Correct the type of DispatchOptions["headers"]

According to core/util@parseHeaders, the current behavior is:

- By default, the entry type is a `string`.
- The type turns to a `string[]` when there are duplicated entries.

This behavior is not as same as what `node:http` does currently;
therefore, `IncomingHttpHeaders` can't reflect our parsed data.

This commit attempts to reflect this parsing behavior
by redefining it to `Record<string, string | string[]>`.

Fixed nodejs#1892
The simpler solution of nodejs#1893

Signed-off-by: pan93412 <[email protected]>

docs/api/Dispatcher.md

@@ -74,7 +74,7 @@ Returns: `void | Promise<ConnectData>` - Only returns a `Promise` if no `callbac
 #### Parameter: `ConnectData`
 
 * **statusCode** `number`
-* **headers** `http.IncomingHttpHeaders`
+* **headers** `Record<string, string | string[]>`
 * **socket** `stream.Duplex`
 * **opaque** `unknown`
 
@@ -383,7 +383,7 @@ Extends: [`RequestOptions`](#parameter-requestoptions)
 #### Parameter: PipelineHandlerData
 
 * **statusCode** `number`
-* **headers** `IncomingHttpHeaders`
+* **headers** `Record<string, string | string[]>`
 * **opaque** `unknown`
 * **body** `stream.Readable`
 * **context** `object`
@@ -477,7 +477,7 @@ The `RequestOptions.method` property should not be value `'CONNECT'`.
 #### Parameter: `ResponseData`
 
 * **statusCode** `number`
-* **headers** `http.IncomingHttpHeaders` - Note that all header keys are lower-cased, e. g. `content-type`.
+* **headers** `Record<string, string | string[]>` - Note that all header keys are lower-cased, e. g. `content-type`.
 * **body** `stream.Readable` which also implements [the body mixin from the Fetch Standard](https://fetch.spec.whatwg.org/#body-mixin).
 * **trailers** `Record<string, string>` - This object starts out
   as empty and will be mutated to contain trailers after `body` has emitted `'end'`.
@@ -644,7 +644,7 @@ Returns: `void | Promise<StreamData>` - Only returns a `Promise` if no `callback
 #### Parameter: `StreamFactoryData`
 
 * **statusCode** `number`
-* **headers** `http.IncomingHttpHeaders`
+* **headers** `Record<string, string | string[]>`
 * **opaque** `unknown`
 * **onInfo** `({statusCode: number, headers: Record<string, string | string[]>}) => void | null` (optional) - Default: `null` - Callback collecting all the info headers (HTTP 100-199) received.
 
@@ -853,9 +853,9 @@ Emitted when dispatcher is no longer busy.
 
 ## Parameter: `UndiciHeaders`
 
-* `http.IncomingHttpHeaders | string[] | null`
+* `Record<string, string | string[]> | string[] | null`
 
-Header arguments such as `options.headers` in [`Client.dispatch`](Client.md#clientdispatchoptions-handlers) can be specified in two forms; either as an object specified by the `http.IncomingHttpHeaders` type, or an array of strings. An array representation of a header list must have an even length or an `InvalidArgumentError` will be thrown.
+Header arguments such as `options.headers` in [`Client.dispatch`](Client.md#clientdispatchoptions-handlers) can be specified in two forms; either as an object specified by the `Record<string, string | string[]>` (`IncomingHttpHeaders`) type, or an array of strings. An array representation of a header list must have an even length or an `InvalidArgumentError` will be thrown.
 
 Keys are lowercase and values are not modified.
 

types/dispatcher.d.ts

@@ -1,8 +1,8 @@
 import { URL } from 'url'
 import { Duplex, Readable, Writable } from 'stream'
 import { EventEmitter } from 'events'
-import { IncomingHttpHeaders } from 'http'
 import { Blob } from 'buffer'
+import { IncomingHttpHeaders } from './header'
 import BodyReadable from './readable'
 import { FormData } from './formdata'
 import Errors from './errors'

types/errors.d.ts

@@ -1,4 +1,4 @@
-import {IncomingHttpHeaders} from "http";
+import { IncomingHttpHeaders } from "./header";
 import Client from './client'
 
 export default Errors

types/header.d.ts

@@ -0,0 +1,4 @@
+/**
+ * The header type declaration of `undici`.
+ */
+export type IncomingHttpHeaders = Record<string, string | string[]>;

types/mock-interceptor.d.ts

@@ -1,4 +1,4 @@
-import { IncomingHttpHeaders } from 'http'
+import { IncomingHttpHeaders } from './header'
 import Dispatcher from './dispatcher';
 import { BodyInit, Headers } from './fetch'
 

types/proxy-agent.d.ts

@@ -1,8 +1,7 @@
-import { IncomingHttpHeaders } from 'http'
-
 import Agent from './agent'
 import buildConnector from './connector';
 import Dispatcher from './dispatcher'
+import { IncomingHttpHeaders } from './header'
 
 export default ProxyAgent