Creating a Golang Reverse Proxy Server from Scratch

A Golang reverse proxy server is a great tool for improving the performance and security of your web applications.

To start, you'll need to import the net/http package, which provides the http.ListenAndServe function that will be used to start the server.

This function takes two arguments: the address to listen on and the handler function.

The handler function is where the magic happens, and it's where you'll configure the reverse proxy behavior.

By using the http.HandlerFunc type, you can create a handler function that will forward requests to the target server.

This approach allows for a high degree of flexibility and customizability.

In the next section, we'll dive deeper into the configuration options available for the handler function.

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To create a simple reverse proxy in Go, you can use the standard library "net/http/httputil" and create a single host reverse proxy.

The code is pretty much self-explanatory if you're from a Go background, and it's all it takes to create a simple reverse proxy.

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Writing a reverse proxy with Gin is also possible, and it involves declaring a catchall route and handling all requests through the reverse proxy.

You can create and run an HTTP server for your reverse proxy by implementing a function called Run, which loads configuration by calling the NewConfiguration function from the config package.

This function creates a new server called mux using the net/http package and registers routes for resources endpoints, allowing the reverse proxy to intercept requests and forward them to their destination URLs.

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The complete code for the reverse proxy is a powerful tool that can be customized to fit your specific needs. It's a good idea to start with the example code provided in the article.

You can create a reverse proxy and its handler by implementing the NewProxy and ProxyRequestHandler functions in the proxy_handlers.go file. This will allow you to create a new proxy and update the HTTP headers to redirect requests coming at a given endpoint to the destination URL.

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The NewProxy function takes a URL and creates a new HTTP reverse proxy, while the ProxyRequestHandler function takes the proxy created by NewProxy, the destination URL, and the endpoint, and returns a new HTTP handler.

To create and run the HTTP server for the reverse proxy, you'll need to implement the Run function in the server.go file. This function loads the configuration from the config package and stores it in a variable called config.

The Run function also creates a new server using the net/http package, registers the /ping route to call the ping handler, and iterates through the resources endpoints to register them into the router. This is where the magic of the reverse proxy happens, allowing you to forward requests to the destination URL.

To make the reverse proxy work, you'll also need to implement the healthcheck handler in the healthcheck.go file. This handler iterates through each resource in the config.yaml file, creates a new proxy using the Newproxy function, and registers the resource endpoint to the handler returned by the ProxyRequestHandler function.

The config.yaml file is where you'll define the parameters for the reverse proxy, including the list of resources and their corresponding destination URLs. This is where you can tune the reverse proxy to fit your specific needs without modifying the code.

By following these steps, you'll have a complete reverse proxy implementation that you can customize to fit your needs.

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To create and run an HTTP server for your reverse proxy, you'll need to implement the Run function in your server package. This function will load the configuration and create a new server using the net/http package.

In the internal/server/server.go file, you'll create a function called Run that loads the configuration by calling the NewConfiguration function from the config package. You'll then create a new server called mux and register a route called /ping to call your http handler ping.

You'll also iterate through the resources endpoints and register them into your router. This will allow your reverse proxy to intercept requests and forward them to their destination URL. For example, when someone tries to access http://localhost:8080/server1, your reverse proxy will forward the request to http://localhost:9001.

The Run function will return an error, so be sure to handle it properly. You can start the server by calling http.ListenAndServe. If everything works out well, you'll return nil; otherwise, you'll return an error.

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To quickly implement your healthcheck handler, you'll need to create a new file called healthcheck.go in the internal/server directory. This handler will iterate through each resource in the config.yaml file and register a handler for each endpoint.

For each resource, you'll take its destination URL and parse it using the url package. This is necessary because the function to create a new proxy will take a *url.URL as an argument. You'll then call the Newproxy function with the parsed URL as input and register the resource.Endpoint to the handler returned by your ProxyRequestHandler.

By following these steps, you'll be able to create and run an HTTP server for your reverse proxy. Just remember to handle any errors that may occur and to test your server thoroughly.

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You can modify the response from the server by using the HttpUtil reverse proxy, which provides a simple mechanism to cache or change the response based on your use cases.

The `modifyResponse` method allows you to set a custom header, read the response body, make changes, cache it, and then set it back for the client.

To use the `modifyResponse` method, you can write a function to modify the response of your ReverseProxy instance. For example, you can add a Server header to all responses.

Here are some key things to keep in mind when using `modifyResponse`:

Alternatively, you can use a middleware to change the response.

The SetURL method is a powerful tool for modifying requests. It allows you to route the outbound request to a specific scheme, host, and base path.

To use SetURL, you need to provide a target URL with a scheme, host, and base path. If the target's path is "/base" and the incoming request was for "/dir", the target request will be for "/base/dir".

You can use SetURL to join the incoming path with the target path, or you can set the URL directly to avoid joining the paths. To preserve the inbound request's Host header, you can use the default behavior of NewSingleHostReverseProxy.

