ndn-js
Version:
A JavaScript client library for Named Data Networking
221 lines (210 loc) • 8.6 kB
JavaScript
/**
* Copyright (C) 2015-2019 Regents of the University of California.
* @author: Jeff Thompson <jefft0@remap.ucla.edu>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
* A copy of the GNU Lesser General Public License is in the file COPYING.
*/
/** @ignore */
var NdnCommon = require('./ndn-common.js').NdnCommon;
/**
* A SyncPromise is a promise which is immediately fulfilled or rejected, used
* to return a promise in synchronous code.
* This private constructor creates a SyncPromise fulfilled or rejected with the
* given value. You should normally not call this constructor but call
* SyncPromise.resolve or SyncPromise.reject. Note that we don't need a
* constructor like SyncPromise(function(resolve, reject)) because this would be
* for scheduling the function to be called later, which we don't do.
* @param {any} value If isRejected is false, this is the value of the fulfilled
* promise, else if isRejected is true, this is the error.
* @param {boolean} isRejected True to create a promise in the rejected state,
* where value is the error.
* @constructor
*/
var SyncPromise = function SyncPromise(value, isRejected)
{
this.value = value;
this.isRejected = isRejected;
};
exports.SyncPromise = SyncPromise;
/**
* If this promise is fulfilled, immediately call onFulfilled with the fulfilled
* value as described below. Otherwise, if this promise is rejected, immediately
* call onRejected with the error as described below.
* @param {function} (optional) onFulfilled If this promise is fulfilled, this
* calls onFulfilled(value) with the value of this promise and returns the
* result. The function should return a promise. To use all synchronous code,
* onFulfilled should return SyncPromise.resolve(newValue).
* @param {function} (optional) onRejected If this promise is rejected, this
* calls onRejected(err) with the error value of this promise and returns the
* result. The function should return a promise. To use all synchronous code,
* onFulfilled should return SyncPromise.resolve(newValue) (or throw an
* exception).
* @return {Promise|SyncPromise} If this promise is fulfilled, return the result
* of calling onFulfilled(value). Note that this does not create a promise which
* is scheduled to execute later. Rather it immediately calls onFulfilled which
* should return a promise. But if onFulfilled is undefined, simply return this
* promise to pass it forward. If this promise is rejected, return the result of
* calling onRejected(err) with the error value. But if onRejected is undefined,
* simply return this promise to pass it forward. However, if onFulfilled or
* onRejected throws an exception, then return a new SyncPromise in the rejected
* state with the exception.
*/
SyncPromise.prototype.then = function(onFulfilled, onRejected)
{
if (this.isRejected) {
if (onRejected) {
try {
return onRejected(this.value);
}
catch(err) {
return new SyncPromise(err, true);
}
}
else
// Pass the error forward.
return this;
}
else {
if (onFulfilled) {
try {
return onFulfilled(this.value);
}
catch(err) {
return new SyncPromise(err, true);
}
}
else
// Pass the fulfilled value forward.
return this;
}
};
/**
* Call this.then(undefined, onRejected) and return the result. If this promise
* is rejected then onRejected will process it. If this promise is fulfilled,
* this simply passes it forward.
*/
SyncPromise.prototype.catch = function(onRejected)
{
return this.then(undefined, onRejected);
};
/**
* Return a new SyncPromise which is already fulfilled to the given value.
* @param {any} value The value of the promise.
*/
SyncPromise.resolve = function(value)
{
return new SyncPromise(value, false);
};
/**
* Return a new SyncPromise which is already rejected with the given error.
* @param {any} err The error for the rejected promise.
*/
SyncPromise.reject = function(err)
{
return new SyncPromise(err, true);
};
/**
* This static method checks if the promise is a SyncPromise and immediately
* returns its value or throws the error if promise is rejected. If promise is
* not a SyncPromise, this throws an exception since it is not possible to
* immediately get the value. This can be used with "promise-based" code which
* you expect to always return a SyncPromise to operate in synchronous mode.
* @param {SyncPromise} promise The SyncPromise with the value to get.
* @return {any} The value of the promise.
* @throws Error If promise is not a SyncPromise.
* @throws any If promise is a SyncPromise in the rejected state, this throws
* the error.
*/
SyncPromise.getValue = function(promise)
{
if (promise instanceof SyncPromise) {
if (promise.isRejected)
throw promise.value;
else
return promise.value;
}
else
throw new Error("Cannot return immediately because promise is not a SyncPromise");
};
/**
* This can be called with complete(onComplete, promise) or
* complete(onComplete, onError, promise) to handle both synchronous and
* asynchronous code based on whether the caller supplies the onComlete callback.
* If onComplete is defined, call promise.then with a function which calls
* onComplete(value) when fulfilled (possibly in asynchronous mode). If
* onComplete is undefined, then we are in synchronous mode so return
* SyncPromise.getValue(promise) which will throw an exception if the promise is
* not a SyncPromise (or is a SyncPromise in the rejected state).
* @param {function} onComplete If defined, this calls promise.then to fulfill
* the promise, then calls onComplete(value) with the value of the promise.
* If onComplete is undefined, the return value is described below.
* NOTE: The library will log any exceptions thrown by this callback, but for
* better error handling the callback should catch and properly handle any
* exceptions.
* @param {function} onError (optional) If defined, then onComplete must be
* defined and if there is an error when this calls promise.then, this calls
* onError(err) with the value of the error. If onComplete is undefined, then
* onError is ignored and this will call SyncPromise.getValue(promise) which may
* throw an exception.
* NOTE: The library will log any exceptions thrown by this callback, but for
* better error handling the callback should catch and properly handle any
* exceptions.
* @param {Promise|SyncPromise} promise If onComplete is defined, this calls
* promise.then. Otherwise, this calls SyncPromise.getValue(promise).
* @return {any} If onComplete is undefined, return SyncPromise.getValue(promise).
* Otherwise, if onComplete is supplied then return undefined and use
* onComplete as described above.
* @throws Error If onComplete is undefined and promise is not a SyncPromise.
* @throws any If onComplete is undefined and promise is a SyncPromise in the
* rejected state.
*/
SyncPromise.complete = function(onComplete, onErrorOrPromise, promise)
{
var onError;
if (promise)
onError = onErrorOrPromise;
else {
promise = onErrorOrPromise;
onError = null;
}
if (onComplete)
promise
.then(function(value) {
try {
onComplete(value);
} catch (ex) {
console.log("Error in onComplete: " + NdnCommon.getErrorWithStackTrace(ex));
}
}, function(err) {
if (onError) {
try {
onError(err);
} catch (ex) {
console.log("Error in onError: " + NdnCommon.getErrorWithStackTrace(ex));
}
}
else {
if (promise instanceof SyncPromise)
throw err;
else
// We are in an async promise callback, so a thrown exception won't
// reach the caller. Just log it.
console.log("Uncaught exception from a Promise: " +
NdnCommon.getErrorWithStackTrace(err));
}
});
else
return SyncPromise.getValue(promise);
};