Tuesday, 18 October 2016

How to download large folders on dropbox

Recently, someone shared a large folder with me and when I tried to download it, I was getting an error; "There was an error downloading your file".
This error seemed very vague and after a quick search online, I figured out that it is not possible to download folders which are bigger than 1 GB.  And according to dropbox's help article, I will be able to download it only if I add it to my dropbox. With dropbox's puny 2GB free storage it was not possible and I was not ready to spend $$$ just for this. 
So, I wrote a simple script in javascript that I can run it on browser console to download all files in a folder!

How to do it?

Step 1. Navigate to the dropbox folder on the browser and open your developer console. Press   cmd + j  on mac or  ctrl + shift + j  on linux and windows.

Step 2. Paste the following code in the console.

Step 3. The browser will try to block the windows trying to download it. Select the option to  Always allow pop-ups from https://www.dropbox.com . For instance this is how it will look on Google Chrome (you have to click on right most icon in the search bar).

Step 4. Your files will be downloaded one by one!

NOTE: If any folder inside the folder is greater than 1GB in size, then you may have to do the same process after navigating to that folder in the browser.

Update: Make sure that you use the list view to see files by clicking on this:

Thursday, 15 September 2016

Right way to set env variable while exec or execFile in nodejs

According to the official documentation, exec allows you to pass additional environment variables as part of options like this:

This looks fine right? except that it totally isn't! By passing "env" as an option, you are not adding on to existing environment variables, but you are replacing it.  This is not clear from the documentation and can leave you scratching your head for a while as it can seem to break the command for no particular reason at all! So, you need to essentially make a copy of process.env and modify it like follows.

Thanks for stopping by!

Thursday, 28 April 2016

Problem with clipboard on Ubuntu

Clipboard on Ubuntu is "broken". Well, maybe not. But copy-paste is broken in a lot of applications on Ubuntu. Let me give you an example,

  • Open LibreOffice.
  • Write something and copy it.
  • Paste it somewhere else. It works as expected.
  • Now close LibreOffice and try pasting. It won't work.
This is a well known bug - Copy-Paste doesn't work if the source is closed before the paste; affecting a lot of applications on Ubuntu. And they are not so keen on fixing it, atleast not any time soon.
The reason for this is that these applications do not comply with the clipboard specification from FreeDesktop
If a client needs to exit while owning the CLIPBOARD selection, it should request the clipboard manager to take over the ownership of the clipboard, using the SAVE_TARGETS mechanism. If there is no clipboard manager, or if the SAVE_TARGETS conversion fails, the application should simply exit.
Applications need to transfer ownership of the clipboard to clipboard manager before exiting for copied data to perisist after it exits. There is certainly nothing you can do about it, unless offcourse you are willing to modify the source code of each of these applications to make it comply to FreeDesktop specs.

Fix. Well.. workaround.

The reporter/ moderator of the bug report suggests that we should install diodon, klipper, glipper, parcellite or xfce4-clipman as a workaround for this issue.
Working of diodon

Tuesday, 26 April 2016

Ubuntu 16.04 won't wake up from suspend

I recently installed Ubuntu 16.04 LTS Xenial Xerus on my Thinkpad E550. I honestly regretted it not just because it doesn't support AMD proprietary fglrx driver aka AMD Catalyst or AMD Radeon Software but because the suspend feature stopped working.

I initially thought that this had something to do with video drivers that I had installed on Ubuntu 15.10 which were now incompatible with 16.04. I realized that this was not the case as the issue persisted even on opensource drivers that it is compatible with.

Also on a closer observation I realized that it was not that my system was not able to wake up from suspend, but that it was not able to suspend at all. On suspending, the screen would go off but my laptop kept running, heating up and draining battery. This problem existed when I hibernate or shutdown as well.

Now the only possible reason for this is some problem in acpi which is not letting my system to suspend. Ubuntu 16.04 is shipped with kernel 4.4. A quick search on this issue on kernel 4.4 made me realize that this exists across several destros and mostly on thinkpads. So I upgraded to kernel 4.5 and the problem is resolved.

Installing kernel 4.5

32 bit


Then reboot!

Friday, 8 January 2016

Parsing wav file in node.js

I have worked with wav audio data in python before. Scipy provides a very nice way to do this using scipy.io.wavfile

I wanted to do exactly the same in node.js. There is a module called wav which sort of does it. However I faced several problems.

1. The Reader() method reads the file stream and converts into chunks of Buffer. This is very good while building web apps as you can send chunks of data separately and combine it later. However, I was just writing a script that'd run offline, So I had to put all the buffers to an array and then use the concat method of Buffer.

2. The wav module doesn't do much processing and just throws the raw binary information at us. So, we have to take care of

  • Combining hex data to get amplitudes - One frame can be represented using several blocks of 8-bit hex. The number of blocks per frame is got using blockAlign parameter in the format.
  • Endianness - Data may or may not be  in little endian format. So, while reading the blocks of hex data, we have to take care of this.
  • Handling negative amplitudes - Frames spanning several blocks when negative can be little challenging to handle as they are just stored as their two's complement.
  • Separating channels - The raw binary contains data of all the channels together. Fortunately, they are mentioned one after the other. Using channels parameter in the format, channels can be separated easily.
So, let's see how I handled all the above cases. First, we need to capture the "format" of the audio file that contains information about the file.

Then, on "end" event i.e after all the chunks have been combined, we will handle all the cases mentioned above as follows

Concluding, in this article I showed you how to handle and parse wav files in node.js by resolving several problems such as merging chunks of Buffer, combining hex data to get amplitudes, endianness, handling negative amplitudes and separating channels.