $result & " must be a ref type" proc processProtocolBody*(p: P2PProtocol, protocolBody: NimNode) proc init*(T: type P2PProtocol, backendFactory: BackendFactory, name: string, version: int, body: NimNode, timeouts: int64, useRequestIds: bool, shortName: string, outgoingRequestDecorator: NimNode, incomingRequestDecorator: NimNode, incomingRequestThunkDecorator: NimNode, incomingResponseDecorator: NimNode, incomingResponseThunkDecorator: NimNode, peerState, networkState: NimNode): P2PProtocol = result = P2PProtocol( name: name, version: version, timeouts: timeouts, useRequestIds: useRequestIds, shortName: shortName, outgoingRequestDecorator: outgoingRequestDecorator, incomingRequestDecorator: incomingRequestDecorator, incomingRequestThunkDecorator: incomingRequestThunkDecorator, incomingResponseDecorator: incomingResponseDecorator, incomingResponseThunkDecorator: incomingResponseThunkDecorator, PeerStateType: verifyStateType peerState, NetworkStateType: verifyStateType networkState, nameIdent: ident(name), protocolInfoVar: ident(name & "Protocol"), outSendProcs: newStmtList(), outRecvProcs: newStmtList(), outProcRegistrations: newStmtList()) result.backend = backendFactory(result) assert(not result.backend.implementProtocolInit.isNil) assert(not result.backend.ResponderType.isNil) if result.backend.ReqIdType.isNil: result.backend.ReqIdType = ident "int" result.processProtocolBody body if not result.backend.afterProtocolInit.isNil: result.backend.afterProtocolInit(result) proc augmentUserHandler(p: P2PProtocol, userHandlerProc: NimNode, msgId = -1) = ## This procs adds a set of common helpers available in all messages handlers ## (e.g. `perProtocolMsgId`, `peer.state`, etc). userHandlerProc.addPragma ident"gcsafe" userHandlerProc.addPragma ident"async" var getState = ident"getState" getNetworkState = ident"getNetworkState" protocolInfoVar = p.protocolInfoVar protocolNameIdent = p.nameIdent PeerType = p.backend.PeerType PeerStateType = p.PeerStateType NetworkStateType = p.NetworkStateType prelude = newStmtList() userHandlerProc.body.insert 0, prelude # We allow the user handler to use `openarray` params, but we turn # those into sequences to make the `async` pragma happy. for i in 1 ..< userHandlerProc.params.len: var param = userHandlerProc.params[i] param[^2] = chooseFieldType(param[^2]) prelude.add quote do: type `currentProtocolSym` = `protocolNameIdent` if msgId >= 0: prelude.add quote do: const `perProtocolMsgIdVar` = `msgId` # Define local accessors for the peer and the network protocol states # inside each user message handler proc (e.g. peer.state.foo = bar) if PeerStateType != nil: prelude.add quote do: template state(p: `PeerType`): `PeerStateType` = cast[`PeerStateType`](`getState`(p, `protocolInfoVar`)) if NetworkStateType != nil: prelude.add quote do: template networkState(p: `PeerType`): `NetworkStateType` = cast[`NetworkStateType`](`getNetworkState`(p.network, `protocolInfoVar`)) proc addPreludeDefs*(userHandlerProc: NimNode, definitions: NimNode) = userHandlerProc.body[0].add definitions proc eventHandlerToProc(p: P2PProtocol, doBlock: NimNode, handlerName: string): NimNode = ## Turns a "named" do block to a regular async proc ## (e.g. onPeerConnected do ...) result = newTree(nnkProcDef) doBlock.copyChildrenTo(result) result.name = ident(p.name & handlerName) # genSym(nskProc, p.name & handlerName) p.augmentUserHandler result proc ensureTimeoutParam(procDef: NimNode, timeouts: int64): NimNode = ## Make sure the messages has a timeout parameter and it has the correct type. ## The parameter will be removed from the signature and returned for caching ## in the Message's timeoutParam field. It is needed only for the send procs. var Duration = bindSym"Duration" milliseconds = bindSym"milliseconds" lastParam = procDef.params[^1] if eqIdent(lastParam[0], "timeout"): if lastParam[2].kind == nnkEmpty: error "You must specify a default value for the `timeout` parameter", lastParam lastParam[2] = newCall(milliseconds, newLit(100))# newCall(Duration, lastParam[2]) if lastParam[1].kind == nnkEmpty: lastParam[1] = Duration elif not eqIdent(lastParam[1], "Duration"): error "The timeout parameter should be of type 'chronos.Duration'", lastParam[1] result = lastParam procDef.params.del(procDef.params.len - 1) else: result = newTree(nnkIdentDefs, ident"timeout", Duration, newCall(milliseconds, newLit(timeouts))) proc hasReqId*(msg: Message): bool = msg.protocol.useRequestIds and msg.kind in {msgRequest, msgResponse} proc ResponderType(msg: Message): NimNode = var resp = if msg.kind == msgRequest: msg.response else: msg newTree(nnkBracketExpr, msg.protocol.backend.ResponderType, resp.recIdent) proc newMsg(protocol: P2PProtocol, kind: MessageKind, id: int, procDef: NimNode, timeoutParam: NimNode = nil, response: Message = nil): Message = if procDef[0].kind == nnkPostfix: error("p2pProcotol procs are public by default. " & "Please remove the postfix `*`.", procDef) var msgIdent = procDef.name msgName = $msgIdent recFields = newTree(nnkRecList) recBody = newTree(nnkObjectTy, newEmptyNode(), newEmptyNode(), recFields) recName = ident(msgName & "Obj") for param, paramType in procDef.typedParams(skip = 1): recFields.add newTree(nnkIdentDefs, newTree(nnkPostfix, ident("*"), param), # The fields are public chooseFieldType(paramType), # some types such as openarray # are automatically remapped newEmptyNode()) result = Message(protocol: protocol, id: id, ident: msgIdent, kind: kind, procDef: procDef, recIdent: recName, recBody: recBody, timeoutParam: timeoutParam, response: response) if procDef.body.kind != nnkEmpty: var userHandler = copy procDef protocol.augmentUserHandler userHandler, id userHandler.name = genSym(nskProc, msgName) # Request and Response handlers get an extra `reqId` parameter if the # protocol uses them: if result.hasReqId: userHandler.params.insert(2, newIdentDefs(reqIdVar, protocol.backend.ReqIdType)) # All request handlers get an automatically inserter `response` variable: if kind == msgRequest: assert response != nil let peerParam = userHandler.params[1][0] ResponderType = result.ResponderType initResponderCall = newCall(ident"init", ResponderType, peerParam) if protocol.useRequestIds: initResponderCall.add reqIdVar userHandler.addPreludeDefs newVarStmt(responseVar, initResponderCall) result.initResponderCall = initResponderCall case kind of msgRequest: userHandler.applyDecorator protocol.incomingRequestDecorator of msgResponse: userHandler.applyDecorator protocol.incomingResponseDecorator else: discard result.userHandler = userHandler protocol.outRecvProcs.add result.userHandler protocol.messages.add result proc identWithExportMarker*(msg: Message): NimNode = newTree(nnkPostfix, ident("*"), msg.ident) proc createSendProc*(msg: Message, procType = nnkProcDef, isRawSender = false): SendProc = # TODO: file an issue: # macros.newProc and macros.params doesn't work with nnkMacroDef let name = if not isRawSender: msg.identWithExportMarker else: ident($msg.ident & "RawSender") pragmas = if procType == nnkProcDef: newTree(nnkPragma, ident"gcsafe") else: newEmptyNode() var def = newNimNode(procType).add( name, newEmptyNode(), newEmptyNode(), copy msg.procDef.params, pragmas, newEmptyNode(), newStmtList()) ## body if proctype == nnkProcDef: for p in msg.procDef.pragma: def.addPragma p result.msg = msg result.def = def for param, paramType in def.typedParams(): if result.peerParam.isNil: result.peerParam = param else: result.msgParams.add param case msg.kind of