Added support for RegExp pattern Validation (#2856)

Sources/Vapor/Validation/Validators/Pattern.swift

@@ -0,0 +1,37 @@
+extension Validator where T == String {
+    /// Validates whether a `String` matches a RegularExpression pattern
+    public static func pattern(_ pattern: String) -> Validator<T> {
+        .init {
+            guard
+                let range = $0.range(of: pattern, options: [.regularExpression]),
+                range.lowerBound == $0.startIndex && range.upperBound == $0.endIndex
+            else {
+                return ValidatorResults.Pattern(isValidPattern: false, pattern: pattern)
+            }
+            return ValidatorResults.Pattern(isValidPattern: true, pattern: pattern)
+        }
+    }
+}
+
+extension ValidatorResults {
+    /// `ValidatorResult` of a validator that validates whether a `String`matches a RegularExpression pattern
+    public struct Pattern {
+        public let isValidPattern: Bool
+        public let pattern: String
+    }
+}
+
+extension ValidatorResults.Pattern: ValidatorResult {
+    public var isFailure: Bool {
+        /// The input is valid for the pattern
+        !self.isValidPattern
+    }
+
+    public var successDescription: String? {
+        "is a valid pattern"
+    }
+
+    public var failureDescription: String? {
+        "is not a valid pattern \(self.pattern)"
+    }
+}

Tests/VaporTests/ValidationTests.swift

@@ -542,6 +542,11 @@ class ValidationTests: XCTestCase {
         assert(true, fails: !.valid, "is valid")
         assert("123", fails: !.valid, "is valid")
     }
+
+    func testPattern() {
+        assert("this are not numbers", fails: .pattern("^[0-9]*$"), "is not a valid pattern ^[0-9]*$")
+        assert("12345", passes: .pattern("^[0-9]*$"))
+    }
 
     func testPreexistingValidatorResultIsIncluded() throws {
         struct CustomValidatorResult: ValidatorResult {