Throw invalid URL error on relative URLs.

Aligns with Node behavior.

index.js

@@ -15,6 +15,11 @@ events.forEach(function (event) {
   };
 });
 
+var InvalidUrlError = createErrorType(
+  "ERR_INVALID_URL",
+  "Invalid URL",
+  TypeError
+);
 // Error types with codes
 var RedirectionError = createErrorType(
   "ERR_FR_REDIRECTION_FAILURE",
@@ -409,7 +414,7 @@ RedirectableRequest.prototype._processResponse = function (response) {
     redirectUrl = url.resolve(currentUrl, location);
   }
   catch (cause) {
-    this.emit("error", new RedirectionError(cause));
+    this.emit("error", new RedirectionError({ cause: cause }));
     return;
   }
 
@@ -454,7 +459,7 @@ RedirectableRequest.prototype._processResponse = function (response) {
     this._performRequest();
   }
   catch (cause) {
-    this.emit("error", new RedirectionError(cause));
+    this.emit("error", new RedirectionError({ cause: cause }));
   }
 };
 
@@ -477,14 +482,18 @@ function wrap(protocols) {
     function request(input, options, callback) {
       // Parse parameters
       if (isString(input)) {
-        var urlStr = input;
+        var parsed;
         try {
-          input = urlToOptions(new URL(urlStr));
+          parsed = urlToOptions(new URL(input));
         }
         catch (err) {
           /* istanbul ignore next */
-          input = url.parse(urlStr);
+          parsed = url.parse(input);
+        }
+        if (!isString(parsed.protocol)) {
+          throw new InvalidUrlError({ input });
         }
+        input = parsed;
       }
       else if (URL && (input instanceof URL)) {
         input = urlToOptions(input);
@@ -562,21 +571,19 @@ function removeMatchingHeaders(regex, headers) {
     undefined : String(lastValue).trim();
 }
 
-function createErrorType(code, defaultMessage) {
-  function CustomError(cause) {
+function createErrorType(code, message, baseClass) {
+  // Create constructor
+  function CustomError(properties) {
     Error.captureStackTrace(this, this.constructor);
-    if (!cause) {
-      this.message = defaultMessage;
-    }
-    else {
-      this.message = defaultMessage + ": " + cause.message;
-      this.cause = cause;
-    }
+    Object.assign(this, properties || {});
+    this.code = code;
+    this.message = this.cause ? message + ": " + this.cause.message : message;
   }
-  CustomError.prototype = new Error();
+
+  // Attach constructor and set default properties
+  CustomError.prototype = new (baseClass || Error)();
   CustomError.prototype.constructor = CustomError;
   CustomError.prototype.name = "Error [" + code + "]";
-  CustomError.prototype.code = code;
   return CustomError;
 }
 

test/test.js

@@ -197,6 +197,20 @@ describe("follow-redirects", function () {
       });
   });
 
+  it("http.get with relative URL path", function () {
+    var error = null;
+    try {
+      http.get("/relative");
+    }
+    catch (e) {
+      error = e;
+    }
+    assert(error instanceof Error);
+    assert(error instanceof TypeError);
+    assert.equal(error.code, "ERR_INVALID_URL");
+    assert.equal(error.input, "/relative");
+  });
+
   it("should return with the original status code if the response does not contain a location header", function () {
     app.get("/a", function (req, res) {
       res.status(307).end();