cache NIOSSLContext (saves 27k allocs per conn) (#362)

Motivation:

At the moment, AHC assumes that creating a `NIOSSLContext` is both cheap
and doesn't block.

Neither of these two assumptions are true.

To create a `NIOSSLContext`, BoringSSL will have to read a lot of
certificates in the trust store (on disk) which require a lot of ASN1
parsing and much much more.

On my Ubuntu test machine, creating one `NIOSSLContext` is about 27,000
allocations!!! To make it worse, AHC allocates a fresh `NIOSSLContext`
for _every single connection_, whether HTTP or HTTPS. Yes, correct.

Modification:

- Cache NIOSSLContexts per TLSConfiguration in a LRU cache
- Don't get an NIOSSLContext for HTTP (plain text) connections

Result:

New connections should be _much_ faster in general assuming that you're
not using a different TLSConfiguration for every connection.

Author: weissi

Diff for: Sources/AsyncHTTPClient/ConnectionPool.swift

@@ -18,6 +18,7 @@ import NIO
 import NIOConcurrencyHelpers
 import NIOHTTP1
 import NIOHTTPCompression
+import NIOSSL
 import NIOTLS
 import NIOTransportServices
 
@@ -41,6 +42,8 @@ final class ConnectionPool {
 
     private let backgroundActivityLogger: Logger
 
+    let sslContextCache = SSLContextCache()
+
     init(configuration: HTTPClient.Configuration, backgroundActivityLogger: Logger) {
         self.configuration = configuration
         self.backgroundActivityLogger = backgroundActivityLogger
@@ -106,6 +109,8 @@ final class ConnectionPool {
             self.providers.values
         }
 
+        self.sslContextCache.shutdown()
+
         return EventLoopFuture.reduce(true, providers.map { $0.close() }, on: eventLoop) { $0 && $1 }
     }
 
@@ -148,7 +153,7 @@ final class ConnectionPool {
         var host: String
         var port: Int
         var unixPath: String
-        var tlsConfiguration: BestEffortHashableTLSConfiguration?
+        private var tlsConfiguration: BestEffortHashableTLSConfiguration?
 
         enum Scheme: Hashable {
             case http
@@ -249,14 +254,15 @@ class HTTP1ConnectionProvider {
                 } else {
                     logger.trace("opening fresh connection (found matching but inactive connection)",
                                  metadata: ["ahc-dead-connection": "\(connection)"])
-                    self.makeChannel(preference: waiter.preference).whenComplete { result in
+                    self.makeChannel(preference: waiter.preference,
+                                     logger: logger).whenComplete { result in
                         self.connect(result, waiter: waiter, logger: logger)
                     }
                 }
             }
         case .create(let waiter):
             logger.trace("opening fresh connection (no connections to reuse available)")
-            self.makeChannel(preference: waiter.preference).whenComplete { result in
+            self.makeChannel(preference: waiter.preference, logger: logger).whenComplete { result in
                 self.connect(result, waiter: waiter, logger: logger)
             }
         case .replace(let connection, let waiter):
@@ -266,7 +272,7 @@ class HTTP1ConnectionProvider {
                 logger.trace("opening fresh connection (replacing exising connection)",
                              metadata: ["ahc-old-connection": "\(connection)",
                                         "ahc-waiter": "\(waiter)"])
-                self.makeChannel(preference: waiter.preference).whenComplete { result in
+                self.makeChannel(preference: waiter.preference, logger: logger).whenComplete { result in
                     self.connect(result, waiter: waiter, logger: logger)
                 }
             }
@@ -434,8 +440,14 @@ class HTTP1ConnectionProvider {
         return self.closePromise.futureResult.map { true }
     }
 
-    private func makeChannel(preference: HTTPClient.EventLoopPreference) -> EventLoopFuture<Channel> {
-        return NIOClientTCPBootstrap.makeHTTP1Channel(destination: self.key, eventLoop: self.eventLoop, configuration: self.configuration, preference: preference)
+    private func makeChannel(preference: HTTPClient.EventLoopPreference,
+                             logger: Logger) -> EventLoopFuture<Channel> {
+        return NIOClientTCPBootstrap.makeHTTP1Channel(destination: self.key,
+                                                      eventLoop: self.eventLoop,
+                                                      configuration: self.configuration,
+                                                      sslContextCache: self.pool.sslContextCache,
+                                                      preference: preference,
+                                                      logger: logger)
     }
 
     /// A `Waiter` represents a request that waits for a connection when none is

Diff for: Sources/AsyncHTTPClient/HTTPClient.swift

@@ -900,7 +900,9 @@ extension ChannelPipeline {
         try sync.addHandler(handler)
     }
 
