Middleware 是现代 Web 框架中必不可少的一部分。通过 Middleware 可以单独处理 Request 和 Response，极其方便。

Middleware

基本用法

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SampleMiddleware.swift

import Vapor
import HTTP

class SampleMiddleware: Middleware {

    func respond(to request: Request, chainingTo chain: Responder) throws -> Response {
        // You can manipulate the request before calling the handler
        // and abort early if necessary, a good injection point for
        // handling auth.

        // 此处可统一处理 Request 请求

        let response = try chain.respond(to: request)

        // 此处可统一处理 Response 响应

        // You can also manipulate the response to add headers
        // cookies, etc.

        return response

        // Vapor Middleware is based on S4 Middleware.
        // This means you can share it with any other project
        // that uses S4 Middleware. 
    }

}

main.swift

drop.middleware.append(SampleMiddleware())

每次 Request 和 Response 都将会响应到 SampleMiddleware 中的 respond 方法。

示例1

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如果想给所有 API 的 Response 增加一个版本号字段，可直接在 SampleMiddleware 中添加代码： response.headers["Api_Version"] = "v1" 即可，而无需在每个 Response 中进行设置。

import Vapor
import HTTP

class SampleMiddleware: Middleware {

    func respond(to request: Request, chainingTo chain: Responder) throws -> Response {
        
        let response = try chain.respond(to: request)

        response.headers["Api_Version"] = "v1"

        return response
    }

}

示例2

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有些 API 需要登录后才能调用，这里涉及到用户鉴权的问题，可通过 Middleware 统一处理 token 异常情况，而无需在每个 Response 中处理。

定义异常类型

enum ZException: Error {
    case ERROR_AUTH_TOKEN_INVALID
}

ERROR_AUTH_TOKEN_INVALID 异常类型统一处理

import Vapor
import HTTP

class SampleMiddleware: Middleware {

    func respond(to request: Request, chainingTo chain: Responder) throws -> Response {
        do {
            return try chain.respond(to: request)
        } catch ZException.ERROR_AUTH_TOKEN_INVALID {
            throw Abort.custom(status: .unauthorized, message: "ERROR_AUTH_TOKEN_INVALID")
        }
    }

}

当检测到 token 无效时，只需要抛出 ERROR_AUTH_TOKEN_INVALID 异常即可。

throw ZException.ERROR_AUTH_TOKEN_INVALID

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