zlib: split JS code as prep for non-zlib-backed streams

Split the `Zlib` class into `ZlibBase` and `Zlib` classes,
to facilitate introduction of similar streams with minor
implementation differences.

PR-URL: nodejs#24939
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

Author: Anna Henningsen

lib/zlib.js

@@ -207,21 +207,10 @@ function checkRangesOrGetDefault(number, name, lower, upper, def) {
   return number;
 }
 
-// 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
-// you call the .write() method.
-function Zlib(opts, mode) {
+// The base class for all Zlib-style streams.
+function ZlibBase(opts, mode, handle, { flush, finishFlush, fullFlush }) {
   var chunkSize = Z_DEFAULT_CHUNK;
-  var flush = Z_NO_FLUSH;
-  var finishFlush = Z_FINISH;
-  var windowBits = Z_DEFAULT_WINDOWBITS;
-  var level = Z_DEFAULT_COMPRESSION;
-  var memLevel = Z_DEFAULT_MEMLEVEL;
-  var strategy = Z_DEFAULT_STRATEGY;
-  var dictionary;
-
-  // The Zlib class is not exported to user land, the mode should only be
+  // The ZlibBase class is not exported to user land, the mode should only be
   // passed in by us.
   assert(typeof mode === 'number');
   assert(mode >= DEFLATE && mode <= UNZIP);
@@ -237,50 +226,11 @@ function Zlib(opts, mode) {
 
     flush = checkRangesOrGetDefault(
       opts.flush, 'options.flush',
-      Z_NO_FLUSH, Z_BLOCK, Z_NO_FLUSH);
+      Z_NO_FLUSH, Z_BLOCK, flush);
 
     finishFlush = checkRangesOrGetDefault(
       opts.finishFlush, 'options.finishFlush',
-      Z_NO_FLUSH, Z_BLOCK, Z_FINISH);
-
-    // windowBits is special. On the compression side, 0 is an invalid value.
-    // But on the decompression side, a value of 0 for windowBits tells zlib
-    // to use the window size in the zlib header of the compressed stream.
-    if ((opts.windowBits == null || opts.windowBits === 0) &&
-        (mode === INFLATE ||
-         mode === GUNZIP ||
-         mode === UNZIP)) {
-      windowBits = 0;
-    } else {
-      windowBits = checkRangesOrGetDefault(
-        opts.windowBits, 'options.windowBits',
-        Z_MIN_WINDOWBITS, Z_MAX_WINDOWBITS, Z_DEFAULT_WINDOWBITS);
-    }
-
-    level = checkRangesOrGetDefault(
-      opts.level, 'options.level',
-      Z_MIN_LEVEL, Z_MAX_LEVEL, Z_DEFAULT_COMPRESSION);
-
-    memLevel = checkRangesOrGetDefault(
-      opts.memLevel, 'options.memLevel',
-      Z_MIN_MEMLEVEL, Z_MAX_MEMLEVEL, Z_DEFAULT_MEMLEVEL);
-
-    strategy = checkRangesOrGetDefault(
-      opts.strategy, 'options.strategy',
-      Z_DEFAULT_STRATEGY, Z_FIXED, Z_DEFAULT_STRATEGY);
-
-    dictionary = opts.dictionary;
-    if (dictionary !== undefined && !isArrayBufferView(dictionary)) {
-      if (isAnyArrayBuffer(dictionary)) {
-        dictionary = Buffer.from(dictionary);
-      } else {
-        throw new ERR_INVALID_ARG_TYPE(
-          'options.dictionary',
-          ['Buffer', 'TypedArray', 'DataView', 'ArrayBuffer'],
-          dictionary
-        );
-      }
-    }
+      Z_NO_FLUSH, Z_BLOCK, finishFlush);
 
     if (opts.encoding || opts.objectMode || opts.writableObjectMode) {
       opts = _extend({}, opts);
@@ -289,40 +239,29 @@ function Zlib(opts, mode) {
       opts.writableObjectMode = false;
     }
   }
+
   Transform.call(this, opts);
+  this._hadError = false;
   this.bytesWritten = 0;
-  this._handle = new binding.Zlib(mode);
+  this._handle = handle;
+  handle[owner_symbol] = this;
   // Used by processCallback() and zlibOnError()
-  this._handle[owner_symbol] = this;
-  this._handle.onerror = zlibOnError;
-  this._hadError = false;
-  this._writeState = new Uint32Array(2);
-
-  if (!this._handle.init(windowBits,
-                         level,
-                         memLevel,
-                         strategy,
-                         this._writeState,
-                         processCallback,
-                         dictionary)) {
-    throw new ERR_ZLIB_INITIALIZATION_FAILED();
-  }
-
+  handle.onerror = zlibOnError;
   this._outBuffer = Buffer.allocUnsafe(chunkSize);
   this._outOffset = 0;
-  this._level = level;
-  this._strategy = strategy;
+
   this._chunkSize = chunkSize;
   this._defaultFlushFlag = flush;
   this._finishFlushFlag = finishFlush;
   this._nextFlush = -1;
-  this._info = opts && opts.info;
+  this._defaultFullFlushFlag = fullFlush;
   this.once('end', this.close);
+  this._info = opts && opts.info;
 }
-Object.setPrototypeOf(Zlib.prototype, Transform.prototype);
-Object.setPrototypeOf(Zlib, Transform);
+Object.setPrototypeOf(ZlibBase.prototype, Transform.prototype);
+Object.setPrototypeOf(ZlibBase, Transform);
 
