Develop Reference

node.js - pngjs error: "Stream not writable" randomly

I am working with pngjs through many of it's methods. Most of the time, they work fine. However, like in the following example, I get an error: "Stream is not writable"
var fs = require('fs'),
PNG = require('pngjs').PNG;
var dst = new PNG({width: 100, height: 50});
fs.createReadStream('http://1.1m.yt/hry7Eby.png') //download this picture in order to examine the code.
.pipe(new PNG())
.on('parsed', function(data) {
console.log(data);
});
This case is not singular, I get this error on 1 random png image once a day, through all of pngjs methods, and that error obviously crashes my app.
(note: you can't use the http link I gave you with a readStream, you will have to download & rename it and do something like):
fs.createReadStream('1.png')
Thank you for your time and effort.

This seems to be a bug in the library, though I'm wary of saying so as I'm no expert in PNGs. The parser seems to complete while the stream is still writing. It encounters the IEND, and so calls this:
ParserAsync.prototype._finished = function() {
if (this.errord) {
return;
}
if (!this._inflate) {
this.emit('error', 'No Inflate block');
}
else {
// no more data to inflate
this._inflate.end();
}
this.destroySoon();
};
If you comment out the this.destroySoon(); it finishes the image correctly, instead of eventually calling this function:
ChunkStream.prototype.end = function(data, encoding) {
if (data) {
this.write(data, encoding);
}
this.writable = false;
// already destroyed
if (!this._buffers) {
return;
}
// enqueue or handle end
if (this._buffers.length === 0) {
this._end();
}
else {
this._buffers.push(null);
this._process();
}
};
...which would otherwise end up setting the stream.writeable to false, or, if you comment that out, to pushing a null value into the _buffers array and screwing up the ChunkStream._processRead.
I'm fairly certain this is a synchronicity problem between the time the zlib parser takes to complete and the time the stream takes to complete, since if you do this synchronously it works fine:
var data = fs.readFileSync('pic.png');
var png = PNG.sync.read(data);
var buff = PNG.sync.write(png);
fs.writeFileSync('out2.png', buff);

Permissions error when running another JS AppleScript from another JSAppleScript

I am trying to separate out my .applescript files into different ones to tidy things up.
I have a JS AppleScript file called Test.applescript that tries to run the JS AppleScript file Group Tracks Dependency.applescript and what I want to do is pass in a parameter into the dependency script and get a return value out of it. (It creates an array of arrays of iTunes tracks).
Test.applescript
(function() {
var app = Application('iTunes');
app.includeStandardAdditions = true;
app.doShellScript('Group Tracks Dependency.applescript');
return "Done";
})();
// For quick logging
function log(obj) {
this.console.log(obj);
}
Group Tracks Dependency.applescript
(function(selection) {
return getGroupsOfTracks(selection);
function getGroupsOfTracks(originalTracksArray) {
if (originalTracksArray == null || originalTracksArray.length == 0)
return null;
var tracks = originalTracksArray.slice();
var groups = [];
while (true) {
var group = [];
group.push(tracks[0]);
tracks = tracks.slice(1);
while (true) {
if (!tracks[0]) break;
if (tracks[0].album() != group[0].album())
break;
if (tracks[0].artist() != group[0].artist())
break;
if (tracks[0].discNumber() != group[0].discNumber())
break;
group.push(tracks[0]);
tracks = tracks.slice(1);
}
groups.push(group);
if (!tracks[0]) break;
}
return groups;
}
})();
When I try to run the Test script I get this error (line 5 is the app.doShellScript line):
Error on line 5: Error: A privilege violation occurred.
Is there any way to get around this? I should also note that I want other people to be able to download these scripts and run them on their own iTunes libraries in the future (currently it's not user-friendly though).
If there's no way to get around this then would importing another JS AppleScript file work?

