import type { MiddlewareHandler } from '../../hono.ts' type CORSOptions = { origin: string | string[] allowMethods?: string[] allowHeaders?: string[] maxAge?: number credentials?: boolean exposeHeaders?: string[] } export const cors = (options?: CORSOptions): MiddlewareHandler => { const defaults: CORSOptions = { origin: '*', allowMethods: ['GET', 'HEAD', 'PUT', 'POST', 'DELETE', 'PATCH'], allowHeaders: [], exposeHeaders: [], } const opts = { ...defaults, ...options, } return async (c, next) => { await next() function set(key: string, value: string) { c.res.headers.append(key, value) } if (typeof opts.origin === 'string') { set('Access-Control-Allow-Origin', opts.origin) } else if (opts.origin.length > 0) { const origin = c.req.headers.get('origin') const allowedOrigin = origin && opts.origin.includes(origin) ? origin : opts.origin[0] set('Access-Control-Allow-Origin', allowedOrigin) } // Suppose the server sends a response with an Access-Control-Allow-Origin value with an explicit origin (rather than the "*" wildcard). // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Allow-Origin if (opts.origin !== '*') { set('Vary', 'Origin') } if (opts.credentials) { set('Access-Control-Allow-Credentials', 'true') } if (opts.exposeHeaders?.length) { set('Access-Control-Expose-Headers', opts.exposeHeaders.join(',')) } if (c.req.method === 'OPTIONS') { // Preflight if (opts.maxAge != null) { set('Access-Control-Max-Age', opts.maxAge.toString()) } if (opts.allowMethods?.length) { set('Access-Control-Allow-Methods', opts.allowMethods.join(',')) } let headers = opts.allowHeaders if (!headers?.length) { const requestHeaders = c.req.headers.get('Access-Control-Request-Headers') if (requestHeaders) { headers = requestHeaders.split(/\s*,\s*/) } } if (headers?.length) { set('Access-Control-Allow-Headers', headers.join(',')) set('Vary', 'Access-Control-Request-Headers') } c.res.headers.delete('Content-Length') c.res.headers.delete('Content-Type') c.res = new Response(null, { headers: c.res.headers, status: 204, statusText: c.res.statusText, }) } } }