import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

js/xpconnect/loader/mozJSSubScriptLoader.cpp

@@ -0,0 +1,929 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* vim: set ts=8 sts=4 et sw=4 tw=99: */
+/* 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/. */
+
+#include "mozJSSubScriptLoader.h"
+#include "mozJSComponentLoader.h"
+#include "mozJSLoaderUtils.h"
+
+#include "nsIURI.h"
+#include "nsIIOService.h"
+#include "nsIChannel.h"
+#include "nsIInputStream.h"
+#include "nsNetCID.h"
+#include "nsNetUtil.h"
+#include "nsIFileURL.h"
+#include "nsScriptLoader.h"
+#include "nsIScriptSecurityManager.h"
+#include "nsThreadUtils.h"
+
+#include "jsapi.h"
+#include "jsfriendapi.h"
+#include "nsJSPrincipals.h"
+#include "xpcprivate.h" // For xpc::OptionsBase
+#include "jswrapper.h"
+
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/ToJSValue.h"
+#include "mozilla/HoldDropJSObjects.h"
+#include "mozilla/scache/StartupCache.h"
+#include "mozilla/scache/StartupCacheUtils.h"
+#include "mozilla/Unused.h"
+#include "nsContentUtils.h"
+#include "nsStringGlue.h"
+#include "nsCycleCollectionParticipant.h"
+
+using namespace mozilla::scache;
+using namespace JS;
+using namespace xpc;
+using namespace mozilla;
+using namespace mozilla::dom;
+
+class MOZ_STACK_CLASS LoadSubScriptOptions : public OptionsBase {
+public:
+    explicit LoadSubScriptOptions(JSContext* cx = xpc_GetSafeJSContext(),
+                                  JSObject* options = nullptr)
+        : OptionsBase(cx, options)
+        , target(cx)
+        , charset(NullString())
+        , ignoreCache(false)
+        , async(false)
+    { }
+
+    virtual bool Parse() {
+      return ParseObject("target", &target) &&
+             ParseString("charset", charset) &&
+             ParseBoolean("ignoreCache", &ignoreCache) &&
+             ParseBoolean("async", &async);
+    }
+
+    RootedObject target;
+    nsString charset;
+    bool ignoreCache;
+    bool async;
+};
+
+
+/* load() error msgs, XXX localize? */
+#define LOAD_ERROR_NOSERVICE "Error creating IO Service."
+#define LOAD_ERROR_NOURI "Error creating URI (invalid URL scheme?)"
+#define LOAD_ERROR_NOSCHEME "Failed to get URI scheme.  This is bad."
+#define LOAD_ERROR_URI_NOT_LOCAL "Trying to load a non-local URI."
+#define LOAD_ERROR_NOSTREAM  "Error opening input stream (invalid filename?)"
+#define LOAD_ERROR_NOCONTENT "ContentLength not available (not a local URL?)"
+#define LOAD_ERROR_BADCHARSET "Error converting to specified charset"
+#define LOAD_ERROR_BADREAD   "File Read Error."
+#define LOAD_ERROR_READUNDERFLOW "File Read Error (underflow.)"
+#define LOAD_ERROR_NOPRINCIPALS "Failed to get principals."
+#define LOAD_ERROR_NOSPEC "Failed to get URI spec.  This is bad."
