Update docs to guide cases with pre-parsed body

Author: Hyunje Jun

docs/pages/api-reference/client.md

@@ -7,9 +7,9 @@ corresponding to [messaging APIs](https://devdocs.line.me/en/#messaging-api).
 
 ``` typescript
 class Client {
-  public config: Config
+  public config: ClientConfig
 
-  constructor(config: Config)
+  constructor(config: ClientConfig)
 
   pushMessage(to: string, messages: Message | Message[]): Promise<{}>
   replyMessage(replyToken: string, messages: Message | Message[]): Promise<{}>
@@ -25,12 +25,12 @@ class Client {
 refer to [Send message object](https://devdocs.line.me/en/#send-message-object)
 of the official document.
 
-`Config` type is like below.
+`ClientConfig` type is like below, except that it also allows fields
+from [MiddlewareConfig](./middleware.md) too.
 
 ``` typescript
-type Config = {
+type ClientConfig = {
   channelAccessToken: string,
-  channelSecret?: string,
 }
 ```
 

docs/pages/api-reference/middleware.md

@@ -6,14 +6,14 @@ by several Node.js web frameworks such as [Express](https://expressjs.com/).
 #### Type signature
 
 ``` typescript
-function middleware(config: Config): Middleware
+function middleware(config: MiddlewareConfig): Middleware
 ```
 
-The types of `Config` and `Middleware` are like below.
+The types of `MiddlewareConfig` and `Middleware` are like below, except that the config allows
+fields from [ClientConfig](./client.md) too.
 
 ``` typescript
-type Config = {
-  channelAccessToken?: string,
+type MiddlewareConfig = {
   channelSecret: string,
 }
 
@@ -44,8 +44,12 @@ app.post('/webhook', middleware(config), (req, res) => {
 
 The middleware returned by `middleware()` parses body and checks signature
 validation, so you do not need to use [`validateSignature()`](./validate-signature.md)
-directly. Also, you do not need to use [body-parser](https://github.com/expressjs/body-parser)
-to parse webhook events. If you have a reason to use body-parser for other
+directly.
+
+You do not need to use [body-parser](https://github.com/expressjs/body-parser)
+to parse webhook events, as `middleware()` embeds body-parser and parses them to
+objects. Please keep in mind that it will not process requests without
+`X-Line-Signature` header. If you have a reason to use body-parser for other
 routes, *please do not use it before the LINE middleware*. body-parser parses
 the request body up and the LINE middleware cannot parse it afterwards.
 
@@ -59,5 +63,9 @@ app.use(middleware(config))
 app.use(bodyParser.json())
 ```
 
+There are environments where `req.body` is pre-parsed, such as [Firebase Cloud Functions](https://firebase.google.com/docs/functions/http-events).
+If it parses the body into string or buffer, do not worry as the middleware will
+work just fine. If the pre-parsed body is an object, please use [`validateSignature()`](../api-reference/validate-signature.md)
+manually with the raw body.
 
 About building webhook server, please refer to [Webhook](../guide/webhook.md).

docs/pages/guide/webhook.md

@@ -76,9 +76,11 @@ app.listen(8080)
 
 We have imported `middleware` from the package and make the Express app to use
 the middleware. The middlware validates the request and parses webhook event
-object. It internally uses [body-parser](https://github.com/expressjs/body-parser),
-so please beware that it will not work with body parsed already by body-parser.
-Please put `middleware()` upper than any body-parser middleware.
+object. It embeds body-parser and parses them to objects. Please keep in mind
+that it will not process requests without `X-Line-Signature` header. If you have
+a reason to use body-parser for other routes, *please do not use it before the
+LINE middleware*. body-parser parses the request body up and the LINE middleware
+cannot parse it afterwards.
 
 ``` js
 // don't
@@ -90,16 +92,18 @@ app.use(middleware(config))
 app.use(bodyParser.json())
 ```
 
-`middleware()` will work only on requests with `X-Line-Signature`, so other body
-parsers will work well with requests without the signature header.
+There are environments where `req.body` is pre-parsed, such as [Firebase Cloud Functions](https://firebase.google.com/docs/functions/http-events).
+If it parses the body into string or buffer, do not worry as the middleware will
+work just fine. If the pre-parsed body is an object, please use [`validateSignature()`](../api-reference/validate-signature.md)
+manually with the raw body.
 
 ## Error handling
 
 There are two types of errors thrown by the middleware, one is `SignatureValidationFailed`
-and the other is `JSONParseError`. `SignatureValidationFailed` is thrown when a
-request has a wrong signature, which usually means the request is not from the
-official LINE servers. `JSONParseError` occurs when a request body cannot be
-parsed as JSON.
+and the other is `JSONParseError`.
+
+- `SignatureValidationFailed` is thrown when a request has a wrong signature.
+- `JSONParseError` occurs when a request body cannot be parsed as JSON.
 
 For type references of the errors, please refer to [the API reference](../api-reference/exceptions.md).