Andy Dixon: BlogDaily technical writing by Andy Dixon: Go and Rust internals, Linux and security how-tos, cryptography and UK privacy law, checked against source.https://dixon.cx/blog2026-09-21T19:39:13ZAndy Dixonhttps://dixon.cx/Copyright 2026 Andy DixonGo's ConstantTimeCompare Returns Early on Length Mismatchhttps://dixon.cx/blog/go-constant-time-compare-length-leak.html2026-09-21T19:39:13Z2026-09-21T19:39:13Zsubtle.ConstantTimeCompare is constant time only for equal-length inputs. What the length shortcut leaks, when it matters, and a hash-first fix.Go's database/sql Pool: SetConnMaxLifetime Behind a Firewallhttps://dixon.cx/blog/go-database-sql-setconnmaxlifetime-firewall.html2026-09-21T15:39:32Z2026-09-21T15:39:32ZWhy the first query after a quiet spell hangs or fails when a firewall forgets your connection, and how lifetime and idle limits in database/sql fix it.Go's crypto/rand.Text and rand.Read: Why Seeded Tokens Get Guessedhttps://dixon.cx/blog/go-crypto-rand-text-read-guessable-tokens.html2026-09-21T11:39:34Z2026-09-21T11:39:34ZWhy session tokens built from Go's non-cryptographic rand package get guessed, and how crypto/rand.Text and rand.Read replace them in a few lines.Go's context.WithoutCancel: Keeping Audit Logs Alive After the Request Dieshttps://dixon.cx/blog/go-context-withoutcancel-audit-logs.html2026-09-21T03:39:29Z2026-09-21T03:39:29ZA client hangs up mid-request and your audit row silently never gets written. How context.WithoutCancel fixes it, and the timeout and shutdown traps it creates.Go's http.Client: When Redirects Strip Authorizationhttps://dixon.cx/blog/go-http-client-redirects-strip-authorization.html2026-09-20T23:41:41Z2026-09-20T23:41:41ZLearn when Go forwards or strips Authorization on redirects, why subdomains and scheme changes surprise, and how to enforce a safer policy.Go's http.Transport Idle Pool: Why MaxIdleConnsPerHost Is 2https://dixon.cx/blog/go-http-transport-max-idle-conns-per-host.html2026-09-20T19:38:52Z2026-09-20T19:38:52ZWhy Go keeps only two idle connections per host, how bursty traffic to one API burns handshakes, and how to measure and fix it with httptrace.Go's http.Request.Clone: Which Fields Get Copied, Which Are Sharedhttps://dixon.cx/blog/go-http-request-clone-shared-headers-body.html2026-09-20T15:38:59Z2026-09-20T15:38:59ZRequest.Clone deep-copies headers but shares the Body, while WithContext shares almost everything. Here is what that means for RoundTrippers and retry loops.Go's ServeMux Method Patterns: Why You Get 405, Not 404https://dixon.cx/blog/go-servemux-method-patterns-405-not-404.html2026-09-20T11:39:19Z2026-09-20T11:39:19ZSince Go 1.22, ServeMux returns 405 with an Allow header when a path matches a method pattern but the verb does not. Here is why, and what PathValue sees.Go's http.ResponseController: Resetting Streaming Deadlineshttps://dixon.cx/blog/go-responsecontroller-resetting-streaming-deadlines.html2026-09-20T03:41:35Z2026-09-20T03:41:35ZGive each streamed chunk its own write deadline, surface flush errors promptly, and keep healthy long-lived HTTP responses alive in Go.Go's net.Dialer and Happy Eyeballs: Why Dual-Stack Connects Laghttps://dixon.cx/blog/go-net-dialer-happy-eyeballs-dual-stack-connect.html2026-09-19T23:39:06Z2026-09-19T23:39:06ZHow net.Dialer races IPv6 against IPv4, what FallbackDelay and Timeout really do, and why a black-holed AAAA record costs you 300ms per new connection.Go's http.Hijacker: Where Buffered Bytes Go After an Upgradehttps://dixon.cx/blog/go-http-hijacker-buffered-bytes-after-upgrade.html2026-09-19T19:42:11Z2026-09-19T19:42:11ZLearn why reading the raw connection after http.Hijacker can hide protocol bytes, and how to handle upgrades without stalls or reordering.Go's io.Pipe Has No Buffer: How a Stalled Reader Freezes Writeshttps://dixon.cx/blog/go-io-pipe-no-buffer-stalled-reader-freezes-writes.html2026-09-19T15:41:27Z2026-09-19T15:41:27ZSee why io.Pipe writes block, reproduce the freeze, and structure Go