[HTTP2ConnectionPool] added HTTP2StateMachine (#447)

Author: dnadoba

Sources/AsyncHTTPClient/ConnectionPool/State Machine/HTTPConnectionPool+HTTP1Connections.swift

@@ -189,6 +189,30 @@ extension HTTPConnectionPool {
                 preconditionFailure("Unexpected state: Did not expect to have connections with this state in the state machine: \(self.state)")
             }
         }
+
+        enum MigrateAction {
+            case removeConnection
+            case keepConnection
+        }
+
+        func migrateToHTTP2(_ context: inout HTTP1Connections.HTTP1ToHTTP2MigrationContext) -> MigrateAction {
+            switch self.state {
+            case .starting:
+                context.starting.append((self.connectionID, self.eventLoop))
+                return .removeConnection
+            case .backingOff:
+                context.backingOff.append((self.connectionID, self.eventLoop))
+                return .removeConnection
+            case .idle(let connection, since: _):
+                // Idle connections can be removed right away
+                context.close.append(connection)
+                return .removeConnection
+            case .leased:
+                return .keepConnection
+            case .closed:
+                preconditionFailure("Unexpected state: Did not expect to have connections with this state in the state machine: \(self.state)")
+            }
+        }
     }
 
     /// A structure to hold the currently active HTTP/1.1 connections.
@@ -298,6 +322,12 @@ extension HTTPConnectionPool {
             var connectionsStartingForUseCase: Int
         }
 
+        struct HTTP1ToHTTP2MigrationContext {
+            var backingOff: [(Connection.ID, EventLoop)] = []
+            var starting: [(Connection.ID, EventLoop)] = []
+            var close: [Connection] = []
+        }
+
         // MARK: Connection creation
 
         mutating func createNewConnection(on eventLoop: EventLoop) -> Connection.ID {
@@ -485,6 +515,21 @@ extension HTTPConnectionPool {
             return (index, context)
         }
 
+        // MARK: Migration
+
+        mutating func migrateToHTTP2() -> HTTP1ToHTTP2MigrationContext {
+            var migrationContext = HTTP1ToHTTP2MigrationContext()
+            self.connections.removeAll { connection in
+                switch connection.migrateToHTTP2(&migrationContext) {
+                case .removeConnection:
+                    return true
+                case .keepConnection:
+                    return false
+                }
+            }
+            return migrationContext
+        }
+
         // MARK: Shutdown
 
         mutating func shutdown() -> CleanupContext {
@@ -610,12 +655,12 @@ extension HTTPConnectionPool {
 
             return nil
         }
-    }
 
-    struct Stats {
-        var idle: Int = 0
-        var leased: Int = 0
-        var connecting: Int = 0
-        var backingOff: Int = 0
+        struct Stats {
+            var idle: Int = 0
+            var leased: Int = 0
+            var connecting: Int = 0
+            var backingOff: Int = 0
+        }
     }
 }

Sources/AsyncHTTPClient/ConnectionPool/State Machine/HTTPConnectionPool+HTTP1StateMachine.swift

@@ -24,12 +24,12 @@ extension HTTPConnectionPool {
 
         typealias Action = HTTPConnectionPool.StateMachine.Action
 
-        private var connections: HTTP1Connections
+        private(set) var connections: HTTP1Connections
         private var failedConsecutiveConnectionAttempts: Int = 0
         /// the error from the last connection creation
         private var lastConnectFailure: Error?
 
-        private var requests: RequestQueue
+        private(set) var requests: RequestQueue
         private var state: State = .running
 
         init(idGenerator: Connection.ID.Generator, maximumConcurrentConnections: Int) {
@@ -41,7 +41,7 @@ extension HTTPConnectionPool {
             self.requests = RequestQueue()
         }
 
-        // MARK: - Events -
+        // MARK: - Events
 
         mutating func executeRequest(_ request: Request) -> Action {
             switch self.state {

Sources/AsyncHTTPClient/ConnectionPool/State Machine/HTTPConnectionPool+HTTP2Connections.swift

@@ -49,6 +49,16 @@ extension HTTPConnectionPool {
             }
         }
 
+        /// A connection is established and can potentially execute requests if not all streams are leased
+        var isActive: Bool {
+            switch self.state {
+            case .active:
+                return true
+            case .starting, .backingOff, .draining, .closed:
+                return false
+            }
+        }
+
         /// A request can be scheduled on the connection
         var isAvailable: Bool {
             switch self.state {
@@ -326,6 +336,11 @@ extension HTTPConnectionPool {
 
         // MARK: Connection creation
 
+        /// true if one ore more connections are active
+        var hasActiveConnections: Bool {
+            self.connections.contains { $0.isActive }
+        }
+
         /// used in general purpose connection scenarios to check if at least one connection exist, or if should we create a new one
         var hasConnectionThatCanOrWillBeAbleToExecuteRequests: Bool {
             self.connections.contains { $0.canOrWillBeAbleToExecuteRequests }