-Object.defineProperty(Zlib.prototype, '_closed', {
+Object.defineProperty(ZlibBase.prototype, '_closed', {
   configurable: true,
   enumerable: true,
   get() {
@@ -334,7 +273,7 @@ Object.defineProperty(Zlib.prototype, '_closed', {
 // perspective, but it is inconsistent with all other streams exposed by Node.js
 // that have this concept, where it stands for the number of bytes read
 // *from* the stream (that is, net.Socket/tls.Socket & file system streams).
-Object.defineProperty(Zlib.prototype, 'bytesRead', {
+Object.defineProperty(ZlibBase.prototype, 'bytesRead', {
   configurable: true,
   enumerable: true,
   get: deprecate(function() {
@@ -347,41 +286,15 @@ Object.defineProperty(Zlib.prototype, 'bytesRead', {
      'This feature will be removed in the future.', 'DEP0108')
 });
 
-// This callback is used by `.params()` to wait until a full flush happened
-// before adjusting the parameters. In particular, the call to the native
-// `params()` function should not happen while a write is currently in progress
-// on the threadpool.
-function paramsAfterFlushCallback(level, strategy, callback) {
-  assert(this._handle, 'zlib binding closed');
-  this._handle.params(level, strategy);
-  if (!this._hadError) {
-    this._level = level;
-    this._strategy = strategy;
-    if (callback) callback();
-  }
-}
-
-Zlib.prototype.params = function params(level, strategy, callback) {
-  checkRangesOrGetDefault(level, 'level', Z_MIN_LEVEL, Z_MAX_LEVEL);
-  checkRangesOrGetDefault(strategy, 'strategy', Z_DEFAULT_STRATEGY, Z_FIXED);
-
-  if (this._level !== level || this._strategy !== strategy) {
-    this.flush(Z_SYNC_FLUSH,
-               paramsAfterFlushCallback.bind(this, level, strategy, callback));
-  } else {
-    process.nextTick(callback);
-  }
-};
-
-Zlib.prototype.reset = function reset() {
+ZlibBase.prototype.reset = function() {
   if (!this._handle)
     assert(false, 'zlib binding closed');
   return this._handle.reset();
 };
 
 // This is the _flush function called by the transform class,
 // internally, when the last chunk has been written.
-Zlib.prototype._flush = function _flush(callback) {
+ZlibBase.prototype._flush = function(callback) {
   this._transform(Buffer.alloc(0), '', callback);
 };
 
@@ -402,12 +315,12 @@ function maxFlush(a, b) {
 }
 
 const flushBuffer = Buffer.alloc(0);
-Zlib.prototype.flush = function flush(kind, callback) {
+ZlibBase.prototype.flush = function(kind, callback) {
   var ws = this._writableState;
 
   if (typeof kind === 'function' || (kind === undefined && !callback)) {
     callback = kind;
-    kind = Z_FULL_FLUSH;
+    kind = this._defaultFullFlushFlag;
   }
 
   if (ws.ended) {
@@ -426,17 +339,17 @@ Zlib.prototype.flush = function flush(kind, callback) {
   }
 };
 
-Zlib.prototype.close = function close(callback) {
+ZlibBase.prototype.close = function(callback) {
   _close(this, callback);
   this.destroy();
 };
 
-Zlib.prototype._destroy = function _destroy(err, callback) {
+ZlibBase.prototype._destroy = function(err, callback) {
   _close(this);
   callback(err);
 };
 
-Zlib.prototype._transform = function _transform(chunk, encoding, cb) {
+ZlibBase.prototype._transform = function(chunk, encoding, cb) {
   var flushFlag = this._defaultFlushFlag;
   // We use a 'fake' zero-length chunk to carry information about flushes from
   // the public API to the actual stream implementation.
@@ -453,7 +366,7 @@ Zlib.prototype._transform = function _transform(chunk, encoding, cb) {
   processChunk(this, chunk, flushFlag, cb);
 };
 
