golang http handler patterngolang http handler pattern

The core of the context package is the Context type: // A Context carries a deadline, cancellation signal, and request-scoped values // across API boundaries. // get takes a HandlerFunc and wraps it to only allow the GET method, // post takes a HandlerFunc and wraps it to only allow the POST method, // allowMethod takes a HandlerFunc and wraps it in a handler that only, // responds if the request method is the given method, otherwise it. Our aim: (1) http.Handler interface, (2) StdLib context, (3) minimal dependencies. In general, when using third-party libraries, always ask yourself if there is no better way to handle the problem. How did this hand from the 2008 WSOP eliminate Scott Montgomery? Find centralized, trusted content and collaborate around the technologies you use most. @xhallix quick example of what that would look like, github.com/xhallix/go-router/blob/master/router.go#L22, What its like to be on the Python Steering Council (Ep. 593), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. Making statements based on opinion; back them up with references or personal experience. When you access the /hello, the log will print: If you want on certain condition the incoming request will not be proceed, then simply don't call the next.ServeHTTP(w, r). You can easily convert them using http.HandlerFunc(h), but its just a bit more noisy. Who counts as pupils or as a student in Germany? For myself, I would probably rule out the other custom approaches: I disagree with Axels assessment that third-party routing libraries make the routes hard to understand: all you typically have to know is whether they match in source order, or in order of most-specific first. // the number of wildcards), which must be of type *string or *int. Instead, we should store this user in the request context. I did find that Gorilla Mux has built in wrappers for this stuff, but I'm having a hard time understanding the API. The statement is used to proceed the incoming request to the next step (it can be next middleware, or the actual handler). (Bathroom Shower Ceiling). Finally, if you don't like the casting, you'll need to define a type instead of a just a function and you'll need to define a method on that type that is required for it to satisfy the http.Handler interface type. The execution it self happen in sequential order, depending on the order of middleware registration. What is the audible level for digital audio dB units? Not the answer you're looking for? Thanks for contributing an answer to Stack Overflow! All HandleFunc does is what we do in the above example, it converts the passed in function to http.HandlerFunc and calls http.Handle with the result. I saw an article written by Mat Ryer about how you can use a server type and http handlers of the type that are wrappers for func(http.ResponseWriter, *http.Request). This is of course much less powerful than regex matching, but generally Ive not needed anything more than match till next slash in my routes. This approach is similar to the regex switch method, but instead of regexes it uses a simple, custom pattern matcher. func snippetView(w http.ResponseWriter, r *http.Request) { w.Write([]byte("Display a specific snippet.")) That said, it's not too hard to create your own handler that can use regular expressions or any other kind of pattern you want. I don't see it as a problem now, but it might be once I start writing more complex middleware for database queries I plan to use this for. In his words, I decided to inline the pieces, so the match arguments reads as the path does: match("foo", &bar, "baz"). I quite like this thanks Yuri! The output of a middleware, by definition, is an HTTP response. First, the five custom techniques: And three versions using third-party router packages: I also tried httprouter, which is supposed to be really fast, but it cant handle URLs with overlapping prefixes like /contact and /:slug. Subtree path handlers, however, will execute whenever the start of the request URL matches the subtree pattern. rev2023.7.24.43543. Can a simply connected manifold satisfy ? Founder at MachineBox.io Gopher, developer, speaker, author BitBar app https://getbitbar.com Author of Go Programming Blueprints, func checkAPIKey(h http.Handler) http.Handler {, func MustParams(h http.Handler, params string) http.Handler {, http.Handler("/user", MustParams(handleUser, "key", "auth")), func MustAuth(h http.Handler) http.Handler {, err := validateAuth(r.URL.Query().Get("auth")), func (r *ResponseLogger) Write(b []byte) (int, error) {. 9 I saw an article written by Mat Ryer about how you can use a server type and http handlers of the type that are wrappers for func (http.ResponseWriter, *http.Request) I see this as a more elegant way to build REST APIs, however I'm totally stumped on getting the wrapper to function correctly. Are there any practical use cases for subtyping primitive types? Id seriously consider using it, especially if building a web app as part of a large team. how to parse multiple parameters in url in GoLang? It's especially good at helping you write large REST API services that are kept maintainable as your project grows and changes. For example, say we also want to add a header to all responses written by all of the handlers added to that mux. Cartoon in which the protagonist used a portal in a theater to travel to other worlds, where he captured monsters. Go Programming Blueprints: Second Edition, Validating the request; such as checking authentication credentials. Is there a way for me to achieve this? If you liked the first edition youll love this one. Defers instantiation of an object to a specialized function for creating instances. