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import { readFile, realpath, stat } from "node:fs/promises"
import { watch, type FSWatcher } from "node:fs"
import { basename, extname, join, 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
}
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",
".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"
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 ---------------------------------------------------------------
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 {
res.writeHead(400).end("bad request")
return
}
Iif (file !== root && !file.startsWith(root + sep)) {
res.writeHead(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("/")) {
res.writeHead(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
res.writeHead(200, {
"content-type": type,
"content-length": payload.byteLength,
"cache-control": "no-store", // the file on disk is always the truth here
})
res.end(payload)
} catch {
res.writeHead(404, { "content-type": "text/plain; charset=utf-8" }).end("not found")
}
}
const server: Server = createServer((req, res) => {
const pathname = (req.url ?? "/").split(/[?#]/)[0]
if (pathname === CLIENT_URL) {
res.writeHead(200, { "content-type": "text/javascript; charset=utf-8", "cache-control": "no-store" })
res.end(CLIENT)
return
}
if (pathname === EVENTS_URL) {
res.writeHead(200, {
"content-type": "text/event-stream",
"cache-control": "no-store",
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
}
void serveStatic(req, res, pathname)
})
// --- 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>()
const changed = async (rel: string) => {
const file = join(root, rel)
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 (rel.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
// the watched directory *itself* under its own basename, which resolves to
// a path inside it that does not exist
if (rel === basename(root)) return
}
// 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 })
}
const watcher: FSWatcher = watch(root, { recursive: true }, (_event, filename) => {
Iif (!filename) return
const rel = relative(root, resolve(root, filename.toString()))
Iif (!rel || rel.startsWith("..") || ignored(rel)) return
clearTimeout(pending.get(rel))
pending.set(rel, setTimeout(() => {
pending.delete(rel)
void changed(rel)
}, 30))
})
// 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)
watcher.close()
pending.forEach(clearTimeout)
clients.forEach(client => client.end())
clients.clear()
server.close(() => done())
}),
}
}
export default devServer
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