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import { readFile, realpath, stat } from "node:fs/promises"
import { watch, type FSWatcher } from "node:fs"
import { basename, dirname, extname, isAbsolute, join, matchesGlob, relative, resolve, sep } from "node:path"
// A dev server for the no-bundle path: serve a directory of .html components
// over HTTP, watch it, and hot-reload the components that changed.
//
// npx jq79 dev // the CLI
// import { devServer } from "jq79/dev" // or from a script
// await devServer({ rootDir: "." })
//
// It is a static file server and nothing else - no transforms, no bundling, no
// module graph. Which is the point: the files it serves are the files you would
// deploy, so what you develop against and what a static host serves are the same
// bytes. The one thing it adds is the hot-reload channel, and it adds it to
// *documents* only (a component fetched by the runtime is served verbatim).
//
// The reload is fine-grained. On a change the server pushes the new source down
// an SSE channel and the runtime swaps it into every live instance of that file,
// keeping its data - see hotUpdate in jq79.ts. Anything the runtime can't place
// (a page, a stylesheet, a component nothing has mounted yet) falls back to a
// full page reload.
export interface DevServerOptions {
// the directory to serve, and to watch (default: the current directory)
rootDir?: string
// default: 4179, or the first free port after it
port?: number
// default: localhost
host?: string
// response headers to send on everything - a static host is configured, and
// these are that configuration (default: none)
headers?: Record<string, string>
// the same thing per request: a hook gets the request and its response before
// anything has been written to it (default: none)
beforeResponse?: ResponseHook[]
// what to watch on top of rootDir, and what to do about it (default: none)
watch?: WatchEntry[]
}
// runs on every response the server makes - a page, a component, the client,
// the event stream, a 404 - with nothing written yet, so `res.setHeader` still
// applies. A hook that answers the request itself (`res.end`) is left alone
export type ResponseHook = (req: IncomingMessage, res: ServerResponse) => void | Promise<void>
// the handler gets every file of the burst that woke it, absolute, so a save
// that touches three of them is one build rather than three
export type WatchHandler = (files: string[]) => void | Promise<void>
export interface WatchEntry {
// glob(s) resolved against the cwd, like rootDir: "styles/**/*.scss". A bare
// directory means everything under it
pattern: string | string[]
// what a match runs. Without one, a match outside the served root reloads the
// page - which is the only other thing a file served from nowhere can do
fn?: WatchHandler
}
export interface DevServer {
url: string
port: number
close: () => Promise<void>
}
const CONTENT_TYPES: Record<string, string> = {
".html": "text/html; charset=utf-8",
".js": "text/javascript; charset=utf-8",
".mjs": "text/javascript; charset=utf-8",
// the streaming WebAssembly APIs reject every other type, including the
// default below - a module served as octet-stream still runs, but it is
// buffered whole instead of compiling as it downloads
".wasm": "application/wasm",
".json": "application/json; charset=utf-8",
".css": "text/css; charset=utf-8",
".svg": "image/svg+xml",
".png": "image/png",
".jpg": "image/jpeg",
".jpeg": "image/jpeg",
".gif": "image/gif",
".webp": "image/webp",
".avif": "image/avif",
".ico": "image/x-icon",
".woff": "font/woff",
".woff2": "font/woff2",
".map": "application/json; charset=utf-8",
}
const CLIENT_URL = "/__jq79/client.js"
const EVENTS_URL = "/__jq79/events"
// Served as a *classic* script, and injected into the <head>: classic scripts
// run at parse time and module scripts are deferred, so the flag is set before
// the page's `import ... from "jq79"` evaluates - which is what the runtime
// waits for before it starts tracking instances. The client can't import the
// runtime itself: the page's copy may come from a CDN or an import map, and a
// second copy would have a second, empty registry.