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. You can find more details at the doc of the ServeMux type. Start by defining a key type and value for the authenticated user we need to store: And now use them in the ServeHTTP() method of our middleware handler to add the currently authenticated user to the request context: Note that putting the user into the request context involves creating a new context based on the current one, adding the user to it as a value, and creating a new request object with that new context. Handlers hang off the server. The Serve function would then instantiate and call the closure as follows: I slightly prefer the context approach, as it keeps the handler signatures simple http.HandlerFuncs, and also avoids a nested function for each handler definition. We could just call regexp.MustCompile, but that would re-compile each regex on every request. What's the DC of a Devourer's "trap essence" attack? Parsing GET parameters from a file to a NewRequest call in Go, Converting URL Params to JSON in Go with http.Request, Calling a GET REST API in golang with a path variable, How to pass path param to httptest request. You can use the following links to skip down to a particular technique. Using robocopy on windows led to infinite subfolder duplication via a stray shortcut file. How can I avoid this? They look much the same as the handlers in the regex table approach, but the custom getField() function is replaced by chi.URLParam(). 6 minutes How I Structure Web Servers in Go Switching to Go from a decade of C# momentum has been an interesting journey. An alternative to passing the fields using context is to make each route.handler a function that takes the fields as a []string and returns an http.HandleFunc closure that closes over the fields parameter. This resource shows how the handlers are written, but not how the routes are set up. Now suppose we want to log all requests made to this server, listing the request method, resource path, and how long it took to handle. How did this hand from the 2008 WSOP eliminate Scott Montgomery? Most libraries with framework in the title dont do it for me, though Im not opposed to using well-maintained libraries that do one or two things well. Its methods are safe for simultaneous use by multiple // goroutines. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. As you can see, Pat and Gorilla are slower than the others, showing that just because something is a well-known library doesnt mean its heavily optimized. Example: Middleware often used to perform some process on the incoming request, before or after the handler called. //. The Basic Principles Making and using middleware in Go is fundamentally simple. A handler or callback is a function invoked to handle a particular type of event. Making statements based on opinion; back them up with references or personal experience. The only helper here is the isId function, which checks that the ID segments are in fact positive integers: So while I like the bare-bones simplicity of this approach just basic string equality comparisons the verbosity of the matching and the error-prone integer constants would make me think twice about actually using it for anything but very simple routing. How can the language or tooling notify the user of infinite loops? Instead maybe consider something like this: What is the purpose of r.Use when it's not registering the url route? By doing so, ServeHTTP will be able to call the handler function and process the error if it fails. So what is executed here when you're setting the routes is the http.Handle function and the HandleSayHello method. This is basically what I have for study purposes at the moment. I just gave it a quick shot and will look at this in depth later on. Upon receiving a request, each handler decides either to process the request or to pass it to the next handler in the chain. We then change our EnsureAuth middleware to wrap one of these authenticated handler functions rather than an http.Handler. functions on the Golang Slack, and I couldn't find a good writeup of the basic Find centralized, trusted content and collaborate around the technologies you use most. Since an http.ServeMux satisfies the http.Handler interface, you can wrap an entire mux with the logger middleware. Generally speaking, they're responsible for carrying out your application logic and writing response headers and bodies. DevOps). Axel Wagner wrote a blog article, How to not use an http-router in go, in which he maintains that routers (third party or otherwise) should not be used. Go Middleware is a collection of standard HTTP middleware packages for Go that you can use individually in your projects. Now let's consider a slightly more complicated example. Its also quite a lot of code, some of which is error prone. The source code for the HTTP router we will implement is shown below. There are probably different ways to do it, but I currently test the method explicitly in the first route the get() wrapper is not strictly necessary here, but Ive included it for consistency: At first I included the HTTP method matching in the match() helper, but that makes it more difficult to return 405 Method Not Allowed responses properly. Is it proper grammar to use a single adjective to refer to two nouns of different genders? Okay, I understand that more clearly. Solution 1 The patterns for http.Handler and http.HandleFunc aren't regular expressions or globs. // match reports whether path matches the given pattern, which is a, // path with '+' wildcards wherever you want to use a parameter. How can the language or tooling notify the user of infinite loops? It could be extended