zlib: expose amount of data read for engines

Added bytesRead property to Zlib engines

Fixes: https://github.com/nodejs/node/issues/8874
PR-URL: https://github.com/nodejs/node/pull/13088
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>

doc/api/zlib.md

@@ -386,6 +386,17 @@ added: v0.5.8
 Not exported by the `zlib` module. It is documented here because it is the base
 class of the compressor/decompressor classes.
 
+### zlib.bytesRead
+<!-- YAML
+added: REPLACEME
+-->
+
+* {number}
+
+The `zlib.bytesRead` property specifies the number of bytes read by the engine
+before the bytes are processed (compressed or decompressed, as appropriate for
+the derived class).
+
 ### zlib.flush([kind], callback)
 <!-- YAML
 added: v0.5.8

lib/zlib.js

@@ -175,6 +175,8 @@ class Zlib extends Transform {
     opts = opts || {};
     super(opts);
 
+    this.bytesRead = 0;
+
     this._opts = opts;
     this._chunkSize = opts.chunkSize || constants.Z_DEFAULT_CHUNK;
 
@@ -429,6 +431,8 @@ class Zlib extends Transform {
       var have = availOutBefore - availOutAfter;
       assert(have >= 0, 'have should not go down');
 
+      self.bytesRead += availInBefore - availInAfter;
+
       if (have > 0) {
         var out = self._buffer.slice(self._offset, self._offset + have);
         self._offset += have;

test/parallel/test-zlib-bytes-read.js

@@ -0,0 +1,93 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const zlib = require('zlib');
+
+const expectStr = 'abcdefghijklmnopqrstuvwxyz'.repeat(2);
+const expectBuf = Buffer.from(expectStr);
+
+function createWriter(target, buffer) {
+  const writer = { size: 0 };
+  const write = () => {
+    target.write(Buffer.from([buffer[writer.size++]]), () => {
+      if (writer.size < buffer.length) {
+        target.flush(write);
+      } else {
+        target.end();
+      }
+    });
+  };
+  write();
+  return writer;
+}
+
+for (const method of [
+  ['createGzip', 'createGunzip', false],
+  ['createGzip', 'createUnzip', false],
+  ['createDeflate', 'createInflate', true],
+  ['createDeflateRaw', 'createInflateRaw', true]
+]) {
+  let compWriter;
+  let compData = new Buffer(0);
+
+  const comp = zlib[method[0]]();
+  comp.on('data', function(d) {
+    compData = Buffer.concat([compData, d]);
+    assert.strictEqual(this.bytesRead, compWriter.size,
+                       `Should get write size on ${method[0]} data.`);
+  });
+  comp.on('end', common.mustCall(function() {
+    assert.strictEqual(this.bytesRead, compWriter.size,
+                       `Should get write size on ${method[0]} end.`);
+    assert.strictEqual(this.bytesRead, expectStr.length,
+                       `Should get data size on ${method[0]} end.`);
+
+    {
+      let decompWriter;
+      let decompData = new Buffer(0);
+
+      const decomp = zlib[method[1]]();
+      decomp.on('data', function(d) {
+        decompData = Buffer.concat([decompData, d]);
+        assert.strictEqual(this.bytesRead, decompWriter.size,
+                           `Should get write size on ${method[0]}/` +
+                           `${method[1]} data.`);
+      });
+      decomp.on('end', common.mustCall(function() {
+        assert.strictEqual(this.bytesRead, compData.length,
+                           `Should get compressed size on ${method[0]}/` +
+                           `${method[1]} end.`);
+        assert.strictEqual(decompData.toString(), expectStr,
+                           `Should get original string on ${method[0]}/` +
+                           `${method[1]} end.`);
+      }));
+      decompWriter = createWriter(decomp, compData);
+    }
+
+    // Some methods should allow extra data after the compressed data
+    if (method[2]) {
+      const compDataExtra = Buffer.concat([compData, new Buffer('extra')]);
+
+      let decompWriter;
+      let decompData = new Buffer(0);
+
+      const decomp = zlib[method[1]]();
+      decomp.on('data', function(d) {
+        decompData = Buffer.concat([decompData, d]);
+        assert.strictEqual(this.bytesRead, decompWriter.size,
+                           `Should get write size on ${method[0]}/` +
+                           `${method[1]} data.`);
+      });
+      decomp.on('end', common.mustCall(function() {
+        assert.strictEqual(this.bytesRead, compData.length,
+                           `Should get compressed size on ${method[0]}/` +
+                           `${method[1]} end.`);
+        assert.strictEqual(decompData.toString(), expectStr,
+                           `Should get original string on ${method[0]}/` +
+                           `${method[1]} end.`);
+      }));
+      decompWriter = createWriter(decomp, compDataExtra);
+    }
+  }));
+  compWriter = createWriter(comp, expectBuf);
+}