const CLIENT = `(() => {
window.__JQ79_HMR_ENABLED__ = true
const events = new EventSource(${JSON.stringify(EVENTS_URL)})
events.addEventListener("update", event => {
const { url, src } = JSON.parse(event.data)
const runtime = window.__JQ79_HMR__
// no runtime (the page doesn't use jq79), or no live instance from this
// file (it isn't mounted, or it *is* the page) - nothing to swap into
const patched = runtime ? runtime.update(url, src) : 0
if (patched) console.log("[jq79] hot-updated " + url + " (" + patched + (patched === 1 ? " instance)" : " instances)"))
else location.reload()
})
events.addEventListener("reload", () => location.reload())
})()`
const posix = (path: string) => path.split(sep).join("/")
const isDocument = (req: IncomingMessage) => req.headers["sec-fetch-dest"] === "document"
// the client goes in the <head> so it is the first thing the page runs. A file
// with neither <head> nor <body> is still a document a browser will render, so
// fall back to the top of it rather than skipping the injection
const injectClient = (html: string): string => {
const tag = `<script src="${CLIENT_URL}"></script>`
// (\s[^>]*)? rather than [^>]*, or <header> would pass for <head>
const open = /<head(\s[^>]*)?>/i.exec(html) ?? /<body(\s[^>]*)?>/i.exec(html)
if (!open) return tag + html
const at = open.index + open[0].length
return html.slice(0, at) + tag + html.slice(at)
}
export const devServer = async (options: DevServerOptions = {}): Promise<DevServer> => {
// the *real* path: the watcher reports what changed relative to the directory
// it actually opened, so a root reached through a symlink (/tmp and /var are
// symlinks on macOS) would hand back paths that don't line up with it
const root = await realpath(resolve(options.rootDir ?? "."))
const host = options.host ?? "localhost"
// a configured header goes on every response, which is the one thing
// content-type and content-length cannot do - each describes the bytes of a
// single response. Dropped here rather than at write time, so that either of
// them still standing by then can only have come from a hook, which saw the
// request and is entitled to say
const headers = Object.entries(options.headers ?? {}).filter(
([name]) => !["content-type", "content-length"].includes(name.toLowerCase()),
)
const hooks = options.beforeResponse ?? []
const clients = new Set<ServerResponse>()
const send = (event: string, data: unknown) => {
const frame = `event: ${event}\ndata: ${JSON.stringify(data)}\n\n`
clients.forEach(client => client.write(frame))
}
// --- serving ---------------------------------------------------------------
// what the response says about its own bytes, written last so the layers
// below can't contradict it. A hook is the one exception: it saw the request,
// so it is entitled to an opinion about what these bytes *are* - never about
// how many there are, since a wrong content-length truncates the body or
// hangs the socket
const head = (res: ServerResponse, status: number, own: Record<string, string | number> = {}) => {
res.removeHeader("content-length")
const write = { ...own }
if (res.hasHeader("content-type")) delete write["content-type"]
return res.writeHead(status, write)
}
const serveStatic = async (req: IncomingMessage, res: ServerResponse, pathname: string) => {
// a URL path is not a file path: decode it, then keep the result inside the
// root (".." in a request must not walk out of the served directory)
let file: string
try {
file = resolve(join(root, decodeURIComponent(pathname)))
} catch {
head(res, 400).end("bad request")
return
}
if (file !== root && !file.startsWith(root + sep)) {
head(res, 403).end("forbidden")
return
}
try {
if ((await stat(file)).isDirectory()) {
// a directory is served through its trailing-slash URL, like every
// static host: /docs rendered as-is would resolve its relative links
// against the parent ("img.png" -> /img.png instead of /docs/img.png)
if (!pathname.endsWith("/")) {
head(res, 301, { location: pathname + "/" }).end()
return
}
file = join(file, "index.html")
}
const body = await readFile(file)
const type = CONTENT_TYPES[extname(file).toLowerCase()] ?? "application/octet-stream"
// only a navigation gets the hot-reload client. A component is fetched by
// the runtime (sec-fetch-dest: empty), and it must arrive as written -
// injecting a <script> into it would make the runtime parse and run it
const html = type.startsWith("text/html") && isDocument(req)
const payload = html ? Buffer.from(injectClient(body.toString("utf8"))) : body