to validate the key in a datastore, or ensure the caller is within acceptable rate limits etc. log.Printf ("Completed %s in %v", r.URL.Path, time.Si. The advantage of this approach is that you can call other functions or test other things in each case. The NewLogger() constructor function takes an http.Handler to wrap and returns a new Logger instance wrapped around it. It is recommended that test code be written during the implementation process, but no explanation of the test code will be provided. You can see an example of this in action in a modified form in this router, which uses exactly the signatures you're after, but handles building a middleware chain and executing it without manual wrapping: https://github.com/fragmenta/mux/blob/master/mux.go. //validate the session token in the request. For example, this is how we would use it in the main() function: Instead of wrapping an entire mux just once, we have to wrap each of our authenticated handler functions as we add them to the mux. The gorilla/mux package is perhaps the most famous Go router, and with good reason. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. It accepts two parameters 1. The current handler switches on the first path segment, then delegates to sub-handlers which do the same thing on the rest of the URL. If you see the code above, on each middleware there is statement next.ServeHTTP(w, r). Id love it if you sponsored me on GitHub it will motivate me to work on my open source projects and write more good content. There are many ways to do more advanced routing yourself, including Axel Wagner's interesting ShiftPath technique. Most of the approaches loop or switch through a list of routes (in contrast to fancy trie-lookup structures). Note http.StripPrefix accepts an http.Handler and returns a new one: You can also nest this behavior using submuxes; http.ServeMux implements http.Handler, so you can pass one into http.StripPrefix just the same. So far you've seen how to build a Go web server that routes requests to different functions depending on the requested URL. The Adapter pattern can be difficult to understand, but it allows you to chain many middleware handlers together in a very elegant way. Is not listing papers published in predatory journals considered dishonest? Why does ksh93 not support %T format specifier of its built-in printf in AIX? We could add similar code to every handler function, but it would be much better if we could handle that logging in just one place. 592), How the Python team is adapting the language for an AI future (Ep. In the circuit below, assume ideal op-amp, find Vout? databases (or other essential runtime application state) to your HTTP handlers. What would naval warfare look like if Dreadnaughts never came to be? The ShiftPath approach doesnt distinguish between no trailing slash and trailing slash, and I cant find a simple way to make it do that. I'm developing a REST API with Go, but I don't know how can I do the path mappings and retrieve the path parameters from them. A middleware handler is simply an http.Handler that wraps another http.Handler to do some pre- and/or post-processing of the request. Connect and share knowledge within a single location that is structured and easy to search. Code example. They're documented here. When coding REST APIs, I do not have to write any complex logic to handle my event because net/http is designed to help me control HTTP requests. Is this mold/mildew? Can somebody be charged for having another person physically assault someone for them? It's called "middleware" because it sits in the middle between the Go web server and the actual handler. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Can a simply connected manifold satisfy ? In the circuit below, assume ideal op-amp, find Vout? I either get a mismatched type error at compilation or a 404 at invocation. // shiftPath splits the given path into the first segment (head) and. You might decide to do this if you want to capture the response body, perhaps to log it: The NewResponseLogger type would provide its own Write function and log the data: It logs the string out, and also writes the bytes to the original http.ResponseWriter, so that the caller of the API still gets the response. The pattern Handler and Middleware design pattern (also called Chain of Responsibility) allows multiple functions to handle an event by decoupling sender and receiver(s). What its like to be on the Python Steering Council (Ep. To learn more, see our tips on writing great answers. Something like: Now create the middleware as usual. Depends on what you mean by "actual function". Go: Get path parameters from http.Request, What its like to be on the Python Steering Council (Ep. I think a decorator is a reasonable approach for this, rather than doing it explicitly in every route in a given web app, youd probably want to either allow trailing slashes and redirect them, or return Not Found as Ive done here. We could duplicate this block of code at the start of every handler, but duplicating code is never a good idea. Of course, theres still no guarantee the object exists in the database that still needs to be done in the handler. To use this and the logger middleware handler at the same time, just wrap one around the other: You can chain together as many middleware handlers as you want by wrapping each around the others. Instead, Ive added a concurrency-safe mustCompileCached function that means the regexes are only compiled the first time theyre used: Overall, despite liking the clarity of this approach and the scan-like match() helper, a point against it is the messiness required to cache the regex compilation. The main chi package just