John Goerzen: A Simple, Delay-Tolerant, Offline-Capable Mesh Network with Syncthing (+ optional NNCP)
A little while back, I spent a week in a remote area. It had no Internet and no cell phone coverage. Sometimes, I would drive in to town where there was a signal to get messages, upload photos, and so forth. I had to take several devices with me: my phone, my wife s, maybe a laptop or a tablet too. It seemed there should have been a better way. And there is.
I ll use this example to talk about a mesh network, but it could just as well apply to people wanting to communicate on a 12-hour flight that has no in-flight wifi, or spacecraft with an intermittent connection, or a person traveling.
Syncthing makes a wonderful solution for things like these. Here are some interesting things about Syncthing:
- You can think of Syncthing as a serverless, peer-to-peer, open source alternative to Dropbox. Machines sync directly with each other without a server, though you can add a server if you want.
- It can operate completely without Internet access or any central server, though if Internet access is available, it can readily be used.
- Syncthing devices connected to the same LAN or Wifi will detect each other s presence and automatically communicate.
- Syncthing is capable of handling a constantly-changing topology. It can also, for instance, handle two disconnected clusters of nodes with one node that travels between them perhaps just a phone.
- Syncthing scales from everything from a phone to thousands of nodes.
- Syncthing normally performs syncs in every direction, but can also do single-direction syncs
- An individual Syncthing node can register its interest or disinterest in certain files or directories based on filename patterns
- Drop a script in a special directory that gets picked up by a remote server and run
- Drop emails in a special directory that get transmitted and then deleted by a remote system when they re seen
- Drop files (eg, photos or videos) in a directory that a remote system will copy or move out of there
- Drop messages (perhaps gpg-encrypted) which could be text files for someone to see and process.
- Drop NNTP bundles for group communication
Recently I have become curious about 
Here is my monthly update covering what I have been doing in the free software world during January 2021 (
Like 
The other day, we went to a designer's fashion shop whose owner was
rather adamant that he was never ever going to wear a face mask, and
that he didn't believe the COVID-19 thing was real. When I argued for
the opposing position, he pretty much dismissed what I said out of hand,
claiming that "the hospitals are empty dude" and "it's all a lie". When
I told him that this really isn't true, he went like "well, that's just
your opinion". Well, no -- certain things are facts, not opinions. Even
if you don't believe that this disease kills people, the idea that this
is a matter of opinion is missing the ball by so much that I was pretty
much stunned by the level of ignorance.
His whole demeanor pissed me off rather quickly. While I disagree with
the position that it should be your decision whether or not to wear a
mask, it's certainly possible to have that opinion. However, whether or
not people need to go to hospitals is not an opinion -- it's something
else entirely.
After calming down, the encounter got me thinking, and made me focus on
something I'd been thinking about before but hadn't fully forumlated:
the fact that some people in this world seem to misunderstand the nature
of what it is to do science, and end up, under the claim of being
"sceptical", with various nonsense things -- see scientology, flat earth
societies, conspiracy theories, and whathaveyou.
So, here's something that might (but probably won't) help some people
figuring out stuff. Even if it doesn't, it's been bothering me and I
want to write it down so it won't bother me again. If you know all this
stuff, it might be boring and you might want to skip this post.
Otherwise, take a deep breath and read on...
Statements are things people say. They can be true or false; "the
sun is blue" is an example of a statement that is trivially false. "The
sun produces light" is another one that is trivially true. "The sun
produces light through a process that includes hydrogen fusion" is
another statement, one that is a bit more difficult to prove true or
false. Another example is "Wouter Verhelst does not have a favourite
color". That happens to be a true statement, but it's fairly difficult
for anyone that isn't me (or any one of the other Wouters Verhelst out
there) to validate as true.
While statements can be true or false, combining statements without more
context is not always possible. As an example, the statement "Wouter
Verhelst is a Debian Developer" is a true statement, as is the statement
"Wouter Verhelst is a professional Volleybal player"; but the statement
"Wouter Verhelst is a professional Volleybal player and a Debian
Developer" is not, because while I am a Debian Developer, I am not a
professional Volleybal player -- I just happen to share a name with
someone who is.