-Zlib.prototype._processChunk = function _processChunk(chunk, flushFlag, cb) {
+ZlibBase.prototype._processChunk = function(chunk, flushFlag, cb) {
   // _processChunk() is left for backwards compatibility
   if (typeof cb === 'function')
     processChunk(this, chunk, flushFlag, cb);
@@ -643,6 +556,110 @@ function _close(engine, callback) {
   engine._handle = null;
 }
 
+const zlibDefaultOpts = {
+  flush: Z_NO_FLUSH,
+  finishFlush: Z_FINISH,
+  fullFlush: Z_FULL_FLUSH
+};
+// Base class for all streams actually backed by zlib and using zlib-specific
+// parameters.
+function Zlib(opts, mode) {
+  var windowBits = Z_DEFAULT_WINDOWBITS;
+  var level = Z_DEFAULT_COMPRESSION;
+  var memLevel = Z_DEFAULT_MEMLEVEL;
+  var strategy = Z_DEFAULT_STRATEGY;
+  var dictionary;
+
+  if (opts) {
+    // windowBits is special. On the compression side, 0 is an invalid value.
+    // But on the decompression side, a value of 0 for windowBits tells zlib
+    // to use the window size in the zlib header of the compressed stream.
+    if ((opts.windowBits == null || opts.windowBits === 0) &&
+        (mode === INFLATE ||
+         mode === GUNZIP ||
+         mode === UNZIP)) {
+      windowBits = 0;
+    } else {
+      windowBits = checkRangesOrGetDefault(
+        opts.windowBits, 'options.windowBits',
+        Z_MIN_WINDOWBITS, Z_MAX_WINDOWBITS, Z_DEFAULT_WINDOWBITS);
+    }
+
+    level = checkRangesOrGetDefault(
+      opts.level, 'options.level',
+      Z_MIN_LEVEL, Z_MAX_LEVEL, Z_DEFAULT_COMPRESSION);
+
+    memLevel = checkRangesOrGetDefault(
+      opts.memLevel, 'options.memLevel',
+      Z_MIN_MEMLEVEL, Z_MAX_MEMLEVEL, Z_DEFAULT_MEMLEVEL);
+
+    strategy = checkRangesOrGetDefault(
+      opts.strategy, 'options.strategy',
+      Z_DEFAULT_STRATEGY, Z_FIXED, Z_DEFAULT_STRATEGY);
+
+    dictionary = opts.dictionary;
+    if (dictionary !== undefined && !isArrayBufferView(dictionary)) {
+      if (isAnyArrayBuffer(dictionary)) {
+        dictionary = Buffer.from(dictionary);
+      } else {
+        throw new ERR_INVALID_ARG_TYPE(
+          'options.dictionary',
+          ['Buffer', 'TypedArray', 'DataView', 'ArrayBuffer'],
+          dictionary
+        );
+      }
+    }
+  }
+
+  const handle = new binding.Zlib(mode);
+  // Ideally, we could let ZlibBase() set up _writeState. I haven't been able
+  // to come up with a good solution that doesn't break our internal API,
+  // and with it all supported npm versions at the time of writing.
+  this._writeState = new Uint32Array(2);
+  if (!handle.init(windowBits,
+                   level,
+                   memLevel,
+                   strategy,
+                   this._writeState,
+                   processCallback,
+                   dictionary)) {
+    throw new ERR_ZLIB_INITIALIZATION_FAILED();
+  }
+
+  ZlibBase.call(this, opts, mode, handle, zlibDefaultOpts);
+
+  this._level = level;
+  this._strategy = strategy;
+}
+Object.setPrototypeOf(Zlib.prototype, ZlibBase.prototype);
+Object.setPrototypeOf(Zlib, ZlibBase);
+
+// This callback is used by `.params()` to wait until a full flush happened
+// before adjusting the parameters. In particular, the call to the native
+// `params()` function should not happen while a write is currently in progress
+// on the threadpool.
+function paramsAfterFlushCallback(level, strategy, callback) {
+  assert(this._handle, 'zlib binding closed');
+  this._handle.params(level, strategy);
+  if (!this._hadError) {
+    this._level = level;
+    this._strategy = strategy;
+    if (callback) callback();
+  }
+}
+
+Zlib.prototype.params = function params(level, strategy, callback) {
+  checkRangesOrGetDefault(level, 'level', Z_MIN_LEVEL, Z_MAX_LEVEL);
+  checkRangesOrGetDefault(strategy, 'strategy', Z_DEFAULT_STRATEGY, Z_FIXED);
+
+  if (this._level !== level || this._strategy !== strategy) {
+    this.flush(Z_SYNC_FLUSH,
+               paramsAfterFlushCallback.bind(this, level, strategy, callback));
+  } else {
+    process.nextTick(callback);
+  }
+};
+
 // generic zlib
 // minimal 2-byte header
 function Deflate(opts) {