workaround Foundation.URL behavior changes (#777)

`Foundation.URL` has various behavior changes in Swift 6 to better match
RFC 3986 which impact AHC.

In particular it now no longer strips the square brackets in IPv6 hosts
which are not tolerated by `inet_pton` so these must be manually
stripped.

swiftlang/swift-foundation#957
swiftlang/swift-foundation#958
swiftlang/swift-foundation#962

Author: rnro

Sources/AsyncHTTPClient/AsyncAwait/HTTPClientRequest+Prepared.swift

@@ -45,7 +45,7 @@ extension HTTPClientRequest {
 @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
 extension HTTPClientRequest.Prepared {
     init(_ request: HTTPClientRequest, dnsOverride: [String: String] = [:]) throws {
-        guard let url = URL(string: request.url) else {
+        guard !request.url.isEmpty, let url = URL(string: request.url) else {
             throw HTTPClientError.invalidURL
         }
 

Sources/AsyncHTTPClient/DeconstructedURL.swift

@@ -48,9 +48,16 @@ extension DeconstructedURL {
 
         switch scheme {
         case .http, .https:
+            #if !canImport(Darwin) && compiler(>=6.0)
+            guard let urlHost = url.host, !urlHost.isEmpty else {
+                throw HTTPClientError.emptyHost
+            }
+            let host = urlHost.trimIPv6Brackets()
+            #else
             guard let host = url.host, !host.isEmpty else {
                 throw HTTPClientError.emptyHost
             }
+            #endif
             self.init(
                 scheme: scheme,
                 connectionTarget: .init(remoteHost: host, port: url.port ?? scheme.defaultPort),
@@ -81,3 +88,26 @@ extension DeconstructedURL {
         }
     }
 }
+
+#if !canImport(Darwin) && compiler(>=6.0)
+extension String {
+    @inlinable internal func trimIPv6Brackets() -> String {
+        var utf8View = self.utf8[...]
+
+        var modified = false
+        if utf8View.first == UInt8(ascii: "[") {
+            utf8View = utf8View.dropFirst()
+            modified = true
+        }
+        if utf8View.last == UInt8(ascii: "]") {
+            utf8View = utf8View.dropLast()
+            modified = true
+        }
+
+        if modified {
+            return String(Substring(utf8View))
+        }
+        return self
+    }
+}
+#endif

Tests/AsyncHTTPClientTests/HTTPClientTests.swift

@@ -43,8 +43,12 @@ final class HTTPClientTests: XCTestCaseHTTPClientTestsBaseClass {
         XCTAssertEqual(request2.url.path, "")
 
         let request3 = try Request(url: "unix:///tmp/file")
-        XCTAssertNil(request3.url.host)
         XCTAssertEqual(request3.host, "")
+        #if os(Linux) && compiler(>=6.0)
+        XCTAssertEqual(request3.url.host, "")
+        #else
+        XCTAssertNil(request3.url.host)
+        #endif
         XCTAssertEqual(request3.url.path, "/tmp/file")
         XCTAssertEqual(request3.port, 80)
         XCTAssertFalse(request3.useTLS)