mirror of
https://github.com/ether/etherpad-lite.git
synced 2025-04-24 09:26:14 -04:00
hooks: Rewrite callAll and aCallAll for consistency
Rewrite the `callAll` and `aCallAll` functions to support all
reasonable hook behaviors and to report errors for unreasonable
behaviors (e.g., calling the callback twice).
Now a hook function like the following works as expected when invoked
by `aCallAll`:
```
exports.myHookFn = (hookName, context, cb) => {
cb('some value');
return;
};
```
This commit is contained in:
Richard Hansen
John McLear
parent
79119baf58
commit
36aceb3aba
6 changed files with 1400 additions and 74 deletions
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@ -1,3 +1,5 @@
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/* global exports, require */
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var _ = require("underscore");
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var pluginDefs = require('./plugin_defs');
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@ -17,8 +19,8 @@ function checkDeprecation(hook) {
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const notice = exports.deprecationNotices[hook.hook_name];
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if (notice == null) return;
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if (deprecationWarned[hook.hook_fn_name]) return;
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console.warn('%s hook used by the %s plugin (%s) is deprecated: %s',
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hook.hook_name, hook.part.name, hook.hook_fn_name, notice);
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console.warn(`${hook.hook_name} hook used by the ${hook.part.name} plugin ` +
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`(${hook.hook_fn_name}) is deprecated: ${notice}`);
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deprecationWarned[hook.hook_fn_name] = true;
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}
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@ -76,49 +78,287 @@ exports.mapFirst = function (lst, fn, cb, predicate) {
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next();
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}
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exports.callAll = function (hook_name, args) {
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if (!args) args = {};
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if (pluginDefs.hooks[hook_name] === undefined) return [];
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return _.flatten(_.map(pluginDefs.hooks[hook_name], function(hook) {
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return hookCallWrapper(hook, hook_name, args);
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}), true);
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}
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// Calls the hook function synchronously and returns the value provided by the hook function (via
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// callback or return value).
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//
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// A synchronous hook function can provide a value in these ways:
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//
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// * Call the callback, passing the desired value (which may be `undefined`) directly as the first
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// argument, then return `undefined`.
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// * For hook functions with three (or more) parameters: Directly return the desired value, which
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// must not be `undefined`. Note: If a three-parameter hook function directly returns
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// `undefined` and it has not already called the callback then it is indicating that it is not
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// yet done and will eventually call the callback. This behavior is not supported by synchronous
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// hooks.
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// * For hook functions with two (or fewer) parameters: Directly return the desired value (which
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// may be `undefined`).
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//
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// The callback passed to a hook function is guaranteed to return `undefined`, so it is safe for
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// hook functions to do `return cb(value);`.
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//
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// A hook function can signal an error by throwing.
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//
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// A hook function settles when it provides a value (via callback or return) or throws. If a hook
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// function attempts to settle again (e.g., call the callback again, or call the callback and also
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// return a value) then the second attempt has no effect except either an error message is logged or
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// there will be an unhandled promise rejection depending on whether the the subsequent attempt is a
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// duplicate (same value or error) or different, respectively.
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//
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// See the tests in tests/backend/specs/hooks.js for examples of supported and prohibited behaviors.
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//
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function callHookFnSync(hook, context) {
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checkDeprecation(hook);
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async function aCallAll(hook_name, args, cb) {
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if (!args) args = {};
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if (!cb) cb = function () {};
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if (pluginDefs.hooks[hook_name] === undefined) return cb(null, []);
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// This var is used to keep track of whether the hook function already settled.
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let outcome;
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var hooksPromises = pluginDefs.hooks[hook_name].map(async function(hook, index) {
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return await hookCallWrapper(hook, hook_name, args, function (res) {
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return Promise.resolve(res);
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});
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});
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// This is used to prevent recursion.
