Other subsystems

A grab-bag of smaller subsystems that exist in src/ but don't warrant a full page. Each has a directory pointer for when you need to dig in.

Subsystem	Source	One-liner
Source maps	src/sourcemap/	VLQ encoder/decoder, source-map join helpers. Used by the printer, the bundler, the runtime, and the crash handler.
Allocators (data)	src/collections/, src/StaticHashMap.zig, src/comptime_string_map.zig, src/identity_context.zig, src/linear_fifo.zig	Hashmaps, fixed-size string maps computed at comptime, ring buffers.
Compression	src/zlib.zig, src/brotli.zig, plus vendored vendor/zlib, vendor/libdeflate, vendor/brotli, vendor/zstd	gzip/deflate/brotli/zstd encoders and decoders. Used by HTTP responses, Web Streams, Bun.gzipSync, etc.
Hashing	src/sha.zig, src/wyhash.zig, src/hmac.zig	SHA, wyhash (bun.hash), HMAC.
DNS	src/dns.zig	c-ares wrapper. Powers node:dns and fetch().
TLS	src/boringssl.zig	BoringSSL bindings.
Glob	src/glob/, src/glob.zig	Pattern matching — used by the shell, bun:test, Bun.Glob, the bundler, bun install workspace patterns.
Markdown	src/md/	Markdown parser used by Bun.Markdown and a few tooling outputs.
YAML / TOML / INI	src/bun.js/api/YAMLObject.zig, src/bun.js/api/TOMLObject.zig, src/ini.zig	Read/write helpers.
NAPI / N-API	src/napi/	Implementation of Node's N-API (*.node binary addons).
V8 C++ API shim	vendor/nodejs/, src/bun.js/bindings/V8/	Compatibility shims so Node addons that link against V8 headers work under JSC.
Standalone module graph	src/StandaloneModuleGraph.zig	Format used by bun build --compile.
REPL line editor	src/repl.zig	Custom line editor (no readline dependency).
CLI completions	src/cli/install_completions_command.zig, src/cli/add_completions.zig	Shell completion logic.
Subprocess	src/bun.js/api/bun/process.zig, src/shell/subproc.zig	Cross-platform spawn (posix_spawn / CreateProcessW).
Cron	src/bun.js/api/cron.zig, src/bun.js/api/cron_parser.zig	The Bun.Cron API.
DNS resolver	src/dns.zig and src/bun.js/node/dns.zig	node:dns Promise + callback APIs.
HTML scanner	src/HTMLScanner.zig, src/HTMLImportManifest.zig (in bundler)	Parse HTML to extract scripts, styles, imports.
init	src/init/	Templates and helpers for bun init.
PE/ELF/Mach-O patchers	src/pe.zig, src/elf.zig, src/macho.zig	Native binary surgery for bun build --compile.
Tracing	src/tracy.zig, src/generated_perf_trace_events.zig	Optional Tracy profiler integration.
Async helpers	src/async/	bun.spawn async coordination primitives.
Watcher backends	src/watcher/	Platform-specific file-system event sources.
VM internals	src/vm/	Internal VM helpers shared across VirtualMachine callers.
base64	src/base64/, src/base64.zig	SIMD base64 encode/decode.
Errno	src/errno/	OS-specific errno enums.
IO threads	src/io/	I/O scheduling primitives (file readers, threaded I/O).
Threading	src/threading/, src/threading.zig	Thread primitives, atomics, work pools.
Mocks/safety	src/safety/, src/safety.zig	Defensive helpers for debug builds (e.g. exception-scope checks).
Pointer helpers	src/ptr/, src/ptr.zig	Tagged-pointer wrappers.
Semver	src/semver/, src/semver.zig	Semantic-version range matching used by the package manager.
Webview	src/bun.js/webview/	Embedded webview API (experimental).

When to extract a separate page

If you find yourself adding to a row above and notice the row growing past a paragraph, that's a sign to promote it to its own page in systems/ and link to it from the table.