From 9677b0641cc5ba7d8b701b4f892ed7e54ceaee9a Mon Sep 17 00:00:00 2001
From: Adnan Chowdhury <bttf@users.noreply.github.com>
Date: Thu, 25 Jan 2018 16:17:58 -0800
Subject: [PATCH] Implement fallback hashing algorithm when crypto module is
 not available (#19941)

* Implement fallback hashing algorithm when crypto module is not available

* Fix lint errors

* Expose method internally and use in watch.ts

* Simplify syntax; Remove fallback from watch.ts
---
 src/compiler/sys.ts | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/src/compiler/sys.ts b/src/compiler/sys.ts
index 3256eef4dc2..ef1a3f8fd49 100644
--- a/src/compiler/sys.ts
+++ b/src/compiler/sys.ts
@@ -126,10 +126,32 @@ namespace ts {
             const _fs = require("fs");
             const _path = require("path");
             const _os = require("os");
-            const _crypto = require("crypto");
+            // crypto can be absent on reduced node installations
+            let _crypto: any;
+            try {
+              _crypto = require("crypto");
+            }
+            catch {
+              _crypto = undefined;
+            }
 
             const useNonPollingWatchers = process.env.TSC_NONPOLLING_WATCHER;
 
+            /**
+             * djb2 hashing algorithm
+             * http://www.cse.yorku.ca/~oz/hash.html
+             */
+            function generateDjb2Hash(data: string): string {
+              const chars = data.split("").map(str => str.charCodeAt(0));
+              return `${chars.reduce((prev, curr) => ((prev << 5) + prev) + curr, 5381)}`;
+            }
+
+            function createMD5HashUsingNativeCrypto(data: string) {
+              const hash = _crypto.createHash("md5");
+              hash.update(data);
+              return hash.digest("hex");
+            }
+
             function createWatchedFileSet() {
                 const dirWatchers = createMap<DirectoryWatcher>();
                 // One file can have multiple watchers
@@ -493,11 +515,7 @@ namespace ts {
                         return undefined;
                     }
                 },
-                createHash(data) {
-                    const hash = _crypto.createHash("md5");
-                    hash.update(data);
-                    return hash.digest("hex");
-                },
+                createHash: _crypto ? createMD5HashUsingNativeCrypto : generateDjb2Hash,
                 getMemoryUsage() {
                     if (global.gc) {
                         global.gc();