response.writeHead(statusCode[, statusMessage][, headers])

• statusCode <number>
• statusMessage <string>
• headers <Object> | <Array>
• 返回: <http2.Http2ServerResponse>

向请求发送响应头。 状态码是 3 位的 HTTP 状态码，如 404。 最后一个参数 headers 是响应头。

返回对 Http2ServerResponse 的引用，以便可以链式调用。

为了与 HTTP/1 兼容，可以将人类可读的 statusMessage 作为第二个参数传入。 但是，由于 statusMessage 在 HTTP/2 中没有意义，该参数将无效并且将触发进程警告。

const body = 'hello world';
response.writeHead(200, {
  'Content-Length': Buffer.byteLength(body),
  'Content-Type': 'text/plain; charset=utf-8',
});

Content-Length 以字节而不是字符给出。 Buffer.byteLength() API 可用于确定给定编码中的字节数。 在出站消息上，Node.js 不会检查 Content-Length 和正在传输的正文的长度是否相等。 但是，在接收消息时，Node.js 会在 Content-Length 与实际负载大小不匹配时自动拒绝消息。

在调用 response.end() 之前，此方法最多可以在一条消息上调用一次。

如果在调用此之前调用了 response.write() 或 response.end()，则将计算隐式/可变的标头并调用此函数。

当标头已使用 response.setHeader() 设置时，则它们将与任何传给 response.writeHead() 的标头合并，其中传给 response.writeHead() 的标头优先。

// 返回 content-type = text/plain
const server = http2.createServer((req, res) => {
  res.setHeader('Content-Type', 'text/html; charset=utf-8');
  res.setHeader('X-Foo', 'bar');
  res.writeHead(200, { 'Content-Type': 'text/plain; charset=utf-8' });
  res.end('ok');
});

尝试设置包含无效字符的标头字段名称或值将导致抛出 TypeError。

• statusCode <number>
• statusMessage <string>
• headers <Object> | <Array>
• Returns: <http2.Http2ServerResponse>

Sends a response header to the request. The status code is a 3-digit HTTP status code, like 404. The last argument, headers, are the response headers.

Returns a reference to the Http2ServerResponse, so that calls can be chained.

For compatibility with HTTP/1, a human-readable statusMessage may be passed as the second argument. However, because the statusMessage has no meaning within HTTP/2, the argument will have no effect and a process warning will be emitted.

const body = 'hello world';
response.writeHead(200, {
  'Content-Length': Buffer.byteLength(body),
  'Content-Type': 'text/plain; charset=utf-8',
});

Content-Length is given in bytes not characters. The Buffer.byteLength() API may be used to determine the number of bytes in a given encoding. On outbound messages, Node.js does not check if Content-Length and the length of the body being transmitted are equal or not. However, when receiving messages, Node.js will automatically reject messages when the Content-Length does not match the actual payload size.

This method may be called at most one time on a message before response.end() is called.

If response.write() or response.end() are called before calling this, the implicit/mutable headers will be calculated and call this function.

When headers have been set with response.setHeader(), they will be merged with any headers passed to response.writeHead(), with the headers passed to response.writeHead() given precedence.

// Returns content-type = text/plain
const server = http2.createServer((req, res) => {
  res.setHeader('Content-Type', 'text/html; charset=utf-8');
  res.setHeader('X-Foo', 'bar');
  res.writeHead(200, { 'Content-Type': 'text/plain; charset=utf-8' });
  res.end('ok');
});

Attempting to set a header field name or value that contains invalid characters will result in a TypeError being thrown.