(142589056) URLComponents.string should percent-encode colons in first path segment if needed (swiftlang#1117)

Author: jrflat

Sources/FoundationEssentials/URL/URL.swift

@@ -1498,7 +1498,7 @@ public struct URL: Equatable, Sendable, Hashable {
         }
         #endif
         if _baseParseInfo != nil {
-            return absoluteURL.path(percentEncoded: percentEncoded)
+            return absoluteURL.relativePath(percentEncoded: percentEncoded)
         }
         if percentEncoded {
             return String(_parseInfo.path)

Sources/FoundationEssentials/URL/URLComponents.swift

@@ -364,6 +364,17 @@ public struct URLComponents: Hashable, Equatable, Sendable {
             return ""
         }
 
+        private var percentEncodedPathNoColon: String {
+            guard percentEncodedPath.utf8.first(where: { $0 == ._colon || $0 == ._slash }) == ._colon else {
+                return percentEncodedPath
+            }
+            let colonEncodedPath = Array(percentEncodedPath.utf8).replacing(
+                [._colon],
+                with: [UInt8(ascii: "%"), UInt8(ascii: "3"), UInt8(ascii: "A")]
+            )
+            return String(decoding: colonEncodedPath, as: UTF8.self)
+        }
+
         mutating func setPercentEncodedPath(_ newValue: String) throws {
             reset(.path)
             guard Parser.validate(newValue, component: .path) else {
@@ -451,7 +462,13 @@ public struct URLComponents: Hashable, Equatable, Sendable {
                 // The parser already validated a special-case (e.g. addressbook:).
                 result += ":\(portString)"
             }
-            result += percentEncodedPath
+            if result.isEmpty {
+                // We must percent-encode colons in the first path segment
+                // as they could be misinterpreted as a scheme separator.
+                result += percentEncodedPathNoColon
+            } else {
+                result += percentEncodedPath
+            }
             if let percentEncodedQuery {
                 result += "?\(percentEncodedQuery)"
             }

Tests/FoundationEssentialsTests/URLTests.swift

@@ -1347,6 +1347,19 @@ final class URLTests : XCTestCase {
         comp = try XCTUnwrap(URLComponents(string: legalURLString))
         XCTAssertEqual(comp.string, legalURLString)
         XCTAssertEqual(comp.percentEncodedPath, colonFirstPath)
+
+        // Colons should be percent-encoded by URLComponents.string if
+        // they could be misinterpreted as a scheme separator.
+
+        comp = URLComponents()
+        comp.percentEncodedPath = "not%20a%20scheme:"
+        XCTAssertEqual(comp.string, "not%20a%20scheme%3A")
+
+        // These would fail if we did not percent-encode the colon.
+        // .string should always produce a valid URL string, or nil.
+
+        XCTAssertNotNil(URL(string: comp.string!))
+        XCTAssertNotNil(URLComponents(string: comp.string!))
     }
 
     func testURLComponentsInvalidPaths() {