Frugal

Frugal is an extension of Apache Thrift which provides additional functionality. Key features include:

• request headers
• request multiplexing
• request interceptors
• per-request timeouts
• thread-safe clients
• code-generated pub/sub APIs
• support for Go, Java, Dart, and Python (2.7 and 3.5)

Frugal is intended to act as a superset of Thrift, meaning it implements the same functionality as Thrift with some additional features. For a more detailed explanation, see the documentation.

Installation

Homebrew

brew install frugal

Download

Pre-compiled binaries for OS X and Linux are available from the Github releases tab. Currently, adding these binaries is a manual process. If a downloadable release is missing, notify the messaging team to have it added.

If go is already installed and setup you can also simply:

$ go get github.com/Workiva/frugal

From Source

If go is already installed and setup, you can run the following commands:

$ git clone [email protected]:Workiva/frugal.git
$ cd frugal
$ go install

When generating go, be aware the frugal go library and the frugal compiler have separate dependencies.

Usage

Define your Frugal file which contains your pub/sub interface, or scopes, and Thrift definitions.

# event.frugal

// Anything allowed in a .thrift file is allowed in a .frugal file.
struct Event {
    1: i64 ID,
    2: string Message
}

// Scopes are a Frugal extension for pub/sub APIs.
scope Events {
    EventCreated: Event
}

Generate the code with frugal. Currently, only Go, Java, Dart, and Python are supported.

$ frugal -gen=go event.frugal

By default, generated code is placed in a gen-* directory. This code can then be used in your application. Example code is avaliable in the examples/ directory for supported languages.

Prefixes

By default, Frugal publishes messages on the topic <scope>.<operation>. For example, the EventCreated operation in the following Frugal definition would be published on Events.EventCreated:

scope Events {
    EventCreated: Event
}

Custom topic prefixes can be defined on a per-scope basis:

scope Events prefix foo.bar {
    EventCreated: Event
}

As a result, EventCreated would be published on foo.bar.Events.EventCreated.

Prefixes can also define variables which are provided at publish and subscribe time:

scope Events prefix foo.{user} {
    EventCreated: Event
}

This variable is then passed to publish and subscribe calls:

var (
    event = &event.Event{ID: 42, Message: "hello, world!"}
    user  = "bill"
)
publisher.PublishEventCreated(frugal.NewFContext(""), event, user)

subscriber.SubscribeEventCreated(user, func(ctx *frugal.FContext, e *event.Event) {
    fmt.Printf("Received event for %s: %s\n", user, e.Message)
})

Generated Comments

In Thrift, comments of the form /** ... */ are included in generated code. In Frugal, to include comments in generated code, they should be of the form /**@ ... */.

/**@
 * This comment is included in the generated code because
 * it has the @ sign.
 */
struct Foo {}

/**@ This comment is included too. */
service FooService {
    /** This comment isn't included because it doesn't have the @ sign. */
    Foo getFoo()
}

Annotations

Annotations are extra directive in the IDL that can alter the way code is generated. Some common annotations are listed below

Vendoring Includes

Frugal does not generate code for includes by default. The -r flag is required to recursively generate includes. If -r is set, Frugal generates the entire IDL tree, including code for includes, in the same output directory (as specified by -out) by default. Since this can cause problems when using a library that uses a Frugal-generated object generated with the same IDL in two or more places, Frugal provides special support for vendoring dependencies through a vendor annotation on includes and namespaces.

The vendor annotation is used on namespace definitions to indicate to any consumers of the IDL where the generated code is vendored so that consumers can generate code that points to it. This cannot be used with * namespaces since it is language-dependent. Consumers then use the vendor annotation on includes they wish to vendor. The value provided on the include-side vendor annotation, if any, is ignored.

When an include is annotated with vendor, Frugal will skip generating the include if use_vendor language option is set since this flag indicates intention to use the vendored code as advertised by the vendor annotation.

If no location is specified by the vendor annotation, the behavior is defined by the language generator.

The vendor annotation is currently only supported by Go, Dart and Java.

The example below illustrates how this works.

bar.frugal ("providing" IDL):

namespace go bar (vendor="github.com/Workiva/my-repo/gen-go/bar")
namespace dart bar (vendor="my-repo/gen-go")
namespace java bar (vendor="com.workiva.bar.custom.pkg")

struct Struct {}

foo.frugal ("consuming" IDL):

include "bar.frugal" (vendor)

service MyService {
    bar.Struct getStruct()
}

frugal -r -gen go:package_prefix=github.com/Workiva/my-other-repo/gen-go,use_vendor foo.frugal

When we run the above command to generate foo.frugal, Frugal will not generate code for bar.frugal since use_vendor is set and the "providing" IDL has a vendor path set for the Go namespace. Instead, the generated code for foo.frugal will reference the vendor path specified in bar.frugal (github.com/Workiva/my-repo/gen-go/bar).

Deprecating

Marks a method or field as deprecated (if supported by the language, or in a comment otherwise), and logs a warning if a deprecated method is called. This is not available on an entire struct, only the fields within the struct.

  Struct GetFooRequest {
      1: String value (deprecated="Use newValue instead")
  }

  GetFooResponse getFoo(10: GetFooRequest request) throws (
    1: FooError error
  ) (deprecated="Use getBar instead")

In Dart, this compiles to

class GetFooRequest implements thrift.TBase {
  ...

  /// Deprecated: Use newValue instead
  @deprecated
  List<String> _value;
  ...
}

  /// Deprecated: Use getBar instead
  @deprecated
  Future<namespace.GetFooResponse> getFoo(frugal.FContext ctx, namespace.GetFooRequest request);

Thrift Parity

Frugal is intended to be a superset of Thrift, meaning valid Thrift should be valid Frugal. File an issue if you discover an inconsistency in compatibility with the IDL.