1 files changed, 134 insertions, 0 deletions
diff --git a/js/xpconnect/src/XPCString.cpp b/js/xpconnect/src/XPCString.cpp
new file mode 100644
index 0000000000..634d7efcbd
--- /dev/null
+++ b/js/xpconnect/src/XPCString.cpp
@@ -0,0 +1,134 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * Infrastructure for sharing DOMString data with JSStrings.
+ *
+ * Importing an nsAString into JS:
+ * If possible (GetSharedBufferHandle works) use the external string support in
+ * JS to create a JSString that points to the readable's buffer.  We keep a
+ * reference to the buffer handle until the JSString is finalized.
+ *
+ * Exporting a JSString as an nsAReadable:
+ * Wrap the JSString with a root-holding XPCJSReadableStringWrapper, which roots
+ * the string and exposes its buffer via the nsAString interface, as
+ * well as providing refcounting support.
+ */
+
+#include "nscore.h"
+#include "nsString.h"
+#include "nsStringBuffer.h"
+#include "jsapi.h"
+#include "xpcpublic.h"
+
+using namespace JS;
+
+const XPCStringConvert::LiteralExternalString
+    XPCStringConvert::sLiteralExternalString;
+
+const XPCStringConvert::DOMStringExternalString
+    XPCStringConvert::sDOMStringExternalString;
+
+const XPCStringConvert::DynamicAtomExternalString
+    XPCStringConvert::sDynamicAtomExternalString;
+
+void XPCStringConvert::LiteralExternalString::finalize(char16_t* aChars) const {
+  // Nothing to do.
+}
+
+size_t XPCStringConvert::LiteralExternalString::sizeOfBuffer(
+    const char16_t* aChars, mozilla::MallocSizeOf aMallocSizeOf) const {
+  // This string's buffer is not heap-allocated, so its malloc size is 0.
+  return 0;
+}
+
+void XPCStringConvert::DOMStringExternalString::finalize(
+    char16_t* aChars) const {
+  nsStringBuffer* buf = nsStringBuffer::FromData(aChars);
+  buf->Release();
+}
+
+size_t XPCStringConvert::DOMStringExternalString::sizeOfBuffer(
+    const char16_t* aChars, mozilla::MallocSizeOf aMallocSizeOf) const {
+  // We promised the JS engine we would not GC.  Enforce that:
+  JS::AutoCheckCannotGC autoCannotGC;
+
+  const nsStringBuffer* buf =
+      nsStringBuffer::FromData(const_cast<char16_t*>(aChars));
+  // We want sizeof including this, because the entire string buffer is owned by
+  // the external string.  But only report here if we're unshared; if we're
+  // shared then we don't know who really owns this data.
+  return buf->SizeOfIncludingThisIfUnshared(aMallocSizeOf);
+}
+
+void XPCStringConvert::DynamicAtomExternalString::finalize(
+    char16_t* aChars) const {
+  nsDynamicAtom* atom = nsDynamicAtom::FromChars(aChars);
+  // nsDynamicAtom::Release is always-inline and defined in a translation unit
+  // we can't get to here.  So we need to go through nsAtom::Release to call
+  // it.
+  static_cast<nsAtom*>(atom)->Release();
+}
+
+size_t XPCStringConvert::DynamicAtomExternalString::sizeOfBuffer(
+    const char16_t* aChars, mozilla::MallocSizeOf aMallocSizeOf) const {
+  // We return 0 here because NS_AddSizeOfAtoms reports all memory associated
+  // with atoms in the atom table.
+  return 0;
+}
+
+// convert a readable to a JSString, copying string data
+// static
+bool XPCStringConvert::ReadableToJSVal(JSContext* cx, const nsAString& readable,
+                                       nsStringBuffer** sharedBuffer,
+                                       MutableHandleValue vp) {
+  *sharedBuffer = nullptr;
+
+  uint32_t length = readable.Length();
+
+  if (readable.IsLiteral()) {
+    return StringLiteralToJSVal(cx, readable.BeginReading(), length, vp);
+  }
+
+  nsStringBuffer* buf = nsStringBuffer::FromString(readable);
+  if (buf) {
+    bool shared;
+    if (!StringBufferToJSVal(cx, buf, length, vp, &shared)) {
+      return false;
+    }
+    if (shared) {
+      *sharedBuffer = buf;
+    }
+    return true;
+  }
+
+  // blech, have to copy.
+  JSString* str = JS_NewUCStringCopyN(cx, readable.BeginReading(), length);
+  if (!str) {
+    return false;
+  }
+  vp.setString(str);
+  return true;
+}
+
+namespace xpc {
+
+bool NonVoidStringToJsval(JSContext* cx, nsAString& str,
+                          MutableHandleValue rval) {
+  nsStringBuffer* sharedBuffer;
+  if (!XPCStringConvert::ReadableToJSVal(cx, str, &sharedBuffer, rval)) {
+    return false;
+  }
+
+  if (sharedBuffer) {
+    // The string was shared but ReadableToJSVal didn't addref it.
+    // Move the ownership from str to jsstr.
+    str.ForgetSharedBuffer();
+  }
+  return true;
+}
+
+}  // namespace xpc