Function writeHead

lib/_http_server.js:408–499

(statusCode, reason, obj)

ServerResponse.prototype.writeHead = writeHead;
function writeHead(statusCode, reason, obj) {

  if (this._header) {
    throw new ERR_HTTP_HEADERS_SENT('write');
  }

  const originalStatusCode = statusCode;

  statusCode |= 0;
  if (statusCode < 100 || statusCode > 999) {
    throw new ERR_HTTP_INVALID_STATUS_CODE(originalStatusCode);
  }


  if (typeof reason === 'string') {
    // writeHead(statusCode, reasonPhrase[, headers])
    this.statusMessage = reason;
  } else {
    // writeHead(statusCode[, headers])
    this.statusMessage ||= STATUS_CODES[statusCode] || 'unknown';
    obj ??= reason;
  }
  this.statusCode = statusCode;

  let headers;
  if (this[kOutHeaders]) {
    // Slow-case: when progressive API and header fields are passed.
    let k;
    if (ArrayIsArray(obj)) {
      if (obj.length % 2 !== 0) {
        throw new ERR_INVALID_ARG_VALUE('headers', obj);
      }

      // Headers in obj should override previous headers but still
      // allow explicit duplicates. To do so, we first remove any
      // existing conflicts, then use appendHeader.

      for (let n = 0; n < obj.length; n += 2) {
        k = obj[n + 0];
        this.removeHeader(k);
      }

      for (let n = 0; n < obj.length; n += 2) {
        k = obj[n + 0];
        if (k) this.appendHeader(k, obj[n + 1]);
      }
    } else if (obj) {
      const keys = ObjectKeys(obj);
      // Retain for(;;) loop for performance reasons
      // Refs: https://github.com/nodejs/node/pull/30958
      for (let i = 0; i < keys.length; i++) {
        k = keys[i];
        if (k) this.setHeader(k, obj[k]);
      }
    }
    // Only progressive api is used
    headers = this[kOutHeaders];
  } else {