terraform-client-go

terraform-client-go provides low-level Go bindings for the Terraform plugin protocol, only as the client.

Why

There is a hashicorp official project https://github.com/hashicorp/terraform-plugin-go that provides low-level Go bindings for the Terraform plugin protocol, while it only support the server part.

There is also a personal project from Mart https://github.com/apparentlymart/terraform-provider that does the similar thing as this project, while it seems not being actively maintained, and some of its dependencies that being exposed in some forms (e.g. user facing types) seems not the hashicorp offically recommended ones (e.g. https://github.com/rpcplugin/go against https://github.com/hashicorp/terraform-plugin-go, https://github.com/apparentlymart/terraform-schema-go against https://github.com/hashicorp/terraform-json).

What

This project provides two layers of client abstractions:

• Raw client: The protocol specific, thin client. It simply builds on top of the terraform-plugin-go by implementing the tfprotov{5,6}.ProviderServer as the client, that is required by terraform-plugin-go. Therefore, the type system being exposed is defined by terraform-plugin-go.

  Example: https://github.com/magodo/terraform-client-go/tree/main/examples/raw

• Normalized client: The normalized client regardless of the protocol version being used (this is how terraform core handles protocol diff). It is built on top of the raw client by adding a type conversion layer to convert between the terraform-plugin-go and cty type systems. As a result, the type system being exposed by this client is defined by terraform-json.

  Example: https://github.com/magodo/terraform-client-go/tree/main/examples/client

How

There are a lot of code duplication&adoption from different sources, for a reason:

• https://github.com/hashicorp/terraform-plugin-go: The tfprotov{5|6}/internal/{from|to}proto is duplicated for type conversion between protobuf generated types and terraform-plugin-go types
• https://github.com/apparentlymart/terraform-provider: The diagnostics type definition and conversion for protobuf generated diagnostics type is duplicated
• https://github.com/hashicorp/terraform:
  • The normalized client interface (with a little difference on the signatures)
  • The schema implied type based on hcldec
  • The type conversion between terraform core types and protobuf generated types is duplicated, but adopted for conversion between terraform-json types and terraform-plugin-go types.
  • The client interface implementations for the two protocols

There is a Terraform module (tools/upstream-change-monitor) being used to keep track of the upstream file changes.

Credit

Parts of this project were adopted from https://github.com/hashicorp/terraform-plugin-go and https://github.com/hashicorp/terraform. I'd like to thank Hashicorp for all these great works!