Larky Syntax Overview

To try it out today, please contact us at [email protected]

Larky overview

Larky, which is a VGS adaptation of Starlark project, lets you manipulate your secure data in an imperative way using the Larky language. Larky operations execute larky code in a secure and isolated environment, using the VGS-provided API to store and retrieve tokens.

Starlark language

Starlark is a dialect of Python; it's a very small and simple language with highly readable syntax.

Example of syntax

# Define a number
number = 18

# Define a dictionary
people = {
    "Alice": 22,
    "Bob": 40,
    "Charlie": 55,
    "Dave": 14,
}

names = ", ".join(people.keys())  # Alice, Bob, Charlie, Dave

# Define a function
def greet(name):
    """Return a greeting."""
    return "Hello {}!".format(name)

greeting = greet(names)

above30 = [name for name, age in people.items() if age >= 30]

Detailed spec can be found here

VGS Larky API

Currently, Larky operation is supported only in an HTTP proxy.

Below is a sample Larky script to redact the account number and all headers in an HTTP request

load("@stdlib//json", json="json") # import json library
load("@stdlib//builtins", builtins="builtins")
load("@vgs//vault", "vault")

def process(input, ctx):
    body = json.loads(input.body.decode("utf-8"))

    # store body in a vault and replace it with an alias
    body['account_number'] = vault.redact(body['account_number'])
    redacted_body = builtins.bytes(json.dumps(body))

    redacted_headers = {}
    for k in input.headers:
        redacted_headers[k] = vault.redact(input.headers[k])

    # construct a redacted response
    input.body = redacted_body
    input.headers = redacted_headers
    return input

Your script can contain an arbitrary number of functions, but it must include the process function with the following signature; this is an entry point for your script.

def process(input, ctx):
    ...

Where input is an HTTP request/response object and ctx is a dictionary object to carry additional information between operations.

Depending on the phase (request or response) of the HTTP message, the input object type will change.

# On Request
def process(input:VGSHttpRequest, ctx:dict[str,str]):
    ...

# On Response
def process(input:VGSHttpResponse, ctx:dict[str,str]):
    ...

VGSHttpRequest/VGSHttpResponse interface

Method/Field	Description
input.body -> bytes	Retrieves HTTP message body in bytes
input.body = redacted_body	Updates HTTP message body
input.headers -> Dict<String, String>	Retrieves a copy of HTTP message headers.
input.headers = redacted_headers	Sets headers with the specified names and values.
input.path -> str	Retrieves HTTP message URI
input.path = new_path	Sets HTTP message URI
input.query_string -> str	Retrieves HTTP URI query string
input.query_string = new_query	Sets HTTP URI query string
input.status_code -> int	Retrieves HTTP message status code
input.status_code = new_status	Sets HTTP message status code

Vault module interface

The Vault module can be imported and used as an API to redact/reveal data stored in VGS's secure storage.

Method	Description
vgs.redact(value: str or [str,str...]) -> str or [str,str...]	Redacts value(s), returns alias(es)
vgs.reveal(alias: str or [str,str...]) -> str or [str,str...]	Reveals alias(es), returns value(s)
vgs.delete(alias: str or [str,str...]) -> str or [str,str...]	Reveals alias(es), returns alias(es)

How to use Larky operation

Send a request to VGS Support to enable the Larky feature flag.

Open the Routes page. Find the filter you want to modify and add the Larky operation to the Larky editor or select the operation from the dropdown list.

1. Another way is to export your route using the dashboard or the CLI.

2. Open the downloaded YAML file in your favourite text editor.

3. Find the filter you want to modify and add the larky operation under operations section

   operations:
     - name: github.com/verygoodsecurity/common/compute/larky/http/Process
       parameters:
         script: |
           def process(input, ctx):
             # insert your larky script from step 2 here
             return input

4. Save the YAML file and import it via the dashboard or use the VGS CLI to programmatically apply the change.

5. Now make an HTTP request to verify your script.

Troubleshooting

In case you received an error, you can see what happened via VGS CLI operations logs vgs logs operations -V <vault_id> -R <request_id> -o json | jq

Ready-to-use code samples

You can find working Larky code snippets in this section. We are in the process of adding more examples and are willing to provide all possible variations based on real use cases that we face.