streaming pipelines so errors and cancellation unblock both ends.Go's http.MaxBytesReader: Limiting Uploads Without Breaking Keep-Alivehttps://dixon.cx/blog/go-http-maxbytesreader-uploads-keep-alive.html2026-09-19T11:42:55Z2026-09-19T11:42:55ZUse http.MaxBytesReader to cap Go uploads, return 413 reliably, and understand when HTTP/1.1 connections can safely stay alive.Go's os.Root: Traversal-Resistant File Access Without openat2https://dixon.cx/blog/go-os-root-traversal-resistant-file-access.html2026-09-19T03:39:02Z2026-09-19T03:39:02ZGo 1.24's os.Root confines file access to a directory, symlinks and .. included. See how it works, a zip-extraction example, and what it does not cover.Go's sync.Pool: Why Pooled Buffers Leak Data Between Requestshttps://dixon.cx/blog/go-sync-pool-buffers-leak-data-between-requests.html2026-09-18T23:39:12Z2026-09-18T23:39:12ZHow sync.Pool buffers end up showing one request's bytes to another: missing resets, aliasing after Put, over-long slices, and stale secrets, with fixes.Go's net/netip vs net.IP: Why == Finally Works on Addresseshttps://dixon.cx/blog/go-netip-vs-net-ip-comparing-addresses.html2026-09-18T19:38:54Z2026-09-18T19:38:54Znet.IP is a byte slice, so == won't compile and map keys need string hacks. netip.Addr is a comparable value type; here are the sharp edges that remain.Go's exec.ErrDot: Why exec.Command Won't Run a Binary From PATH's Dothttps://dixon.cx/blog/go-os-exec-errdot-relative-path-lookup.html2026-09-18T15:38:55Z2026-09-18T15:38:55ZSince Go 1.19, os/exec refuses to run a program found via a relative PATH entry. What ErrDot means, why it exists, and the correct fixes.Signal's Double Ratchet in Go: A Toy Forward-Secret Messengerhttps://dixon.cx/blog/signals-double-ratchet-in-go.html2026-09-18T11:41:08Z2026-09-18T11:41:08ZBuild a working Double Ratchet in Go from crypto/ecdh, HMAC and AES-GCM alone, and see exactly where forward secrecy and post-compromise security come from.Go's bufio.Scanner Stops at 64 KiB: Reading Long Lines Safelyhttps://dixon.cx/blog/go-bufio-scanner-64-kib-long-lines.html2026-09-18T03:42:27Z2026-09-18T03:42:27ZLearn why Go's bufio.Scanner rejects long lines, when to raise its buffer limit, and how to read bounded records without risking runaway memory use.Right to Repair Meets Firmware Locks: What the UK's New Ecodesign Rules Actually Requirehttps://dixon.cx/blog/right-to-repair-firmware-locks-uk-ecodesign-rules.html2026-09-17T23:44:34Z2026-09-17T23:44:34ZThe UK's 2021 right to repair rules cover washing machines and TVs, not phones: the ban on firmware-locked spare parts is still years away in Great Britain.ESP8266 vs ESP32 for a Battery Sensor: Why the Older, Slower Chip Still Wins on Idle Currenthttps://dixon.cx/blog/esp8266-vs-esp32-battery-sensor-idle-current.html2026-09-17T19:40:35Z2026-09-17T19:40:35ZDeep sleep numbers suggest the ESP32 should be the more efficient chip, but RTC power domains and default configuration often leave it drawing more current.Go's singleflight: Stop Cache Misses Stampeding the Databasehttps://dixon.cx/blog/go-singleflight-stop-cache-misses-stampeding-database.html2026-09-17T15:41:58Z2026-09-17T15:41:58ZUse singleflight to collapse concurrent cache misses, handle cancellation safely, and avoid subtle duplicate database reads in Go services.Go's log/slog: Structured Logging Without Reaching for a Third-Party Loggerhttps://dixon.cx/blog/go-slog-structured-logging.html2026-09-17T03:39:30Z2026-09-17T03:39:30ZHow Go's log/slog package gives you structured, leveled logging with context propagation, without adding zap or zerolog to go.mod.Go's GOMEMLIMIT: Keeping the OOM Killer Away From a Containerhttps://dixon.cx/blog/go-gomemlimit-oom-killer-containers.html2026-09-16T23:40:07Z2026-09-16T23:40:07ZWhy a Go service can be OOM-killed inside a memory-limited container despite having a garbage collector, and how GOMEMLIMIT fixes the pacing.Digital Forensics 101: Why dd and a Hash Beat cp When Imaging a