improve registry client handling of alternative locations (#4142)

motication: preparation work for mixed graphs

changes:
* rename RegistryClient::listVersions API to getPackageMetadata and revise it to parse the link header that contains the alternative URLs for the package
* enhance RegistryClient::getIdentifers API to use codable for parsing the server result
* add small utility to drop prefx from string to Basics
* cleanup redundant HTTPClientProtocol which was used for RegistryClient testing but since deprecated
* add and adjust tests

Author: tomerd

Sources/Basics/HTPClient+URLSession.swift

@@ -17,7 +17,7 @@ import struct TSCUtility.Versioning
 import FoundationNetworking
 #endif
 
-public struct URLSessionHTTPClient: HTTPClientProtocol {
+public struct URLSessionHTTPClient {
     private let dataTasksManager: DataTaskManager
     private let downloadsTasksManager: DownloadTaskManager
 
@@ -26,11 +26,11 @@ public struct URLSessionHTTPClient: HTTPClientProtocol {
         self.downloadsTasksManager = DownloadTaskManager(configuration: configuration)
     }
 
-    public func execute(_ request: HTTPClient.Request, progress: ProgressHandler?, completion: @escaping CompletionHandler) {
+    public func execute(_ request: HTTPClient.Request, progress: HTTPClient.ProgressHandler?, completion: @escaping HTTPClient.CompletionHandler) {
         self.execute(request, observabilityScope: nil, progress: progress, completion: completion)
     }
 
-    public func execute(_ request: HTTPClient.Request, observabilityScope: ObservabilityScope? = nil, progress: ProgressHandler?, completion: @escaping CompletionHandler) {
+    public func execute(_ request: HTTPClient.Request, observabilityScope: ObservabilityScope? = nil, progress: HTTPClient.ProgressHandler?, completion: @escaping HTTPClient.CompletionHandler) {
         switch request.kind {
         case .generic:
             let task = self.dataTasksManager.makeTask(request: request, progress: progress, completion: completion)

Sources/Basics/HTTPClient.swift

@@ -24,23 +24,6 @@ import Glibc
 import CRT
 #endif
 
-public protocol HTTPClientProtocol {
-    typealias ProgressHandler = (_ bytesReceived: Int64, _ totalBytes: Int64?) -> Void
-    typealias CompletionHandler = (Result<HTTPClientResponse, Error>) -> Void
-
-    /// Execute an HTTP request asynchronously
-    ///
-    /// - Parameters:
-    ///   - request: The `HTTPClientRequest` to perform.
-    ///   - observabilityScope: the observability scope to emit diagnostics on
-    ///   - progress: A closure to handle progress for example for downloads
-    ///   - callback: A closure to be notified of the completion of the request.
-    func execute(_ request: HTTPClientRequest,
-                 observabilityScope: ObservabilityScope?,
-                 progress: ProgressHandler?,
-                 completion: @escaping CompletionHandler)
-}
-
 public enum HTTPClientError: Error, Equatable {
     case invalidResponse
     case badResponseStatusCode(Int)
@@ -51,11 +34,13 @@ public enum HTTPClientError: Error, Equatable {
 
 // MARK: - HTTPClient
 
-public struct HTTPClient: HTTPClientProtocol {
+public struct HTTPClient {
     public typealias Configuration = HTTPClientConfiguration
     public typealias Request = HTTPClientRequest
     public typealias Response = HTTPClientResponse
     public typealias Handler = (Request, ProgressHandler?, @escaping (Result<Response, Error>) -> Void) -> Void
+    public typealias ProgressHandler = (_ bytesReceived: Int64, _ totalBytes: Int64?) -> Void
+    public typealias CompletionHandler = (Result<HTTPClientResponse, Error>) -> Void
 
     public var configuration: HTTPClientConfiguration
     private let underlying: Handler
@@ -70,6 +55,13 @@ public struct HTTPClient: HTTPClientProtocol {
         self.underlying = handler ?? URLSessionHTTPClient().execute
     }
 
+    /// Execute an HTTP request asynchronously
+    ///
+    /// - Parameters:
+    ///   - request: The `HTTPClientRequest` to perform.
+    ///   - observabilityScope: the observability scope to emit diagnostics on
+    ///   - progress: A progress handler to handle progress for example for downloads
+    ///   - completion: A completion handler to be notified of the completion of the request.
     public func execute(_ request: Request, observabilityScope: ObservabilityScope? = nil, progress: ProgressHandler? = nil, completion: @escaping CompletionHandler) {
         // merge configuration
         var request = request

Sources/Basics/String+Extensions.swift

@@ -17,4 +17,12 @@ extension String {
     public var sha256Checksum: String {
         return SHA256().hash(self).hexadecimalRepresentation
     }
+
+    /// Drops the given suffix from the string, if present.
+    public func spm_dropPrefix(_ prefix: String) -> String {
+        if self.hasPrefix(prefix) {
+            return String(self.dropFirst(prefix.count))
+        }
+        return self
+    }
 }