+#define LOAD_ERROR_CONTENTTOOBIG "ContentLength is too large"
+
+mozJSSubScriptLoader::mozJSSubScriptLoader() : mSystemPrincipal(nullptr)
+{
+}
+
+mozJSSubScriptLoader::~mozJSSubScriptLoader()
+{
+    /* empty */
+}
+
+NS_IMPL_ISUPPORTS(mozJSSubScriptLoader, mozIJSSubScriptLoader)
+
+static void
+ReportError(JSContext* cx, const char* msg)
+{
+    RootedValue exn(cx, JS::StringValue(JS_NewStringCopyZ(cx, msg)));
+    JS_SetPendingException(cx, exn);
+}
+
+static void
+ReportError(JSContext* cx, const char* origMsg, nsIURI* uri)
+{
+    if (!uri) {
+        ReportError(cx, origMsg);
+        return;
+    }
+
+    nsAutoCString spec;
+    nsresult rv = uri->GetSpec(spec);
+    if (NS_FAILED(rv))
+        spec.Assign("(unknown)");
+
+    nsAutoCString msg(origMsg);
+    msg.Append(": ");
+    msg.Append(spec);
+    ReportError(cx, msg.get());
+}
+
+bool
+PrepareScript(nsIURI* uri,
+              JSContext* cx,
+              RootedObject& targetObj,
+              const char* uriStr,
+              const nsAString& charset,
+              const char* buf,
+              int64_t len,
+              bool reuseGlobal,
+              MutableHandleScript script,
+              MutableHandleFunction function)
+{
+    JS::CompileOptions options(cx);
+    options.setFileAndLine(uriStr, 1)
+           .setVersion(JSVERSION_LATEST);
+    if (!charset.IsVoid()) {
+        char16_t* scriptBuf = nullptr;
+        size_t scriptLength = 0;
+
+        nsresult rv =
+            nsScriptLoader::ConvertToUTF16(nullptr, reinterpret_cast<const uint8_t*>(buf), len,
+                                           charset, nullptr, scriptBuf, scriptLength);
+
+        JS::SourceBufferHolder srcBuf(scriptBuf, scriptLength,
+                                      JS::SourceBufferHolder::GiveOwnership);
+
+        if (NS_FAILED(rv)) {
+            ReportError(cx, LOAD_ERROR_BADCHARSET, uri);
+            return false;
+        }
+
+        if (!reuseGlobal) {
+            if (JS_IsGlobalObject(targetObj)) {
+                return JS::Compile(cx, options, srcBuf, script);
+            }
+            return JS::CompileForNonSyntacticScope(cx, options, srcBuf, script);
+        } else {
+            AutoObjectVector envChain(cx);
+            if (!JS_IsGlobalObject(targetObj) && !envChain.append(targetObj)) {
+                return false;
+            }
+            return JS::CompileFunction(cx, envChain, options, nullptr, 0, nullptr,
+                                       srcBuf, function);
+        }
+    } else {
+        // We only use lazy source when no special encoding is specified because
+        // the lazy source loader doesn't know the encoding.
+        if (!reuseGlobal) {
+            options.setSourceIsLazy(true);
+            if (JS_IsGlobalObject(targetObj)) {
+                return JS::Compile(cx, options, buf, len, script);
+            }
+            return JS::CompileForNonSyntacticScope(cx, options, buf, len, script);
+        } else {
+            AutoObjectVector envChain(cx);
+            if (!JS_IsGlobalObject(targetObj) && !envChain.append(targetObj)) {
+                return false;
+            }
+            return JS::CompileFunction(cx, envChain, options, nullptr, 0, nullptr,
+                                       buf, len, function);
+        }
+    }
+}
+
+bool
+EvalScript(JSContext* cx,
+           RootedObject& target_obj,
+           MutableHandleValue retval,
+           nsIURI* uri,
+           bool cache,
+           RootedScript& script,
+           RootedFunction& function)
+{
+    if (function) {
+        script = JS_GetFunctionScript(cx, function);
+    }
+
+    if (function) {
+        if (!JS_CallFunction(cx, target_obj, function, JS::HandleValueArray::empty(), retval)) {
+            return false;
+        }
+    } else {
+        if (JS_IsGlobalObject(target_obj)) {
+            if (!JS_ExecuteScript(cx, script, retval)) {
+                return false;
+            }
+        } else {
+            JS::AutoObjectVector envChain(cx);
+            if (!envChain.append(target_obj)) {
+                return false;
+            }
+            if (!JS_ExecuteScript(cx, envChain, script, retval)) {
+                return false;
+            }
+        }
+    }
+
+    JSAutoCompartment rac(cx, target_obj);
+    if (!JS_WrapValue(cx, retval)) {
+        return false;
+    }
+
+    if (cache && !!script) {
+        nsAutoCString cachePath;
+        JSVersion version = JS_GetVersion(cx);
+        cachePath.AppendPrintf("jssubloader/%d", version);
+        PathifyURI(uri, cachePath);
+
+        nsCOMPtr<nsIScriptSecurityManager> secman =