Drivehttps://dixon.cx/blog/forensic-disk-imaging-dd-vs-cp.html2026-09-16T19:39:25Z2026-09-16T19:39:25ZWhy bit-for-bit disk imaging with dd, a write blocker and a SHA-256 checksum beats a filesystem copy when acquiring a drive for forensic analysis.Go's io.Copy Can Write Gigabytes Before Reporting an Errorhttps://dixon.cx/blog/go-io-copy-partial-writes-errors.html2026-09-16T15:41:30Z2026-09-16T15:41:30ZLearn why io.Copy can partially mutate a destination before failing, how its byte count helps, and when to stage writes for an atomic result.TOTP From Scratch in Go: Implementing RFC 6238 Without a Libraryhttps://dixon.cx/blog/totp-from-scratch-in-go-rfc6238.html2026-09-16T03:39:49Z2026-09-16T03:39:49ZHow the six digits in your authenticator app are actually produced: HMAC-SHA1, dynamic truncation and time steps, built in plain Go.OAuth 2.0 Device Authorization Grant: How CLI Tools Log In Without a Browser Redirecthttps://dixon.cx/blog/oauth-device-authorization-grant-cli-login.html2026-09-15T23:39:35Z2026-09-15T23:39:35ZRFC 8628 explained: how tools like gh, docker and kubectl authenticate on headless machines by polling a token endpoint instead of a browser redirect.Go's errgroup: Cancelling Goroutines Without Reinventing sync.WaitGrouphttps://dixon.cx/blog/go-errgroup-cancelling-goroutines.html2026-09-15T19:39:26Z2026-09-15T19:39:26ZHow golang.org/x/sync/errgroup collects errors, cancels sibling goroutines on first failure, and bounds concurrency without a semaphore channel.Go's errors.Join: Combining Errors Without Losing errors.Ishttps://dixon.cx/blog/go-errors-join-combining-errors.html2026-09-15T17:22:11Z2026-09-15T17:22:11ZHow errors.Join builds a tree of errors that still works with errors.Is and errors.As, and where the abstraction leaks.DKIM, SPF and DMARC for Self-Hosted Mail: A Practical Setuphttps://dixon.cx/blog/dkim-spf-dmarc-self-hosted-mail.html2026-09-15T12:25:10Z2026-09-15T12:25:10ZA step-by-step guide to configuring SPF, DKIM and DMARC for a self-hosted mail server, and why the DNS records alone will not stop spam folders.Shamir's Secret Sharing in Go: Splitting a Key So No Single Person Holds Ithttps://dixon.cx/blog/shamirs-secret-sharing-in-go.html2026-09-15T11:42:55Z2026-09-15T11:42:55ZHow Shamir's Secret Sharing splits a key into shares using polynomial interpolation over GF(256), with a working Go implementation.Age Verification Under the Online Safety Act: What 'Highly Effective' Actually Means in Practicehttps://dixon.cx/blog/age-verification-online-safety-act-highly-effective.html2026-09-15T03:40:40Z2026-09-15T03:40:40ZOfcom's 'highly effective' age assurance rests on four criteria, not a fixed toolset, and 2026 enforcement shows what that means for real services.Encrypted Client Hello: The TLS Extension That Finally Hides Which Site You're Visitinghttps://dixon.cx/blog/encrypted-client-hello-tls-sni-privacy.html2026-09-14T23:42:01Z2026-09-14T23:42:01ZTLS 1.3 still leaks the hostname you're connecting to in plaintext. Here's how Encrypted Client Hello fixes that, and where it still falls short.seccomp-bpf in Go: Restricting Syscalls Without a Containerhttps://dixon.cx/blog/seccomp-bpf-go-restricting-syscalls-without-a-container.html2026-09-14T19:41:29Z2026-09-14T19:41:29ZHow to build and install a seccomp-bpf syscall filter from a plain Go binary with golang.org/x/net/bpf, and why goroutines need the TSYNC flag.The UK-US Data Bridge: Where GDPR Adequacy Actually Stands in 2026https://dixon.cx/blog/uk-us-data-bridge-gdpr-adequacy-2026.html2026-09-14T15:42:48Z2026-09-14T15:42:48ZA status check on the UK-US Data Bridge: PCLOB's quorum collapse, the Latombe appeal at the CJEU, and the UK's own EU adequacy renewal.Go's testing/synctest: Testing Concurrent Code Without Sleeping in Testshttps://dixon.cx/blog/go-synctest-testing-concurrent-code.html2026-09-14T11:40:51Z2026-09-14T11:40:51ZHow Go 1.25's testing/synctest package lets you test timers, retries and debounce logic deterministically, without real time.Sleep calls.Go's