zlib: don't assert on missing dictionary

Handle Z_NEED_DICT errors graciously. Fixes the following assertion:

  node: ../src/node_zlib.cc:161: static void node::ZCtx::Process
  (uv_work_t*): Assertion`ctx->dictionary_ != __null && "Stream
  has no dictionary"' failed.
  Aborted (core dumped)

Fixes #4632.

src/node_zlib.cc

@@ -157,20 +157,18 @@ class ZCtx : public ObjectWrap {
         ctx->err_ = inflate(&ctx->strm_, ctx->flush_);
 
         // If data was encoded with dictionary
-        if (ctx->err_ == Z_NEED_DICT) {
-          assert(ctx->dictionary_ != NULL && "Stream has no dictionary");
-          if (ctx->dictionary_ != NULL) {
-
-            // Load it
-            ctx->err_ = inflateSetDictionary(&ctx->strm_,
-                                             ctx->dictionary_,
-                                             ctx->dictionary_len_);
-            assert(ctx->err_ == Z_OK && "Failed to set dictionary");
-            if (ctx->err_ == Z_OK) {
-
-              // And try to decode again
-              ctx->err_ = inflate(&ctx->strm_, ctx->flush_);
-            }
+        if (ctx->err_ == Z_NEED_DICT && ctx->dictionary_ != NULL) {
+
+          // Load it
+          ctx->err_ = inflateSetDictionary(&ctx->strm_,
+                                           ctx->dictionary_,
+                                           ctx->dictionary_len_);
+          // TODO Handle Z_DATA_ERROR, wrong dictionary
+          assert(ctx->err_ == Z_OK && "Failed to set dictionary");
+          if (ctx->err_ == Z_OK) {
+
+            // And try to decode again
+            ctx->err_ = inflate(&ctx->strm_, ctx->flush_);
           }
         }
         break;
@@ -197,6 +195,9 @@ class ZCtx : public ObjectWrap {
       case Z_BUF_ERROR:
         // normal statuses, not fatal
         break;
+      case Z_NEED_DICT:
+        ZCtx::Error(ctx, "Missing dictionary");
+        return;
       default:
         // something else.
         ZCtx::Error(ctx, "Zlib error");

test/simple/test-zlib-dictionary-fail.js

@@ -0,0 +1,36 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common.js');
+var assert = require('assert');
+var zlib = require('zlib');
+
+// Should raise an error, not trigger an assertion in src/node_zlib.cc
+(function() {
+  var stream = zlib.createInflate();
+
+  stream.on('error', common.mustCall(function(err) {
+    assert(/Missing dictionary/.test(err.message));
+  }));
+
+  // String "test" encoded with dictionary "dict".
+  stream.write(Buffer([0x78,0xBB,0x04,0x09,0x01,0xA5]));
+})();