I think you may be fighting a battle that you can’t win using .doShellScript.
The Apple way is to use a Script Library as defined on https://developer.apple.com/library/mac/releasenotes/InterapplicationCommunication/RN-JavaScriptForAutomation/Articles/OSX10-11.html#//apple_ref/doc/uid/TP40014508-CH110-SW1
Unfortunately a script library has constraints where you can only pass simple variables.
Another way is to use require, which can be defined with code like https://github.com/dtinth/JXA-Cookbook/wiki/Importing-Scripts

I'm not sure what you are trying to accomplish, but this works for me using Script Editor 2.8.1 (183.1) on OSX 10.11.4:
Create a main JXA Script file
Create a JXA Script Library file
BOTH of these MUST be saved as compiled script files (.scpt)
It is INCORRECT that "Unfortunately a script library has constraints where you can only pass simple variables."
You can call any of the functions in the Script Library file from any JXA script.
In your MAIN script file, which I will call "Get iTunes Group Selection.scpt":
var app = Application('iTunes');
app.includeStandardAdditions = true;
var myLib = Library("My JXA Lib")
var selectionArr = app.selection() // ### Change as needed ###
var groupArr = myLib.getGroupsOfTracks(selectionArr)
groupArr
~~~~~~~~~~~~~~~~~~~~~
And then in a separate script file, saved as:
~/Library/Script Libraries/My JXA Lib.scpt
function getGroupsOfTracks(originalTracksArray) {
if (originalTracksArray == null || originalTracksArray.length == 0)
return null;
var tracks = originalTracksArray.slice();
var groups = [];
while (true) {
var group = [];
group.push(tracks[0]);
tracks = tracks.slice(1);
while (true) {
if (!tracks[0]) break;
if (tracks[0].album() != group[0].album())
break;
if (tracks[0].artist() != group[0].artist())
break;
if (tracks[0].discNumber() != group[0].discNumber())
break;
group.push(tracks[0]);
tracks = tracks.slice(1);
}
groups.push(group);
if (!tracks[0]) break;
}
return groups;
}

Well, it's been a few years...
I ran into errors with JXA and doShellScript when I tried to run with Application("Finder"). These errors went away when I instead ran the script from Application.currentApplication(). So for my script, I used const finder = Application("Finder") for Finder specific stuff, then const app = Application.currentApplication() for running the script.
For example:
//test1.scpt
function run() {
const app = Application.currentApplication()
app.includeStandardAdditions = true
app.doShellScript("osascript ~/Desktop/test2.scpt")
}
//test2.scpt
function run() {
const app = Application.currentApplication()
app.includeStandardAdditions = true
app.displayDialog("foo")
app.doShellScript("osascript -e 'display dialog \"bar\"'")
}
As expected, running test1.scpt gives me two dialogs: foo and `bar.

Update HTML object with node.js and javascript

I'm new to nodejs and jquery, and I'm trying to update one single html object using a script.
I am using a Raspberry pi 2 and a ultrasonic sensor, to measure distance. I want to measure continuous, and update the html document at the same time with the real time values.
When I try to run my code it behaves like a server and not a client. Everything that i console.log() prints in the cmd and not in the browesers' console. When I run my code now i do it with "sudo node surveyor.js", but nothing happens in the html-document. I have linked it properly to the script. I have also tried document.getElementsByTagName("h6").innerHTML = distance.toFixed(2), but the error is "document is not defiend".
Is there any easy way to fix this?
My code this far is:
var statistics = require('math-statistics');
var usonic = require('r-pi-usonic');
var fs = require("fs");
var path = require("path");
var jsdom = require("jsdom");
var htmlSource = fs.readFileSync("../index.html", "utf8");
var init = function(config) {
usonic.init(function (error) {
if (error) {
console.log('error');
} else {
var sensor = usonic.createSensor(config.echoPin, config.triggerPin, config.timeout);
//console.log(config);
var distances;
(function measure() {
if (!distances || distances.length === config.rate) {
if (distances) {
print(distances);
}
distances = [];
}
setTimeout(function() {
distances.push(sensor());
measure();
}, config.delay);
}());
}
});
};
var print = function(distances) {
var distance = statistics.median(distances);
process.stdout.clearLine();
process.stdout.cursorTo(0);
if (distance < 0) {
process.stdout.write('Error: Measurement timeout.\n');
} else {
process.stdout.write('Distance: ' + distance.toFixed(2) + ' cm');
call_jsdom(htmlSource, function (window) {
var $ = window.$;
$("h6").replaceWith(distance.toFixed(2));
