Properly test, reproduce, and fix the multiple non-null-pointer exter…

…nal empty buffer situation that parcel often generates, #161

native.js

@@ -2,7 +2,7 @@ import { dirname, default as pathModule } from 'path';
 import { fileURLToPath } from 'url';
 import { createRequire } from 'module';
 
-export let Env, Txn, Dbi, Compression, Cursor, getAddress, clearKeptObjects, setGlobalBuffer,
+export let Env, Txn, Dbi, Compression, Cursor, getAddress, createBufferForAddress, clearKeptObjects, setGlobalBuffer,
 	require, arch, fs, os, onExit, tmpdir, lmdbError, path, EventEmitter, orderedBinary, MsgpackrEncoder, WeakLRUCache, setEnvMap, getEnvMap, getByBinary, detachBuffer, write, position, iterate, native, v8AccelerationEnabled = false;
 
 require = createRequire(import.meta.url);
@@ -36,6 +36,7 @@ export function setNativeFunctions(externals) {
 	Dbi = externals.Dbi;
 	Compression = externals.Compression;
 	getAddress = externals.getAddress;
+	createBufferForAddress = externals.createBufferForAddress;
 	clearKeptObjects = externals.clearKeptObjects || function() {};
 	Cursor = externals.Cursor;
 	lmdbError = externals.lmdbError;

src/lmdb-js.h

@@ -141,7 +141,7 @@ bool getVersionAndUncompress(MDB_val &data, DbiWrap* dw);
 int compareFast(const MDB_val *a, const MDB_val *b);
 Value setGlobalBuffer(const CallbackInfo& info);
 Value lmdbError(const CallbackInfo& info);
-//NAN_METHOD(getBufferForAddress);
+napi_value createBufferForAddress(napi_env env, napi_callback_info info);
 napi_value getViewAddress(napi_env env, napi_callback_info info);
 napi_value detachBuffer(napi_env env, napi_callback_info info);
 Value getAddress(const CallbackInfo& info);

src/misc.cpp

@@ -24,8 +24,8 @@ void setupExportMisc(Napi::Env env, Object exports) {
 	exports.Set("version", versionObj);
 	exports.Set("setGlobalBuffer", Function::New(env, setGlobalBuffer));
 	exports.Set("lmdbError", Function::New(env, lmdbError));
-	//exports.Set("getBufferForAddress", Function::New(env, getBufferForAddress));
 	exports.Set("enableDirectV8", Function::New(env, enableDirectV8));
+	EXPORT_NAPI_FUNCTION("createBufferForAddress", createBufferForAddress);
 	EXPORT_NAPI_FUNCTION("getAddress", getViewAddress);
 	EXPORT_NAPI_FUNCTION("detachBuffer", detachBuffer);
 }
@@ -134,6 +134,16 @@ Value setGlobalBuffer(const CallbackInfo& info) {
 	auto array_buffer = v8::ArrayBuffer::New(Isolate::GetCurrent(), std::move(backing));
 	info.GetReturnValue().Set(array_buffer);
 }*/
+NAPI_FUNCTION(createBufferForAddress) {
+	ARGS(2)
+	void* data;
+	GET_INT64_ARG(data, 0);
+	size_t length;
+	GET_INT64_ARG(length, 1);
+	napi_create_external_buffer(env, length, data, nullptr, nullptr, &returnValue);
+	return returnValue;
+}
+
 NAPI_FUNCTION(getViewAddress) {
 	ARGS(1)
 	void* data;

test/index.test.js

@@ -13,6 +13,7 @@ import inspector from 'inspector'
 let nativeMethods, dirName = dirname(fileURLToPath(import.meta.url))
 
 import { open, levelup, bufferToKeyValue, keyValueToBuffer, asBinary, ABORT, IF_EXISTS } from '../index.js';
+import { createBufferForAddress } from '../native.js'
 import { RangeIterable } from '../util/RangeIterable.js'
 import { assert } from 'console';
 import { openAsClass } from '../open.js';
@@ -97,6 +98,8 @@ describe('lmdb-js', function() {
     it('zero length values', async function() {
       await db.committed // should be able to await db even if nothing has happened
       db.put(5, asBinary(Buffer.from([])));
+		db.put(5, asBinary(createBufferForAddress(16, 0)));// externally allocated buffers of zero-length with the same non-null-pointer can crash node, #161
+		db.put(5, asBinary(createBufferForAddress(16, 0)));
       await db2.put('key1', asBinary(Buffer.from([])));
       should.equal(db.getBinary(5).length, 0);
       should.equal(db2.getBinary('key1').length, 0);

write.js

@@ -175,7 +175,8 @@ export function addWriteMethods(LMDBStore, { env, fixedBuffer, resetReadTxn, use
 					let valueArrayBuffer = valueBuffer.buffer;
 					// record pointer to value buffer
 					float64[position] = (valueArrayBuffer.address ||
-						(valueArrayBuffer.address = (getAddress(valueBuffer) - valueBuffer.byteOffset)))
+						(valueBuffer.length === 0 ? 0 : // externally allocated buffers of zero-length with the same non-null-pointer can crash node, #161
+						(valueArrayBuffer.address = (getAddress(valueBuffer) - valueBuffer.byteOffset))))
 							+ valueBuffer.byteOffset;
 					mustCompress = valueBuffer[0] >= 250; // this is the compression indicator, so we must compress
 				}