head(res, 200, { "content-type": type, "content-length": payload.byteLength })
res.end(payload)
} catch {
head(res, 404, { "content-type": "text/plain; charset=utf-8" }).end("not found")
}
}
// three layers, general to specific, each one free to replace the last: the
// server's own defaults, the configured headers over them, and a hook - which
// saw the request - over those. They go on with setHeader rather than into an
// object, because setHeader is case-insensitive where an object is not: a
// "Cache-Control" replaces the cache-control below it instead of arriving
// beside it, and the same goes for whatever a hook names
const handle = async (req: IncomingMessage, res: ServerResponse) => {
res.setHeader("cache-control", "no-store") // the file on disk is always the truth here
for (const [name, value] of headers) res.setHeader(name, value)
for (const hook of hooks) await hook(req, res)
// a hook can answer the request itself, and one that did needs nothing else
if (res.headersSent || res.writableEnded) return
const pathname = (req.url ?? "/").split(/[?#]/)[0]
if (pathname === CLIENT_URL) {
head(res, 200, { "content-type": "text/javascript; charset=utf-8" })
res.end(CLIENT)
return
}
if (pathname === EVENTS_URL) {
head(res, 200, { "content-type": "text/event-stream", connection: "keep-alive" })
res.write(": jq79\n\n") // opens the stream, so the browser fires onopen
clients.add(res)
req.on("close", () => clients.delete(res))
return
}
await serveStatic(req, res, pathname)
}
const server: Server = createServer((req, res) => {
// a hook is someone's code, and the watch handlers already settled what that
// means around here: report it and stay up. This one owes the browser a
// reply as well, because a socket nobody answers hangs the page
void handle(req, res).catch(error => {
console.error(`jq79 dev: failed to respond to ${req.url}\n`, error)
Eif (!res.headersSent) {
// whatever the hook had said about the bytes, it is not what is being
// sent now - and a content-length it set before throwing would hang this
res.removeHeader("content-length")
res.writeHead(500, { "content-type": "text/plain; charset=utf-8" })
}
Eif (!res.writableEnded) res.end("internal error")
})
})
// --- watching --------------------------------------------------------------
const ignored = (rel: string) =>
rel.split(sep).some(part => part.startsWith(".") || part === "node_modules")
// one save can arrive as several events (a rename plus a change, an editor's
// atomic write); collapsing per file keeps that down to one push
const pending = new Map<string, NodeJS.Timeout>()
// a pattern is written against the cwd (`resolve` reads it the same way), and
// captured here so a later chdir can't move what the globs mean
const cwd = process.cwd()
type Entry = {
patterns: string[]
fn?: WatchHandler
batch: Set<string>
timer?: NodeJS.Timeout
running: boolean
}
const entries: Entry[] = (options.watch ?? []).map(entry => ({
patterns: [entry.pattern].flat(),
fn: entry.fn,
batch: new Set(),
running: false,
}))
const claims = (entry: Entry, file: string) =>
entry.patterns.some(pattern =>
matchesGlob(isAbsolute(pattern) ? posix(file) : posix(relative(cwd, file)), pattern),
)
// a burst is one call: the handler is a build step, and building once per file
// of a save that touched four is three builds nobody asked for
const collect = (entry: Entry, file: string) => {
entry.batch.add(file)
clearTimeout(entry.timer)
entry.timer = setTimeout(() => void fire(entry), 30)
}
const fire = async (entry: Entry) => {
Iif (entry.running || !entry.batch.size) return
const files = [...entry.batch]
entry.batch.clear()
entry.running = true
try {
await entry.fn?.(files)
} catch (error) {
// a handler is someone's build script, and a build that fails is a normal
// morning. Reporting it and staying up beats taking the server with it
console.error(`jq79 dev: watch handler for ${entry.patterns.join(", ")} failed\n`, error)
} finally {
entry.running = false
Iif (entry.batch.size) void fire(entry) // saved again while it ran
}
}
// `dir` is the directory whose watcher reported this - only needed for the
// macOS quirk below, and only when the file turns out not to exist
const changed = async (file: string, dir: string) => {
// where the browser knows the file from, which only exists for a file under
// the served root: a watched path outside it is served from nowhere, so
// there is no url for the runtime to match an instance against
const rel = relative(root, file)
const served = !!rel && !rel.startsWith("..")