msgHandshake, msgRequest: # Add a timeout parameter for all request procs let timeout = copy msg.timeoutParam def[3].add timeout result.timeoutParam = timeout[0] of msgResponse: # A response proc must be called with a response object that originates # from a certain request. Here we change the Peer parameter at position # 1 to the correct strongly-typed ResponderType. The incoming procs still # gets the normal Peer paramter. let ResponderType = msg.ResponderType sendProcName = msg.ident def[3][1][1] = ResponderType # We create a helper that enables the `response.send()` syntax # inside the user handler of the request proc: result.extraDefs = quote do: template send*(r: `ResponderType`, args: varargs[untyped]): auto = `sendProcName`(r, args) of msgNotification: discard def[3][0] = if procType == nnkMacroDef: ident "untyped" elif msg.kind == msgRequest and not isRawSender: Fut(Opt(msg.response.recIdent)) elif msg.kind == msgHandshake and not isRawSender: Fut(msg.recIdent) else: Fut(Void) proc setBody*(sendProc: SendProc, body: NimNode) = var msg = sendProc.msg protocol = msg.protocol def = sendProc.def # TODO: macros.body triggers an assertion error when the proc type is nnkMacroDef def[6] = body if msg.kind == msgRequest: def.applyDecorator protocol.outgoingRequestDecorator msg.protocol.outSendProcs.add def if sendProc.extraDefs != nil: msg.protocol.outSendProcs.add sendProc.extraDefs proc useStandardBody*(sendProc: SendProc, preSerializationStep: proc(stream: NimNode): NimNode, postSerializationStep: proc(stream: NimNode): NimNode, sendCallGenerator: proc (peer, bytes: NimNode): NimNode) = let msg = sendProc.msg outputStream = ident "outputStream" msgBytes = ident "msgBytes" writer = ident "writer" writeField = ident "writeField" initFuture = bindSym "initFuture" recipient = sendProc.peerParam msgRecName = msg.recIdent Format = msg.protocol.backend.SerializationFormat preSerialization = if preSerializationStep.isNil: newStmtList() else: preSerializationStep(outputStream) postSerialization = if postSerializationStep.isNil: newStmtList() else: postSerializationStep(outputStream) appendParams = newStmtList() initResultFuture = if msg.kind != msgRequest: newStmtList() else: newCall(initFuture, resultIdent) sendCall = sendCallGenerator(recipient, msgBytes) tracing = when tracingEnabled: logSentMsgFields(recipient, newLit(msg.protocol.name), $msg.ident, sendProc.msgParams) else: newStmtList() for param in sendProc.msgParams: appendParams.add newCall(writeField, writer, newLit($param), param) sendProc.setBody quote do: mixin init, WriterType, beginRecord, endRecord, getOutput `initResultFuture` var `outputStream` = init OutputStream `preSerialization` var `writer` = init(WriterType(`Format`), `outputStream`) var recordStartMemo = beginRecord(`writer`, `msgRecName`) `appendParams` `tracing` endRecord(`writer`, recordStartMemo) `postSerialization` let `msgBytes` = getOutput(`outputStream`) `sendCall` proc defineThunk*(msg: Message, thunk: NimNode) = let protocol = msg.protocol case msg.kind of msgRequest: thunk.applyDecorator protocol.incomingRequestThunkDecorator of msgResponse: thunk.applyDecorator protocol.incomingResponseThunkDecorator else: discard protocol.outRecvProcs.add thunk proc genAwaitUserHandler*(msg: Message, receivedMsg: NimNode, leadingParams: varargs[NimNode]): NimNode = if msg.userHandler == nil: return newStmtList() var userHandlerCall = newCall(msg.userHandler.name, leadingParams) for param, paramType in msg.procDef.typedParams(skip = 1): # If there is user message handler, we'll place a call to it by # unpacking the fields of the received message: userHandlerCall.add newDotExpr(receivedMsg, param) return newCall("await", userHandlerCall) proc appendAllParams*(node: