Fix: Allow absolute URLs as paths, e.g. for load()

When using protobuf.js in a browser, it's useful to be able to load
proto files from other origins. But currently, path.normalize() mangles
URLs by removing the second slash after the scheme (e.g.
"https://example.com/" becomes "https:/example.com").

Fix that issue, and better integrate the existing UNC support, by
introducing a new path.absolutePrefix() function that checks for all the
various prefixes that indicate a path is absolute and returns the one it
finds (if any). By including both slashes in the return value for URLs,
we exclude them from the normalization logic.

Author: tchebb

index.d.ts

@@ -2423,6 +2423,13 @@ export namespace util {
     /** A minimal path module to resolve Unix, Windows and URL paths alike. */
     namespace path {
 
+        /**
+         * Gets the prefix of an absolute UNC path, Unix path, or URL that makes it absolute, if present.
+         * @param path Path to test
+         * @returns the prefix, or null if path is relative
+         */
+        function absolutePrefix(path: string): (string|null);
+
         /**
          * Tests if the specified path is absolute.
          * @param path Path to test

lib/path/README.md

@@ -16,4 +16,7 @@ API
 * **path.resolve(originPath: `string`, includePath: `string`, [alreadyNormalized=false: `boolean`]): `string`**<br />
   Resolves the specified include path against the specified origin path.
 
+* **path.absolutePrefix(path: `string`): `string|null`**<br />
+  Gets the prefix of an absolute Windows, UNC, or Unix path or a URL that indicates it's absolute.
+
 **License:** [BSD 3-Clause License](https://opensource.org/licenses/BSD-3-Clause)

lib/path/index.d.ts

@@ -1,3 +1,10 @@
+/**
+ * Gets the prefix of an absolute Windows, UNC, or Unix path or a URL that indicates it's absolute.
+ * @param {string} path Path to test
+ * @returns {string|null} the prefix, or null if path is relative
+ */
+export function absolutePrefix(path: string): (string|null);
+
 /**
  * Tests if the specified path is absolute.
  * @param {string} path Path to test

lib/path/index.js

@@ -7,14 +7,39 @@
  */
 var path = exports;
 
+var absolutePrefix =
+/**
+ * Gets the prefix of an absolute Windows, UNC, or Unix path or a URL that indicates it's absolute.
+ * @param {string} path Path to test
+ * @returns {string|null} the prefix, or null if path is relative
+ */
+path.absolutePrefix = function absolutePrefix(path) {
+    var match;
+    if (path.startsWith("\\\\")) {
+        // UNC path
+        return "\\\\";
+    } else if ((match = /^\w*:\/\//.exec(path)) !== null) {
+        // URL
+        return match[0];
+    } else if ((match = /^\w:/.exec(path)) !== null) {
+        // Windows path
+        return match[0];
+    } else if (path.startsWith("/")) {
+        // Unix path
+        return "/";
+    } else {
+        return null;
+    }
+}
+
 var isAbsolute =
 /**
  * Tests if the specified path is absolute.
  * @param {string} path Path to test
  * @returns {boolean} `true` if path is absolute
  */
 path.isAbsolute = function isAbsolute(path) {
-    return /^(?:\/|\w+:|\\\\\w+)/.test(path);
+    return absolutePrefix(path) !== null;
 };
 
 var normalize =
@@ -24,20 +49,18 @@ var normalize =
  * @returns {string} Normalized path
  */
 path.normalize = function normalize(path) {
-    var firstTwoCharacters = path.substring(0,2);
-    var uncPrefix = "";
-    if (firstTwoCharacters === "\\\\") {
-        uncPrefix = firstTwoCharacters;
-        path = path.substring(2);
+    var absolute = false;
+    var prefix = absolutePrefix(path);
+    if (prefix !== null) {
+        absolute = true;
+        path = path.substring(prefix.length);
+    } else {
+        prefix = "";
     }
 
     path = path.replace(/\\/g, "/")
                .replace(/\/{2,}/g, "/");
-    var parts    = path.split("/"),
-        absolute = isAbsolute(path),
-        prefix   = "";
-    if (absolute)
-        prefix = parts.shift() + "/";
+    var parts = path.split("/");
     for (var i = 0; i < parts.length;) {
         if (parts[i] === "..") {
             if (i > 0 && parts[i - 1] !== "..")
@@ -51,7 +74,7 @@ path.normalize = function normalize(path) {
         else
             ++i;
     }
-    return uncPrefix + prefix + parts.join("/");
+    return prefix + parts.join("/");
 };
 
 /**

lib/path/tests/index.js

@@ -12,6 +12,9 @@ tape.test("path", function(test) {
 
     test.ok(path.isAbsolute("\\\\some-unc\\path\\file.js"), "should identify windows unc paths");
 
+    test.ok(path.isAbsolute("https://example.com/path/file.js"), "should identify absolute URLs");
+    test.ok(path.isAbsolute("://example.com/path/file.js"), "should identify protocol-relative URLs");
+
     var paths = [
         {
             actual: "X:\\some\\..\\.\\path\\\\file.js",
@@ -61,6 +64,20 @@ tape.test("path", function(test) {
                 origin: "\\\\some-unc\\path\\..\\origin.js",
                 expected: "\\\\some-unc/file.js"
             }
+        }, {
+            actual: "https://example.com/path/../file.js",
+            normal: "https://example.com/file.js",
+            resolve: {
+                origin: "/some/local/path",
+                expected: "https://example.com/file.js"
+            }
+        }, {
+            actual: "path/file2.js",
+            normal: "path/file2.js",
+            resolve: {
+                origin: "https://example.com/file1.js",
+                expected: "https://example.com/path/file2.js"
+            }
         }
     ];