+            do_GetService(NS_SCRIPTSECURITYMANAGER_CONTRACTID);
+        if (!secman) {
+            return false;
+        }
+
+        nsCOMPtr<nsIPrincipal> principal;
+        nsresult rv = secman->GetSystemPrincipal(getter_AddRefs(principal));
+        if (NS_FAILED(rv) || !principal) {
+            ReportError(cx, LOAD_ERROR_NOPRINCIPALS, uri);
+            return false;
+        }
+
+        WriteCachedScript(StartupCache::GetSingleton(),
+                          cachePath, cx, principal, script);
+    }
+
+    return true;
+}
+
+class AsyncScriptLoader : public nsIIncrementalStreamLoaderObserver
+{
+public:
+    NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+    NS_DECL_NSIINCREMENTALSTREAMLOADEROBSERVER
+
+    NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(AsyncScriptLoader)
+
+    AsyncScriptLoader(nsIChannel* aChannel, bool aReuseGlobal,
+                      JSObject* aTargetObj, const nsAString& aCharset,
+                      bool aCache, Promise* aPromise)
+        : mChannel(aChannel)
+        , mTargetObj(aTargetObj)
+        , mPromise(aPromise)
+        , mCharset(aCharset)
+        , mReuseGlobal(aReuseGlobal)
+        , mCache(aCache)
+    {
+        // Needed for the cycle collector to manage mTargetObj.
+        mozilla::HoldJSObjects(this);
+    }
+
+private:
+    virtual ~AsyncScriptLoader() {
+        mozilla::DropJSObjects(this);
+    }
+
+    RefPtr<nsIChannel>      mChannel;
+    Heap<JSObject*>           mTargetObj;
+    RefPtr<Promise>         mPromise;
+    nsString                  mCharset;
+    bool                      mReuseGlobal;
+    bool                      mCache;
+};
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(AsyncScriptLoader)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(AsyncScriptLoader)
+  NS_INTERFACE_MAP_ENTRY(nsIIncrementalStreamLoaderObserver)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(AsyncScriptLoader)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mPromise)
+  tmp->mTargetObj = nullptr;
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(AsyncScriptLoader)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mPromise)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(AsyncScriptLoader)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mTargetObj)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(AsyncScriptLoader)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(AsyncScriptLoader)
+
+class MOZ_STACK_CLASS AutoRejectPromise
+{
+public:
+    AutoRejectPromise(AutoEntryScript& aAutoEntryScript,
+                      Promise* aPromise,
+                      nsIGlobalObject* aGlobalObject)
+        : mAutoEntryScript(aAutoEntryScript)
+        , mPromise(aPromise)
+        , mGlobalObject(aGlobalObject) {}
+
+    ~AutoRejectPromise() {
+        if (mPromise) {
+            JSContext* cx = mAutoEntryScript.cx();
+            RootedValue rejectionValue(cx, JS::UndefinedValue());
+            if (mAutoEntryScript.HasException()) {
+                Unused << mAutoEntryScript.PeekException(&rejectionValue);
+            }
+            mPromise->MaybeReject(cx, rejectionValue);
+        }
+    }
+
+    void ResolvePromise(HandleValue aResolveValue) {
+        mPromise->MaybeResolve(aResolveValue);
+        mPromise = nullptr;
+    }
+
+private:
+    AutoEntryScript&          mAutoEntryScript;
+    RefPtr<Promise>           mPromise;
+    nsCOMPtr<nsIGlobalObject> mGlobalObject;
+};
+
+NS_IMETHODIMP
+AsyncScriptLoader::OnIncrementalData(nsIIncrementalStreamLoader* aLoader,
+                                     nsISupports* aContext,
+                                     uint32_t aDataLength,
+                                     const uint8_t* aData,
+                                     uint32_t *aConsumedData)
+{
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+AsyncScriptLoader::OnStreamComplete(nsIIncrementalStreamLoader* aLoader,
+                                    nsISupports* aContext,
+                                    nsresult aStatus,
+                                    uint32_t aLength,
+                                    const uint8_t* aBuf)
+{
+    nsCOMPtr<nsIURI> uri;
+    mChannel->GetURI(getter_AddRefs(uri));
+
+    nsCOMPtr<nsIGlobalObject> globalObject = xpc::NativeGlobal(mTargetObj);
+    AutoEntryScript aes(globalObject, "async loadSubScript");
+    AutoRejectPromise autoPromise(aes, mPromise, globalObject);
+    JSContext* cx = aes.cx();
+
+    if (NS_FAILED(aStatus)) {
+        ReportError(cx, "Unable to load script.", uri);
+    }
+    // Just notify that we are done with this load.
