Fix: support protocol-relative registry URLs (#4347)

**Summary**

Fixes matching protocol-relative registry URLs from config.
Reported here: #3987 (comment)

**Test plan**

Added one new test.

__tests__/registries/npm-registry.js

@@ -245,6 +245,9 @@ describe('isRequestToRegistry functional test', () => {
     expect(npmRegistry.isRequestToRegistry('http://pkgs.host.com:80/foo/bar/baz', 'http://pkgs.host.com/bar/baz')).toBe(
       true,
     );
+    expect(npmRegistry.isRequestToRegistry('http://pkgs.host.com:80/foo/bar/baz', '//pkgs.host.com/bar/baz')).toBe(
+      true,
+    );
   });
 });
 

src/registries/npm-registry.js

@@ -19,7 +19,8 @@ import url from 'url';
 import ini from 'ini';
 
 const DEFAULT_REGISTRY = 'https://registry.npmjs.org/';
-const REGEX_REGISTRY_PREFIX = /^https?:/;
+const REGEX_REGISTRY_HTTP_PROTOCOL = /^https?:/i;
+const REGEX_REGISTRY_PREFIX = /^(https?:)?\/\//i;
 const REGEX_REGISTRY_SUFFIX = /registry\/?$/;
 
 export const SCOPE_SEPARATOR = '%2f';
@@ -85,7 +86,7 @@ export default class NpmRegistry extends Registry {
   }
 
   getRequestUrl(registry: string, pathname: string): string {
-    const isUrl = /^https?:/i.test(pathname);
+    const isUrl = REGEX_REGISTRY_PREFIX.test(pathname);
 
     if (isUrl) {
       return pathname;
@@ -241,7 +242,7 @@ export default class NpmRegistry extends Registry {
 
   getRegistry(packageIdent: string): string {
     // Try extracting registry from the url, then scoped registry, and default registry
-    if (packageIdent.match(/^https?:/)) {
+    if (packageIdent.match(REGEX_REGISTRY_PREFIX)) {
       const availableRegistries = this.getAvailableRegistries();
       const registry = availableRegistries.find(registry => packageIdent.startsWith(registry));
       if (registry) {
@@ -303,7 +304,7 @@ export default class NpmRegistry extends Registry {
   }
 
   getRegistryOption(registry: string, option: string): mixed {
-    const pre = REGEX_REGISTRY_PREFIX;
+    const pre = REGEX_REGISTRY_HTTP_PROTOCOL;
     const suf = REGEX_REGISTRY_SUFFIX;
 
     // When registry is used config scope, the trailing '/' is required
@@ -314,8 +315,8 @@ export default class NpmRegistry extends Registry {
     // 3nd attempt, remove the 'registry/?' suffix of the registry URL
     return (
       this.getScopedOption(reg, option) ||
-      (reg.match(pre) && this.getRegistryOption(reg.replace(pre, ''), option)) ||
-      (reg.match(suf) && this.getRegistryOption(reg.replace(suf, ''), option))
+      (pre.test(reg) && this.getRegistryOption(reg.replace(pre, ''), option)) ||
+      (suf.test(reg) && this.getRegistryOption(reg.replace(suf, ''), option))
     );
   }