Function proxyWebSocketRequest

packages/server/src/routes/previews.ts:416–474

(
  req: IncomingMessage,
  socket: Duplex,
  head: Buffer,
  workspaceId: string,
  target: NormalizedPreviewTarget,
)

  const head = /<head(?:\s[^>]*)?>/i;
  if (head.test(body)) return body.replace(head, (match) => `${match}${script}`);
  return `${script}${body}`;
}

export function rewritePreviewBody(
  body: string,
  workspaceId: string,
  contentType?: string | string[],
  previewToken?: string | null,
  target?: NormalizedPreviewTarget,
): string {
  const prefix = buildPreviewPathPrefix(workspaceId, previewToken);
  const value = Array.isArray(contentType) ? contentType.join(';') : contentType ?? '';
  const lower = value.toLowerCase();

  let next = body;

  if (lower.includes('text/html')) {
    next = next
      .replace(/(\s(?:src|href|action|poster|data|content)=["'])\/(?!\/|view\/)([^"']*)/gi, `$1${prefix}/$2`)
      .replace(/(\s(?:srcset)=["'])([^"']*)(["'])/gi, (_match, before: string, srcset: string, after: string) => {
        const rewritten = srcset.replace(/(^|,\s*)\/(?!\/|view\/)([^\s,]+)/g, `$1${prefix}/$2`);
        return `${before}${rewritten}${after}`;
      });
  }

  if (lower.includes('text/css') || lower.includes('text/html')) {
    next = next.replace(/url\((['"]?)\/(?!\/|view\/)([^)'"]+)\1\)/g, `url($1${prefix}/$2$1)`);
  }

  if (lower.includes('javascript') || lower.includes('ecmascript') || lower.includes('text/html')) {
    next = rewriteJavaScriptRouterBasenameDefaults(next, prefix);
    next = rewriteJavaScriptPathLiterals(next, prefix);
  }

  if (lower.includes('text/html') && target) {
    next = injectPreviewRuntimeBridge(next, prefix, target);
  }

  return next;
}

function requestBodyBuffer(request: FastifyRequest): Buffer | null {
  const method = request.method.toUpperCase();
  if (method === 'GET' || method === 'HEAD') return null;

  const body = request.body;
  if (body === undefined || body === null) return null;
  if (Buffer.isBuffer(body)) return body;
  if (typeof body === 'string') return Buffer.from(body);
  return Buffer.from(JSON.stringify(body));
}

async function proxyHttpRequest(
  request: FastifyRequest,
  response: ServerResponse,
  workspaceId: string,
  target: NormalizedPreviewTarget,
  previewToken?: string | null,