+    NS_ENSURE_SUCCESS(aStatus, NS_OK);
+
+    if (aLength == 0) {
+        ReportError(cx, LOAD_ERROR_NOCONTENT, uri);
+        return NS_OK;
+    }
+
+    if (aLength > INT32_MAX) {
+        ReportError(cx, LOAD_ERROR_CONTENTTOOBIG, uri);
+        return NS_OK;
+    }
+
+    RootedFunction function(cx);
+    RootedScript script(cx);
+    nsAutoCString spec;
+    nsresult rv = uri->GetSpec(spec);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    RootedObject target_obj(cx, mTargetObj);
+
+    if (!PrepareScript(uri, cx, target_obj, spec.get(), mCharset,
+                       reinterpret_cast<const char*>(aBuf), aLength,
+                       mReuseGlobal, &script, &function))
+    {
+        return NS_OK;
+    }
+
+    JS::Rooted<JS::Value> retval(cx);
+    if (EvalScript(cx, target_obj, &retval, uri, mCache, script, function)) {
+        autoPromise.ResolvePromise(retval);
+    }
+
+    return NS_OK;
+}
+
+nsresult
+mozJSSubScriptLoader::ReadScriptAsync(nsIURI* uri, JSObject* targetObjArg,
+                                      const nsAString& charset,
+                                      nsIIOService* serv, bool reuseGlobal,
+                                      bool cache, MutableHandleValue retval)
+{
+    RootedObject target_obj(RootingCx(), targetObjArg);
+
+    nsCOMPtr<nsIGlobalObject> globalObject = xpc::NativeGlobal(target_obj);
+    ErrorResult result;
+
+    AutoJSAPI jsapi;
+    if (NS_WARN_IF(!jsapi.Init(globalObject))) {
+        return NS_ERROR_UNEXPECTED;
+    }
+
+    RefPtr<Promise> promise = Promise::Create(globalObject, result);
+    if (result.Failed()) {
+        return result.StealNSResult();
+    }
+
+    DebugOnly<bool> asJS = ToJSValue(jsapi.cx(), promise, retval);
+    MOZ_ASSERT(asJS, "Should not fail to convert the promise to a JS value");
+
+    // We create a channel and call SetContentType, to avoid expensive MIME type
+    // lookups (bug 632490).
+    nsCOMPtr<nsIChannel> channel;
+    nsresult rv;
+    rv = NS_NewChannel(getter_AddRefs(channel),
+                       uri,
+                       nsContentUtils::GetSystemPrincipal(),
+                       nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_IS_NULL,
+                       nsIContentPolicy::TYPE_OTHER,
+                       nullptr,  // aLoadGroup
+                       nullptr,  // aCallbacks
+                       nsIRequest::LOAD_NORMAL,
+                       serv);
+
+    if (!NS_SUCCEEDED(rv)) {
+        return rv;
+    }
+
+    channel->SetContentType(NS_LITERAL_CSTRING("application/javascript"));
+
+    RefPtr<AsyncScriptLoader> loadObserver =
+        new AsyncScriptLoader(channel,
+                              reuseGlobal,
+                              target_obj,
+                              charset,
+                              cache,
+                              promise);
+
+    nsCOMPtr<nsIIncrementalStreamLoader> loader;
+    rv = NS_NewIncrementalStreamLoader(getter_AddRefs(loader), loadObserver);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<nsIStreamListener> listener = loader.get();
+    return channel->AsyncOpen2(listener);
+}
+
+bool
+mozJSSubScriptLoader::ReadScript(nsIURI* uri, JSContext* cx, JSObject* targetObjArg,
+                                 const nsAString& charset, const char* uriStr,
+                                 nsIIOService* serv, nsIPrincipal* principal,
+                                 bool reuseGlobal, JS::MutableHandleScript script,
+                                 JS::MutableHandleFunction function)
+{
+    script.set(nullptr);
+    function.set(nullptr);
+
+    RootedObject target_obj(cx, targetObjArg);
+
+    // We create a channel and call SetContentType, to avoid expensive MIME type
+    // lookups (bug 632490).
