# Overview Rocket provides primitives to build web servers and applications with Rust: the rest is up to you. In short, Rocket provides routing, pre-processing of requests, and post-processing of responses. Your application code instructs Rocket on what to pre-process and post-process and fills the gaps between pre-processing and post-processing. ## Lifecycle Rocket's main task is to listen for incoming web requests, dispatch the request to the application code, and return a response to the client. We call the process that goes from request to response: the _lifecycle_. We summarize the lifecycle as the sequence of steps: 1. **Routing** Rocket parses an incoming HTTP request into native structures that your code operates on indirectly. Rocket determines which request handler to invoke by matching against route attributes declared by your application. 2. **Validation** Rocket validates the incoming request against types and request guards present in the matched route. If validation fails, Rocket _forwards_ the request to the next matching route or calls an _error handler_. 3. **Processing** The request handler associated with the route is invoked with validated arguments. This is the main business logic of the application. Processing completes by returning a `Response`. 4. **Response** The returned `Response` is processed. Rocket generates the appropriate HTTP response and sends it to the client. This completes the lifecycle. Rocket continues listening for requests, restarting the lifecycle for each incoming request. The remainder of this section details the _routing_ phase as well as additional components needed for Rocket to begin dispatching requests to request handlers. The sections following describe the request and response phases. ## Routing Rocket applications are centered around routes and handlers. A _handler_ is simply a function that takes an arbitrary number of arguments and returns any arbitrary type. A _route_ is a combination of: * A set of parameters to match an incoming request against. * A handler to process the request and return a response. The parameters to match against include static paths, dynamic paths, path segments, forms, query strings, request format specifiers, and body data. Rocket uses attributes, which look like function decorators in other languages, to make declaring routes easy. Routes are declared by annotating a function, the handler, with the set of parameters to match against. A complete route declaration looks like this: ```rust #[get("/world")] // <- route attribute fn world() -> &'static str { // <- request handler "Hello, world!" } ``` This declares the `world` route to match against the static path `"/world"` on incoming `GET` requests. The `world` route is simple, but additional route parameters are necessary when building more interesting applications. The [Requests](/guide/requests) section describes the available options for constructing routes. ## Mounting Before Rocket can dispatch requests to a route, the route needs to be _mounted_. Mounting a route is like namespacing it. Routes are mounted via the `mount` method on a `Rocket` instance. Rocket instances can be created with the `ignite()` static method. The `mount` method takes **1)** a path to namespace a list of routes under, and **2)** a list of route handlers through the `routes!` macro. The `routes!` macro ties Rocket's code generation to your application. For instance, to mount the `world` route we declared above, we would use the following code: ```rust rocket::ignite().mount("/hello", routes![world]) ``` Altogether, this creates a new `Rocket` instance via the `ignite` function and mounts the `world` route to the `"/hello"` path. As a result, `GET` requests to the `"/hello/world"` path will be directed to the `world` function. ### Namespacing When a route is declared inside a module other than the root, you may find yourself with unexpected errors when mounting: ```rust mod other { #[get("/world")] pub fn world() -> &'static str { "Hello, world!" } } use other::world; fn main() { // error[E0425]: cannot find value `static_rocket_route_info_for_world` in this scope rocket::ignite().mount("/hello", routes![world]) } ``` This occurs because the `routes!` macro implicitly converts the route's name into the name of a structure generated by Rocket's code generation. The solution is to name the route by a module path instead: ```rust rocket::ignite().mount("/hello", routes![other::world]) ``` ## Launching Now that Rocket knows about the route, you can tell Rocket to start accepting requests via the `launch` method. The method starts up the server and waits for incoming requests. When a request arrives, Rocket finds the matching route and dispatches the request to the route's handler. We typically call `launch` from the `main` function. Our complete _Hello, world!