zlib: Make the finish flush flag configurable

Up to now, `Z_FINISH` was always the flushing flag that was used
for the last chunk of input data. This patch makes this choice
configurable so that advanced users can perform e.g. decompression of
partial data using `Z_SYNC_FLUSH`, if that suits their needs.

Add tests to make sure that an error is thrown upon encountering
invalid `flush` or `finishFlush` flags.

Fixes: https://github.com/nodejs/node/issues/5761
PR-URL: https://github.com/nodejs/node/pull/6069
Reviewed-By: James M Snell <jasnell@gmail.com>

2 files changed, 45 insertions, 0 deletions

diff --git a/test/parallel/test-zlib-flush-flags.js b/test/parallel/test-zlib-flush-flags.js
new file mode 100644
index 0000000000..08c79f138b
--- /dev/null
+++ b/test/parallel/test-zlib-flush-flags.js
@@ -0,0 +1,28 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+const zlib = require('zlib');
+
+assert.doesNotThrow(() => {
+  zlib.createGzip({ flush: zlib.Z_SYNC_FLUSH });
+});
+
+assert.throws(() => {
+  zlib.createGzip({ flush: 'foobar' });
+}, /Invalid flush flag: foobar/);
+
+assert.throws(() => {
+  zlib.createGzip({ flush: 10000 });
+}, /Invalid flush flag: 10000/);
+
+assert.doesNotThrow(() => {
+  zlib.createGzip({ finishFlush: zlib.Z_SYNC_FLUSH });
+});
+
+assert.throws(() => {
+  zlib.createGzip({ finishFlush: 'foobar' });
+}, /Invalid flush flag: foobar/);
+
+assert.throws(() => {
+  zlib.createGzip({ finishFlush: 10000 });
+}, /Invalid flush flag: 10000/);
diff --git a/test/parallel/test-zlib-truncated.js b/test/parallel/test-zlib-truncated.js
index 38888b68be..1798a2ca97 100644
--- a/test/parallel/test-zlib-truncated.js
+++ b/test/parallel/test-zlib-truncated.js
@@ -45,5 +45,22 @@ const inputString = 'ΩΩLorem ipsum dolor sit amet, consectetur adipiscing el'
     zlib[methods.decomp](truncated, function(err, result) {
       assert(/unexpected end of file/.test(err.message));
     });
+
+    const syncFlushOpt = { finishFlush: zlib.Z_SYNC_FLUSH };
+
+    // sync truncated input test, finishFlush = Z_SYNC_FLUSH
+    assert.doesNotThrow(function() {
+      const result = zlib[methods.decompSync](truncated, syncFlushOpt)
+        .toString();
+      assert.equal(result, inputString.substr(0, result.length));
+    });
+
+    // async truncated input test, finishFlush = Z_SYNC_FLUSH
+    zlib[methods.decomp](truncated, syncFlushOpt, function(err, decompressed) {
+      assert.ifError(err);
+
+      const result = decompressed.toString();
+      assert.equal(result, inputString.substr(0, result.length));
+    });
   });
 });