[][src]Crate rocket_cors

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Cross-origin resource sharing (CORS) for Rocket applications


If you are using Rocket 0.3, use the 0.3.0 version of this crate.

Nightly Rust

Rocket requires nightly Rust. You should probably install Rust with rustup, then override the code directory to use nightly instead of stable. See installation instructions.

In particular, rocket_cors is currently targetted for the latest nightly. Older nightlies might work, but they are subject to the minimum that Rocket sets.


Add the following to Cargo.toml:

rocket_cors = "0.5.1"

To use the latest master branch, for example:

rocket_cors = { git = "https://github.com/lawliet89/rocket_cors", branch = "master" }


By default, a serialization feature is enabled in this crate that allows you to (de)serialize the CorsOptions struct that is described below. If you would like to disable this, simply change your Cargo.toml to:

rocket_cors = { version = "0.5.1", default-features = false }


Before you can add CORS responses to your application, you need to create a CorsOptions struct that will hold the settings. Then, you need to create a Cors struct using CorsOptions::to_cors which will validate and optimise the settings for Rocket to use.

Each of the examples can be run off the repository via cargo run --example xxx where xxx is

CorsOptions Struct

The CorsOptions struct contains the settings for CORS requests to be validated and for responses to be generated. Defaults are defined for every field in the struct, and are documented on the CorsOptions page. You can also deserialize the struct from some format like JSON, YAML or TOML when the default serialization feature is enabled.

Cors Struct

The Cors struct is what will be used with Rocket. After creating or deserializing a CorsOptions struct, use CorsOptions::to_cors to create a Cors struct.

Three modes of operation

You can add CORS to your routes via one of three ways, in descending order of ease and in ascending order of flexibility.

Unfortunately, you cannot mix and match Fairing with any other of the methods, due to the limitation of Rocket's fairing API. That is, the checks for Fairing will always happen first, and if they fail, the route is never executed and so your guard or manual checks will never get executed.

You can, however, mix and match guards and manual checks.

In summary:

FairingRequest GuardManual
Must apply to all routes
Different settings for different routes
May define custom OPTIONS routes


Fairing is the easiest to use and also the most inflexible. You don't have to define OPTIONS routes for your application, and the checks are done transparently.

However, you can only have one set of settings that must apply to all routes. You cannot opt any route out of CORS checks.

To use this, simply create a Cors from CorsOptions::to_cors and then attach it to Rocket.

Refer to the example.

Injected Route

The fairing implementation will inject a route during attachment to Rocket. This route is used to handle errors during CORS validation.

This is due to the limitation in Rocket's Fairing lifecycle. Ideally, we want to validate the CORS request during on_request, and if the validation fails, we want to stop the route from even executing to

  1. prevent side effects
  2. prevent resource usage from unnecessary computation

The only way to do this is to hijack the request and route it to our own injected route to handle errors. Rocket does not allow Fairings to stop the processing of a route.

You can configure the behaviour of the injected route through a couple of fields in the CorsOptions.

Request Guard

Using request guard requires you to sacrifice the convenience of Fairings for being able to opt some routes out of CORS checks and enforcement. BUT you are still restricted to only one set of CORS settings and you have to mount additional routes to catch and process OPTIONS requests. The OPTIONS routes are used for CORS preflight checks.

You will have to do the following:

Refer to the example.

Truly Manual

This mode is the most difficult to use but offers the most amount of flexibility. You might have to understand how the library works internally to know how to use this mode. In exchange, you can selectively choose which routes to offer CORS protection to, and you can mix and match CORS settings for the routes. You can combine usage of this mode with "guard" to offer a mix of ease of use and flexibility.

You really do not need to use this unless you have a truly ad-hoc need to respond to CORS differently in a route. For example, you have a ping endpoint that allows all origins but the rest of your routes do not.


This mode requires that you pass in a closure that will be lazily evaluated once a CORS request has been validated. If validation fails, the closure will not be run. You should put any code that has any side effects or with an appreciable computation cost inside this handler.

Steps to perform:

Notes about route lifetime

You might have to specify a 'r lifetime in your routes and then return impl Responder<'r>. If you are not sure what to do, you can try to leave the lifetime out and then add it in when the compiler complains.

Generally, you will need to manually annotate the lifetime for the following cases where the compiler is unable to elide the lifetime:

You can see examples when the lifetime annotation is required (or not) in examples/manual.rs.

See the example.

Mixing Guard and Manual

You can mix Guard and Truly Manual modes together for your application. For example, your application might restrict the Origins that can access it, except for one ping route that allows all access.

See the example.




CORS specific Request Headers



Response generator and Fairing for CORS


Configuration options for CORS request handling.


A request guard to check CORS headers before a route is run. Will not execute the route if checks fail.


A Manual Responder used in the "truly manual" mode of operation.


A wrapper type around rocket::http::Method to support serialization and deserialization


Origins that are allowed to make CORS requests.


A Responder which will simply wraps another Responder with CORS headers.



An enum signifying that some of type T is allowed, or All (everything is allowed).


Errors during operations



Returns "catch all" OPTIONS routes that you can mount to catch all OPTIONS request. Only works if you have put a Cors struct into Rocket's managed state.

Type Definitions


A list of allowed headers


A list of allowed methods


A list of allowed origins. Either Some origins are allowed, or all origins are allowed.