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 ${response.status_code}')69	}70	document := json2.decode[Document](response.body) or {71		return error('${url} is not a release document: ${err.msg()}')72	}73	if document.version == '' || compare_versions(document.version, now) <= 0 {74		return Checked{}75	}76	file := document.platforms[platform] or {77		return error('koh ${document.version} has no ${platform} file — run it on another machine')78	}79	return Checked{80		update:    true81		available: Available{82			version:  document.version83			notes:    document.notes or { '' }84			url:      file.url85			blake3:   file.blake386			platform: platform87		}88	}89}9091// compare_versions orders two versions the way the spec asks: dot-separated92// components compared as numbers, so 2.10.0 is newer than 2.9.9. A component93// that is not a number is compared as text, so a strange version can never win94// by accident. Returns 1, 0 or -1.95pub fn compare_versions(a string, b string) int {96	left := a.split('.')97	right := b.split('.')98	for index in 0 .. if left.len > right.len { left.len } else { right.len } {99		one := if index < left.len { left[index] } else { '0' }100		two := if index < right.len { right[index] } else { '0' }101		order := compare_component(one, two)102		if order != 0 {103			return order104		}105	}106	return 0107}108109fn compare_component(a string, b string) int {110	// Leading zeros are not part of a number: 01 and 1 are the same version.111	left := a.trim_left('0')112	right := b.trim_left('0')113	if left == right {114		return 0115	}116	if left.len != right.len {117		return if left.len > right.len { 1 } else { -1 }118	}119	return if left > right { 1 } else { -1 }120}121122// install downloads the new binary, checks it, and swaps it in for the one123// running. The rename is the only step that changes anything, and it is the124// last one.125pub fn install(available Available) !string {126	bytes := download(available.url)!127	verify(bytes, available.blake3)!128	target := os.executable()129	staged := stage(os.dir(target), bytes)!130	if os.user_os() == 'macos' {131		// An unsigned binary cannot run on Apple silicon at all, so a refused132		// signature is a refusal to install, not a warning.133		signed := os.execute('codesign -f -s - ${sh_quote(staged)}')134		if signed.exit_code != 0 {135			os.rm(staged) or {}136			return error('codesign refused the downloaded binary: ${signed.output.trim_space()}')137		}138	}139	os.mv(staged, target)!140	return target141}142143fn download(url string) ![]u8 {144	if url.starts_with(file_scheme) {145		// A Kepr with a folder bucket hands out `file://` download URLs (dev and146		// tests only), so updating from one is the same code path with the file147		// read instead of fetched.148		path := url[file_scheme.len..]149		return os.read_file(path) or {150			return error('could not read ${url}: ${err.msg()}')151		}.bytes()152	}153	response := http.get(url) or { return error('could not download ${url}: ${err.msg()}') }154	if response.status_code != 200 {155		return error('${url} answered ${response.status_code}')156	}157	return response.body.bytes()158}159160// verify is the check that makes installing anything safe: the bytes must be161// what the document said, or they are thrown away.162fn verify(bytes []u8, expected string) ! {163	if bytes.len == 0 {164		return error('the download was empty')165	}166	if expected == '' {167		return error('the release document carries no Blake3 checksum — refusing to install it')168	}169	got := blake3.sum256(bytes).hex()170	if got != expected {171		return error('the download is not the published file (Blake3 ${got} instead of ${expected}) — refusing to install it')172	}173}174175// stage writes the new binary beside the one it will replace, so the rename is176// within one filesystem and therefore atomic. A folder that cannot be written177// is refused here, with the write's own error.178fn stage(dir string, bytes []u8) !string {179	staged := os.join_path(dir, '.koh-new-${os.getpid()}')180	os.write_file_array(staged, bytes) or {181		return error('cannot write beside ${dir} — put koh where this user can replace it (${err.msg()})')182	}183	os.chmod(staged, 0o755)!184	return staged185}186187// sh_quote keeps a path with a space in it one argument, and cannot be broken188// out of by a quote inside the path.189fn sh_quote(text string) string {190	return "'" + text.replace("'", "'\\''") + "'"191}