+    nsCOMPtr<nsIChannel> chan;
+    nsCOMPtr<nsIInputStream> instream;
+    nsresult rv;
+    rv = NS_NewChannel(getter_AddRefs(chan),
+                       uri,
+                       nsContentUtils::GetSystemPrincipal(),
+                       nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_IS_NULL,
+                       nsIContentPolicy::TYPE_OTHER,
+                       nullptr,  // aLoadGroup
+                       nullptr,  // aCallbacks
+                       nsIRequest::LOAD_NORMAL,
+                       serv);
+
+    if (NS_SUCCEEDED(rv)) {
+        chan->SetContentType(NS_LITERAL_CSTRING("application/javascript"));
+        rv = chan->Open2(getter_AddRefs(instream));
+    }
+
+    if (NS_FAILED(rv)) {
+        ReportError(cx, LOAD_ERROR_NOSTREAM, uri);
+        return false;
+    }
+
+    int64_t len = -1;
+
+    rv = chan->GetContentLength(&len);
+    if (NS_FAILED(rv) || len == -1) {
+        ReportError(cx, LOAD_ERROR_NOCONTENT, uri);
+        return false;
+    }
+
+    if (len > INT32_MAX) {
+        ReportError(cx, LOAD_ERROR_CONTENTTOOBIG, uri);
+        return false;
+    }
+
+    nsCString buf;
+    rv = NS_ReadInputStreamToString(instream, buf, len);
+    NS_ENSURE_SUCCESS(rv, false);
+
+    return PrepareScript(uri, cx, target_obj, uriStr, charset,
+                         buf.get(), len,
+                         reuseGlobal,
+                         script, function);
+}
+
+NS_IMETHODIMP
+mozJSSubScriptLoader::LoadSubScript(const nsAString& url,
+                                    HandleValue target,
+                                    const nsAString& charset,
+                                    JSContext* cx,
+                                    MutableHandleValue retval)
+{
+    /*
+     * Loads a local url and evals it into the current cx
+     * Synchronous (an async version would be cool too.)
+     *   url: The url to load.  Must be local so that it can be loaded
+     *        synchronously.
+     *   target_obj: Optional object to eval the script onto (defaults to context
+     *               global)
+     *   charset: Optional character set to use for reading
+     *   returns: Whatever jsval the script pointed to by the url returns.
+     * Should ONLY (O N L Y !) be called from JavaScript code.
+     */
+    LoadSubScriptOptions options(cx);
+    options.charset = charset;
+    options.target = target.isObject() ? &target.toObject() : nullptr;
+    return DoLoadSubScriptWithOptions(url, options, cx, retval);
+}
+
+
+NS_IMETHODIMP
+mozJSSubScriptLoader::LoadSubScriptWithOptions(const nsAString& url,
+                                               HandleValue optionsVal,
+                                               JSContext* cx,
+                                               MutableHandleValue retval)
+{
+    if (!optionsVal.isObject())
+        return NS_ERROR_INVALID_ARG;
+    LoadSubScriptOptions options(cx, &optionsVal.toObject());
+    if (!options.Parse())
+        return NS_ERROR_INVALID_ARG;
+    return DoLoadSubScriptWithOptions(url, options, cx, retval);
+}
+
+nsresult
+mozJSSubScriptLoader::DoLoadSubScriptWithOptions(const nsAString& url,
+                                                 LoadSubScriptOptions& options,
+                                                 JSContext* cx,
+                                                 MutableHandleValue retval)
+{
+    nsresult rv = NS_OK;
+
+    /* set the system principal if it's not here already */
+    if (!mSystemPrincipal) {
+        nsCOMPtr<nsIScriptSecurityManager> secman =
+            do_GetService(NS_SCRIPTSECURITYMANAGER_CONTRACTID);
+        if (!secman)
+            return NS_OK;
+
+        rv = secman->GetSystemPrincipal(getter_AddRefs(mSystemPrincipal));
+        if (NS_FAILED(rv) || !mSystemPrincipal)
+            return rv;
+    }
+
+    RootedObject targetObj(cx);
+    mozJSComponentLoader* loader = mozJSComponentLoader::Get();
+    rv = loader->FindTargetObject(cx, &targetObj);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // We base reusingGlobal off of what the loader told us, but we may not
+    // actually be using that object.
