gno.land/r/moul/x/daily/crc32demo/v0⧉

1// Package crc32demo is a small gnoweb demo of the CRC-32 checksum provided by2// the [p/moul/x/daily/crc32](/p/moul/x/daily/crc32/v0) library: it checksums a3// few strings and shows that a one-character change moves the result4// completely.5//6// It contains no checksum logic of its own. Stateless, so Render is7// deterministic.8package crc32demo910import (11	"strings"1213	"gno.land/p/moul/x/daily/crc32/v0"14)1516var samples = []string{"", "a", "abc", "123456789", "hello world", "hello worle"}1718// Render renders the demo for gnoweb.19//20//	Render("")       / Render("/") -> the samples table21//	Render("/<text>")              -> checksum that text22func Render(path string) string {23	var b strings.Builder24	b.WriteString("# CRC-32\n\n")25	b.WriteString("The IEEE checksum behind zip, gzip and PNG, demoing the ")26	b.WriteString("[`p/moul/x/daily/crc32`](/p/moul/x/daily/crc32/v0) library.\n\n")2728	if in := parseArg(path); in != "" {29		b.WriteString("## `")30		b.WriteString(in)31		b.WriteString("`\n\n`")32		b.WriteString(crc32.ChecksumHex(in))33		b.WriteString("`\n")34		return b.String()35	}3637	b.WriteString("| input | crc32 |\n|---|---|\n")38	for _, s := range samples {39		b.WriteString("| ")40		if s == "" {41			b.WriteString("_(empty)_")42		} else {43			b.WriteString("`" + s + "`")44		}45		b.WriteString(" | `")46		b.WriteString(crc32.ChecksumHex(s))47		b.WriteString("` |\n")48	}49	b.WriteString("\n`123456789` → `cbf43926` is the standard CRC-32 check value, ")50	b.WriteString("so this table doubles as a conformance test.\n\n")51	b.WriteString("> The last two rows differ by one letter and share no digits: ")52	b.WriteString("that avalanche is the point.\n\n")53	b.WriteString("> A CRC detects **accidents**, not tampering — it is linear, so a ")54	b.WriteString("matching message is easy to craft. Never authenticate with it.\n")55	return b.String()56}5758func parseArg(path string) string {59	s := strings.TrimSpace(path)60	s = strings.TrimPrefix(s, "/")61	if i := strings.IndexByte(s, '/'); i >= 0 {62		s = s[:i]63	}64	return s65}66