Programming

A basic webserver Docker containers are small OS images in themselves that one can deploy and run without worrying about dependencies or interoperability. All the dependencies are packed in the same container file. And the docker runtime takes care of the interoperability. You are not tied to using a single language or framework. You can write code in Python, Go, Java, Node.js, or any of your favorite languages and pack it in a container. Consider a simple example of a Go-based webserver

A single developer has to sometimes deal with 7 different consoles by the same company…

Emulator: Process finished with exit code 1 You opened AVD Manager in Android Studio and tried to start an AVD, you got “Emulator: Process finished with exit code 1”. Following are the steps to debug this Find out the name of the emulator. Click the down arrow 🔽 which is to the right of play arrow ▶️, to find out the name of the AVD. Let’s say the name is “Nexus_5X_API_28_x86”....

Die with me is a chat app which can be used only when the phone’s battery is below 5%. Here is a fun way to use the app without draining your phone’s battery. Connect the phone via ADB or start Android emulator and fake the battery level to 4%. Bash 1 2 sudo pip3 install adb-enhanced adbe battery level 4 # Set battery level to 4% And now, you can use the app....

Sh 1 2 #!/usr/bin/env bash set -euo pipefail The first statement is a Mac, GNU/Linux, and BSD portable way of finding the location of the bash interpreter. The second statement combines “set -e” which ensures that your script stops on first command failure. By default, when a command fails, BASH executes the next command. Looking at the logs, you might feel that the script executed successfully while some commands might have failed....

Update: As of April 2020, I have switched over to GitHub Actions. Travis CI has become buggy and flaky over time and I got tired of trying to keep the builds green. My GitHub action scripts can be seen here. Just like many software engineers, I maintain my config files for GNU/Linux and Mac OS in a git repository. Given that, I wrote a fair bit of them in interpreted code, notably, Bash, it is a bit hard to ensure that it is bug-free. The other problem I face is that packages on homebrew, the Mac OS package manager becomes obsolete and gets deleted from time to time. I added CI testing on Travis CI to prevent these breakages and to ensure that my dotfiles are always in good shape for installation. The great thing about Travis CI is that it is entirely free for open-source repositories even for testing on Mac OS containers.

Update: As of Mar 2022, I recommend everyone to use GitHub Actions I maintain a somewhat popular Android developer tool ( adb-enhanced). The tool is written in Python, supporting both Python 2 and 3. Testing the tool requires both Python runtime as well a running Android emulator. I, initially, used Travis CI for setting up continuous testing of this tool. Later, I felt that Travis CI was too slow and when I came across Circle CI, I decided to give it a try. As of now, both Travis and Circle CI are used for testing. Here is what I learned from my experience.

Lectures Introduction Creating a Digital currency Bitcoin Overview Bitcoin Blockchain Bitcoin Mining Bitcoin Miner interactions and Game Theory Cryptocurrencies: Community, Economics, and Politics Alternative Consensus Wallet & Anonymity Anonymity on Blockchain Altcoins Ethereum Ethereum Ethereum Governance Bitcoin Side-chains (guest talk) Bitcoin Payment channel Guest talk on Legal by Ben Lawsky - does not seem worthy of transcribing Advanced Topics - Quantum Computing, Threshold Signatures, and storing secret state on public chains Advanced Topics - Smart property, publicly verifiable randomness, and prediction markets Guest talk by Adam Ludwin (CEO, chain....

Lecture 19: Advanced Topics Topic 1: Smart Property Manage ownership of some property like stocks on the blockchain. Colored coins allow arbitrary properties on Smart Contract. Similar to Namecoin, there cannot be a light node/SPV for this. Another example is rental, car’s ownership goes from Alice to Carol in a 2-of-2 transaction from Alice to Carol and locked transaction to return the car’s possession after a fixed time. One still has to trust the car’s hardware and manufacturer....

Lecture 18: Advanced Topics Three topics are chosen by students (another three for the next lecture) Topic 1: Quantum Computing An electron has two states top and bottom spins, represented as |1> and |0>. An electron is in a superposition of those two states with wave functions Ψ0 and Ψ1, so, the combined wave function is Ψ = Ψ0. |0> + Ψ1. |1> with |Ψ0|2 + Ψ12 = 1. |Ψ0|2 is the proability of seeing state |0> and Ψ12 is the probability of seeing state |1> respectively....