let src: string | null = null
try {
// a directory changes whenever anything inside it does, and the event for
// the file itself is already on its way - acting on both would reload the
// page every time a component is saved
if ((await stat(file)).isDirectory()) return
if (served && file.endsWith(".html")) src = await readFile(file, "utf8")
} catch {
// gone: deleted, or renamed away - and there is nothing to swap in, so the
// page has to reload. Unless it was never there: macOS reports a change to
// a watched directory *itself* under its own basename, which resolves to a
// path inside it that does not exist
if (file === join(dir, basename(dir))) return
}
// every entry that names this file gets it, wherever the file lives. What
// the root does with its own files is not up for negotiation: no pattern can
// switch hot reload off, so a handler can never cost you the thing you came
// for by matching more than its author meant it to
const claimed = entries.filter(entry => claims(entry, file))
claimed.forEach(entry => entry.fn && collect(entry, file))
if (served) {
// the url is the one the component was served from, because that is what
// the runtime resolves its instances' filenames against
const url = "/" + posix(rel)
if (src === null) send("reload", { url })
else send("update", { url, src })
return
}
// outside the root a handler *is* the answer: it ran, and whatever it writes
// into the served directory comes back round as a change of its own, with a
// url. An entry with no handler is asking for the page, and gets a path
// relative to the root - the client only logs it, and an absolute one would
// publish the machine's layout to the page
if (claimed.some(entry => !entry.fn)) send("reload", { url: posix(rel) })
}
const queue = (file: string, dir: string) => {
clearTimeout(pending.get(file))
pending.set(file, setTimeout(() => {
pending.delete(file)
void changed(file, dir)
}, 30))
}
const watchers: FSWatcher[] = []
// a directory is watched whole. A single file is watched through the directory
// it sits in (`only` filtering the rest back out), because a watcher on a file
// holds its inode, and an editor's atomic save renames a new one over it - the
// watcher survives as a handle on a file nothing will ever write to again
const watchTree = (dir: string, only?: string) => {
watchers.push(watch(dir, { recursive: !only }, (_event, filename) => {
Iif (!filename) return
const file = resolve(dir, filename.toString())
const rel = relative(dir, file)
Iif (!rel || rel.startsWith("..")) return
if (only ? rel !== only : ignored(rel)) return
queue(file, dir)
}))
}
// a glob is a filter and a watcher needs a directory to open, so the watch
// starts at the literal head of the pattern - everything before the first
// magic character. "styles/**/*.scss" opens styles/, "**/*.scss" opens the cwd
const literalHead = (pattern: string) => {
const parts = pattern.split("/")
const magic = parts.findIndex(part => /[*?[\]{}!]/.test(part))
return resolve(magic === -1 ? pattern : parts.slice(0, magic).join("/") || ".")
}
// the patterns are resolved like rootDir, against the cwd, and all checked
// before anything is watched: a path that isn't there is a typo, and a watcher
// that silently isn't running is worse than a server that won't start
const extra = new Map<string, { dir: string; only?: string }>()
for (const entry of entries) {
for (const [i, pattern] of entry.patterns.entries()) {
const head = literalHead(pattern)
const info = await stat(head).catch(() => null)
if (!info) throw new Error(`jq79 dev: nothing to watch at ${head}`)
// a bare directory means everything under it, which is what it looks like
// it means - as a pattern it would watch the directory and match nothing
// in it, and the mistake is invisible until a save doesn't fire
if (info.isDirectory() && head === resolve(pattern)) {
entry.patterns[i] = pattern.replace(/\/+$/, "") + "/**"
}
// real paths on both sides, so a symlink pointing out of the root reads as
// what it is - outside, and not covered by the recursive watch below
const real = await realpath(head)
if (real === root || real.startsWith(root + sep)) continue // already watched
const watched = info.isDirectory() ? { dir: real } : { dir: dirname(real), only: basename(real) }
extra.set(`${watched.dir}\0${watched.only ?? ""}`, watched) // two patterns can share a head
}
}
watchTree(root)
extra.forEach(({ dir, only }) => watchTree(dir, only))
// proxies and load balancers cut an idle stream; a comment every 30s is the
// conventional way to keep it open. unref'd, so it never holds the process up
const heartbeat = setInterval(() => clients.forEach(client => client.write(": ping\n\n")), 30_000)
heartbeat.unref()
// --- go --------------------------------------------------------------------
await new Promise<void>((done, fail) => {
server.once("error", fail)
server.listen(options.port ?? 4179, host, done)
})
const { port } = server.address() as { port: number }
return {
url: `http://${host}:${port}`,
port,
close: () =>
new Promise(done => {
clearInterval(heartbeat)
watchers.forEach(watcher => watcher.close())
pending.forEach(clearTimeout)
entries.forEach(entry => clearTimeout(entry.timer))
clients.forEach(client => client.end())
clients.clear()
server.close(() => done())
}),
}
}
export default devServer
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