SetURL also rewrites the outbound Host header to match the target's host. This can be useful if you need to update the Host header for the target request.

The SetXForwarded function is a game-changer when it comes to modifying client requests. It sets the X-Forwarded-For, X-Forwarded-Host, and X-Forwarded-Proto headers of the outbound request.

The X-Forwarded-For header is set to the client IP address. This is useful for tracking the origin of requests.

The X-Forwarded-Host header is set to the host name requested by the client. This ensures that the correct host is used for the outbound request.

The X-Forwarded-Proto header is set to "http" or "https", depending on whether the inbound request was made on a TLS-enabled connection.

If the outbound request contains an existing X-Forwarded-For header, SetXForwarded appends the client IP address to it. This allows you to track multiple hops in the request chain.

Here are the details of the headers set by SetXForwarded:

To set up a reverse proxy in Go, you'll need to create a new instance of the http.Server struct and pass the proxy handler as the Handler for the http.DefaultServeMux.

The proxy handler is typically created using the http.HandlerFunc function, which takes a single argument - the handler function to be proxied.

In the example code, the proxy handler is created using the http.HandlerFunc function, passing the handler function as an argument.

You'll also need to configure the reverse proxy to forward requests to the correct backend server, which can be done using the http.Request object.

To forward requests, you'll need to set the URL of the backend server in the Request object using the http.Request.URL = url.Parse method.

In the example code, the URL of the backend server is set using the url.Parse method, which takes the URL of the backend server as an argument.

The reverse proxy also needs to be configured to handle HTTPS requests, which can be done by setting the TLS configuration using the http.Server.TLSConfig field.

In the example code, the TLS configuration is set using the tls.Config struct, which takes the certificate and key as arguments.

The reverse proxy can also be configured to handle multiple backend servers, which can be done by creating multiple instances of the proxy handler and registering them with the http.DefaultServeMux.

This allows you to handle requests to different backend servers based on the URL or other request attributes.

In the example code, multiple instances of the proxy handler are created and registered with the http.DefaultServeMux, allowing you to handle requests to different backend servers.

In Go, a server is created using the net/http package, as seen in internal/server/server.go, where a new server called mux is created and routes are registered.

The Run function loads the configuration from config.go and stores it in a variable called config. It then creates a new server and registers routes for each resource endpoint.

A reverse proxy server is created using the NewProxy function, which takes a URL and returns a new http reverse proxy. This proxy is then used to forward requests to the destination URL.

The ProxyRequestHandler function takes the created proxy, destination URL, and endpoint, and returns an http handler similar to the ping handler. This handler updates the http headers to redirect requests coming to the given endpoint to the destination URL.

The healthcheck handler iterates through each resource in config.yaml, parses the destination URL, and creates a new proxy using the Newproxy function. It then registers the resource endpoint to the handler returned by the ProxyRequestHandler function.

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The healthcheck handler does more than just register handlers for each resource; it also parses the destination URL to get a *url.URL type, which is required by the Newproxy function.

The net/http package provides functions for reading and writing to the wire, such as Read and Write, but these are not directly related to the reverse proxy server.

The ServerConn Hijack function detaches the server connection and returns the underlying connection as well as the read-side bufio, which may have leftover data. However, this is not directly related to the reverse proxy server.

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You can modify the response you get from servers using HttpUtil reverse proxy, which provides a simple mechanism to cache or change the response based on your use cases.

To modify the response, you can use the modifyResponse method, which allows you to set a custom header, read the response body, make changes to it, cache it, and then set it back for the client. You can also return an error if you encounter it while processing the response, which will then be handled by proxy.ErrorHandler.

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The httputil package provides a hook for your custom function to modify responses from the origin server. To use this hook, you can write a function to modify the response of your ReverseProxy instance. For example, you can add a Server header to all responses.

Logging requests body is a common solution used to debug server applications, but it's not always easy. With the simple reverse proxy, it's very easy to achieve this goal without modifying the server application code. All you need to do is to log the request body in the Director func.

You can also create and run an HTTP server for your reverse proxy by implementing the Run function. This function loads the configuration, creates a new server, and registers routes for the resources endpoints.

Request and response management is a crucial aspect of a reverse proxy. You can modify the response, log the request body, and even create and run an HTTP server for your reverse proxy. The httputil package provides a hook for your custom function to modify responses from the origin server.

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You can easily check if demo servers are running by testing server2, where our reverse proxy server is serving requests and sending them to the appropriate destination URLs.

Logging requests body is also a crucial aspect, and one common solution is to log the request body, which can be achieved by simply logging it in the Director func.

This approach allows you to debug server applications without modifying the source code directly, which can be a big relief when working with complex systems.

To log the request body, you can import a log package or class, but in this case, it's as simple as logging it in the Director func.