-    func syncAddLateSSLHandlerIfNeeded(for key: ConnectionPool.Key, tlsConfiguration: TLSConfiguration?, handshakePromise: EventLoopPromise<Void>) {
+    func syncAddLateSSLHandlerIfNeeded(for key: ConnectionPool.Key,
+                                       sslContext: NIOSSLContext,
+                                       handshakePromise: EventLoopPromise<Void>) {
         precondition(key.scheme.requiresTLS)
 
         do {
@@ -913,10 +915,9 @@ extension ChannelPipeline {
             try synchronousPipelineView.addHandler(eventsHandler, name: TLSEventsHandler.handlerName)
 
             // Then we add the SSL handler.
-            let tlsConfiguration = tlsConfiguration ?? TLSConfiguration.forClient()
-            let context = try NIOSSLContext(configuration: tlsConfiguration)
             try synchronousPipelineView.addHandler(
-                try NIOSSLClientHandler(context: context, serverHostname: (key.host.isIPAddress || key.host.isEmpty) ? nil : key.host),
+                try NIOSSLClientHandler(context: sslContext,
+                                        serverHostname: (key.host.isIPAddress || key.host.isEmpty) ? nil : key.host),
                 position: .before(eventsHandler)
             )
         } catch {

Diff for: Sources/AsyncHTTPClient/LRUCache.swift

@@ -0,0 +1,104 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the AsyncHTTPClient open source project
+//
+// Copyright (c) 2021 Apple Inc. and the AsyncHTTPClient project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of AsyncHTTPClient project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+struct LRUCache<Key: Equatable, Value> {
+    private typealias Generation = UInt64
+    private struct Element {
+        var generation: Generation
+        var key: Key
+        var value: Value
+    }
+
+    private let capacity: Int
+    private var generation: Generation = 0
+    private var elements: [Element]
+
+    init(capacity: Int = 8) {
+        precondition(capacity > 0, "capacity needs to be > 0")
+        self.capacity = capacity
+        self.elements = []
+        self.elements.reserveCapacity(capacity)
+    }
+
+    private mutating func bumpGenerationAndFindIndex(key: Key) -> Int? {
+        self.generation += 1
+
+        let found = self.elements.firstIndex { element in
+            element.key == key
+        }
+
+        return found
+    }
+
+    mutating func find(key: Key) -> Value? {
+        if let found = self.bumpGenerationAndFindIndex(key: key) {
+            self.elements[found].generation = self.generation
+            return self.elements[found].value
+        } else {
+            return nil
+        }
+    }
+
+    @discardableResult
+    mutating func append(key: Key, value: Value) -> Value {
+        let newElement = Element(generation: self.generation,
+                                 key: key,
+                                 value: value)
+        if let found = self.bumpGenerationAndFindIndex(key: key) {
+            self.elements[found] = newElement
+            return value
+        }
+
+        if self.elements.count < self.capacity {
+            self.elements.append(newElement)
+            return value
+        }
+        assert(self.elements.count == self.capacity)
+        assert(self.elements.count > 0)
+
+        let minIndex = self.elements.minIndex { l, r in
+            l.generation < r.generation
+        }!
+
+        self.elements.swapAt(minIndex, self.elements.endIndex - 1)
+        self.elements.removeLast()
+        self.elements.append(newElement)
+
+        return value
+    }
+
+    mutating func findOrAppend(key: Key, _ valueGenerator: (Key) -> Value) -> Value {
+        if let found = self.find(key: key) {
+            return found
+        }
+
+        return self.append(key: key, value: valueGenerator(key))
+    }
+}
+
+extension Array {
+    func minIndex(by areInIncreasingOrder: (Element, Element) throws -> Bool) rethrows -> Index? {
+        guard var minSoFar: (Index, Element) = self.first.map({ (0, $0) }) else {
+            return nil
+        }
+
+        for indexElement in self.enumerated() {
+            if try areInIncreasingOrder(indexElement.1, minSoFar.1) {
+                minSoFar = indexElement
+            }
+        }
+
+        return minSoFar.0
+    }
+}

Diff for: Sources/AsyncHTTPClient/NIOTransportServices/NWErrorHandler.swift

@@ -13,13 +13,14 @@
 //===----------------------------------------------------------------------===//
 
 #if canImport(Network)
-
     import Network
-    import NIO
-    import NIOHTTP1
-    import NIOTransportServices
+#endif
+import NIO
+import NIOHTTP1
+import NIOTransportServices
 
-    extension HTTPClient {
+extension HTTPClient {
+    #if canImport(Network)
         public struct NWPOSIXError: Error, CustomStringConvertible {
             /// POSIX error code (enum)
             public let errorCode: POSIXErrorCode
@@ -57,28 +58,35 @@
 
             public var description: String { return self.reason }
         }
+    #endif
 
-        @available(macOS 10.14, iOS 12.0, tvOS 12.0, watchOS 6.0, *)
-        class NWErrorHandler: ChannelInboundHandler {
-            typealias InboundIn = HTTPClientResponsePart
+    class NWErrorHandler: ChannelInboundHandler {
+        typealias InboundIn = HTTPClientResponsePart
 
