The `HTTP2_HEADER_*` constants provide names for HTTP/2 pseudo-headers and

known HTTP header names. Using these string constants is optional. For example,

`http2.constants.HTTP2_HEADER_CONTENT_TYPE` is equal to `'content-type'`.

For APIs that accept regular header names,

`http2.constants.HTTP2_HEADER_CONTENT_TYPE`, `'content-type'`, and

`'Content-Type'` have the same effect; Node.js serializes the name in

lower-case.

Regular header constants can be used with the compatibility API wherever the

corresponding literal header name is accepted. In compatibility API request

handlers, prefer `request.method`, `request.authority`, `request.scheme`, and

`request.url` for the corresponding pseudo-headers. Other incoming

pseudo-headers remain available through `request.headers`. Set response status

through `response.statusCode` or the `statusCode` argument to

`response.writeHead()`. Passing `HTTP2_HEADER_STATUS` (`':status'`) to

`response.setHeader()` or in `response.writeHead()`'s headers object throws

`ERR_HTTP2_PSEUDOHEADER_NOT_ALLOWED`. `HTTP2_HEADER_PROTOCOL` is a request

pseudo-header and cannot be sent in a response.

Incoming header object keys are lower-case, so use a constant or a lower-case

literal when accessing them as object properties. Using a constant does not

change header validation, and the availability of a constant does not imply

that the header is valid in every HTTP/2 context. See [HTTP/2 Headers Object][]

and [Invalid character handling in header names and values][] for details about

header casing and validation.

`HTTP2_HEADER_METHOD`, `HTTP2_HEADER_AUTHORITY`, `HTTP2_HEADER_SCHEME`, and

`HTTP2_HEADER_PATH` identify request pseudo-headers. `HTTP2_HEADER_STATUS`

identifies the response pseudo-header. `HTTP2_HEADER_PROTOCOL` identifies the

extended `CONNECT` request pseudo-header. Pseudo-headers are not permitted in

trailers.

| Constant | Value |

| ---------------------------------------- | -------------- |

| `http2.constants.HTTP2_HEADER_STATUS` | `':status'` |

| `http2.constants.HTTP2_HEADER_METHOD` | `':method'` |

| `http2.constants.HTTP2_HEADER_AUTHORITY` | `':authority'` |

| `http2.constants.HTTP2_HEADER_SCHEME` | `':scheme'` |

| `http2.constants.HTTP2_HEADER_PATH` | `':path'` |

| `http2.constants.HTTP2_HEADER_PROTOCOL` | `':protocol'` |

The `HTTP2_HEADER_CONNECTION`, `HTTP2_HEADER_UPGRADE`,

`HTTP2_HEADER_HTTP2_SETTINGS`, `HTTP2_HEADER_KEEP_ALIVE`,

`HTTP2_HEADER_PROXY_CONNECTION`, and `HTTP2_HEADER_TRANSFER_ENCODING`

constants identify connection-specific headers that HTTP/2 does not permit.

`HTTP2_HEADER_TE` is permitted only when its value is `'trailers'`.

| Constant | Value |

| --------------------------------------------------------------- | ------------------------------------ |

| `http2.constants.HTTP2_HEADER_ACCEPT_ENCODING` | `'accept-encoding'` |

| `http2.constants.HTTP2_HEADER_ACCEPT_LANGUAGE` | `'accept-language'` |

| `http2.constants.HTTP2_HEADER_ACCEPT_RANGES` | `'accept-ranges'` |

| `http2.constants.HTTP2_HEADER_ACCEPT` | `'accept'` |

| `http2.constants.HTTP2_HEADER_ACCESS_CONTROL_ALLOW_CREDENTIALS` | `'access-control-allow-credentials'` |

| `http2.constants.HTTP2_HEADER_ACCESS_CONTROL_ALLOW_HEADERS` | `'access-control-allow-headers'` |

| `http2.constants.HTTP2_HEADER_ACCESS_CONTROL_ALLOW_METHODS` | `'access-control-allow-methods'` |

