[−][src]Crate dropshot

Dropshot is a general-purpose crate for exposing REST APIs from a Rust program. Planned highlights include:

Suitability for production use on a largely untrusted network. Dropshot-based systems should be high-performing, reliable, debuggable, and secure against basic denial of service attacks (intentional or otherwise).
First-class OpenAPI support, in the form of precise OpenAPI specs generated directly from code. This works because the functions that serve HTTP resources consume arguments and return values of specific types from which a schema can be statically generated.
Ease of integrating into a diverse team. An important use case for Dropshot consumers is to have a team of engineers where individuals might add a few endpoints at a time to a complex server, and it should be relatively easy to do this. Part of this means an emphasis on the principle of least surprise: like Rust itself, we may choose abstractions that require more time to learn up front in order to make it harder to accidentally build systems that will not perform, will crash in corner cases, etc.

By "REST API", we primarily mean an API built atop existing HTTP primitives, organized into hierarchical resources, and providing consistent, idempotent mechanisms to create, update, list, and delete those resources. "REST" can mean a range of things depending on who you talk to, and some people are dogmatic about what is or isn't RESTy. We find such dogma not only unhelpful, but poorly defined. (Consider such a simple case as trying to update a resource in a REST API. Popular APIs sometimes use PUT, PATCH, or POST for the verb; and JSON Merge Patch or JSON Patch as the format. (sometimes without even knowing it!). There's hardly a clear standard, yet this is a really basic operation for any REST API.)

For a discussion of alternative crates considered, see Oxide RFD 10.

We hope Dropshot will be fairly general-purpose, but it's primarily intended to address the needs of the Oxide control plane.

Usage

The bare minimum might look like this:

use dropshot::ApiDescription;
use dropshot::ConfigDropshot;
use dropshot::ConfigLogging;
use dropshot::ConfigLoggingLevel;
use dropshot::HttpServer;
use std::sync::Arc;

#[tokio::main]
async fn main() -> Result<(), String> {
    // Set up a logger.
    let log =
        ConfigLogging::StderrTerminal {
            level: ConfigLoggingLevel::Info,
        }
        .to_logger("minimal-example")
        .map_err(|e| e.to_string())?;

    // Describe the API.
    let mut api = ApiDescription::new();
    // Register API functions -- see detailed example or ApiDescription docs.

    // Start the server.
    let mut server =
        HttpServer::new(
            &ConfigDropshot {
                bind_address: "127.0.0.1:0".parse().unwrap(),
            },
            api,
            Arc::new(()),
            &log,
        )
        .map_err(|error| format!("failed to start server: {}", error))?;

    let server_task = server.run();
    server.wait_for_shutdown(server_task).await
}

This server returns a 404 for all resources because no API functions were registered. See examples/basic.rs for a simple, documented example that provides a few resources using shared state.

For a given ApiDescription, you can also print out an OpenAPI spec describing the API. See ApiDescription::print_openapi.

API Handler Functions

HTTP talks about resources. For a REST API, we often talk about endpoints or operations, which are identified by a combination of the HTTP method and the URI path

Example endpoints for a resource called a "project" might include:

GET /projects (list projects)
POST /projects (one way to create a project)
GET /projects/my_project (fetch one project)
PUT /projects/my_project (update (or possibly create) a project)
DELETE /projects/my_project (delete a project)

With Dropshot, an incoming request for a given API endpoint is handled by a particular Rust function. That function is called an entrypoint, an endpoint handler, or a handler function. When you set up a Dropshot server, you configure the set of available API endpoints and which functions will handle each one by setting up an ApiDescription.

The most convenient way to define an endpoint with a handler function uses the endpoint! macro. Here's an example of a single endpoint that lists three hardcoded projects:

use dropshot::endpoint;
use dropshot::ApiDescription;
use dropshot::HttpError;
use dropshot::HttpResponseOkObjectList;
use dropshot::RequestContext;
use http::Method;
use schemars::JsonSchema;
use serde::Serialize;
use std::sync::Arc;

/** Represents a project in our API */
#[derive(Serialize, JsonSchema)]
struct Project {
    /** name of the project */
    name: String,
}

/** Fetch the list of projects. */
#[endpoint {
    method = GET,
    path = "/projects",
}]
async fn myapi_projects_get(
    rqctx: Arc<RequestContext>,
) -> Result<HttpResponseOkObjectList<Project>, HttpError>
{
   let projects = vec![
       Project { name: String::from("project1") },
       Project { name: String::from("project2") },
       Project { name: String::from("project3") },
   ];
   Ok(HttpResponseOkObjectList(projects))
}

fn main() {
    let mut api = ApiDescription::new();