-            func errorCaught(context: ChannelHandlerContext, error: Error) {
-                context.fireErrorCaught(NWErrorHandler.translateError(error))
-            }
+        func errorCaught(context: ChannelHandlerContext, error: Error) {
+            context.fireErrorCaught(NWErrorHandler.translateError(error))
+        }
 
-            static func translateError(_ error: Error) -> Error {
-                if let error = error as? NWError {
-                    switch error {
-                    case .tls(let status):
-                        return NWTLSError(status, reason: error.localizedDescription)
-                    case .posix(let errorCode):
-                        return NWPOSIXError(errorCode, reason: error.localizedDescription)
-                    default:
-                        return error
+        static func translateError(_ error: Error) -> Error {
+            #if canImport(Network)
+                if #available(OSX 10.14, iOS 12.0, tvOS 12.0, watchOS 6.0, *) {
+                    if let error = error as? NWError {
+                        switch error {
+                        case .tls(let status):
+                            return NWTLSError(status, reason: error.localizedDescription)
+                        case .posix(let errorCode):
+                            return NWPOSIXError(errorCode, reason: error.localizedDescription)
+                        default:
+                            return error
+                        }
                     }
+                    return error
+                } else {
+                    preconditionFailure("\(self) used on a non-NIOTS Channel")
                 }
-                return error
-            }
+            #else
+                preconditionFailure("\(self) used on a non-NIOTS Channel")
+            #endif
         }
     }
-#endif
+}

Diff for: Sources/AsyncHTTPClient/SSLContextCache.swift

@@ -0,0 +1,104 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the AsyncHTTPClient open source project
+//
+// Copyright (c) 2021 Apple Inc. and the AsyncHTTPClient project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of AsyncHTTPClient project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import Logging
+import NIO
+import NIOConcurrencyHelpers
+import NIOSSL
+
+class SSLContextCache {
+    private var state = State.activeNoThread
+    private let lock = Lock()
+    private var sslContextCache = LRUCache<BestEffortHashableTLSConfiguration, NIOSSLContext>()
+    private let threadPool = NIOThreadPool(numberOfThreads: 1)
+
+    enum State {
+        case activeNoThread
+        case active
+        case shutDown
+    }
+
+    init() {}
+
+    func shutdown() {
+        self.lock.withLock { () -> Void in
+            switch self.state {
+            case .activeNoThread:
+                self.state = .shutDown
+            case .active:
+                self.state = .shutDown
+                self.threadPool.shutdownGracefully { maybeError in
+                    precondition(maybeError == nil, "\(maybeError!)")
+                }
+            case .shutDown:
+                preconditionFailure("SSLContextCache shut down twice")
+            }
+        }
+    }
+
+    deinit {
+        assert(self.state == .shutDown)
+    }
+}
+
+extension SSLContextCache {
+    private struct SSLContextCacheShutdownError: Error {}
+
+    func sslContext(tlsConfiguration: TLSConfiguration,
+                    eventLoop: EventLoop,
+                    logger: Logger) -> EventLoopFuture<NIOSSLContext> {
+        let earlyExitError: Error? = self.lock.withLock { () -> Error? in
+            switch self.state {
+            case .activeNoThread:
+                self.state = .active
+                self.threadPool.start()
+                return nil
+            case .active:
+                return nil
+            case .shutDown:
+                return SSLContextCacheShutdownError()
+            }
+        }
+
+        if let error = earlyExitError {
+            return eventLoop.makeFailedFuture(error)
+        }
+
+        let eqTLSConfiguration = BestEffortHashableTLSConfiguration(wrapping: tlsConfiguration)
+        let sslContext = self.lock.withLock {
+            self.sslContextCache.find(key: eqTLSConfiguration)
+        }
+
+        if let sslContext = sslContext {
+            logger.debug("found SSL context in cache",
+                         metadata: ["ahc-tls-config": "\(tlsConfiguration)"])
+            return eventLoop.makeSucceededFuture(sslContext)
+        }
+
+        logger.debug("creating new SSL context",
+                     metadata: ["ahc-tls-config": "\(tlsConfiguration)"])
+        let newSSLContext = self.threadPool.runIfActive(eventLoop: eventLoop) {
+            try NIOSSLContext(configuration: tlsConfiguration)
+        }
+
+        newSSLContext.whenSuccess { (newSSLContext: NIOSSLContext) -> Void in
+            self.lock.withLock { () -> Void in
+                self.sslContextCache.append(key: eqTLSConfiguration,
+                                            value: newSSLContext)
+            }
+        }
+
+        return newSSLContext
+    }
+}