console.log(documentToSource(window.document));
});
}
};
function documentToSource(doc) {
// The non-standard window.document.outerHTML also exists,
// but currently does not preserve source code structure as well
// The following two operations are non-standard
return doc.doctype.toString()+doc.innerHTML;
}
function call_jsdom(source, callback) {
jsdom.env(
source,
[ 'jquery-1.7.1.min.js' ],
function(errors, window) {
process.nextTick(
function () {
if (errors) {
throw new Error("There were errors: "+errors);
}
callback(window);
}
);
}
);
}
init({
echoPin: 15, //Echo pin
triggerPin: 14, //Trigger pin
timeout: 1000, //Measurement timeout in µs
delay: 60, //Measurement delay in ms
rate: 5 //Measurements per sample
});

Node.js is a server-side implementation of JavaScript. It's ok to do all the sensors operations and calculations on server-side, but you need some mechanism to provide the results to your clients. If they are going to use your application by using a web browser, you must run a HTTP server, like Express.js, and create a route (something like http://localhost/surveyor or just http://localhost/) that calls a method you have implemented on server-side and do something with the result. One possible way to return this resulting data to the clients is by rendering an HTML page that shows them. For that you should use a Template Engine.
Any DOM manipulation should be done on client-side (you could, for example, include a <script> tag inside your template HTML just to try and understand how it works, but it is not recommended to do this in production environments).
Try searching google for Node.js examples and tutorials and you will get it :)

Firefox Addon Reading Local XPI, File and Directory Listing

Following a chat in #amo-editors, I was wondering if the following are possible from a Firefox Addon:
Opening a local XPI for reading
Listing all files in above XPI with their sizes
Reading selected files

Absolutely possible.
1 + 2) Have to use nsIZipReader to read the xpi. This gives you all files within it.
3) To read contents you have to use zip readers getInputStream function and then wrap it in stream instance, then read it with argument of entry.realSize as read on stream takes characters to read.
MDN :: nsIZipWriter
MDN :: nsIZipReader
edit: i was curious. i think i got it. heres example of how to make it dump contents of a zip (list all files within). see the console.log(entryPointer) that spits out the "zip path". it also reads the contents of the files.
var zr = Cc["#mozilla.org/libjar/zip-reader;1"].createInstance(Ci.nsIZipReader);
Cu.import('resource://gre/modules/osfile.jsm');
Cu.import('resource://gre/modules/FileUtils.jsm');
var reusableStreamInstance = Cc['#mozilla.org/scriptableinputstream;1'].createInstance(Ci.nsIScriptableInputStream);
//var pathExtFolder = OS.Path.join(OS.Constants.Path.profileDir, 'extensions');
var pathToXpiToRead = OS.Path.join(OS.Constants.Path.profileDir, 'extensions', 'PortableTester#jetpack.xpi');
var nsiFileXpi = new FileUtils.File(pathToXpiToRead);
//Services.ww.activeWindow.alert(pathToXpiToRead);
try {
zr.open(nsiFileXpi); //if file dne it throws here
var entries = zr.findEntries('*');
while (entries.hasMore()) {
var entryPointer = entries.getNext(); //just a string of "zip path" (this means path to file in zip, and it uses forward slashes remember)
var entry = zr.getEntry(entryPointer); // should return true on `entry instanceof Ci.nsIZipEntry`
console.log('entryPointer', entryPointer);
/* CONSOLE OUTPUT
* "entryPointer" "bootstrap.js" Scratchpad/1:18
*/
console.info('entry', entry);
/* CONSOLE OUTPUT
* "entry" XPCWrappedNative_NoHelper { QueryInterface: QueryInterface(), compression: Getter, size: Getter, realSize: Getter, CRC32: Getter, isDirectory: Getter, lastModifiedTime: Getter, isSynthetic: Getter, permissions: Getter, compression: 8 } Scratchpad/1:19
*/
if (!entry.isDirectory) {
var inputStream = zr.getInputStream(entryPointer);
reusableStreamInstance.init(inputStream);
var fileContents = reusableStreamInstance.read(entry.realSize);
console.log('contenst of file=', fileContents);
} else {
console.log('is directory, no stream to read');
}
}
} catch (ex) {
console.warn('exception occured = ', ex);
if (ex.name == 'NS_ERROR_FILE_NOT_FOUND') {
Services.ww.activeWindow.alert('XPI at path does not exist!\n\nPath = ' + pathToXpiToRead);
}
} finally {
zr.close();
console.log('zr closed');
//Cu.forceGC(); //im not sure shoud i do this here?
}
I'm not sure if I should do a Cu.forceGC() in the finally, maybe #nmaier can advise us on that.
I'm also not sure if I handled reading the input stream properly, it works, but i dont know memory wise. I did .read(entry.realSize) first time doing this.