+    bool reusingGlobal = !JS_IsGlobalObject(targetObj);
+
+    if (options.target)
+        targetObj = options.target;
+
+    // Remember an object out of the calling compartment so that we
+    // can properly wrap the result later.
+    nsCOMPtr<nsIPrincipal> principal = mSystemPrincipal;
+    RootedObject result_obj(cx, targetObj);
+    targetObj = JS_FindCompilationScope(cx, targetObj);
+    if (!targetObj)
+        return NS_ERROR_FAILURE;
+
+    if (targetObj != result_obj)
+        principal = GetObjectPrincipal(targetObj);
+
+    /* load up the url.  From here on, failures are reflected as ``custom''
+     * js exceptions */
+    nsCOMPtr<nsIURI> uri;
+    nsAutoCString uriStr;
+    nsAutoCString scheme;
+
+    // Figure out who's calling us
+    JS::AutoFilename filename;
+    if (!JS::DescribeScriptedCaller(cx, &filename)) {
+        // No scripted frame means we don't know who's calling, bail.
+        return NS_ERROR_FAILURE;
+    }
+
+    JSAutoCompartment ac(cx, targetObj);
+
+    // Suppress caching if we're compiling as content.
+    StartupCache* cache = (principal == mSystemPrincipal)
+                          ? StartupCache::GetSingleton()
+                          : nullptr;
+    nsCOMPtr<nsIIOService> serv = do_GetService(NS_IOSERVICE_CONTRACTID);
+    if (!serv) {
+        ReportError(cx, LOAD_ERROR_NOSERVICE);
+        return NS_OK;
+    }
+
+    // Make sure to explicitly create the URI, since we'll need the
+    // canonicalized spec.
+    rv = NS_NewURI(getter_AddRefs(uri), NS_LossyConvertUTF16toASCII(url).get(), nullptr, serv);
+    if (NS_FAILED(rv)) {
+        ReportError(cx, LOAD_ERROR_NOURI);
+        return NS_OK;
+    }
+
+    rv = uri->GetSpec(uriStr);
+    if (NS_FAILED(rv)) {
+        ReportError(cx, LOAD_ERROR_NOSPEC);
+        return NS_OK;
+    }
+
+    rv = uri->GetScheme(scheme);
+    if (NS_FAILED(rv)) {
+        ReportError(cx, LOAD_ERROR_NOSCHEME, uri);
+        return NS_OK;
+    }
+
+    if (!scheme.EqualsLiteral("chrome") && !scheme.EqualsLiteral("app")) {
+        // This might be a URI to a local file, though!
+        nsCOMPtr<nsIURI> innerURI = NS_GetInnermostURI(uri);
+        nsCOMPtr<nsIFileURL> fileURL = do_QueryInterface(innerURI);
+        if (!fileURL) {
+            ReportError(cx, LOAD_ERROR_URI_NOT_LOCAL, uri);
+            return NS_OK;
+        }
+
+        // For file URIs prepend the filename with the filename of the
+        // calling script, and " -> ". See bug 418356.
+        nsAutoCString tmp(filename.get());
+        tmp.AppendLiteral(" -> ");
+        tmp.Append(uriStr);
+
+        uriStr = tmp;
+    }
+
+    JSVersion version = JS_GetVersion(cx);
+    nsAutoCString cachePath;
+    cachePath.AppendPrintf("jssubloader/%d", version);
+    PathifyURI(uri, cachePath);
+
+    RootedFunction function(cx);
+    RootedScript script(cx);
+    if (cache && !options.ignoreCache) {
+        rv = ReadCachedScript(cache, cachePath, cx, mSystemPrincipal, &script);
+        if (NS_FAILED(rv)) {
+            // ReadCachedScript may have set a pending exception.
+            JS_ClearPendingException(cx);
+        }
+    }
+
+    // If we are doing an async load, trigger it and bail out.