| `http2.constants.HTTP2_HEADER_ACCESS_CONTROL_ALLOW_ORIGIN` | `'access-control-allow-origin'` |

| `http2.constants.HTTP2_HEADER_ACCESS_CONTROL_EXPOSE_HEADERS` | `'access-control-expose-headers'` |

| `http2.constants.HTTP2_HEADER_ACCESS_CONTROL_REQUEST_HEADERS` | `'access-control-request-headers'` |

| `http2.constants.HTTP2_HEADER_ACCESS_CONTROL_REQUEST_METHOD` | `'access-control-request-method'` |

| `http2.constants.HTTP2_HEADER_AGE` | `'age'` |

| `http2.constants.HTTP2_HEADER_AUTHORIZATION` | `'authorization'` |

| `http2.constants.HTTP2_HEADER_CACHE_CONTROL` | `'cache-control'` |

| `http2.constants.HTTP2_HEADER_CONNECTION` | `'connection'` |

| `http2.constants.HTTP2_HEADER_CONTENT_DISPOSITION` | `'content-disposition'` |

| `http2.constants.HTTP2_HEADER_CONTENT_ENCODING` | `'content-encoding'` |

| `http2.constants.HTTP2_HEADER_CONTENT_LENGTH` | `'content-length'` |

| `http2.constants.HTTP2_HEADER_CONTENT_TYPE` | `'content-type'` |

| `http2.constants.HTTP2_HEADER_COOKIE` | `'cookie'` |

| `http2.constants.HTTP2_HEADER_DATE` | `'date'` |

| `http2.constants.HTTP2_HEADER_ETAG` | `'etag'` |

| `http2.constants.HTTP2_HEADER_FORWARDED` | `'forwarded'` |

| `http2.constants.HTTP2_HEADER_HOST` | `'host'` |

| `http2.constants.HTTP2_HEADER_IF_MODIFIED_SINCE` | `'if-modified-since'` |

| `http2.constants.HTTP2_HEADER_IF_NONE_MATCH` | `'if-none-match'` |

| `http2.constants.HTTP2_HEADER_IF_RANGE` | `'if-range'` |

| `http2.constants.HTTP2_HEADER_LAST_MODIFIED` | `'last-modified'` |

| `http2.constants.HTTP2_HEADER_LINK` | `'link'` |

| `http2.constants.HTTP2_HEADER_LOCATION` | `'location'` |

| `http2.constants.HTTP2_HEADER_RANGE` | `'range'` |

| `http2.constants.HTTP2_HEADER_REFERER` | `'referer'` |

| `http2.constants.HTTP2_HEADER_SERVER` | `'server'` |

| `http2.constants.HTTP2_HEADER_SET_COOKIE` | `'set-cookie'` |

| `http2.constants.HTTP2_HEADER_STRICT_TRANSPORT_SECURITY` | `'strict-transport-security'` |

| `http2.constants.HTTP2_HEADER_TRANSFER_ENCODING` | `'transfer-encoding'` |

| `http2.constants.HTTP2_HEADER_TE` | `'te'` |

| `http2.constants.HTTP2_HEADER_UPGRADE_INSECURE_REQUESTS` | `'upgrade-insecure-requests'` |

| `http2.constants.HTTP2_HEADER_UPGRADE` | `'upgrade'` |

| `http2.constants.HTTP2_HEADER_USER_AGENT` | `'user-agent'` |

| `http2.constants.HTTP2_HEADER_VARY` | `'vary'` |

| `http2.constants.HTTP2_HEADER_X_CONTENT_TYPE_OPTIONS` | `'x-content-type-options'` |