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let doubleSettleErr;
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var result = await Promise.all(hooksPromises);
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// after forEach
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cb(null, _.flatten(result, true));
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}
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/* return a Promise if cb is not supplied */
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exports.aCallAll = function (hook_name, args, cb) {
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if (cb === undefined) {
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try{
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return new Promise(function(resolve, reject) {
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aCallAll(hook_name, args, function(err, res) {
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return err ? reject(err) : resolve(res);
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});
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});
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}catch(e){
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$.gritter.removeAll();
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$.gritter.add("Please update your web browser")
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const settle = (err, val, how) => {
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doubleSettleErr = null;
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const state = err == null ? 'resolved' : 'rejected';
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if (outcome != null) {
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// It was already settled, which indicates a bug.
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const action = err == null ? 'resolve' : 'reject';
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const msg = (`DOUBLE SETTLE BUG IN HOOK FUNCTION (plugin: ${hook.part.name}, ` +
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`function name: ${hook.hook_fn_name}, hook: ${hook.hook_name}): ` +
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`Attempt to ${action} via ${how} but it already ${outcome.state} ` +
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`via ${outcome.how}. Ignoring this attempt to ${action}.`);
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console.error(msg);
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if (state !== outcome.state || (err == null ? val !== outcome.val : err !== outcome.err)) {
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// The second settle attempt differs from the first, which might indicate a serious bug.
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doubleSettleErr = new Error(msg);
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throw doubleSettleErr;
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}
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return;
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}
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} else {
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return aCallAll(hook_name, args, cb);
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outcome = {state, err, val, how};
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if (val && typeof val.then === 'function') {
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console.error(`PROHIBITED PROMISE BUG IN HOOK FUNCTION (plugin: ${hook.part.name}, ` +
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`function name: ${hook.hook_fn_name}, hook: ${hook.hook_name}): ` +
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'The hook function provided a "thenable" (e.g., a Promise) which is ' +
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'prohibited because the hook expects to get the value synchronously.');
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}
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};
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// IMPORTANT: This callback must return `undefined` so that a hook function can safely do
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// `return callback(value);` for backwards compatibility.
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const callback = (ret) => {
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settle(null, ret, 'callback');
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};
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let val;
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try {
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val = hook.hook_fn(hook.hook_name, context, callback);
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} catch (err) {
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if (err === doubleSettleErr) throw err; // Avoid recursion.
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try {
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settle(err, null, 'thrown exception');
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} catch (doubleSettleErr) {
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// Schedule the throw of the double settle error on the event loop via
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// Promise.resolve().then() (which will result in an unhandled Promise rejection) so that the
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// original error is the error that is seen by the caller. Fixing the original error will
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// likely fix the double settle bug, so the original error should get priority.
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Promise.resolve().then(() => { throw doubleSettleErr; });
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}
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throw err;
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}
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// IMPORTANT: This MUST check for undefined -- not nullish -- because some hooks intentionally use
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// null as a special value.
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if (val === undefined) {
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if (outcome != null) return outcome.val; // Already settled via callback.
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if (hook.hook_fn.length >= 3) {
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console.error(`UNSETTLED FUNCTION BUG IN HOOK FUNCTION (plugin: ${hook.part.name}, ` +
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`function name: ${hook.hook_fn_name}, hook: ${hook.hook_name}): ` +
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'The hook function neither called the callback nor returned a non-undefined ' +
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'value. This is prohibited because it will result in freezes when a future ' +
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'version of Etherpad updates the hook to support asynchronous behavior.');
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} else {
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// The hook function is assumed to not have a callback parameter, so fall through and accept
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// `undefined` as the resolved value.
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//
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// IMPORTANT: "Rest" parameters and default parameters are not counted in`Function.length`, so
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// the assumption does not hold for wrappers like `(...args) => { real(...args); }`. Such
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// functions will still work properly without any logged warnings or errors for now, but:
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// * Once the hook is upgraded to support asynchronous hook functions, calling the callback
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// will (eventually) cause a double settle error, and the function might prematurely
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// resolve to `undefined` instead of the desired value.
