Move CompressionAlgorithm to core (#1858)

Motivation:

`CallOptions` only let you enable/disable compression, it doesn't allow
you to control which algorithm should be used. This is an unnecessary
limitation. This was done because `CompressionAlgorithm` lives in the
http2 module.

Modifications:

- Move `CompressionAlgorithm` to the core module
- Rename 'identity' to 'none' as that's clearer for users
- Add extensions in the http2 module to create an algorithm from its
  name
- Add a `CompressionAlgorithmSet` type which uses an option set which
  allows for cheaper updates.
- Update call options

Result:

- `CallOptions` is more flexible
- Updating the call options set is cheaper

Author: glbrntt

Sources/GRPCCore/Call/Client/CallOptions.swift

@@ -77,46 +77,27 @@ public struct CallOptions: Sendable {
   /// reported to the client. Hedging is only suitable for idempotent RPCs.
   public var executionPolicy: RPCExecutionPolicy?
 
-  /// Whether compression is enabled or not for request and response messages.
-  public var compression: Compression
-
-  public struct Compression: Sendable {
-    /// Whether request messages should be compressed.
-    ///
-    /// Note that this option is _advisory_: transports are not required to support compression.
-    public var requests: Bool
-
-    /// Whether response messages are permitted to be compressed.
-    public var responses: Bool
-
-    /// Creates a new ``Compression`` configuration.
-    ///
-    /// - Parameters:
-    ///   - requests: Whether request messages should be compressed.
-    ///   - responses: Whether response messages may be compressed.
-    public init(requests: Bool, responses: Bool) {
-      self.requests = requests
-      self.responses = responses
-    }
-
-    /// Sets ``requests`` and ``responses`` to `true`.
-    public static var enabled: Self {
-      Self(requests: true, responses: true)
-    }
-
-    /// Sets ``requests`` and ``responses`` to `false`.
-    public static var disabled: Self {
-      Self(requests: false, responses: false)
-    }
-  }
+  /// The compression used for the call.
+  ///
+  /// Compression in gRPC is asymmetrical: the server may compress response messages using a
+  /// different algorithm than the client used to compress request messages. This configuration
+  /// controls the compression used by the client for request messages.
+  ///
+  /// Note that this configuration is advisory: not all transports support compression and may
+  /// ignore this configuration. Transports which support compression will use this configuration
+  /// in preference to the algorithm configured at a transport level. If the transport hasn't
+  /// enabled the use of the algorithm then compression won't be used for the call.
+  ///
+  /// If `nil` the value configured on the transport will be used instead.
+  public var compression: CompressionAlgorithm?
 
   internal init(
     timeout: Duration?,
     waitForReady: Bool?,
     maxRequestMessageBytes: Int?,
     maxResponseMessageBytes: Int?,
     executionPolicy: RPCExecutionPolicy?,
-    compression: Compression
+    compression: CompressionAlgorithm?
   ) {
     self.timeout = timeout
     self.waitForReady = waitForReady
@@ -131,17 +112,15 @@ public struct CallOptions: Sendable {
 extension CallOptions {
   /// Default call options.
   ///
-  /// The default values defer values to the underlying transport. In most cases this means values
-  /// are `nil`, with the exception of ``compression-swift.property`` which is set
-  /// to ``Compression-swift.struct/disabled``.
+  /// The default values (`nil`) defer values to the underlying transport.
   public static var defaults: Self {
     Self(
       timeout: nil,
       waitForReady: nil,
       maxRequestMessageBytes: nil,
       maxResponseMessageBytes: nil,
       executionPolicy: nil,
-      compression: .disabled
+      compression: nil
     )
   }
 }