_ application thus looks like: ```rust #![feature(plugin)] #![plugin(rocket_codegen)] extern crate rocket; #[get("/world")] fn world() -> &'static str { "Hello, world!" } fn main() { rocket::ignite().mount("/hello", routes![world]).launch(); } ``` Note that we've added the `#![feature(plugin)]` and `#![plugin(rocket_codegen)]` lines to tell Rust that we'll be using Rocket's code generation plugin. We've also imported the `rocket` crate into our namespace via `extern crate rocket`. Finally, we call the `launch` method in the `main` function. Running the application, the console shows: ```sh 🔧 Configured for development. => address: localhost => port: 8000 => log: normal => workers: {logical cores} 🛰 Mounting '/world': => GET /hello/world 🚀 Rocket has launched from http://localhost:8000... ``` If we visit `localhost:8000/hello/world`, we see `Hello, world!`, exactly as we expected. A version of this example's complete crate, ready to `cargo run`, can be found on [GitHub](https://github.com/SergioBenitez/Rocket/tree/v0.2.6/examples/hello_world). You can find dozens of other complete examples, spanning all of Rocket's features, in the [GitHub examples directory](https://github.com/SergioBenitez/Rocket/tree/v0.2.6/examples/). ## Configuration At any point in time, a Rocket application is operating in a given _configuration environment_. There are three such environments: * `development` (short: `dev`) * `staging` (short: `stage`) * `production` (short: `prod`) Without any action, Rocket applications run in the `development` environment. The environment can be changed via the `ROCKET_ENV` environment variable. For example, to launch the `Hello, world!` application in the `staging` environment, we can run: ```sh ROCKET_ENV=stage cargo run ``` You'll likely need `sudo` for the command to succeed since `staging` defaults to listening on port `80`. Note that you can use the short or long form of the environment name to specify the environment, `stage` _or_ `staging` here. Rocket tells us the environment we have chosen and its configuration when it launches: ```sh $ sudo ROCKET_ENV=staging cargo run 🔧 Configured for staging. => address: 0.0.0.0 => port: 80 => log: normal => workers: {logical cores} 🛰 Mounting '/': => GET / 🚀 Rocket has launched from http://0.0.0.0:80... ``` Configuration settings can be changed in one of two ways: via the `Rocket.toml` configuration file, or via environment variables. ### Configuration File A `Rocket.toml` file can be used to specify the configuration parameters for each environment. The file is optional. If it is not present, the default configuration parameters are used. The file must be a series of TOML tables, at most one for each environment and an optional "global" table, where each table contains key-value pairs corresponding to configuration parameters for that environment. If a configuration parameter is missing, the default value is used. The following is a complete `Rocket.toml` file, where every standard configuration parameter is specified with the default value: ```toml [development] address = "localhost" port = 8000 workers = max(number_of_cpus, 2) log = "normal" [staging] address = "0.0.0.0" port = 80 workers = max(number_of_cpus, 2) log = "normal" [production] address = "0.0.0.0" port = 80 workers = max(number_of_cpus, 2) log = "critical" ``` The `workers` parameter is computed by Rocket automatically; the value above is not valid TOML syntax. The "global" pseudo-environment can be used to set and/or override configuration parameters globally. A parameter defined in a `[global]` table sets, or overrides if already present, that parameter in every environment. For example, given the following `Rocket.toml` file, the value of `address` will be `"1.2.3.4"` in every environment: ```toml [global] address = "1.2.3.4" [development] address = "localhost" [production] address = "0.0.0.0" ``` ### Extras In addition to overriding default configuration parameters, a configuration file can also define values for any number of _extra_ configuration parameters. While these parameters aren't used by Rocket directly, other libraries, or your own application, can use them as they wish. As an example, the [Template](https://api.rocket.rs/rocket_contrib/struct.Template.html) type accepts a value for the `template_dir` configuration parameter. The parameter can be set in `Rocket.toml` as follows: ```toml [development] template_dir = "dev_templates/" [production] template_dir = "prod_templates/" ``` This sets the `template_dir` extra configuration parameter to `"dev_templates/"` when operating in the `development` environment and `"prod_templates/"` when operating in the `production` environment. Rocket will prepend the `[extra]` tag to extra configuration parameters when launching: ```sh 🔧 Configured for development. => ... => [extra] template_dir: "dev_templates/" ``` ### Environment Variables All configuration parameters, including extras, can be overridden through environment variables. To override the configuration parameter `{param}`, use an environment variable named `ROCKET_{PARAM}`. For instance, to override the "port" configuration parameter, you can run your application with: ```sh ROCKET_PORT=3721 cargo run 🔧 Configured for staging. => ... => port: 3721 ``` Environment variables take precedence over all other configuration methods: if a variable is set, it will be used as that parameter's value.