ESP32-C3 Adblock

ESP32-C3 Adblock implements a Pi-hole-style DNS sinkhole on a $2 ESP32-C3 by storing sorted 40-bit FNV-1a domain hashes in flash and binary-searching them at query time. That fixed 5-byte hash-per-domain design fits large blocklists in flash instead of RAM: about 141k domains take ~0.67 MB flash and use ~50 KB RAM, with lookups taking ~10 ms (≈18 flash reads including Wi‑Fi RTT). The author explains the 40-bit tradeoff (near-zero collisions at 141k, ~1 collision at 537k), compares it to string-in-RAM approaches that require PSRAM and megabytes of RAM, and notes the same hash-in-flash method scales on larger ESP32 chips. Hardware tested is any ESP32‑C3 with 4 MB flash (C3 SuperMini), and a printable enclosure is provided.

Setup and operation are handled via PlatformIO for initial USB flash, then firmware and blocklists update over Wi‑Fi from a web dashboard at c3adblock.local or via remote URLs. A build script accepts hosts, domain lists, and AdGuard-style rules to produce blocklist.bin; the device offers a captive portal for Wi‑Fi setup if needed. Security uses HTTP Basic Auth for all mutating endpoints and a separate OTA password; read-only stats stay open. Because the device serves plain HTTP, credentials are sent as base64 and CSRF is mitigated by requiring a custom X-Requested-With header on state-changing requests. Partition choices affect OTA capability and maximum blocklist size.