Forward Proxy and Reverse Proxy

Forward proxy

A forward proxy is a special network service that allows a network terminal (usually a client) to make a non-direct connection with another network terminal (usually a server) through this service. Some network devices such as gateways and routers have network proxy functions. Proxy services are generally considered to be beneficial to safeguard the privacy or security of network terminals and prevent attacks.

A complete proxy request process is that the client first creates a connection to the proxy server, and then requests to create a connection to the target server, or to obtain the specified resources of the target server, according to the proxy protocol used by the proxy server.

Install

Hertz has a built-in function for accessing a forward proxy.

Definition

// Proxy struct, which selects the proxy uri to access based on the request
type Proxy func(*protocol.Request) (*protocol.URI, error)

// ProxyURI is used to generate a Proxy that only returns a fixed proxy uri
func ProxyURI(fixedURI *protocol.URI) Proxy

// SetProxy is used to set the proxy of the client, after setting, the client will build concatenated requests with the proxy
func (c *Client) SetProxy(p protocol.Proxy)

Example

package main

import (
    "context"

    "github.com/cloudwego/hertz/pkg/app/client"
    "github.com/cloudwego/hertz/pkg/protocol"
)

func main() {
    proxyURL := "http://<__user_name__>:<__password__>@<__proxy_addr__>:<__proxy_port__>"

    // Convert the proxy uri to *protocol.URI
    parsedProxyURL := protocol.ParseURI(proxyURL)

    c, err := client.NewClient()
    if err != nil {
       return
    }

    // Set proxy
    c.SetProxy(protocol.ProxyURI(parsedProxyURL))

    upstreamURL := "http://google.com"
    _, body, _ := client.Get(context.Background(), nil, upstreamURL)
}

The client does not support TLS by default, if you want to access https addresses, you should use the standard library.

c, err := client.NewClient(client.WithDialer(standard.NewDialer()))

If a certificate error is reported, certificate verification needs to be skipped.

clientCfg := &tls.Config{
    InsecureSkipVerify: true,
}
c, err := client.NewClient(client.WithTLSConfig(clientCfg), client.WithDialer(standard.NewDialer()))

Reverse proxy

In computer networks, a reverse proxy is an application that sits in front of back-end applications and forwards client (e.g. browser) requests to those applications.

Reverse proxies help increase scalability, performance, resilience and security. The resources returned to the client appear as if they originated from the web server itself.

Install

go get github.com/hertz-contrib/reverseproxy

Specific implementation

type ReverseProxy struct {
    client *client.Client

    // target is set as a reverse proxy address
    target string

    // director must be a function which modifies the request
    // into a new request. Its response is then redirected
    // back to the original client unmodified.
    // director must not access the provided Request
    // after returning.
    director func (*protocol.Request)

    // modifyResponse is an optional function that modifies the
    // Response from the backend. It is called if the backend
    // returns a response at all, with any HTTP status code.
    // If the backend is unreachable, the optional errorHandler is
    // called without any call to modifyResponse.
    //
    // If modifyResponse returns an error, errorHandler is called
    // with its error value. If errorHandler is nil, its default
    // implementation is used.
    modifyResponse func(*protocol.Response) error

    // errorHandler is an optional function that handles errors
    // reaching the backend or errors from modifyResponse.
    // If nil, the default is to log the provided error and return
    // a 502 Status Bad Gateway response.
    errorHandler func(*app.RequestContext, error)
}

// NewSingleHostReverseProxy returns a new ReverseProxy that routes
// URLs to the scheme, host, and base path provided in target. If the
// target's path is "/base" and the incoming request was for "/dir",
// the target request will be for /base/dir.
// NewSingleHostReverseProxy does not rewrite the Host header.
// To rewrite Host headers, use ReverseProxy directly with a custom
// director policy.
func NewSingleHostReverseProxy(target string, opts ...config.Option) (*reverseProxy, error)
  • For NewSingleHostReverseProxy function, if no config.ClientOption is passed it will use the default global client.Client instance. When passing config.ClientOption it will initialize a local client.Client instance. Using ReverseProxy.SetClient if there is need for shared customized client.Client instance.
  • The reverse proxy resets the header of the response, any such modifications before the request is made will be discarded.

We provide the SetXxx() method for setting private properties

MethodDescription
SetDirectoruse to customize protocol.Request
SetClientuse to customize client
SetModifyResponseuse to customize modify response function
SetErrorHandleruse to customize error handler

Example

package main

import (
    "context"
    
    "github.com/cloudwego/hertz/pkg/app"
    "github.com/cloudwego/hertz/pkg/app/server"
    "github.com/cloudwego/hertz/pkg/common/utils"
    "github.com/hertz-contrib/reverseproxy"
)

func main() {
    h := server.Default(server.WithHostPorts("127.0.0.1:8000"))
    // set target address
    proxy, err := reverseproxy.NewSingleHostReverseProxy("http://127.0.0.1:8000/proxy")
    if err != nil {
        panic(err)
    }
    h.GET("/proxy/backend", func(cc context.Context, c *app.RequestContext) {
        c.JSON(200, utils.H{
            "msg": "proxy success!!",
        })
    })
    
    h.GET("/backend", proxy.ServeHTTP)
    h.Spin()
}

FAQ

How to proxy HTTPS

Netpoll does not support TLS, Client needs to use standard network library.

Proxying HTTPS requires some additional configuration.

  • Use WithDialer in the NewSingleHostReverseProxy method to pass standard.NewDialer() to specify the standard network library.
  • Use SetClient to set up a Hertz Client using the standard networking library.

How to use with middleware

You can also use ReverseProxy.ServeHTTP in the hertz handler to implement complex requirements instead of registering ReverseProxy.ServeHTTP directly to the route.

Example Code

package main

import (
    //...
)

func main() {
    //...
    r.Use(func(c context.Context, ctx *app.RequestContext) {
        if ctx.Query("country") == "cn" {
            proxy.ServeHTTP(c, ctx)
            ctx.Response.Header.Set("key", "value")
            ctx.Abort()
        } else {
            ctx.Next(c)
        }
    })
    //...
}

More Examples

PurposeSample Code
Proxy tlscode
Using service discoverycode
Use with middlewarecode

For more usages, please refer to the following examples.