| `http2.constants.HTTP2_HEADER_X_FRAME_OPTIONS` | `'x-frame-options'` |

| `http2.constants.HTTP2_HEADER_KEEP_ALIVE` | `'keep-alive'` |

| `http2.constants.HTTP2_HEADER_PROXY_CONNECTION` | `'proxy-connection'` |

| `http2.constants.HTTP2_HEADER_X_XSS_PROTECTION` | `'x-xss-protection'` |

| `http2.constants.HTTP2_HEADER_ALT_SVC` | `'alt-svc'` |

| `http2.constants.HTTP2_HEADER_CONTENT_SECURITY_POLICY` | `'content-security-policy'` |

| `http2.constants.HTTP2_HEADER_EARLY_DATA` | `'early-data'` |

| `http2.constants.HTTP2_HEADER_EXPECT_CT` | `'expect-ct'` |

| `http2.constants.HTTP2_HEADER_ORIGIN` | `'origin'` |

| `http2.constants.HTTP2_HEADER_PURPOSE` | `'purpose'` |

| `http2.constants.HTTP2_HEADER_TIMING_ALLOW_ORIGIN` | `'timing-allow-origin'` |

| `http2.constants.HTTP2_HEADER_X_FORWARDED_FOR` | `'x-forwarded-for'` |

| `http2.constants.HTTP2_HEADER_PRIORITY` | `'priority'` |

| `http2.constants.HTTP2_HEADER_ACCEPT_CHARSET` | `'accept-charset'` |

| `http2.constants.HTTP2_HEADER_ACCESS_CONTROL_MAX_AGE` | `'access-control-max-age'` |

| `http2.constants.HTTP2_HEADER_ALLOW` | `'allow'` |

| `http2.constants.HTTP2_HEADER_CONTENT_LANGUAGE` | `'content-language'` |

| `http2.constants.HTTP2_HEADER_CONTENT_LOCATION` | `'content-location'` |

| `http2.constants.HTTP2_HEADER_CONTENT_MD5` | `'content-md5'` |

| `http2.constants.HTTP2_HEADER_CONTENT_RANGE` | `'content-range'` |

| `http2.constants.HTTP2_HEADER_DNT` | `'dnt'` |

| `http2.constants.HTTP2_HEADER_EXPECT` | `'expect'` |

| `http2.constants.HTTP2_HEADER_EXPIRES` | `'expires'` |

| `http2.constants.HTTP2_HEADER_FROM` | `'from'` |

| `http2.constants.HTTP2_HEADER_IF_MATCH` | `'if-match'` |

| `http2.constants.HTTP2_HEADER_IF_UNMODIFIED_SINCE` | `'if-unmodified-since'` |

| `http2.constants.HTTP2_HEADER_MAX_FORWARDS` | `'max-forwards'` |

| `http2.constants.HTTP2_HEADER_PREFER` | `'prefer'` |

| `http2.constants.HTTP2_HEADER_PROXY_AUTHENTICATE` | `'proxy-authenticate'` |

| `http2.constants.HTTP2_HEADER_PROXY_AUTHORIZATION` | `'proxy-authorization'` |

| `http2.constants.HTTP2_HEADER_REFRESH` | `'refresh'` |

| `http2.constants.HTTP2_HEADER_RETRY_AFTER` | `'retry-after'` |

| `http2.constants.HTTP2_HEADER_TRAILER` | `'trailer'` |

| `http2.constants.HTTP2_HEADER_TK` | `'tk'` |

| `http2.constants.HTTP2_HEADER_VIA` | `'via'` |

| `http2.constants.HTTP2_HEADER_WARNING` | `'warning'` |

| `http2.constants.HTTP2_HEADER_WWW_AUTHENTICATE` | `'www-authenticate'` |

| `http2.constants.HTTP2_HEADER_HTTP2_SETTINGS` | `'http2-settings'` |

res.writeHead(200, {

'Content-Type': 'text/plain; charset=utf-8',

'X-Foo': 'bar',

});

res.writeHead(200, {

'Content-Type': 'text/plain; charset=utf-8',

'X-Foo': 'bar',

});

[Invalid character handling in header names and values]: #invalid-character-handling-in-header-names-and-values