Tighten character sets to conform strictly to RFC

Sources/ScreamURITemplate/Internal/CharacterSets.swift

@@ -14,15 +14,16 @@
 
 import Foundation
 
-let unreservedCharacterSet = CharacterSet.alphanumerics.union(CharacterSet(charactersIn: "-._~"))
+private let asciiAlphanumerics = CharacterSet(charactersIn: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789")
+let unreservedCharacterSet = asciiAlphanumerics.union(CharacterSet(charactersIn: "-._~"))
 private let genDelimsCharacterSet = CharacterSet(charactersIn: ":/?#[]@")
 private let subDelimsCharacterSet = CharacterSet(charactersIn: "!$&'()*+,;=")
 let reservedCharacterSet = genDelimsCharacterSet.union(subDelimsCharacterSet)
 let reservedAndUnreservedCharacterSet = reservedCharacterSet.union(unreservedCharacterSet)
 let invertedLiteralCharacterSet = CharacterSet.illegalCharacters.union(CharacterSet.controlCharacters).union(CharacterSet(charactersIn: " \"%<>\\^`{|}"))
 let literalCharacterSet = invertedLiteralCharacterSet.inverted
 let hexCharacterSet = CharacterSet(charactersIn: "0123456789abcdefABCDEF")
-let varnameCharacterSet = CharacterSet.alphanumerics.union(CharacterSet(charactersIn: "_%."))
+let varnameCharacterSet = asciiAlphanumerics.union(CharacterSet(charactersIn: "_%."))
 let invertedVarnameCharacterSet = varnameCharacterSet.inverted
 let expressionOperatorCharacterSet = CharacterSet(charactersIn: "+#./;?&=,!@|")
-let invertedDecimalDigitsCharacterSet = CharacterSet.decimalDigits.inverted
+let invertedDecimalDigitsCharacterSet = CharacterSet(charactersIn: "0123456789").inverted

Tests/ScreamURITemplateTests/Tests.swift

@@ -41,6 +41,20 @@ class Tests: XCTestCase {
         XCTAssertThrowsError(try URITemplate(string: "https://api.github.com/repos/%2"))
     }
 
+    func testNonASCIIVariableNameRejected() throws {
+        XCTAssertThrowsError(try URITemplate(string: "{é}"))
+    }
+
+    func testNonASCIIPrefixLengthDigitRejected() throws {
+        XCTAssertThrowsError(try URITemplate(string: "{var:\u{0661}}")) { error in
+            guard let templateError = error as? URITemplate.Error else {
+                XCTFail("Unexpected error type")
+                return
+            }
+            XCTAssertEqual(templateError.reason, "Prefix length not specified")
+        }
+    }
+
     func testVariableProvider() throws {
         let template: URITemplate = "https://api.github.com/repos/{owner}/{repo}/collaborators/{username}"
         let urlString = try template.process(variables: TestVariableProvider())
@@ -78,6 +92,18 @@ class Tests: XCTestCase {
         XCTAssertEqual(urlString, "https://api.example.com/SwiftScream/42/true")
     }
 
+    func testSimpleExpansionPercentEncodesNonASCII() throws {
+        let template: URITemplate = "{value}"
+        let result = try template.process(variables: ["value": "Grüner Weg"])
+        XCTAssertEqual(result, "Gr%C3%BCner%20Weg")
+    }
+
+    func testReservedExpansionStillPercentEncodesNonASCII() throws {
+        let template: URITemplate = "{+value}"
+        let result = try template.process(variables: ["value": "/café"])
+        XCTAssertEqual(result, "/caf%C3%A9")
+    }
+
     func testVariableDictionaryList() throws {
         let template: URITemplate = "https://api.example.com/{list}"
         let variables: VariableDictionary = [