NimNode, procDef: NimNode, skipFirst = 0): NimNode = result = node for p, _ in procDef.typedParams(skip = skipFirst): result.add p proc netInit*(p: P2PProtocol): NimNode = if p.NetworkStateType == nil: newNilLit() else: newTree(nnkBracketExpr, bindSym"createNetworkState", p.backend.NetworkType, p.NetworkStateType) proc createHandshakeTemplate*(msg: Message, rawSendProc, handshakeImpl, nextMsg: NimNode): SendProc = let handshakeExchanger = msg.createSendProc(procType = nnkTemplateDef) forwardCall = newCall(rawSendProc).appendAllParams(handshakeExchanger.def) peerValue = forwardCall[1] timeoutValue = msg.timeoutParam[0] peerVarSym = genSym(nskLet, "peer") msgRecName = msg.recIdent forwardCall[1] = peerVarSym forwardCall.del(forwardCall.len - 1) handshakeExchanger.setBody quote do: let `peerVarSym` = `peerValue` let sendingFuture = `forwardCall` `handshakeImpl`(`peerVarSym`, sendingFuture, `nextMsg`(`peerVarSym`, `msgRecName`), `timeoutValue`) return handshakeExchanger proc peerInit*(p: P2PProtocol): NimNode = if p.PeerStateType == nil: newNilLit() else: newTree(nnkBracketExpr, bindSym"createPeerState", p.backend.PeerType, p.PeerStateType) proc processProtocolBody*(p: P2PProtocol, protocolBody: NimNode) = ## This procs handles all DSL statements valid inside a p2pProtocol. ## ## It will populate the protocol's fields such as: ## * handshake ## * requests ## * notifications ## * onPeerConnected ## * onPeerDisconnected ## ## All messages will have properly computed numeric IDs ## var nextId = 0 for n in protocolBody: case n.kind of {nnkCall, nnkCommand}: if eqIdent(n[0], "nextID"): # By default message IDs are assigned in increasing order # `nextID` can be used to skip some of the numeric slots if n.len == 2 and n[1].kind == nnkIntLit: nextId = n[1].intVal.int else: error("nextID expects a single int value", n) elif eqIdent(n[0], "requestResponse"): # `requestResponse` can be given a block of 2 or more procs. # The last one is considered to be a response message, while # all preceeding ones are requests triggering the response. # The system makes sure to automatically insert a hidden `reqId` # parameter used to discriminate the individual messages. let procs = expectBlockWithProcs(n) if procs.len < 2: error "requestResponse expects a block with at least two proc definitions" var queries = newSeq[Message]() let responseMsg = p.newMsg(msgResponse, nextId + procs.len - 1, procs[^1]) for i in 0 .. procs.len - 2: var timeout = ensureTimeoutParam(procs[i], p.timeouts) queries.add p.newMsg(msgRequest, nextId + i, procs[i], timeout, response = responseMsg) p.requests.add Request(queries: queries, response: responseMsg) inc nextId, procs.len elif eqIdent(n[0], "handshake"): let procs = expectBlockWithProcs(n) if procs.len != 1: error "handshake expects a block with a single proc definition", n if p.handshake != nil: error "The handshake for the protocol is already defined", n var timeout = ensureTimeoutParam(procs[0], p.timeouts) p.handshake = p.newMsg(msgHandshake, nextId, procs[0], timeout) inc nextId elif eqIdent(n[0], "onPeerConnected"): p.onPeerConnected = p.eventHandlerToProc(n[1], "PeerConnected") elif eqIdent(n[0], "onPeerDisconnected"): p.onPeerDisconnected = p.eventHandlerToProc(n[1], "PeerDisconnected") else: error(repr(n) & " is not a recognized call in P2P protocol definitions", n) of nnkProcDef: p.notifications.add p.newMsg(msgNotification, nextId, n) inc nextId of nnkCommentStmt: discard else: error "Illegal syntax in a P2P protocol definition", n proc genTypeSection*(p: P2PProtocol): NimNode = var protocolName = p.nameIdent peerState = p.PeerStateType networkState= p.NetworkStateType result = newStmtList() result.add quote do: # Create a type acting as a pseudo-object representing the