does routing, but the module also comes with a whole bunch of composable middleware to do things like HTTP authentication, logging, trailing slash handling, and so on. Say we have several handlers that all require an authenticated user, and let's also say that we have a function that can return that authenticated user or an error from an http.Request. The article explaining the three techniques is at http://lpar.ATH0.com/2020/08/golang-db-patterns/. If you don't want to use any of the multitude of the available routing packages, then you need to parse the path yourself: Route the /provisions path to your handler, Then split up the path as needed in the handler. The r.Use() is useful for registering a middleware. I asked myself. I get what Use does now. What should I do after I found a coding mistake in my masters thesis? Focusing on #1 only, I'm trying to understand what makes something satisfies the requirements for ServerHTTP. // assigns any capture groups to the *string or *int vars. Looking for story about robots replacing actors. Can consciousness simply be a brute fact connected to some physical processes that dont need explanation? Aside from just wrapping individual handlers as we have done so far, since everything is an http.Handler, we can wrap entire servers in one go: If youre interested in learning more about writing middleware in Go, check out Writing middleware in #golang and how Go makes it so much fun. Any library providing event parsing should also adopt a Handler, Middleware approach; It would feel natural for most programmers because it is the foundation of most APIs. The noop router is a router that actually doesnt route anything, so represents the overhead of the base case. Back at my desk, plunging myself bask into my code, something strikes me. Release my children from my debts at the time of my death. There's the standard library's http.ServeMux, but it only supports basic prefix matching. Is being passed as a function argument to other parts of the code, or is it in a parent scope and accessed directly by those other parts of the code. Golang: HTTP & Networking Creating a simple "Hello World!" HTTP Server in Go In this article, we will learn how to launch a simple HTTP server that responds with `Hello World!` text for all. Asking for help, clarification, or responding to other answers. Why can't sunlight reach the very deep parts of an ocean? This way of working does not feel right! One small advantage is that parameters are accessible by name instead of number: As with my regex table router, Im ignoring the error value from strconv.Atoi() as the path parameters regex has already checked that its made of digits. Heres what a handler looks like: One of the interesting things is that instead of using context to store path parameters (and a helper function to retrieve them), Pat stuffs them into the query parameters, prefixed with : (colon). How can the language or tooling notify the user of infinite loops? The middleware should create a function which returns an error if it fails or calls the next in the chain on success. You can register middleware as many as possible. I don't fully understand what's going on in these examples because the types they're defining don't seem to be getting used. Just think of your middleware separately from the handlers it contains, you don't need the middleware to pass errors. Can consciousness simply be a brute fact connected to some physical processes that dont need explanation? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Build up a chain of handlers containing both our middleware handler and our normal application handler, which we can register with a router. Conclusions from title-drafting and question-content assistance experiments golang http: how to route requests to handlers, How does default server mux match url pattern, Weird Go Regular Expression mismatch when routing http requests, Regular expression to validate '/' in URL. This approach simply splits the request path on / and then uses a switch with case statements that compare the number of path segments and the content of each segment. Or use an external library like Gorilla MUX. 593), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. // At first you will need some sort of start point. So we can use the MustParams wrapper inside our MustAuth one: The http.ResponseWriter type is an interface, which means we can intercept a request and swap it for a different object provided our object satisfies the same interface. At times I revel in Go's simplicity; at other times frustration swells when familiar OOP patterns don't harmonize in a Go codebase. For example, a simple logging wrapper might look like this: Here, our log function returns a new handler (remember that http.HandlerFunc is a valid http.Handler too) that will print the Before string, and call the original handler before printing out the After string. Create a new directory inside your $GOPATH/src directory, and create a file within that directory named main.go. Do I have a misconception about probability? // if not. Our ServeHTTP() method can then simply pass the user to the authenticated handler function as a third parameter. (A modification to) Jon Prez Laraudogoitas "Beautiful Supertask" What assumptions of Noether's theorem fail? Request contexts were introduced in Go version 1.7, and they allow several advanced techniques, but the one we are concerned with here is the storage of request-scoped values. For example like: CORS configuration, CRSF checking, gzip compression, logging, etc. We want to: Implement our middleware so that it satisfies the http.Handler interface. (Yes, that is the port I've set in my config file.). This works fine, but