flowheater

Flowheater

Flowheater is an annotation based router generator for go with automatic resolution of parameters as well as marshalling and unmarshalling of requests and responses.

Installing

Install flowheater by running:

$ go get github.com/lukasdietrich/flowheater

Ensure that $GOPATH/bin is added to your $PATH.

Usage

Flowheater works by scanning a package for annotated structs and methods. Since go does not support annotations, flowheater uses a special comment syntax: All trailing lines of the format Key: Value are considered an annotation.

Service

First flowheater looks for struct types with a Path annotation. Each such struct is then traversed for methods with another Path annotation. Every annotated method of an annotated struct is considered a service endpoint and will be registered in the generated router with a joined path of the struct and the method.

Endpoints also support an optional Method annotation, which indicates the expected http-method. If no such annotation is present, GET will be used as a default.

Parameters

A service endpoint does not have to manually extract path-parameters or unmarshal a request. Instead you can directly declare function parameters and flowheater will try its best to resolve them.

Native parameter

There are three special types, that you can declare and flowheater injects them as is. *net/http.Request and net/http.ResponseWriter are directly passed forward from the net/http.Handler interface. Additionally context.Context is resolved as the requests context.

Path parameters

Builtin types (string, int, int..., uint, uint..., bool) are extracted and converted if necessary using the methods parameter name as the path-parameter name.

Resolver

Flowheater supports a third and very powerful type of parameters to be automatically resolved.

You can define a struct with a method named resolveParam that returns a value of any type. That type can then be declared as a parameter in service endpoints and flowheater will resolve the value using the resolver struct type. The resolveParam method in turn can declare any kind of parameters. This can be used to inject values otherwise implemented via middlewares, for example a user inferred from a cookie.

Payload

Flowheater tries to resolve parameters as either a native, path or resolver parameter. If none of these is applicable, it is assumed to be the request payload. Only one parameter can be the payload. If more than one parameter is assumed to be the payload, flowheater will complain accordingly.

Response

Both service endpoints and custom resolvers can or must return values. A resolver obviously must return the value to be resolved, but can also optionaly return an error. An endpoint can return nothing, a response, an error or both. The returned value will be marshalled and writted to the responsewriter if no error occured.