    /*
     * Register our endpoint and its handler function.  The "endpoint" macro
     * specifies the HTTP method and URI path that identify the endpoint,
     * allowing this metadata to live right alongside the handler function.
     */
    api.register(myapi_projects_get).unwrap();

    /* ... (use `api` to set up an `HttpServer` ) */
}

There's quite a lot going on here:

The endpoint macro specifies the HTTP method and URI path. When we invoke ApiDescription::register(), this information is used to register the endpoint that will be handled by our function.
The signature of our function indicates that on success, it returns a HttpResponseOkObjectList<Project>. This means that the function will return an HTTP 200 status code ("OK") with a list of objects, each being an instance of Project.
The function itself has a Rustdoc comment that will be used to document this endpoint in the OpenAPI schema.

From this information, Dropshot can generate an OpenAPI specification for this API that describes the endpoint (which OpenAPI calls an "operation"), its documentation, the possible responses that it can return, and the schema for each type of response (which can also include documentation). This is largely known statically, though generated at runtime.

Function arguments

In general, a handler function looks like this:

async fn f(
     rqctx: Arc<RequestContext>,
     [query_params: Query<Q>,]
     [path_params: Path<P>,]
     [body_param: Json<J>,]
) -> Result< SomeResponseType , HttpError>

Other than the RequestContext, parameters may appear in any order. The types Query, Path, and Json are called Extractors because they cause information to be pulled out of the request and made available to the handler function.

Query<Q> extracts parameters from a query string, deserializing them into an instance of type Q. Q must implement serde::Deserialize and dropshot::ExtractedParameter.
Path<P> extracts parameters from HTTP path, deserializing them into an instance of type P. P must implement serde::Deserialize and dropshot::ExtractedParameter.
Json<J> extracts content from the request body by parsing the body as JSON and deserializing it into an instance of type J. J must implement serde::Deserialize and schemars::JsonSchema.

If the handler takes a Query<Q>, Path<P>, or a Json<J> and the corresponding extraction cannot be completed, the request fails with status code 400 and an error message reflecting a validation error.

As with any serde-deserializable type, you can make fields optional by having the corresponding property of the type be an Option. Here's an example of an endpoint that takes two arguments via query parameters: "limit", a required u32, and "marker", an optional string:

use http::StatusCode;
use dropshot::ExtractedParameter;
use dropshot::HttpError;
use dropshot::Json;
use dropshot::Query;
use dropshot::RequestContext;
use hyper::Body;
use hyper::Response;
use std::sync::Arc;

#[derive(serde::Deserialize, ExtractedParameter)]
struct MyQueryArgs {
    limit: u32,
    marker: Option<String>
}

async fn myapi_projects_get(
    _: Arc<RequestContext>,
    query: Query<MyQueryArgs>)
    -> Result<Response<Body>, HttpError>
{
    let query_args = query.into_inner();
    let limit: u32 = query_args.limit;
    let marker: Option<String> = query_args.marker;
    Ok(Response::builder()
        .status(StatusCode::OK)
        .body(format!("limit = {}, marker = {:?}\n", limit, marker).into())?)
}

Endpoint function return types

Endpoint handler functions are async, so they always return a Future. When we say "return type" below, we use that as shorthand for the output of the future.

An endpoint function must return a type that implements HttpResponse. Typically this should be a type that implements HttpTypedResponse (either one of the Dropshot-provided ones or one of your own creation). In situations where the response schema is not fixed, the endpoint should return Response<Body>, which also implements HttpResponse.

The more specific a type returned by the handler function, the more can be validated at build-time, and the more specific an OpenAPI schema can be generated from the source code. For example, a POST to an endpoint "/projects" might return Result<HttpResponseCreated<Project>, HttpError>. As you might expect, on success, this turns into an HTTP 201 "Created" response whose body is constructed by serializing the Project. In this example, OpenAPI tooling can identify at build time that this function produces a 201 "Created" response on success with a body whose schema matches Project (which we already said implements Serialize), and there would be no way to violate this contract at runtime. If the function just returned Response<Body>, it would be harder to tell what it actually produces (for generating the OpenAPI spec), and no way to validate that it really does that.

Modules

test_util

Automated testing facilities. These are intended for use both by this crate and dependents of this crate.