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// * The above "unsettled function" warning is not logged if the function fails to call the
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// callback like it is supposed to.
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}
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}
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settle(null, val, 'returned value');
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return outcome.val;
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}
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// Invokes all registered hook functions synchronously.
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//
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// Arguments:
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// * hookName: Name of the hook to invoke.
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// * context: Passed unmodified to the hook functions, except nullish becomes {}.
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//
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// Return value:
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// A flattened array of hook results. Specifically, it is equivalent to doing the following:
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// 1. Collect all values returned by the hook functions into an array.
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// 2. Convert each `undefined` entry into `[]`.
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// 3. Flatten one level.
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exports.callAll = function (hookName, context) {
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if (context == null) context = {};
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const hooks = pluginDefs.hooks[hookName] || [];
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return _.flatten(hooks.map((hook) => {
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const ret = callHookFnSync(hook, context);
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// `undefined` (but not `null`!) is treated the same as [].
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if (ret === undefined) return [];
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return ret;
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}), 1);
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};
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// Calls the hook function asynchronously and returns a Promise that either resolves to the hook
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// function's provided value or rejects with an error generated by the hook function.
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//
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// An asynchronous hook function can provide a value in these ways:
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//
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// * Call the callback, passing a Promise (or thenable) that resolves to the desired value (which
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// may be `undefined`) as the first argument.
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// * Call the callback, passing the desired value (which may be `undefined`) directly as the first
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// argument.
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// * Return a Promise (or thenable) that resolves to the desired value (which may be `undefined`).
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// * For hook functions with three (or more) parameters: Directly return the desired value, which
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// must not be `undefined`. Note: If a hook function directly returns `undefined` and it has not
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// already called the callback then it is indicating that it is not yet done and will eventually
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// call the callback.
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// * For hook functions with two (or fewer) parameters: Directly return the desired value (which
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// may be `undefined`).
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//
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// The callback passed to a hook function is guaranteed to return `undefined`, so it is safe for
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// hook functions to do `return cb(valueOrPromise);`.
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//
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// A hook function can signal an error in these ways:
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//
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// * Throw.
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// * Return a Promise that rejects.
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// * Pass a Promise that rejects as the first argument to the provided callback.
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//
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// A hook function settles when it directly provides a value, when it throws, or when the Promise it
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// provides settles (resolves or rejects). If a hook function attempts to settle again (e.g., call
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// the callback again, or return a value and also call the callback) then the second attempt has no
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// effect except either an error message is logged or an Error object is thrown depending on whether
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// the the subsequent attempt is a duplicate (same value or error) or different, respectively.
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//
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// See the tests in tests/backend/specs/hooks.js for examples of supported and prohibited behaviors.
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//
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async function callHookFnAsync(hook, context) {
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checkDeprecation(hook);
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return await new Promise((resolve, reject) => {
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// This var is used to keep track of whether the hook function already settled.
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let outcome;
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const settle = (err, val, how) => {
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const state = err == null ? 'resolved' : 'rejected';
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if (outcome != null) {
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// It was already settled, which indicates a bug.
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const action = err == null ? 'resolve' : 'reject';
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const msg = (`DOUBLE SETTLE BUG IN HOOK FUNCTION (plugin: ${hook.part.name}, ` +
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`function name: ${hook.hook_fn_name}, hook: ${hook.hook_name}): ` +
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`Attempt to ${action} via ${how} but it already ${outcome.state} ` +
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`via ${outcome.how}. Ignoring this attempt to ${action}.`);
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console.error(msg);
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if (state !== outcome.state || (err == null ? val !== outcome.val : err !== outcome.err)) {
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// The second settle attempt differs from the first, which might indicate a serious bug.
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throw new Error(msg);
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}
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return;
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}
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outcome = {state, err, val, how};
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if (err == null) { resolve(val); } else { reject(err); }
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};
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// IMPORTANT: This callback must return `undefined` so that a hook function can safely do
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// `return callback(value);` for backwards compatibility.
