add support for TrafficPolicy

[TheConcierge]

Why

This is part of an effort to remove strict PolicyEngine definitions from our public SDKs. By doing so, we can rapidly iterate changes to the PolicyEngine without having to update client definitions every single time. The backend has already been updated to support policy-as-string, so now the SDK needs to be updated.

Note

The required backend changes are still under review and are not yet part of production ngrok.

How

The protobuf definition was updated to contain a new TrafficPolicy field of type string. In the config/policy.go file, a new type was defined on top of string, adding functionality that adheres to the various required interfaces for our various connection types. These functions do nothing more than populate the new TrafficPolicy field with the provided string representation, which will eventually get passed to the appropriate backend service.

Additionally, to support backwards compatibility, WithPolicy was updated to convert the original, structured definition into an appropriate string. While this won't work forever, it should allow users who upgrade their SDK version to not have to change anything until we do the larger, phased-based cutover in the future. A printout was added to warn users about the upcoming deprecation of WithPolicy.

Validation

Unit tests were updated, checking that:

• YAML policy strings are validated
• JSON policy strings are validated
• policies specified by WithPolicy are properly converted to a policy string and placed in TrafficPolicy.

Tunnels were started using both WithPolicy and WithPolicyString. Both started without error and applied the correct policy.

traffic-policy-demo.mp4

[nikolay-ngrok]

👍