Structs

ApiDescription	An ApiDescription represents the endpoints and handler functions in your API. Other metadata could also be provided here. This object can be used to generate an OpenAPI spec or to run an HTTP server implementing the API.
ApiEndpoint	ApiEndpoint represents a single API endpoint associated with an ApiDescription. It has a handler, HTTP method (e.g. GET, POST), and a path-- provided explicitly--as well as parameters and a description which can be inferred from function parameter types and doc comments (respectively).
ApiEndpointParameter	ApiEndpointParameter represents the discrete path and query parameters for a given API endpoint. These are typically derived from the members of stucts used as parameters to handler functions.
ApiEndpointResponse	Metadata for an API endpoint response: type information and status code.
ConfigDropshot	Configuration for a Dropshot server.
HttpError	`HttpError` represents an error generated as part of handling an API request. When these bubble up to the top of the request handling stack (which is most of the time that they're generated), these are turned into an HTTP response, which includes:
HttpErrorResponseBody	Body of an HTTP response for an `HttpError`. This type can be used to deserialize an HTTP response corresponding to an error in order to access the error code, message, etc.
HttpResponseAccepted	`HttpResponseAccepted<T: Serialize>` wraps an object of any serializable type. It denotes an HTTP 202 "Accepted" response whose body is generated by serializing the object.
HttpResponseCreated	`HttpResponseCreated<T: Serialize>` wraps an object of any serializable type. It denotes an HTTP 201 "Created" response whose body is generated by serializing the object.
HttpResponseDeleted	`HttpResponseDeleted` represents an HTTP 204 "No Content" response, intended for use when an API operation has successfully deleted an object.
HttpResponseOkObject	`HttpResponseOkObject<T: Serialize>` wraps an object of any serializable type. It denotes an HTTP 200 "OK" response whose body is generated by serializing the object.
HttpResponseOkObjectList	`HttpResponseOkObjectList<T: Serialize>` wraps a collection of serializable types. It denotes an HTTP 200 "OK" response whose body is generated by serializing the sequence of objects. TODO-polish We will probably want to add headers for the total result set size and the number of results that we're returning here, plus the marker. TODO-cleanup move/copy the type aliases from src/api_model.rs?
HttpResponseUpdatedNoContent	`HttpResponseUpdatedNoContent` represents an HTTP 204 "No Content" response, intended for use when an API operation has successfully updated an object and has nothing to return.
HttpServer	A thin wrapper around a Hyper Server object that exposes some interfaces that we find useful (e.g., close()). TODO-cleanup: this mechanism should probably do better with types. In particular, once you call run(), you shouldn't be able to call it again (i.e., it should consume self). But you should be able to close() it. Once you've called close(), you shouldn't be able to call it again.
Json	`Json<JsonType>` is an extractor used to deserialize an instance of `JsonType` from an HTTP request body. `JsonType` is any structure of yours that implements `serde::Deserialize`. See this module's documentation for more information.
Method	The Request Method (VERB)
Path	`Path<PathType>` is an extractor used to deserialize an instance of `PathType` from an HTTP request's path parameters. `PathType` is any structure of yours that implements `serde::Deserialize`. See this module's documentation for more information.
Query	`Query<QueryType>` is an extractor used to deserialize an instance of `QueryType` from an HTTP request's query string. `QueryType` is any structure of yours that implements `serde::Deserialize`. See this module's documentation for more information.
RequestContext	Handle for various interfaces useful during request processing. TODO-cleanup What's the right way to package up "request"? The only time we need it to be mutable is when we're reading the body (e.g., as part of the JSON extractor). In order to support that, we wrap it in something that supports interior mutability. It also needs to be thread-safe, since we're using async/await. That brings us to Arc<Mutex<...>>, but it seems like overkill since it will only really be used by one thread at a time (at all, let alone mutably) and there will never be contention on the Mutex.

Enums

ApiEndpointParameterLocation
ConfigLogging	Represents the logging configuration for a server. This is expected to be a top-level block in a TOML config file, although that's not required.
ConfigLoggingIfExists	Specifies the behavior when logging to a file that already exists.
ConfigLoggingLevel	Log messages have a level that's used for filtering in the usual way.

Constants

CONTENT_TYPE_JSON	MIME type for plain JSON data
CONTENT_TYPE_NDJSON	MIME type for newline-delimited JSON data
HEADER_REQUEST_ID	header name for conveying request ids ("x-request-id")

Traits

ExtractedParameter
Extractor	`Extractor` defines an interface allowing a type to be constructed from a `RequestContext`. Unlike most traits, `Extractor` essentially defines only a constructor function, not instance functions.
HttpResponse	HttpResponse must produce a `Result<Response<Body>, HttpError>` and generate the response metadata. Typically one should use `Response<Body>` or an implementation of `HttpTypedResponse`.

Attribute Macros

endpoint

Attribute to apply to an HTTP endpoint. TODO(doc) explain intended use

Derive Macros

ExtractedParameter

Derive the implementation for dropshot::ExtractedParameter