zlib: be strict about what strategies are accepted

Currently, strategy constants are integers but Node.js will accept
string versions of those integers. Users should be using the provided
zlib constants and not hardcoding numbers, strings, or anything else. As
such, Node.js should be strict about accepting only exactly those values
that are in the provided zlib constants.

PR-URL: #10934
Fixes: #10932
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/zlib.js

@@ -277,6 +277,12 @@ function isValidFlushFlag(flag) {
          flag === constants.Z_BLOCK;
 }
 
+const strategies = [constants.Z_FILTERED,
+                    constants.Z_HUFFMAN_ONLY,
+                    constants.Z_RLE,
+                    constants.Z_FIXED,
+                    constants.Z_DEFAULT_STRATEGY];
+
 // the Zlib class they all inherit from
 // This thing manages the queue of requests, and returns
 // true or false if there is anything in the queue when
@@ -326,15 +332,8 @@ function Zlib(opts, mode) {
     }
   }
 
-  if (opts.strategy) {
-    if (opts.strategy != constants.Z_FILTERED &&
-        opts.strategy != constants.Z_HUFFMAN_ONLY &&
-        opts.strategy != constants.Z_RLE &&
-        opts.strategy != constants.Z_FIXED &&
-        opts.strategy != constants.Z_DEFAULT_STRATEGY) {
-      throw new Error('Invalid strategy: ' + opts.strategy);
-    }
-  }
+  if (opts.strategy && !(strategies.includes(opts.strategy)))
+    throw new Error('Invalid strategy: ' + opts.strategy);
 
   if (opts.dictionary) {
     if (!(opts.dictionary instanceof Buffer)) {
@@ -378,7 +377,7 @@ function Zlib(opts, mode) {
   this.once('end', this.close);
 
   Object.defineProperty(this, '_closed', {
-    get: () => { return !this._handle; },
+    get: () => !this._handle,
     configurable: true,
     enumerable: true
   });
@@ -391,13 +390,8 @@ Zlib.prototype.params = function(level, strategy, callback) {
       level > constants.Z_MAX_LEVEL) {
     throw new RangeError('Invalid compression level: ' + level);
   }
-  if (strategy != constants.Z_FILTERED &&
-      strategy != constants.Z_HUFFMAN_ONLY &&
-      strategy != constants.Z_RLE &&
-      strategy != constants.Z_FIXED &&
-      strategy != constants.Z_DEFAULT_STRATEGY) {
+  if (!(strategies.includes(strategy)))
     throw new TypeError('Invalid strategy: ' + strategy);
-  }
 
   if (this._level !== level || this._strategy !== strategy) {
     var self = this;

test/parallel/test-zlib-deflate-constructors.js

@@ -86,6 +86,12 @@ assert.doesNotThrow(
   () => { new zlib.Deflate({ strategy: zlib.constants.Z_DEFAULT_STRATEGY}); }
 );
 
+// Throws if opt.strategy is the wrong type.
+assert.throws(
+  () => { new zlib.Deflate({strategy: '' + zlib.constants.Z_RLE }); },
+  /^Error: Invalid strategy: 3$/
+);
+
 // Throws if opts.strategy is invalid
 assert.throws(
   () => { new zlib.Deflate({strategy: 'this is a bogus strategy'}); },