protocol # (e.g. p2p) type `protocolName`* = object if peerState != nil: result.add quote do: template State*(P: type `protocolName`): type = `peerState` if networkState != nil: result.add quote do: template NetworkState*(P: type `protocolName`): type = `networkState` for msg in p.messages: let msgId = msg.id msgName = msg.ident msgRecName = msg.recIdent msgRecBody = msg.recBody result.add quote do: # This is a type featuring a single field for each message param: type `msgRecName`* = `msgRecBody` # Add a helper template for accessing the message type: # e.g. p2p.hello: template `msgName`*(T: type `protocolName`): type = `msgRecName` # Add a helper template for obtaining the message Id for # a particular message type: template msgId*(T: type `msgRecName`): int = `msgId` template msgProtocol*(T: type `msgRecName`): type = `protocolName` proc genCode*(p: P2PProtocol): NimNode = # TODO: try switching to a simpler for msg in p.messages: loop when true: for msg in p.messages: p.backend.implementMsg msg else: if p.handshake != nil: p.backend.implementMsg p.handshake for msg in p.notifications: p.backend.implementMsg msg for req in p.requests: p.backend.implementMsg req.response for query in req.queries: p.backend.implementMsg(query) result = newStmtList() result.add p.genTypeSection() let protocolInfoVar = p.protocolInfoVar protocolName = p.nameIdent protocolInit = p.backend.implementProtocolInit(p) result.add quote do: # One global variable per protocol holds the protocol run-time data var p = `protocolInit` var `protocolInfoVar` = addr p # The protocol run-time data is available as a pseudo-field # (e.g. `p2p.protocolInfo`) template protocolInfo*(P: type `protocolName`): auto = `protocolInfoVar` result.add p.outSendProcs, p.outRecvProcs, p.outProcRegistrations if p.onPeerConnected != nil: result.add p.onPeerConnected if p.onPeerDisconnected != nil: result.add p.onPeerDisconnected result.add newCall(p.backend.setEventHandlers, protocolInfoVar, nameOrNil p.onPeerConnected, nameOrNil p.onPeerDisconnected) result.add newCall(p.backend.registerProtocol, protocolInfoVar) macro emitForSingleBackend( name: static[string], version: static[int], backend: static[BackendFactory], body: untyped, # TODO Nim can't handle a proper duration paramter here timeouts: static[int64] = defaultReqTimeout.milliseconds, useRequestIds: static[bool] = true, shortName: static[string] = "", outgoingRequestDecorator: untyped = nil, incomingRequestDecorator: untyped = nil, incomingRequestThunkDecorator: untyped = nil, incomingResponseDecorator: untyped = nil, incomingResponseThunkDecorator: untyped = nil, peerState = type(nil), networkState = type(nil)): untyped = var p = P2PProtocol.init( backend, name, version, body, timeouts, useRequestIds, shortName, outgoingRequestDecorator, incomingRequestDecorator, incomingRequestThunkDecorator, incomingResponseDecorator, incomingResponseThunkDecorator, peerState.getType, networkState.getType) result = p.genCode() when defined(debugP2pProtocol) or defined(debugMacros): echo repr(result) macro emitForAllBackends(backendSyms: typed, options: untyped, body: untyped): untyped = let name = $(options[0]) var backends = newSeq[NimNode]() if backendSyms.kind == nnkSym: backends.add backendSyms else: for backend in backendSyms: backends.add backend result = newStmtList() for backend in backends: let call = copy options call[0] = bindSym"emitForSingleBackend" call.add newTree(nnkExprEqExpr, ident("name"), newLit(name)) call.add newTree(nnkExprEqExpr, ident("backend"), backend) call.add newTree(nnkExprEqExpr, ident("body"), body) result.add call template p2pProtocol*(options: untyped, body: untyped) {.dirty.} = bind emitForAllBackends emitForAllBackends(p2pProtocolBackendImpl, options, body)