variable viewer on entry:

Is there a way to increase the size of localStorage in Google Chrome to avoid QUOTA_EXCEEDED_ERR: DOM Exception 22

I've written a webapp that allows you to store the images in the localStorage until you hit save (so it works offline, if signal is poor).
When the localStorage reaches 5MB Google Chrome produces an error in the javascript console log:
Uncaught Error: QUOTA_EXCEEDED_ERR: DOM Exception 22
How do I increase the size of the localStorage quota on Google Chrome?

5MB is a hard limit and that is stupid. IndexedDB gives you ~50MB which is more reasonable. To make it easier to use try Dexie.js https://github.com/dfahlander/Dexie.js
Update:
Dexie.js was actually still an overkill for my simple key-value purposes so I wrote this much simpler script https://github.com/DVLP/localStorageDB
with this you have 50MB and can get and set values like that
// Setting values
ldb.set('nameGoesHere', 'value goes here');
// Getting values - callback is required because the data is being retrieved asynchronously:
ldb.get('nameGoesHere', function (value) {
console.log('And the value is', value);
});
Copy/paste the line below so ldb.set() and ldb.get() from the example above will become available.
!function(){function e(t,o){return n?void(n.transaction("s").objectStore("s").get(t).onsuccess=function(e){var t=e.target.result&&e.target.result.v||null;o(t)}):void setTimeout(function(){e(t,o)},100)}var t=window.indexedDB||window.mozIndexedDB||window.webkitIndexedDB||window.msIndexedDB;if(!t)return void console.error("indexDB not supported");var n,o={k:"",v:""},r=t.open("d2",1);r.onsuccess=function(e){n=this.result},r.onerror=function(e){console.error("indexedDB request error"),console.log(e)},r.onupgradeneeded=function(e){n=null;var t=e.target.result.createObjectStore("s",{keyPath:"k"});t.transaction.oncomplete=function(e){n=e.target.db}},window.ldb={get:e,set:function(e,t){o.k=e,o.v=t,n.transaction("s","readwrite").objectStore("s").put(o)}}}();

You can't, it's hard-wired at 5MB. This is a design decision by the Chrome developers.
In Chrome, the Web SQL db and cache manifest also have low limits by default, but if you package the app for the Chrome App Store you can increase them.
See also Managing HTML5 Offline Storage - Google Chrome.

The quota is for the user to set, how much space he wishes to allow to each website.
Therefore since the purpose is to restrict the web pages, the web pages cannot change the restriction.
If storage is low, you can prompt the user to increase local storage.
To find out if storage is low, you could probe the local storage size by saving an object then deleting it.

You can't but if you save JSON in your localStorage you can use a library to compress data like : https://github.com/k-yak/JJLC
demo : http://k-yak.github.io/JJLC/

Here you can test your program , you should handle also the cases when the cuota is exceed

https://stackoverflow.com/a/5664344/2630686 The above answer is much amazing. I applied it in my project and implement a full solution to request all kinds of resource.
// Firstly reference the above ldb code in the answer I mentioned.
export function get_file({ url, d3, name, enable_request = false }) {
if (name === undefined) { // set saved data name by url parsing alternatively
name = url.split('?')[0].split('/').at(-1).split('.')[0];
}
const html_name = location.href.split('/').at(-1).split('.')[0]
name = `${html_name}_${name}`
let ret = null;
const is_outer = is_outer_net(url); // check outer net url by its start with http or //
// try to access data from local. Return null if not found
if (is_outer && !enable_request) {
if (localStorage[name]) {
ret = new Promise(resolve => resolve(JSON.parse(localStorage[name])));
} else {
ret = new Promise(r => {
ldb.get(name, function (value) {
r(value)
})
});
}
} else {
ret = new Promise(r => r(null))
}
ret.then(data => {
if (data) {
return data
} else {
const method = url.split('.').at(-1)
// d3 method supported
if (d3 && d3[method]) {
ret = d3[method](url)
} else {
if (url.startsWith('~/')) { // local files accessed supported. You need a local service that can return local file data by requested url's address value
url = `http://localhost:8010/get_file?address=${url}`
}
ret = fetch(url).then(data => {
// parse data by requested data type
if (url.endsWith('txt')) {
return data.text()
} else {
return data.json()
}
})
}
ret = ret.then(da => {
data = da
if (is_outer) { // save data to localStorage firstly
localStorage[name] = JSON.stringify(data);
}
}).catch(e => { // save to ldb if 5MB exceed
ldb.set(name, data);
}).finally(_ => {
return data;
});
}
})
return ret;
}