Support running multiple dev instances on offset ports #1495
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,115 @@ | ||
| #!/usr/bin/env node | ||
| // Assigns a unique PORT_OFFSET so multiple instances of this project can run in parallel. | ||
| // The *_PORT values in .env embed the offset digit via ${PORT_OFFSET} (e.g. API_PORT=4${PORT_OFFSET}00). | ||
| // Prefers offset 0 (the .env default) and only writes a PORT_OFFSET override to .env.local when needed. | ||
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| import { existsSync, readFileSync, writeFileSync } from "node:fs"; | ||
| import { createServer } from "node:net"; | ||
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| const ENV_FILE = ".env"; | ||
| const ENV_LOCAL_FILE = ".env.local"; | ||
| const PLACEHOLDER = "${PORT_OFFSET}"; | ||
| const MAX_OFFSET = 9; | ||
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| function fail(message: string): never { | ||
| console.error(`Error: ${message}`); | ||
| process.exit(1); | ||
| } | ||
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| function readPortEntries(): { name: string; template: string }[] { | ||
| if (!existsSync(ENV_FILE)) { | ||
| fail(`No ${ENV_FILE} file found in ${process.cwd()}`); | ||
| } | ||
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| return readFileSync(ENV_FILE, "utf8") | ||
| .split("\n") | ||
| .map((line) => /^([A-Z_]+_PORT)=(\S+)$/.exec(line.trim())) | ||
| .filter((match) => match !== null) | ||
| .map((match) => ({ name: match[1], template: match[2] })); | ||
| } | ||
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| function portForOffset(entry: { name: string; template: string }, offset: number): number { | ||
| const value = entry.template.replaceAll(PLACEHOLDER, String(offset)); | ||
| if (!/^\d+$/.test(value)) { | ||
| fail(`${entry.name}=${entry.template} in ${ENV_FILE} does not resolve to a number (expected digits and ${PLACEHOLDER} only)`); | ||
| } | ||
| return Number(value); | ||
| } | ||
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| // Node sets SO_REUSEADDR, so a wildcard bind coexists with specific-address binds (and vice versa). | ||
| // Probe all three addresses to also catch localhost-only listeners like Vite's dev server. | ||
| async function portIsFree(port: number): Promise<boolean> { | ||
| for (const host of ["0.0.0.0", "127.0.0.1", "::1"]) { | ||
| const free = await new Promise<boolean>((resolve) => { | ||
| const server = createServer(); | ||
| server.once("error", (error: NodeJS.ErrnoException) => resolve(error.code !== "EADDRINUSE")); | ||
| server.once("listening", () => server.close(() => resolve(true))); | ||
| server.listen(port, host); | ||
| }); | ||
| if (!free) return false; | ||
| } | ||
| return true; | ||
| } | ||
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| async function findFreeOffset(entries: { name: string; template: string }[]): Promise<number> { | ||
| for (let offset = 0; offset <= MAX_OFFSET; offset++) { | ||
| let conflict: { name: string; port: number } | undefined; | ||
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| for (const entry of entries) { | ||
| const port = portForOffset(entry, offset); | ||
| if (!(await portIsFree(port))) { | ||
| conflict = { name: entry.name, port }; | ||
| break; | ||
| } | ||
| } | ||
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| if (!conflict) return offset; | ||
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| console.error(`Offset ${offset} has a port conflict (${conflict.name}=${conflict.port} in use), trying next...`); | ||
| } | ||
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| fail(`Could not find a free port offset (tried 0-${MAX_OFFSET})`); | ||
| } | ||
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| function writeEnvLocal(entries: { name: string; template: string }[], offset: number): void { | ||
| const existingLines = existsSync(ENV_LOCAL_FILE) ? readFileSync(ENV_LOCAL_FILE, "utf8").split("\n") : []; | ||
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| // Drop any existing PORT_OFFSET and *_PORT assignments from .env.local to avoid duplicates/stale overrides | ||
| const names = new Set(["PORT_OFFSET", ...entries.map((entry) => entry.name)]); | ||
| const keptLines = existingLines.filter((line) => !names.has(line.split("=")[0].trim())); | ||
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| while (keptLines.length > 0 && keptLines[keptLines.length - 1] === "") { | ||
| keptLines.pop(); | ||
| } | ||
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| // Offset 0 means the base ports are free, so no override is written and the .env default applies | ||
| const lines = offset === 0 ? keptLines : [...keptLines, `PORT_OFFSET=${offset}`]; | ||
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| if (lines.length === 0 && existingLines.length === 0) return; | ||
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| writeFileSync(ENV_LOCAL_FILE, lines.length > 0 ? `${lines.join("\n")}\n` : ""); | ||
| } | ||
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| async function main(): Promise<void> { | ||
| const entries = readPortEntries(); | ||
| if (entries.length === 0) { | ||
| fail(`No *_PORT entries found in ${ENV_FILE}`); | ||
| } | ||
| if (!entries.some((entry) => entry.template.includes(PLACEHOLDER))) { | ||
| fail(`No *_PORT entry in ${ENV_FILE} contains ${PLACEHOLDER}, so ports cannot be offset`); | ||
| } | ||
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| const offset = await findFreeOffset(entries); | ||
| writeEnvLocal(entries, offset); | ||
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| if (offset === 0) { | ||
| console.error(`All base ports are free, using PORT_OFFSET=0 (${ENV_FILE} default applies)`); | ||
| } else { | ||
| console.error(`PORT_OFFSET=${offset} written to ${ENV_LOCAL_FILE}`); | ||
| } | ||
| } | ||
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| main().catch((error) => { | ||
| console.error(error); | ||
| process.exit(1); | ||
| }); | ||
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We could use the get-port package for this, but the custom implementation is fine as well.