zlib: fix windowBits validation to allow 0 for decompression mode

From the zlib v1.2.11 manual:

> ZEXTERN int ZEXPORT inflateInit2 OF((z_streamp strm,
>                                      int  windowBits));
>
> ...
> windowBits can also be zero to request that inflate use the window
> size in the zlib header of the compressed stream.

The current validation of windowBits in zlib.js doesn't check for this
case.

PR-URL: #19686
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/zlib.js

@@ -251,9 +251,19 @@ function Zlib(opts, mode) {
       opts.finishFlush, 'options.finishFlush',
       Z_NO_FLUSH, Z_BLOCK, Z_FINISH);
 
-    windowBits = checkRangesOrGetDefault(
-      opts.windowBits, 'options.windowBits',
-      Z_MIN_WINDOWBITS, Z_MAX_WINDOWBITS, Z_DEFAULT_WINDOWBITS);
+    // 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',

src/node_zlib.cc

@@ -438,9 +438,17 @@ class ZCtx : public AsyncWrap {
     ZCtx* ctx;
     ASSIGN_OR_RETURN_UNWRAP(&ctx, args.Holder());
 
+    // 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.
     int windowBits = args[0]->Uint32Value();
-    CHECK((windowBits >= Z_MIN_WINDOWBITS && windowBits <= Z_MAX_WINDOWBITS) &&
-      "invalid windowBits");
+    if (!((windowBits == 0) &&
+          (ctx->mode_ == INFLATE ||
+           ctx->mode_ == GUNZIP ||
+           ctx->mode_ == UNZIP))) {
+      CHECK((windowBits >= Z_MIN_WINDOWBITS &&
+             windowBits <= Z_MAX_WINDOWBITS) && "invalid windowBits");
+    }
 
     int level = args[1]->Int32Value();
     CHECK((level >= Z_MIN_LEVEL && level <= Z_MAX_LEVEL) &&

test/parallel/test-zlib-zero-windowBits.js

@@ -0,0 +1,33 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const zlib = require('zlib');
+
+
+// windowBits is a special case in zlib. On the compression side, 0 is invalid.
+// On the decompression side, it indicates that zlib should use the value from
+// the header of the compressed stream.
+{
+  const inflate = zlib.createInflate({ windowBits: 0 });
+  assert(inflate instanceof zlib.Inflate);
+}
+
+{
+  const gunzip = zlib.createGunzip({ windowBits: 0 });
+  assert(gunzip instanceof zlib.Gunzip);
+}
+
+{
+  const unzip = zlib.createUnzip({ windowBits: 0 });
+  assert(unzip instanceof zlib.Unzip);
+}
+
+{
+  common.expectsError(() => zlib.createGzip({ windowBits: 0 }), {
+    code: 'ERR_OUT_OF_RANGE',
+    type: RangeError,
+    message: 'The value of "options.windowBits" is out of range. ' +
+             'It must be >= 8 and <= 15. Received 0'
+  });
+}