Remove trimmingCharacters(in:)

Sources/OpenAPIRuntime/Base/ContentDisposition.swift

@@ -12,8 +12,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Full Foundation needed for String.trimmingCharacters
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 /// A parsed representation of the `content-disposition` header described by RFC 6266 containing only
 /// the features relevant to OpenAPI multipart bodies.
@@ -104,15 +107,15 @@ extension ContentDisposition: RawRepresentable {
     /// https://datatracker.ietf.org/doc/html/rfc6266#section-4.1
     /// - Parameter rawValue: The raw value to use for the new instance.
     init?(rawValue: String) {
-        var components = rawValue.split(separator: ";").map { $0.trimmingCharacters(in: .whitespacesAndNewlines) }
+        var components = rawValue.split(separator: ";").map { $0.trimmingLeadingAndTrailingSpaces }
         guard !components.isEmpty else { return nil }
         self.dispositionType = DispositionType(rawValue: components.removeFirst())
         let parameterTuples: [(ParameterName, String)] = components.compactMap {
             (component: String) -> (ParameterName, String)? in
             let parameterComponents = component.split(separator: "=", maxSplits: 1)
-                .map { $0.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines) }
+                .map { $0.trimmingLeadingAndTrailingSpaces }
             guard parameterComponents.count == 2 else { return nil }
-            let valueWithoutQuotes = parameterComponents[1].trimmingCharacters(in: ["\""])
+            let valueWithoutQuotes = parameterComponents[1].trimming(while: { $0 == "\"" })
             return (.init(rawValue: parameterComponents[0]), valueWithoutQuotes)
         }
         self.parameters = Dictionary(parameterTuples, uniquingKeysWith: { a, b in a })

Sources/OpenAPIRuntime/Conversion/Converter+Server.swift

@@ -55,7 +55,7 @@ extension Converter {
         let acceptValues = acceptHeader.split(separator: ",")
             .map { value in
                 // Drop everything after the optional semicolon (q, extensions, ...)
-                value.split(separator: ";")[0].trimmingCharacters(in: .whitespacesAndNewlines).lowercased()
+                value.split(separator: ";")[0].trimmingLeadingAndTrailingSpaces.lowercased()
             }
         if acceptValues.isEmpty { return }
         guard let parsedSubstring = OpenAPIMIMEType(substring) else {

Sources/OpenAPIRuntime/Conversion/FoundationExtensions.swift

@@ -12,11 +12,23 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
-extension String {
-
+extension StringProtocol {
     /// Returns the string with leading and trailing whitespace (such as spaces
     /// and newlines) removed.
-    var trimmingLeadingAndTrailingSpaces: Self { trimmingCharacters(in: .whitespacesAndNewlines) }
+    var trimmingLeadingAndTrailingSpaces: String { self.trimming { $0.isWhitespace } }
+
+    /// Returns a new string by removing leading and trailing characters
+    /// that satisfy the given predicate.
+    func trimming(while predicate: (Character) -> Bool) -> String {
+        guard let start = self.firstIndex(where: { !predicate($0) }) else { return "" }
+        let end = self.lastIndex(where: { !predicate($0) })!
+
+        return String(self[start...end])
+    }
 }

Tests/OpenAPIRuntimeTests/Conversion/Test_FoundationExtensions.swift

@@ -0,0 +1,49 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftOpenAPIGenerator open source project
+//
+// Copyright (c) 2026 Apple Inc. and the SwiftOpenAPIGenerator project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftOpenAPIGenerator project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+import XCTest
+import Foundation
+@testable import OpenAPIRuntime
+
+final class Test_FoundationExtensions: Test_Runtime {
+
+    func testTrimmingMatchesFoundationBehavior() {
+        let testCases = [
+            "  Hello World  ",  // Standard spaces
+            "\n\tHello World\r\n",  // Newlines and tabs
+            "NoTrimmingNeeded",  // No whitespace
+            "    ",  // Only spaces
+            "",  // Empty string
+            " Hello\nWorld ",  // Internal whitespace (should stay)
+            "\u{00A0}Unicode\u{00A0}",  // Non-breaking space
+            "\u{3000}Ideographic\u{3000}",  // Japanese/Chinese full-width space
+        ]
+
+        for input in testCases {
+            let foundationResult = input.trimmingCharacters(in: .whitespacesAndNewlines)
+            let swiftNativeResult = input.trimmingLeadingAndTrailingSpaces
+
+            XCTAssertEqual(swiftNativeResult, foundationResult, "Failed for input: \(input)")
+        }
+    }
+
+    func testGenericTrimming() {
+        let numericString = "0001234500"
+        let result = numericString.trimming(while: { $0 == "0" })
+        XCTAssertEqual(result, "12345")
+
+        let punctuationString = "...Hello!.."
+        let puncResult = punctuationString.trimming(while: { $0.isPunctuation })
+        XCTAssertEqual(puncResult, "Hello")
+    }
+}