what if we start adding more handlers that also require the currently authenticated user? //TODO: call the real handler, but how do we share the user? As this is right now, I'll only get back a 404 invoking localhost:8091/sayhello. One way to do this is using a struct passing it to your loggingHandler as parameter like this : Thanks for contributing an answer to Stack Overflow! Can a simply connected manifold satisfy ? Is it a concern? Created by Dave Stearns, The Information School, University of Washington, //Logger is a middleware handler that does request logging, //ServeHTTP handles the request by passing it to the real, //handler and logging the request details, //NewLogger constructs a new Logger middleware handler, //use wrappedMux instead of mux as root handler, //ResponseHeader is a middleware handler that adds a header to the response, //NewResponseHeader constructs a new ResponseHeader middleware handler, //ServeHTTP handles the request by adding the response header, //wrap entire mux with logger and response header middleware. This is because the .HandleFunc() method requires a function with only two parameters, not three. Your ErrorHandler(h http.Handler) http.Handler func is basically just "middleware" and not a real handler. Say a key URL parameter is mandatory in our API: The checkAPIKey wrapper will make sure there is a key, and if there isnt, it will return with an Unauthorized error. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. If these handler functions truly require these values, then they should make those dependencies explicit, and require some sort of middleware adapter when being added to a web server mux. I would like to use just http package instead of web frameworks, if it is possible. The request context gives us a spot to store and retrieve key/value pairs that stay with the http.Request object. The middleware is like a chain which executes each one in turn, and then the very last middleware is one which is aware of your handler signature, and deals with the error appropriately. Writing middleware in #golang and how Go makes it so much fun. Connect and share knowledge within a single location that is structured and easy to search. The function being passed in. http://lpar.ATH0.com/2020/08/golang-db-patterns/. http.HandleFunc() can not be used to register a pattern to match a regular expression. What is the audible level for digital audio dB units? rev2023.7.24.43543. This is where designs pattern comes into play. Making statements based on opinion; back them up with references or personal experience. It's easy to spin up to serve http urls. How to use regular expression matching URL, which does decide to use the corresponding function processing. Why do capacitors have less energy density than batteries? 3 Answers Sorted by: 10 Pattern func Middleware (next http.Handler) http.Handler { return http.HandlerFunc (func (w http.ResponseWriter, r *http.Request) { // Do something next.ServeHTTP (w, r) }) } often used to construct middleware chain like Not the answer you're looking for? In this article Im going to do a comparison of several custom techniques and some off-the-shelf packages. Thanks for contributing an answer to Stack Overflow! Correct way to match URL path to page name with URL routing in Go? Conclusions from title-drafting and question-content assistance experiments Golang HTTP custom error handling response, Can I use my function as `negroni` middleware. Stop HTTP call and return an error using a chain of handlers; is it possible? How to reduce repetitive http handler code in golang? Is it possible to split transaction fees across multiple payers? Ive defined a custom context key type, as well as a getField helper function thats used inside the handlers: A typical handler with path parameters looks like this: I havent checked the error returned by Atoi(), because the regex for the ID parameter only matches digits: [0-9]+. Cold water swimming - go in quickly? The most flexible solution would be like this: First define a type that matches your handler signature and implement ServeHTTP to satisfy the http.Handler interface. The http.ListenAndServe (..) function is the most straightforward approach to start a HTTP 1.1 server. We can use a middleware handler to do just that. Find centralized, trusted content and collaborate around the technologies you use most. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. (A modification to) Jon Prez Laraudogoitas "Beautiful Supertask" What assumptions of Noether's theorem fail? Can somebody be charged for having another person physically assault someone for them? Why is this Etruscan letter sometimes transliterated as "ch"? How does hardware RAID handle firmware updates for the underlying drives? thanks. I am familiar with the Go middleware pattern like this: So for example if I had a loggingHandler: But I like the idea of Handlers being able to return errors like normal functions do. How difficult was it to spoof the sender of a telegram in 1890-1920's in USA? English abbreviation : they're or they're not. The same is true for CI. Instead, let's use a middleware handler to ensure that the user is authenticated before calling the ultimate handler. It also scales better. July 2020 There are many ways to do HTTP path routing in Go - for better or worse. // the rest (tail). Three Go http.HandlerFunc design patterns. Because http.Handler is an interface, it's possible to create your own struct that implements the I'm trying to write handler that don't handle requests, but return functions that do according to Mat Ryer's post, Understanding the http handlerfunc wrapper technique in Go, What its like to be on the Python Steering Council (Ep.