//
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// RequestCompression.swift
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//
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// Copyright (c) 2023 Alamofire Software Foundation (http://alamofire.org/)
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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// THE SOFTWARE.
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//
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#if canImport(zlib)
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import Foundation
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import zlib
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/// `RequestAdapter` which compresses outgoing `URLRequest` bodies using the `deflate` `Content-Encoding` and adds the
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/// appropriate header.
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///
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/// - Note: Most requests to most APIs are small and so would only be slowed down by applying this adapter. Measure the
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/// size of your request bodies and the performance impact of using this adapter before use. Using this adapter
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/// with already compressed data, such as images, will, at best, have no effect. Additionally, body compression
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/// is a synchronous operation, so measuring the performance impact may be important to determine whether you
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/// want to use a dedicated `requestQueue` in your `Session` instance. Finally, not all servers support request
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/// compression, so test with all of your server configurations before deploying.
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@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
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public struct DeflateRequestCompressor: RequestInterceptor {
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/// Type that determines the action taken when the `URLRequest` already has a `Content-Encoding` header.
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public enum DuplicateHeaderBehavior {
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/// Throws a `DuplicateHeaderError`. The default.
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case error
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/// Replaces the existing header value with `deflate`.
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case replace
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/// Silently skips compression when the header exists.
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case skip
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}
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/// `Error` produced when the outgoing `URLRequest` already has a `Content-Encoding` header, when the instance has
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/// been configured to produce an error.
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public struct DuplicateHeaderError: Error {}
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/// Behavior to use when the outgoing `URLRequest` already has a `Content-Encoding` header.
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public let duplicateHeaderBehavior: DuplicateHeaderBehavior
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/// Closure which determines whether the outgoing body data should be compressed.
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public let shouldCompressBodyData: (_ bodyData: Data) -> Bool
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/// Creates an instance with the provided parameters.
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///
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/// - Parameters:
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/// - duplicateHeaderBehavior: `DuplicateHeaderBehavior` to use. `.error` by default.
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/// - shouldCompressBodyData: Closure which determines whether the outgoing body data should be compressed. `true` by default.
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public init(duplicateHeaderBehavior: DuplicateHeaderBehavior = .error,
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shouldCompressBodyData: @escaping (_ bodyData: Data) -> Bool = { _ in true }) {
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self.duplicateHeaderBehavior = duplicateHeaderBehavior
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self.shouldCompressBodyData = shouldCompressBodyData
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}
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public func adapt(_ urlRequest: URLRequest, for session: Session, completion: @escaping (Result<URLRequest, Error>) -> Void) {
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// No need to compress unless we have body data. No support for compressing streams.
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guard let bodyData = urlRequest.httpBody else {
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completion(.success(urlRequest))
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return
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}
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guard shouldCompressBodyData(bodyData) else {
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completion(.success(urlRequest))
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return
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}
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if urlRequest.headers.value(for: "Content-Encoding") != nil {
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switch duplicateHeaderBehavior {
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case .error:
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completion(.failure(DuplicateHeaderError()))
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return
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case .replace:
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// Header will be replaced once the body data is compressed.
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break
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case .skip:
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completion(.success(urlRequest))
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return
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}
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}
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var compressedRequest = urlRequest
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do {
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compressedRequest.httpBody = try deflate(bodyData)
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compressedRequest.headers.update(.contentEncoding("deflate"))
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completion(.success(compressedRequest))
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} catch {
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completion(.failure(error))
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}
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}
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func deflate(_ data: Data) throws -> Data {
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var output = Data([0x78, 0x5E]) // Header
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try output.append((data as NSData).compressed(using: .zlib) as Data)
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var checksum = adler32Checksum(of: data).bigEndian
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output.append(Data(bytes: &checksum, count: MemoryLayout<UInt32>.size))
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return output
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}
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func adler32Checksum(of data: Data) -> UInt32 {
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data.withUnsafeBytes { buffer in
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UInt32(adler32(1, buffer.baseAddress, UInt32(buffer.count)))
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}
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}
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}
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@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
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extension RequestInterceptor where Self == DeflateRequestCompressor {
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/// Create a `DeflateRequestCompressor` with default `duplicateHeaderBehavior` and `shouldCompressBodyData` values.
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public static var deflateCompressor: DeflateRequestCompressor {
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DeflateRequestCompressor()
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}
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/// Creates a `DeflateRequestCompressor` with the provided `DuplicateHeaderBehavior` and `shouldCompressBodyData`
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/// closure.
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///
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/// - Parameters:
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/// - duplicateHeaderBehavior: `DuplicateHeaderBehavior` to use.
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/// - shouldCompressBodyData: Closure which determines whether the outgoing body data should be compressed. `true` by default.
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///
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/// - Returns: The `DeflateRequestCompressor`.
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public static func deflateCompressor(
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duplicateHeaderBehavior: DeflateRequestCompressor.DuplicateHeaderBehavior = .error,
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shouldCompressBodyData: @escaping (_ bodyData: Data) -> Bool = { _ in true }
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) -> DeflateRequestCompressor {
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DeflateRequestCompressor(duplicateHeaderBehavior: duplicateHeaderBehavior,
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shouldCompressBodyData: shouldCompressBodyData)
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}
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}
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#endif
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