I recently needed to set up a dynamic web backend to both serve dynamically generated files as well as HTTP POST forms. Thus, I thought long and hard to find a solution that is both modern and versatile yet hassle-free to set up — since my systems administration skills are rather sparse.
The solution I found is to write a Go webserver; implicitly concurrent and enabling a high level of control.
Of course, nowadays you cannot run a (esp. dynamic) website without HTTPS; every browser worth its salt will display potential visitors a message framing you as a ruthless criminal. Fortunately, Let’s Encrypt gifts you the required bits: an SSL certificate! Since I need a URL for the upcoming snippet and am personally thinking of switching my own homepage from a webserver to a self-hosted VPS setup, I chose to use www.jfrech.com as an example domain herein.
% # ... installing certbot (for example via `apt update && apt install certbot`) ...
% certbot certonly --standalone --preferred-challenges http -d www.jfrech.com
% # ... cli certbot interaction ...
% # ... installing Go ... (for example via `apt install golang`) ...
% # ... periodically renewing certificates ...
Once certbot has issued a certificate (the URL has to have a DNS entry linked to the current VPS and port 80 has to be unoccupied), incorporating it into the server is made straight forward by http.ListenAndServeTLS:
One advantage of writing one’s one web server is full control of how the website behaves. One implication, which can be seen as a downside, is that you have to do everything; even the most basic of logging. However, writing your own log files enables you to confidently follow the logging policy you employ. From a security standpoint, you can exactly control which files are served and which result in a 404 response; avoiding accidently exposing the whole server’s directory structure for the world to see.
I wanted to create a maze generator for quite some while now and recently picked up the project again, using a naive approach consisting of applying a randomized depth-first search algorithm on a given rectangle. Thus, the resulting maze’s internal path structure is quite shallow, with most path forks having one degenerated short section. Nevertheless, mazes are generated:
Whilst pondering the lost control one has over pastebin posts as a guest; the inability to remove a text one has published themselves and the entailed virtually temporally unbounded availability to anyone of this text, I decided to look at pastebin’s “archive” site — a chronologically sorted collection of the most recent public pastebin posts.
One interesting post was titled Filter — Stringrid — Delphi and appears to be a Delphi program with German comments accomplishing some two-dimensional array manipulation task.
However, when looking further down the archive, a post published around two minutes earlier caught my attention — exmp1 . This innocuously titled Java source file upon closer contains inspection an impressive 𝟥𝟦𝟫 lines of code. Now, source files of such a line count are not unreasonable (especially when writing Java), however it is not the typical size of an example — as this paste’s title suggests. Thus, I decided to read it to know what it is meant to accomplish and how it is written — the source’s line count is highly misleading regarding its functionality.
I have been using zsh for a while now, and whilst I like its minimalistic approach, I felt that my prompt lacked a certain graphical oomph. Thus, I built what most graphical environments hide away at the screen’s corner directly into the prompt — a clock. Paired with a time-sensitive rainbow color scheme, I find the result quite visually pleasing.
If you want to try out my prompt, the following installer automatically downloads jprompt.c, compiles it and asks if .zshrc should be set up to load my prompt. Since jblog has moved, the below script might not work.
I have designed and implemented a new esoteric programming language called Zpr’(h. It is a language built upon iterated symbolic pattern matching, requiring the user to define their own semantics and interpreting them as computations. Whilst developing Zpr’(h, I implemented a rudimentary standard library, defining semantics for natural numbers, mappings, lists and logic. Furthermore, I used these semantics to define a lazy computation of all prime numbers — albeit executing at a rather slow pace. Having finalized the language’s specifications I began investigating its computational bounds. After all, testing primality is a primitive recursive relation. Thus, it a priori is not even clear if Zpr’(h is Turing complete — a useful feature for a programming language to have.
Pondering this question, I thought about how to show that Zpr’(h is indeed Turing complete — driven by hope that I have not created a primitively weak language. I briefly thought about implementing a Turing machine but quickly opted to implement a brainfuck interpreter — equivalent, since both can simulate each other. After having written said brainfuck interpreter (zprh_brainfuck.zpr), I proceeded to test it only to realize that using byte-based pattern matching to implement a brainfuck interpreter in a functional manner does not lead to the most efficient implementation. Interpreting the brainfuck program ++[->+++<]>. — that is, multiplying two by three — takes a respectable twenty seconds at 𝟦.𝟢𝟢 GHz. Yet more excruciatingly, adhering to commutativity and interpreting +++[->++<]>. yields the same correct numerical result, although at a steep slowdown to over three minutes. Time constraints are not the only factor — since the current Zpr’(h implementation does not alias any byte sequences if long byte sequences are duplicated, the memory footprint rises to the unmanageable, easily blowing the 𝟣 GiB provided by default. Increasing the available memory most likely not make much of a difference given the aforementioned exponential behavior. Thus, testing larger brainfuck programs appears not to be feasible due to computational resource limitations. Nevertheless, I am now fairly certain of Zpr’(h being Turing complete, even though my brainfuck implementation may not be correct. To input brainfuck source code into the above interpreter, I used this translator.
Not being satisfied with a nigh untestable brainfuck implementation, I attempted to fulfil another classical interpretation of computability; recursive functions. As seen above, primitive recursive functions can already be modelled, leaving only the existence of µ-recursion open; a one-liner using the standard library:
(µ .p) |> (head (filter p |N0))
In conclusio, I am convinced that Zpr’(h is Turing complete, if not very efficient — a common fate of esoteric programming languages.
Contact is a board game designed by Ken Garland in which players draw square tiles containing colored connections from a pile, attempting to form matches. Whilst the game is enjoyable to play — allowing the odd trading of cards in unfortunate circumstances — it seldom leads to a complete configuration, meaning a valid contacting arrangement using all available cards.
With the power of stochastically driven brute-force, however, finding such complete configurations turns out to be feasible — at least when playing with the 𝟣𝟦𝟢 cards my Contact version contains. Not surprisingly, many solutions are of rather linear nature since the game only contains two branching cards, i. e. cards where three sides boast connections. Thus, the search is further narrowed in by demanding a maximum dimension, that is the final configuration has to lie in a card rectangle of a given area. From my testing, a maximum dimension of 𝟧𝟢𝟢 is moderately quickly computed (~ 𝟥𝟢 sec @ 4.00 GHz), whilst lower maximum dimensions appear to be less likely.
From an implementation point of view, a generalized Contact card (defined as four sides, each with three nodes being blank or colored one of three colors) snuggly fits into 𝟤𝟦 bits, allowing for card rotation, reflection and match determination being implemented through integer bit fiddling. The stochastic process is driven by an (ideally assumed) uniformly distributed random number generator, being recursively applied until all cards are consumed. Finally, an image is created as a portable pixmap .ppm and resized to a .png using ImageMagick.