update.v

1//! `koh update` — put a newer published koh in place of this one (§12).2//!3//! The source is a release document: Kepr's `/koh/releases/latest.json` by4//! default, or whatever `KOH_UPDATE_SOURCE` names. Koh installs only a5//! **newer** version than the one running, never merely a different one, so a6//! stale mirror cannot walk the binary backwards. Nothing is ever built here.78module update910import crypto.blake311import json212import net.http13import os1415pub const default_source = 'https://kepr.uk/koh/releases/latest.json'16pub const source_env = 'KOH_UPDATE_SOURCE'17pub const repo = 'koh'18const file_scheme = 'file://'1920// One platform's file, in the shape Kepr answers with (§22.4).21struct PlatformFile {22	url    string23	blake3 string24	sha256 string25}2627// The release document: `notes` is omitted by Kepr when it is empty, so it is28// optional rather than an empty string.29struct Document {30	version   string31	notes     ?string32	platforms map[string]PlatformFile33}3435pub struct Available {36pub:37	version  string38	notes    string39	url      string40	blake3   string41	platform string42}4344// source is the document to read: the environment wins, so a self-hosted Kepr45// can serve its own koh.46pub fn source() string {47	named := os.getenv(source_env)48	if named != '' {49		return named50	}51	return default_source52}5354// Checked is what the source had to say: whether there is anything newer, and55// what it is when there is.56pub struct Checked {57pub:58	update    bool59	available Available60}6162// check asks the source what the newest koh is. Errors are errors; "nothing to63// do" is not one of them, so it is a field, not a failed call.64pub fn check(now string, platform string) !Checked {65	url := source()66	response := http.get(url) or { return error('could not reach ${url}: ${err.msg()}') }67	if response.status_code != 200 {68		return error('${url} answered ${response.status_code}')69	}70	document := json2.decode[Document](response.body) or {71		// The parser's own message, carets and colour included, means nothing here.72		return error('${url} did not answer with a release document — try again later')73	}74	if document.version == '' {75		// A document with no version is not a release document, so say that rather76		// than pretending there is simply nothing to do.77		return error('${url} has no version — it is not a release document')78	}79	if compare_versions(document.version, now) <= 0 {80		return Checked{}81	}82	file := document.platforms[platform] or {83		return error('koh ${document.version} has no ${platform} file — run it on another machine')84	}85	return Checked{86		update:    true87		available: Available{88			version:  document.version89			notes:    document.notes or { '' }90			url:      file.url91			blake3:   file.blake392			platform: platform93		}94	}95}9697// compare_versions orders two versions the way the spec asks: dot-separated98// components compared as numbers, so 2.10.0 is newer than 2.9.9. A component99// that is not a number is compared as text, so a strange version can never win100// by accident. Returns 1, 0 or -1.101pub fn compare_versions(a string, b string) int {102	left := a.split('.')103	right := b.split('.')104	for index in 0 .. if left.len > right.len { left.len } else { right.len } {105		one := if index < left.len { left[index] } else { '0' }106		two := if index < right.len { right[index] } else { '0' }107		order := compare_component(one, two)108		if order != 0 {109			return order110		}111	}112	return 0113}114115fn compare_component(a string, b string) int {116	// Leading zeros are not part of a number: 01 and 1 are the same version.117	left := a.trim_left('0')118	right := b.trim_left('0')119	if left == right {120		return 0121	}122	if left.len != right.len {123		return if left.len > right.len { 1 } else { -1 }124	}125	return if left > right { 1 } else { -1 }126}127128// install downloads the new binary, checks it, and swaps it in for the one129// running. The rename is the only step that changes anything, and it is the130// last one.131pub fn install(available Available) !string {132	bytes := download(available.url)!133	verify(bytes, available.blake3)!134	target := os.executable()135	fresh := write_beside(os.dir(target), bytes)!136	if os.user_os() == 'macos' {137		// An unsigned binary cannot run on Apple silicon at all, so a refused138		// signature is a refusal to install, not a warning.139		signed := os.execute('codesign -f -s - ${sh_quote(fresh)}')140		if signed.exit_code != 0 {141			os.rm(fresh) or {}142			return error('codesign refused the downloaded binary: ${signed.output.trim_space()}')143		}144	}145	// rename, not move: both paths are in one folder, so this is the atomic step146	// and a failure is a failure, never a half-written binary.147	os.rename(fresh, target)!148	return target149}150151fn download(url string) ![]u8 {152	if url.starts_with(file_scheme) {153		// A Kepr with a folder bucket hands out `file://` download URLs (dev and154		// tests only), so updating from one is the same code path with the file155		// read instead of fetched.156		path := url[file_scheme.len..]157		size := os.file_size(path)158		bytes := os.read_file(path) or {159			return error('could not read ${url}: ${err.msg()}')160		}.bytes()161		// The download is verified against the size it was said to be, and then162		// against its Blake3, before anything is signed or moved.163		if size > 0 && bytes.len != size {164			return error('${url} is ${size} bytes but ${bytes.len} arrived — refusing a partial download')165		}166		return bytes167	}168	response := http.get(url) or { return error('could not download ${url}: ${err.msg()}') }169	if response.status_code != 200 {170		return error('${url} answered ${response.status_code}')171	}172	bytes := response.body.bytes()173	declared := response.header.get(.content_length) or { '' }174	if declared != '' && i64(declared.trim_space().int()) != bytes.len {175		return error('${url} said ${declared} bytes and sent ${bytes.len} — refusing a partial download')176	}177	return bytes178}179180// verify is the check that makes installing anything safe: the bytes must be181// what the document said, or they are thrown away.182fn verify(bytes []u8, expected string) ! {183	if bytes.len == 0 {184		return error('the download was empty')185	}186	if expected == '' {187		return error('the release document carries no Blake3 checksum — refusing to install it')188	}189	got := blake3.sum256(bytes).hex()190	if got != expected {191		return error('the download is not the published file (Blake3 ${got} instead of ${expected}) — refusing to install it')192	}193}194195// write_beside writes the new binary beside the one it will replace, so the rename is196// within one filesystem and therefore atomic. A folder that cannot be written197// is refused here, with the write's own error.198fn write_beside(dir string, bytes []u8) !string {199	fresh := os.join_path(dir, '.koh-new-${os.getpid()}')200	os.write_file_array(fresh, bytes) or {201		return error('cannot write beside ${dir} — put koh where this user can replace it (${err.msg()})')202	}203	os.chmod(fresh, 0o755)!204	return fresh205}206207// sh_quote keeps a path with a space in it one argument, and cannot be broken208// out of by a quote inside the path.209fn sh_quote(text string) string {210	return "'" + text.replace("'", "'\\''") + "'"211}