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Systems Programming & Open-Source Software Notes

Programming languages, free software, and the systems underneath everyday tools.

C and Haskell, Python and Nix, protocols and self-hosting. Small examples, awkward boundaries, and a closer look at how things work.

Cap’n Proto Python NixOS

Featured note / Protocols

A fast wire layout still needs a trust boundary

Cap’n Proto’s word-aligned layout supports efficient traversal, but a receiver still has to validate bounds and resource use. Serialization also says nothing by itself about who sent a message or what that sender may do.

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2026 current notes

27 Oct 2026A fast wire layout still needs a trust boundaryProtocols
16 Oct 2026Promise pipelining removes a wait, not a dependencyProtocols
08 Oct 2026A useful setup log starts with the question it can answerNix and Unix
01 Oct 2026A command line is an argument vector before it is a shell stringNix and Unix
17 Sep 2026Endianness belongs in the format, not in a lucky host assumptionProtocols
03 Sep 2026A virtual environment has an interpreter boundaryPython and Haskell
20 Aug 2026Make an invalid state unrepresentable at the interfacePython and Haskell
06 Aug 2026Rolling back NixOS does not roll back a databaseNix and Unix
23 Jul 2026The grain is a useful boundary for application stateSelf-hosting
09 Jul 2026Pass a capability instead of looking up ambient authoritySelf-hosting
04 Jul 2026Validate CSV headers before building dictionariesPython
30 Jun 2026Testing a schedule cache across feed revisionsProtocols
26 Jun 2026A durable idempotency key in one SQLite transactionSelf-hosting
22 Jun 2026Parsing GTFS times beyond midnightProtocols
18 Jun 2026CSV round trips: commas, quotes and embedded newlinesPython
14 Jun 2026A byte stream does not know where your messages endProtocols
10 Jun 2026Reading Tempest as a systems projectSelf-hosting
06 Jun 2026IRC presence is not an appointment to answerFree software
02 Jun 2026ActivityPub has actor identity, object identity and delivery identityProtocols
29 May 2026Read the ownership boundary before upgrading an RPC bindingPython and Haskell
25 May 2026Why len(x) is not just x.__len__() in disguisePython and Haskell
21 May 2026A Python name is a binding, not a box containing a copyPython and Haskell
17 May 2026A Nix derivation describes a build; it does not prove reproducibilityNix and Unix
13 May 2026Changing a Cap’n Proto schema without renumbering historyProtocols
09 May 2026Cross compilation: build, host and target are different questionsC and compilers
05 May 2026A closure in C is a function plus an environmentC and compilers
01 May 2026C is an abstract machine, even on familiar hardwareC and compilers

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