Add ref to buffer during fs.write and fs.read

There was the possibility the buffer could be GCed while the eio_req was
pending.  Still needs test coverage for the fs.read() problem.

See:
http://groups.google.com/group/nodejs/browse_thread/thread/c11f8b683f37cef

src/node_file.cc

@@ -31,6 +31,7 @@ using namespace v8;
   ThrowException(Exception::TypeError(String::New("Bad argument")))
 static Persistent<String> encoding_symbol;
 static Persistent<String> errno_symbol;
+static Persistent<String> buf_symbol;
 
 // Buffer for readlink()  and other misc callers; keep this scoped at
 // file-level rather than method-level to avoid excess stack usage.
@@ -638,6 +639,10 @@ static Handle<Value> Write(const Arguments& args) {
   Local<Value> cb = args[5];
 
   if (cb->IsFunction()) {
+    // Grab a reference to buffer so it isn't GCed
+    Local<Object> cb_obj = cb->ToObject();
+    cb_obj->Set(buf_symbol, buffer_obj);
+
     ASYNC_CALL(write, cb, fd, buf, len, pos)
   } else {
     ssize_t written = pos < 0 ? write(fd, buf, len) : pwrite(fd, buf, len, pos);
@@ -702,6 +707,11 @@ static Handle<Value> Read(const Arguments& args) {
   cb = args[5];
 
   if (cb->IsFunction()) {
+    // Grab a reference to buffer so it isn't GCed
+    // TODO: need test coverage
+    Local<Object> cb_obj = cb->ToObject();
+    cb_obj->Set(buf_symbol, buffer_obj);
+
     ASYNC_CALL(read, cb, fd, buf, len, pos);
   } else {
     // SYNC
@@ -792,6 +802,7 @@ void File::Initialize(Handle<Object> target) {
 
   errno_symbol = NODE_PSYMBOL("errno");
   encoding_symbol = NODE_PSYMBOL("node:encoding");
+  buf_symbol = NODE_PSYMBOL("__buf");
 }
 
 void InitFs(Handle<Object> target) {

test/simple/test-fs-sir-writes-alot.js

@@ -0,0 +1,50 @@
+var common = require('../common');
+var fs = require("fs");
+var assert = require("assert");
+var join = require('path').join;
+
+var filename = join(common.tmpDir, 'out.txt');
+
+try {
+  fs.unlinkSync(filename);
+} catch (e) {
+  // might not exist, that's okay.
+}
+
+var fd = fs.openSync(filename, "w");
+
+var line = "aaaaaaaaaaaaaaaaaaaaaaaaaaaa\n";
+
+var N = 10240, complete = 0;
+for (var i = 0; i < N; i ++) {
+  // Create a new buffer for each write. Before the write is actually
+  // executed by the thread pool, the buffer will be collected.
+  var buffer = new Buffer(line);
+  fs.write(fd, buffer, 0, buffer.length, null, function (er, written) {
+    complete++;
+    if (complete === N) {
+      fs.closeSync(fd);
+      var s = fs.createReadStream(filename);
+      s.on("data", testBuffer);
+    }
+  });
+}
+
+var bytesChecked = 0;
+
+function testBuffer (b) {
+  for (var i = 0; i < b.length; i++) {
+    bytesChecked++;
+    if (b[i] !== 'a'.charCodeAt(0) && b[i] !== '\n'.charCodeAt(0)) {
+      throw new Error("invalid char "+i+","+b[i]);
+    }
+  }
+}
+
+process.on('exit', function () {
+  // Probably some of the writes are going to overlap, so we can't assume
+  // that we get (N * line.length). Let's just make sure we've checked a
+  // few...
+  assert.ok(bytesChecked > 1000);
+});
+