Require full IPv4 address string to be treated as valid URL (#616)

Task/Issue URL: https://app.asana.com/0/0/1206262563462715/f

Description:
When an IPv4-like string is passed to URL constructor, require that it contains 4 octets and otherwise return nil.
This allows clients to fall back to treating the string as search query and constructing search URLs, instead
of making most likely unwanted navigation to an IP address where missing octets are filled with zeros
(e.g. 1.4 -> 1.0.0.4).

Sources/Common/Extensions/URLExtension.swift

@@ -17,6 +17,7 @@
 //
 
 import Foundation
+import Network
 
 extension URL {
 
@@ -193,6 +194,12 @@ extension URL {
                     // could be a local domain but user needs to use the protocol to specify that
                     return nil
                 }
+                if IPv4Address(String(hostname)) != nil {
+                    // Require 4 octets specified explicitly for an IPv4 address (avoid 1.4 -> 1.0.0.4 expansion)
+                    guard hostname.split(separator: ".").count == 4 else {
+                        return nil
+                    }
+                }
             } else {
                 return nil
             }

Tests/CommonTests/Extensions/URLExtensionTests.swift

@@ -89,6 +89,16 @@ final class URLExtensionTests: XCTestCase {
         XCTAssertNil("localdomain".url)
     }
 
+    func testThatIPv4AddressMustContainFourOctets() {
+        XCTAssertNil("1.4".url)
+        XCTAssertNil("1.4/3.4".url)
+        XCTAssertNil("1.0.4".url)
+        XCTAssertNil("127.0.1".url)
+
+        XCTAssertEqual("127.0.0.1".url?.absoluteString, "http://127.0.0.1")
+        XCTAssertEqual("1.0.0.4/3.4".url?.absoluteString, "http://1.0.0.4/3.4")
+    }
+
     func testWhenNakedIsCalled_ThenURLWithNoSchemeWWWPrefixAndLastSlashIsReturned() {
         let url = URL(string: "http://duckduckgo.com")!
         let duplicate = URL(string: "https://www.duckduckgo.com/")!