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const callback = (ret) => {
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// Wrap ret in a Promise so that a hook function can do `callback(asyncFunction());`. Note: If
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// ret is a Promise (or other thenable), Promise.resolve() will flatten it into this new
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// Promise.
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Promise.resolve(ret).then(
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(val) => settle(null, val, 'callback'),
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(err) => settle(err, null, 'rejected Promise passed to callback'));
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};
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let ret;
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try {
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ret = hook.hook_fn(hook.hook_name, context, callback);
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} catch (err) {
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try {
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settle(err, null, 'thrown exception');
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} catch (doubleSettleErr) {
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// Schedule the throw of the double settle error on the event loop via
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// Promise.resolve().then() (which will result in an unhandled Promise rejection) so that
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// the original error is the error that is seen by the caller. Fixing the original error
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// will likely fix the double settle bug, so the original error should get priority.
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Promise.resolve().then(() => { throw doubleSettleErr; });
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}
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throw err;
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}
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// IMPORTANT: This MUST check for undefined -- not nullish -- because some hooks intentionally
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// use null as a special value.
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if (ret === undefined) {
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if (hook.hook_fn.length >= 3) {
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// The hook function has a callback parameter and it returned undefined, which means the
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// hook function will settle (or has already settled) via the provided callback.
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return;
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} else {
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// The hook function is assumed to not have a callback parameter, so fall through and accept
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// `undefined` as the resolved value.
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//
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// IMPORTANT: "Rest" parameters and default parameters are not counted in `Function.length`,
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// so the assumption does not hold for wrappers like `(...args) => { real(...args); }`. For
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// such functions, calling the callback will (eventually) cause a double settle error, and
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// the function might prematurely resolve to `undefined` instead of the desired value.
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}
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}
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// Wrap ret in a Promise so that hook functions can be async (or otherwise return a Promise).
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// Note: If ret is a Promise (or other thenable), Promise.resolve() will flatten it into this
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// new Promise.
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Promise.resolve(ret).then(
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(val) => settle(null, val, 'returned value'),
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(err) => settle(err, null, 'Promise rejection'));
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});
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}
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// Invokes all registered hook functions asynchronously.
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//
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// Arguments:
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// * hookName: Name of the hook to invoke.
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// * context: Passed unmodified to the hook functions, except nullish becomes {}.
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// * cb: Deprecated callback. The following:
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// const p1 = hooks.aCallAll('myHook', context, cb);
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// is equivalent to:
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// const p2 = hooks.aCallAll('myHook', context).then((val) => cb(null, val), cb);
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//
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// Return value:
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// If cb is nullish, this function resolves to a flattened array of hook results. Specifically, it
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// is equivalent to doing the following:
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// 1. Collect all values returned by the hook functions into an array.
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// 2. Convert each `undefined` entry into `[]`.
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// 3. Flatten one level.
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// If cb is non-null, this function resolves to the value returned by cb.
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exports.aCallAll = async (hookName, context, cb) => {
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if (context == null) context = {};
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const hooks = pluginDefs.hooks[hookName] || [];
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let resultsPromise = Promise.all(hooks.map((hook) => {
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return callHookFnAsync(hook, context)
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// `undefined` (but not `null`!) is treated the same as [].
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.then((result) => (result === undefined) ? [] : result);
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})).then((results) => _.flatten(results, 1));
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if (cb != null) resultsPromise = resultsPromise.then((val) => cb(null, val), cb);
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return await resultsPromise;
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};
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exports.callFirst = function (hook_name, args) {
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if (!args) args = {};
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if (pluginDefs.hooks[hook_name] === undefined) return [];
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@ -165,3 +405,9 @@ exports.callAllStr = function(hook_name, args, sep, pre, post) {
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}
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return newCallhooks.join(sep || "");
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}
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exports.exportedForTestingOnly = {
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callHookFnAsync,
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callHookFnSync,
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deprecationWarned,
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};
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