+    if (!script && options.async) {
+        return ReadScriptAsync(uri, targetObj, options.charset, serv,
+                               reusingGlobal, !!cache, retval);
+    }
+
+    if (!script) {
+        if (!ReadScript(uri, cx, targetObj, options.charset,
+                        static_cast<const char*>(uriStr.get()), serv,
+                        principal, reusingGlobal, &script, &function))
+        {
+            return NS_OK;
+        }
+    } else {
+        cache = nullptr;
+    }
+
+    Unused << EvalScript(cx, targetObj, retval, uri, !!cache, script, function);
+    return NS_OK;
+}
+
+/**
+  * Let us compile scripts from a URI off the main thread.
+  */
+
+class ScriptPrecompiler : public nsIIncrementalStreamLoaderObserver
+{
+public:
+    NS_DECL_ISUPPORTS
+    NS_DECL_NSIINCREMENTALSTREAMLOADEROBSERVER
+
+    ScriptPrecompiler(nsIObserver* aObserver,
+                      nsIPrincipal* aPrincipal,
+                      nsIChannel* aChannel)
+        : mObserver(aObserver)
+        , mPrincipal(aPrincipal)
+        , mChannel(aChannel)
+        , mScriptBuf(nullptr)
+        , mScriptLength(0)
+    {}
+
+    static void OffThreadCallback(void* aToken, void* aData);
+
+    /* Sends the "done" notification back. Main thread only. */
+    void SendObserverNotification();
+
+private:
+    virtual ~ScriptPrecompiler()
+    {
+      if (mScriptBuf) {
+        js_free(mScriptBuf);
+      }
+    }
+
+    RefPtr<nsIObserver> mObserver;
+    RefPtr<nsIPrincipal> mPrincipal;
+    RefPtr<nsIChannel> mChannel;
+    char16_t* mScriptBuf;
+    size_t mScriptLength;
+};
+
+NS_IMPL_ISUPPORTS(ScriptPrecompiler, nsIIncrementalStreamLoaderObserver);
+
+class NotifyPrecompilationCompleteRunnable : public Runnable
+{
+public:
+    NS_DECL_NSIRUNNABLE
+
+    explicit NotifyPrecompilationCompleteRunnable(ScriptPrecompiler* aPrecompiler)
+        : mPrecompiler(aPrecompiler)
+        , mToken(nullptr)
+    {}
+
+    void SetToken(void* aToken) {
+        MOZ_ASSERT(aToken && !mToken);
+        mToken = aToken;
+    }
+
+protected:
+    RefPtr<ScriptPrecompiler> mPrecompiler;
+    void* mToken;
+};
+
+/* RAII helper class to send observer notifications */
+class AutoSendObserverNotification {
+public:
+    explicit AutoSendObserverNotification(ScriptPrecompiler* aPrecompiler)
+        : mPrecompiler(aPrecompiler)
+    {}
+
+    ~AutoSendObserverNotification() {
+        if (mPrecompiler) {
+            mPrecompiler->SendObserverNotification();
+        }
+    }
+
+    void Disarm() {
+        mPrecompiler = nullptr;
+    }
+
+private:
+    ScriptPrecompiler* mPrecompiler;
+};
+
+NS_IMETHODIMP
+NotifyPrecompilationCompleteRunnable::Run(void)
+{
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(mPrecompiler);
+
+    AutoSendObserverNotification notifier(mPrecompiler);
+
+    if (mToken) {
+        JSContext* cx = XPCJSContext::Get()->Context();
+        NS_ENSURE_TRUE(cx, NS_ERROR_FAILURE);
+        JS::CancelOffThreadScript(cx, mToken);
+    }
+
+    return NS_OK;
+}
+
+NS_IMETHODIMP
+ScriptPrecompiler::OnIncrementalData(nsIIncrementalStreamLoader* aLoader,
+                                     nsISupports* aContext,
+                                     uint32_t aDataLength,
+                                     const uint8_t* aData,
+                                     uint32_t *aConsumedData)
+{
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ScriptPrecompiler::OnStreamComplete(nsIIncrementalStreamLoader* aLoader,
+                                    nsISupports* aContext,
+                                    nsresult aStatus,
+                                    uint32_t aLength,
+                                    const uint8_t* aString)
+{
+    AutoSendObserverNotification notifier(this);
+
+    // Just notify that we are done with this load.