Sources/GRPCCore/Coding/CompressionAlgorithm.swift

@@ -0,0 +1,129 @@
+/*
+ * Copyright 2024, gRPC Authors All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/// Message compression algorithms.
+public struct CompressionAlgorithm: Hashable, Sendable {
+  @_spi(Package)
+  public enum Value: UInt8, Hashable, Sendable, CaseIterable {
+    case none = 0
+    case deflate
+    case gzip
+  }
+
+  @_spi(Package)
+  public let value: Value
+
+  fileprivate init(_ algorithm: Value) {
+    self.value = algorithm
+  }
+
+  /// No compression, sometimes referred to as 'identity' compression.
+  public static var none: Self {
+    Self(.none)
+  }
+
+  /// The 'deflate' compression algorithm.
+  public static var deflate: Self {
+    Self(.deflate)
+  }
+
+  /// The 'gzip' compression algorithm.
+  public static var gzip: Self {
+    Self(.gzip)
+  }
+}
+
+/// A set of compression algorithms.
+public struct CompressionAlgorithmSet: OptionSet, Hashable, Sendable {
+  public var rawValue: UInt32
+
+  public init(rawValue: UInt32) {
+    self.rawValue = rawValue
+  }
+
+  private init(value: CompressionAlgorithm.Value) {
+    self.rawValue = 1 << value.rawValue
+  }
+
+  /// No compression, sometimes referred to as 'identity' compression.
+  public static var none: Self {
+    return Self(value: .none)
+  }
+
+  /// The 'deflate' compression algorithm.
+  public static var deflate: Self {
+    return Self(value: .deflate)
+  }
+
+  /// The 'gzip' compression algorithm.
+  public static var gzip: Self {
+    return Self(value: .gzip)
+  }
+
+  /// All compression algorithms.
+  public static var all: Self {
+    return [.gzip, .deflate, .none]
+  }
+
+  /// Returns whether a given algorithm is present in the set.
+  ///
+  /// - Parameter algorithm: The algorithm to check.
+  public func contains(_ algorithm: CompressionAlgorithm) -> Bool {
+    return self.contains(CompressionAlgorithmSet(value: algorithm.value))
+  }
+}
+
+extension CompressionAlgorithmSet {
+  /// A sequence of ``CompressionAlgorithm`` values present in the set.
+  public var elements: Elements {
+    Elements(algorithmSet: self)
+  }
+
+  /// A sequence of ``CompressionAlgorithm`` values present in a ``CompressionAlgorithmSet``.
+  public struct Elements: Sequence {
+    public typealias Element = CompressionAlgorithm
+
+    private let algorithmSet: CompressionAlgorithmSet
+
+    init(algorithmSet: CompressionAlgorithmSet) {
+      self.algorithmSet = algorithmSet
+    }
+
+    public func makeIterator() -> Iterator {
+      return Iterator(algorithmSet: self.algorithmSet)
+    }
+
+    public struct Iterator: IteratorProtocol {
+      private let algorithmSet: CompressionAlgorithmSet
+      private var iterator: IndexingIterator<[CompressionAlgorithm.Value]>
+
+      init(algorithmSet: CompressionAlgorithmSet) {
+        self.algorithmSet = algorithmSet
+        self.iterator = CompressionAlgorithm.Value.allCases.makeIterator()
+      }
+
+      public mutating func next() -> CompressionAlgorithm? {
+        while let value = self.iterator.next() {
+          if self.algorithmSet.contains(CompressionAlgorithmSet(value: value)) {
+            return CompressionAlgorithm(value)
+          }
+        }
+
+        return nil
+      }
+    }
+  }
+}

Sources/GRPCHTTP2Core/Client/GRPCClientStreamHandler.swift

@@ -35,7 +35,7 @@ final class GRPCClientStreamHandler: ChannelDuplexHandler {
     methodDescriptor: MethodDescriptor,
     scheme: Scheme,
     outboundEncoding: CompressionAlgorithm,
-    acceptedEncodings: [CompressionAlgorithm],
+    acceptedEncodings: CompressionAlgorithmSet,
     maximumPayloadSize: Int,
     skipStateMachineAssertions: Bool = false
   ) {

Sources/GRPCHTTP2Core/Compression/CompressionAlgorithm.swift

@@ -14,39 +14,40 @@
  * limitations under the License.
  */
 
-/// Supported message compression algorithms.
-///
-/// These algorithms are indicated in the "grpc-encoding" header. As such, a lack of "grpc-encoding"
-/// header indicates that there is no message compression.
-public struct CompressionAlgorithm: Hashable, Sendable {
-  /// Identity compression; "no" compression but indicated via the "grpc-encoding" header.
-  public static let identity = CompressionAlgorithm(.identity)
-  public static let deflate = CompressionAlgorithm(.deflate)
-  public static let gzip = CompressionAlgorithm(.gzip)
+@_spi(Package) import GRPCCore
 
-  // The order here is important: most compression to least.
-  public static let all: [CompressionAlgorithm] = [.gzip, .deflate, .identity]
-
-  public var name: String {
-    return self.algorithm.rawValue
+extension CompressionAlgorithm {
+  init?(name: String) {
+    self.init(name: name[...])
   }
 
-  internal enum Algorithm: String {
-    case identity
-    case deflate
-    case gzip
+  init?(name: Substring) {
+    switch name {
+    case "gzip":
+      self = .gzip
+    case "deflate":
+      self = .deflate
+    case "identity":
+      self = .none
+    default:
+      return nil
+    }
   }
 
-  internal let algorithm: Algorithm
-
-  private init(_ algorithm: Algorithm) {
-    self.algorithm = algorithm
+  var name: String {
+    switch self.value {
+    case .gzip:
+      return "gzip"
+    case .deflate:
+      return "deflate"
+    case .none:
+      return "identity"
+    }
   }
+}
 
-  internal init?(rawValue: String) {
-    guard let algorithm = Algorithm(rawValue: rawValue) else {
-      return nil
-    }
-    self.algorithm = algorithm
+extension CompressionAlgorithmSet {
+  var count: Int {
+    self.rawValue.nonzeroBitCount
   }
 }