rate.Limiter: Token Buckets Explained by Reading the Sourcehttps://dixon.cx/blog/go-rate-limiter-token-buckets-source.html2026-09-14T03:40:19Z2026-09-14T03:40:19ZA walk through golang.org/x/time/rate's actual source to see how Go's token bucket limiter tracks tokens without a background goroutine.Linux pidfds: Closing the PID Reuse Race in Supervisorshttps://dixon.cx/blog/linux-pidfds-closing-pid-reuse-race.html2026-09-13T23:42:01Z2026-09-13T23:42:01ZLearn how Linux pidfds provide a stable handle for polling, signalling and waiting without accidentally targeting a reused PID.Go's comparable Constraint: Why a Struct with a Slice Field Can't Satisfy Ithttps://dixon.cx/blog/go-comparable-constraint-slice-field.html2026-09-13T19:39:23Z2026-09-13T19:39:23ZWhy Go's generics compiler rejects structs containing slices as comparable, the reasoning behind it, and how to work around it.Right to Erasure vs Backups: What UK GDPR Actually Requireshttps://dixon.cx/blog/right-to-erasure-vs-backups-uk-gdpr.html2026-09-13T15:40:39Z2026-09-13T15:40:39ZWhy UK GDPR's right to erasure doesn't mean scrubbing every backup tape immediately, and what the ICO actually expects organisations to do instead.What 'Authorisation' Actually Means Under the Computer Misuse Acthttps://dixon.cx/blog/computer-misuse-act-penetration-testing-authorisation.html2026-09-13T11:39:55Z2026-09-13T11:39:55ZThe Computer Misuse Act has no good-faith defence, so a pentest's legality rests entirely on paperwork. Here's what that paperwork actually needs to say.Go's sync.Map: When It Actually Beats a Mutex-Protected Maphttps://dixon.cx/blog/sync-map-vs-mutex-map-go.html2026-09-13T03:40:51Z2026-09-13T03:40:51ZWhy sync.Map only wins for two specific access patterns, how Go 1.24's trie-based rewrite changed the numbers, and when a plain mutex wins instead.ESP32 Deep Sleep Power Budgeting: Why 'Low Power' Mode Still Drains a Battery in Dayshttps://dixon.cx/blog/esp32-deep-sleep-power-budgeting.html2026-09-12T23:39:30Z2026-09-12T23:39:30ZDeep sleep current specs look great on paper, but wake-up current spikes and a board's regulator usually decide the real battery life.Postgres Advisory Locks in Go: Cheaper Than a Distributed Lock Servicehttps://dixon.cx/blog/postgres-advisory-locks-go.html2026-09-12T19:39:52Z2026-09-12T19:39:52ZHow to use Postgres advisory locks from Go for cron dedup and leader election, and the connection-pooling pitfall that breaks them silently.Hybrid Post-Quantum TLS 1.3: Why ML-KEM Rides Alongside ECDHEhttps://dixon.cx/blog/hybrid-post-quantum-tls-mlkem-ecdhe.html2026-09-12T15:40:54Z2026-09-12T15:40:54ZWhy TLS 1.3's post-quantum key exchange combines ML-KEM with ECDHE instead of replacing it, and what that costs in handshake size.Rural Broadband and CGNAT: Why Self-Hosting Needs a Reverse Tunnelhttps://dixon.cx/blog/rural-broadband-cgnat-reverse-tunnel.html2026-09-12T03:31:23Z2026-09-12T03:31:23ZStarlink and most 4G home routers hide you behind CGNAT, so port forwarding does nothing. Here's how a reverse WireGuard tunnel fixes it.Ed25519 vs ECDSA: How Deterministic Nonces Ended a Recurring Bughttps://dixon.cx/blog/ed25519-vs-ecdsa-deterministic-nonces.html2026-09-11T19:01:36Z2026-09-11T19:01:36ZHow a reused ECDSA nonce leaks a private key, why Sony and Android wallets fell to it, and how Ed25519 designs the whole bug class out.Flipper Blue++: Giving the Flipper Zero the Bluetooth Stack It Was Built Forhttps://dixon.cx/blog/flipper-bluepp-full-bluetooth-stack.html2026-09-11T16:29:13Z2026-09-11T16:29:13ZWhy stock Flipper Zero firmware cannot scan or connect over BLE, the three patches that unlock the full stack, and how to drive it from your own app.Go HTTP Response Bodies: Why Close Alone Loses Connectionshttps://dixon.cx/blog/go-http-response-bodies-close-connection-reuse.html2026-09-11T03:35:40Z2026-09-11T03:35:40ZClosing a Go HTTP response body prevents leaks, but HTTP/1 connection reuse depends on reaching EOF. Learn when to drain, cap or abandon a body.