Signatures are one of the core concepts behind Scale Functions. They allow developers to define the inputs and outputs of their plugins in a type-safe way. This feature is especially useful when working with Golang, as it enables developers to leverage the language’s strong typing system. They are used to define the inputs and outputs of a function using a declarative syntax we call the Scale Signature DSL, and once they are parsed by our compiler we are able to generated cross-language type safety. We use the Polyglot library under the hood to facilitate efficient serialization and deserialization of structured data between host and guest languages and to cross the WASM boundary. We also publish and support a number of Official Scale Signatures for common use cases:
SignatureDescriptionSupported LanguagesAvailable AdaptersLatest Version
HTTPHTTP Signature meant to be used for HTTP handlers and middleware.Go, Rust, TypeScript, JavaScriptnet/http, FastHTTP, NextJS0.3.8
Official are maintained by the Scale Functions team and come with Adapters which allow them to be used seamlessly from popular Frameworks and Libraries.

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Getting Started

To start using Scale Signatures in Golang, you’ll need to have the Scale framework installed and set up. If you haven’t done this yet, please refer to the Getting Started guide.

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Defining a Signature

Defining a Scale Signature in Golang involves creating a struct that represents the input and output of your function. Here’s the default output of the scale signature new command: 
version = "v1alpha"
context = "context"
model Context {
  string MyString {
    default = "DefaultValue"
  }
}
In this example, Context is a Scale Signature that defines a struct with a string and a default string value. For more information on using this syntax, using HCL format

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Using a Signature

Generate the signature, defined in the example above, by again using the CLI: 
scale signature generate <name:tag>
This will generate both the guest and host signatures, each of which are set of functions/interfaces that handle getting the data in, and out, of the associated scale function(s), in a type-safe, and performant manner. For more information on why we need bindings for the guest and the host, see the overview. Now, to use a Scale Signature in Golang, using the generated signature above, you can define a function accordingly. Here’s an example: 

import (
    signature "./path/to/your/scale.signature"
)

func scale(ctx *signature.Context) (*signature.Context, error) {
    // Your function implementation goes here
}
In fact, once you have a scalefile, this can be done for you, with the scale signature use <name:tag> command. Once this is done, you can use the types defined in your signature file for input and output of your scale function. All of the commands for working with signatures are in the CLI API reference.

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Next Steps

Now that you know the basics of Scale Signatures in Golang, you can start integrating them into your Scale plugins/functions. For more info, please refer to the API Reference.

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Chaining Functions

Scale Functions are designed to be chained together to form a pipeline of functions that can be executed sequentially. To allow developers to make decisions about when the next function in the chain should be executed, all signatures provide a Next() method which runs the next function in the chain. 
//go:build tinygo || js || wasm
package scale

import (
    signature "github.com/loopholelabs/scale-signature-http"
)

func Scale(ctx *signature.Context) (*signature.Context, error) {
    ctx.Response().SetBody("Hello, World!")
    return ctx.Next()
}
If there is no next function in the chain, the Next() method will not do anything and will return the same context.