A statement is never a fact, but it can describe a fact. When a
statement is a true statement, either because we trivially know what it
states to be true or because we have performed an experiment that
proved beyond any possible doubt that the statement is true, then what
the statement describes is a fact. For example, "Red is a color" is a
statement that describes a fact (because, yes, red is definitely a
color, that is a fact). Such statements are called statements of
fact. There are other possible statements. "Grass is purple" is a
statement, but it is not a statement of fact; because as everyone knows,
grass is (usually) green.
A statement can also describe an opinion. "The Porsche 911 is a nice
car" is a statement of opinion. It is one I happen to agree with, but it
is certainly valid for someone else to make a statement that conflicts
with this position, and there is nothing wrong with that. As the saying
goes, "opinions are like assholes: everyone has one". Statements
describing opinions are known as statements of opinion.
The differentiating factor between facts and opinions is that facts are
universally true, whereas opinions only hold for the people who state
the opinion and anyone who agrees with them. Sometimes it's difficult or
even impossible to determine whether a statement is true or not. The
statement "The numbers that win the South African Powerball lottery on
the 31st of July 2020 are 2, 3, 5, 19, 35, and powerball 14" is not a
statement of fact, because at the time of writing, the 31st of July 2020
is in the future, which at this point gives it a 1 in 24,435,180 chance
to be true). However, that does not make it a statement of opinion; it
is not my opinion that the above numbers will win the South African
powerball; instead, it is my guess that those numbers will be correct.
Another word for "guess" is hypothesis: a hypothesis is a statement
that may be universally true or universally false, but for which the
truth -- or its lack thereof -- cannot currently be proven beyond doubt.
On Saturday, August 1st, 2020 the above statement about the South
African Powerball may become a statement of fact; most likely however,
it will instead become a false statement.
An unproven hypothesis may be expressed as a matter of belief. The
statement "There is a God who rules the heavens and the Earth" cannot
currently (or ever) be proven beyond doubt to be either true or false,
which by definition makes it a hypothesis; however, for matters of
religion this is entirely unimportant, as for believers the belief that
the statement is correct is all that matters, whereas for nonbelievers
the truth of that statement is not at all relevant. A belief is not an
opinion; an opinion is not a belief.
Scientists do not deal with unproven hypotheses, except insofar that
they attempt to prove, through direct observation of nature (either out
in the field or in a controlled laboratory setting) that the hypothesis
is, in fact, a statement of fact. This makes unprovable hypotheses
unscientific -- but that does not mean that they are false, or even
that they are uninteresting statements. Unscientific statements are
merely statements that science cannot either prove or disprove, and that
therefore lie outside of the realm of what science deals with.
Given that background, I have always found the so-called "conflict"
between science and religion to be a non-sequitur. Religion deals in one
type of statements; science deals in another. The do not overlap, since
a statement can either be proven or it cannot, and religious statements
by their very nature focus on unprovable belief rather than universal
truth. Sure, the range of things that science has figured out the facts
about has grown over time, which implies that religious statements have
sometimes been proven false; but is it heresy to say that "animals exist
that can run 120 kph" if that is the truth, even if such animals don't
exist in, say, Rome?
Something very similar can be said about conspiracy theories. Yes, it is
possible to hypothesize that NASA did not send men to the moon, and that
all the proof contrary to that statement was somehow fabricated.
However, by its very nature such a hypothesis cannot be proven or
disproven (because the statement states that all proof was
fabricated), which therefore implies that it is an unscientific
statement.
It is good to be sceptical about what is being said to you. People can
have various ideas about how the world works, but only one of those
ideas -- one of the possible hypotheses -- can be true. As long as a
hypothesis remains unproven, scientists love to be sceptical
themselves. In fact, if you can somehow prove beyond doubt that a
scientific hypothesis is false, scientists will love you -- it means
they now know something more about the world and that they'll have to
come up with something else, which is a lot of fun.
When a scientific experiment or observation proves that a certain
hypothesis is true, then this probably turns the hypothesis into a
statement of fact. That is, it is of course possible that there's a flaw
in the proof, or that the experiment failed (but that the failure was
somehow missed), or that no observance of a particular event happened
when a scientist tried to observe something, but that this was only
because the scientist missed it. If you can show that any of those
possibilities hold for a scientific proof, then you'll have turned a
statement of fact back into a hypothesis, or even (depending on the
exact nature of the flaw) into a false statement.