+    NS_ENSURE_SUCCESS(aStatus, NS_OK);
+
+    // Convert data to char16_t* and prepare to call CompileOffThread.
+    nsAutoString hintCharset;
+    nsresult rv =
+        nsScriptLoader::ConvertToUTF16(mChannel, aString, aLength,
+                                       hintCharset, nullptr,
+                                       mScriptBuf, mScriptLength);
+
+    NS_ENSURE_SUCCESS(rv, NS_OK);
+
+    // Our goal is to cache persistently the compiled script and to avoid quota
+    // checks. Since the caching mechanism decide the persistence type based on
+    // the principal, we create a new global with the app's principal.
+    // We then enter its compartment to compile with its principal.
+    AutoSafeJSContext cx;
+    RootedValue v(cx);
+    SandboxOptions sandboxOptions;
+    sandboxOptions.sandboxName.AssignASCII("asm.js precompilation");
+    sandboxOptions.invisibleToDebugger = true;
+    sandboxOptions.discardSource = true;
+    rv = CreateSandboxObject(cx, &v, mPrincipal, sandboxOptions);
+    NS_ENSURE_SUCCESS(rv, NS_OK);
+
+    JSAutoCompartment ac(cx, js::UncheckedUnwrap(&v.toObject()));
+
+    JS::CompileOptions options(cx, JSVERSION_DEFAULT);
+    options.forceAsync = true;
+    options.installedFile = true;
+
+    nsCOMPtr<nsIURI> uri;
+    mChannel->GetURI(getter_AddRefs(uri));
+    nsAutoCString spec;
+    uri->GetSpec(spec);
+    options.setFile(spec.get());
+
+    if (!JS::CanCompileOffThread(cx, options, mScriptLength)) {
+        NS_WARNING("Can't compile script off thread!");
+        return NS_OK;
+    }
+
+    RefPtr<NotifyPrecompilationCompleteRunnable> runnable =
+        new NotifyPrecompilationCompleteRunnable(this);
+
+    if (!JS::CompileOffThread(cx, options,
+                              mScriptBuf, mScriptLength,
+                              OffThreadCallback,
+                              static_cast<void*>(runnable))) {
+        NS_WARNING("Failed to compile script off thread!");
+        return NS_OK;
+    }
+
+    Unused << runnable.forget();
+    notifier.Disarm();
+
+    return NS_OK;
+}
+
+/* static */
+void
+ScriptPrecompiler::OffThreadCallback(void* aToken, void* aData)
+{
+    RefPtr<NotifyPrecompilationCompleteRunnable> runnable =
+        dont_AddRef(static_cast<NotifyPrecompilationCompleteRunnable*>(aData));
+    runnable->SetToken(aToken);
+
+    NS_DispatchToMainThread(runnable);
+}
+
+void
+ScriptPrecompiler::SendObserverNotification()
+{
+    MOZ_ASSERT(mChannel && mObserver);
+    MOZ_ASSERT(NS_IsMainThread());
+
+    nsCOMPtr<nsIURI> uri;
+    mChannel->GetURI(getter_AddRefs(uri));
+    mObserver->Observe(uri, "script-precompiled", nullptr);
+}
+
+NS_IMETHODIMP
+mozJSSubScriptLoader::PrecompileScript(nsIURI* aURI,
+                                       nsIPrincipal* aPrincipal,
+                                       nsIObserver* aObserver)
+{
+    nsCOMPtr<nsIChannel> channel;
+    nsresult rv = NS_NewChannel(getter_AddRefs(channel),
+                                aURI,
+                                nsContentUtils::GetSystemPrincipal(),
+                                nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_DATA_IS_NULL,
+                                nsIContentPolicy::TYPE_OTHER);
+
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    RefPtr<ScriptPrecompiler> loadObserver =
+        new ScriptPrecompiler(aObserver, aPrincipal, channel);
+
+    nsCOMPtr<nsIIncrementalStreamLoader> loader;
+    rv = NS_NewIncrementalStreamLoader(getter_AddRefs(loader), loadObserver);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<nsIStreamListener> listener = loader.get();
+    rv = channel->AsyncOpen2(listener);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    return NS_OK;
+}