zlib: allow changing of level and strategy

Author: mscdex

doc/api/zlib.markdown

@@ -151,6 +151,11 @@ class of the compressor/decompressor classes.
 Flush pending data. Don't call this frivolously, premature flushes negatively
 impact the effectiveness of the compression algorithm.
 
+### zlib.params(level, strategy, callback)
+
+Dynamically update the compression level and compression strategy.
+Only applicable to deflate algorithm.
+
 ### zlib.reset()
 
 Reset the compressor/decompressor to factory defaults. Only applicable to

lib/zlib.js

@@ -341,13 +341,43 @@ function Zlib(opts, mode) {
   this._buffer = new Buffer(this._chunkSize);
   this._offset = 0;
   this._closed = false;
+  this._level = level;
+  this._strategy = strategy;
 
   this.once('end', this.close);
 }
 
 util.inherits(Zlib, Transform);
 
-Zlib.prototype.reset = function reset() {
+Zlib.prototype.params = function(level, strategy, callback) {
+  if (level < exports.Z_MIN_LEVEL ||
+      level > exports.Z_MAX_LEVEL) {
+    throw new RangeError('Invalid compression level: ' + level);
+  }
+  if (strategy != exports.Z_FILTERED &&
+      strategy != exports.Z_HUFFMAN_ONLY &&
+      strategy != exports.Z_RLE &&
+      strategy != exports.Z_FIXED &&
+      strategy != exports.Z_DEFAULT_STRATEGY) {
+    throw new TypeError('Invalid strategy: ' + strategy);
+  }
+
+  if (this._level !== level || this._strategy !== strategy) {
+    var self = this;
+    this.flush(binding.Z_SYNC_FLUSH, function() {
+      self._binding.params(level, strategy);
+      if (!self._hadError) {
+        self._level = level;
+        self._strategy = strategy;
+        if (callback) callback();
+      }
+    });
+  } else {
+    process.nextTick(callback);
+  }
+};
+
+Zlib.prototype.reset = function() {
   return this._binding.reset();
 };
 

src/node_zlib.cc

@@ -360,6 +360,18 @@ class ZCtx : public ObjectWrap {
     return Undefined(node_isolate);
   }
 
+  static Handle<Value> Params(const Arguments& args) {
+    HandleScope scope(node_isolate);
+
+    assert(args.Length() == 2 && "params(level, strategy)");
+
+    ZCtx* ctx = ObjectWrap::Unwrap<ZCtx>(args.This());
+
+    Params(ctx, args[0]->Int32Value(), args[1]->Int32Value());
+
+    return Undefined(node_isolate);
+  }
+
   static Handle<Value> Reset(const Arguments &args) {
     HandleScope scope(node_isolate);
 
@@ -455,6 +467,23 @@ class ZCtx : public ObjectWrap {
     }
   }
 
+  static void Params(ZCtx* ctx, int level, int strategy) {
+    ctx->err_ = Z_OK;
+
+    switch (ctx->mode_) {
+      case DEFLATE:
+      case DEFLATERAW:
+        ctx->err_ = deflateParams(&ctx->strm_, level, strategy);
+        break;
+      default:
+        break;
+    }
+
+    if (ctx->err_ != Z_OK && ctx->err_ != Z_BUF_ERROR) {
+      ZCtx::Error(ctx, "Failed to set parameters");
+    }
+  }
+
   static void Reset(ZCtx* ctx) {
     ctx->err_ = Z_OK;
 
@@ -514,6 +543,7 @@ void InitZlib(Handle<Object> target) {
   NODE_SET_PROTOTYPE_METHOD(z, "write", ZCtx::Write);
   NODE_SET_PROTOTYPE_METHOD(z, "init", ZCtx::Init);
   NODE_SET_PROTOTYPE_METHOD(z, "close", ZCtx::Close);
+  NODE_SET_PROTOTYPE_METHOD(z, "params", ZCtx::Params);
   NODE_SET_PROTOTYPE_METHOD(z, "reset", ZCtx::Reset);
 
   z->SetClassName(String::NewSymbol("Zlib"));

test/simple/test-zlib-params.js

@@ -0,0 +1,33 @@
+var common = require('../common.js');
+var assert = require('assert');
+var zlib = require('zlib');
+var path = require('path');
+var fs = require('fs');
+
+var file = fs.readFileSync(path.resolve(common.fixturesDir, 'person.jpg')),
+    chunkSize = 24 * 1024,
+    opts = { level: 9, strategy: zlib.Z_DEFAULT_STRATEGY },
+    deflater = zlib.createDeflate(opts);
+
+var chunk1 = file.slice(0, chunkSize),
+    chunk2 = file.slice(chunkSize),
+    blkhdr = new Buffer([0x00, 0x48, 0x82, 0xb7, 0x7d]),
+    expected = Buffer.concat([blkhdr, chunk2]),
+    actual;
+
+deflater.write(chunk1, function() {
+  deflater.params(0, zlib.Z_DEFAULT_STRATEGY, function() {
+    while (deflater.read());
+    deflater.end(chunk2, function() {
+      var bufs = [], buf;
+      while (buf = deflater.read())
+        bufs.push(buf);
+      actual = Buffer.concat(bufs);
+    });
+  });
+  while (deflater.read());
+});
+
+process.once('exit', function() {
+  assert.deepEqual(actual, expected);
+});