There's more. It's human nature to want to be rich and famous, sometimes
no matter what the cost. As such, there have been scientists who have
falsified experimental results, or who have claimed to have observed
something when this was not the case. For that reason, a scientific
paper that gets written after an experiment turned a hypothesis into
fact describes not only the results of the experiment and the observed
behavior, but also the methodology: the way in which the experiment
was run, with enough details so that anyone can retry the experiment.
Sometimes that may mean spending a large amount of money just to be able
to run the experiment (most people don't have an LHC in their backyard,
say), and in some cases some of the required materials won't be
available (the latter is expecially true for, e.g., certain chemical
experiments that involve highly explosive things); but the information
is always there, and if you spend enough time and money reading
through the available papers, you will be able to independently prove
the hypothesis yourself. Scientists tend to do just that; when the
results of a new experiment are published, they will try to rerun the
experiment, partially because they want to see things with their own
eyes; but partially also because if they can find fault in the
experiment or the observed behavior, they'll have reason to write a
paper of their own, which will make them a bit more rich and famous.
I guess you could say that there's three types of people who deal with
statements: scientists, who deal with provable hypotheses and
statements of fact (but who have no use for unprovable hypotheses and
statements of opinion); religious people and conspiracy theorists,
who deal with unprovable hypotheses (where the religious people deal
with these to serve a large cause, while conspiracy theorists only
care about the unprovable hypotheses); and politicians, who should
care about proven statements of fact and produce statements of
opinion, but who usually attempt the reverse of those two these days 
Anyway...
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There is no denying in the fact that 2020 was a challenging year for everybody, including animals.
In India, animals such as dogs who mostly filled their bellies at street food stalls, were starving as there were no street eateries operating during a long long lockdown. I was in my home town, New Delhi, working from home like most of us.
During the month of July 2020, a dog near the place I live (we fondly called her Brownie) delivered 7 pups in wilderness.
I would never forget my first sight of them, inside a dirty, garbage filled land there were the cutest, cleanest, tiniest ball of fur! All of them were toppled as the land s surface was uneven.. The first instinct was to put them all together on a flat surface. After the search mission completed, this was the sight..
Brownie and her litter put together in the same land where she gave birth.
The adorable, Robin !
Don and his new big brother!
The naughty and handsome, Swayze !
First Pup who got adopted Pluto 
Playful and Beautiful, Bella !
Brownie, the mom dog!
This is a puppy!
She did not let us put coat on her 
When I see them now, healthier, happier, running around, with no fear of getting attacked by dogs, I can t express the content I feel. For 2 of the dogs (Brownie and her friend) I got it done personally from a private vet. For the other 3, I got it done via Municipal Corporations who do it for free for dogs, you d have to call them and they come with dog catchers and a van and drop them back in the same area, but volunteers like us have to be very vigilant and active during the whole process to follow up with them.
Dogs getting dropped off after sterilization.
Reviving Very Old X Code
I've taken the week between Christmas and New Year's off this year. I
didn't really have anything serious planned, just taking a break from
the usual routine. As often happens, I got sucked into doing a project
when I received this simple bug report
Over the course of the last year and a half, I ve been doing some self-directed
learning on how radios work. I ve gone from a very basic understanding of
wireless communications (there s usually some sort of antenna, I guess?) all
the way through the process of learning about and implementing a set of
libraries to modulate and demodulate data using my now formidable stash of SDRs.
I ve been implementing all of the RF processing code from first principals and
purely based on other primitives I ve written myself to prove to myself that I
understand each concept before moving on.
I figured that there was a fun capstone to be done here - the blind reverse
engineering and implementation of the protocol my cheep Amazon power switch
uses to turn on and off my Christmas Tree. All the work described in this post
was done over the course of a few hours thanks to help during the demodulation
from 
After taking a capture, I started to look at understanding what the modulation
type of the signal was, and how I may go about demodulating it.
Using 
Next, I started to measure the smallest pulse, and see if I could infer the
symbols per second, and try to decode it by hand. These types of signals are
generally pretty easy to decode by eye.
After some googling, I found a single lone
It s a bummer that we missed the clock sync / preamble pulse before the data
message, but that s OK somehow. It also turns out that 8 or 10 bit series of of
0"s wasn t clock sync at all - it was part of the address! Since it also turns
out that all devices made by this manufacturer have the hardcoded address of
And even more interestingly, one of our scancodes ( Off , which is 0x94) shows up just
below this table, in the examples.
Over all, I think this tells us we have the right bits to look at for
determining the scan code! Great news there!
