github.com/hashicorp/terraform

The Terraform Go SDK provides a comprehensive foundation for building custom Terraform providers. The plugin framework (v6+) offers excellent type safety with well-structured schema definitions, validators, and plan modifiers. The `schema.Resource` and `schema.Attribute` patterns are intuitive once you grasp the declarative model, and the framework handles the gRPC protocol details transparently.

Error handling is generally well-designed with the diagnostics system, allowing you to accumulate warnings and errors with clear context. The framework's separation of concerns between Create, Read, Update, and Delete operations feels natural for infrastructure lifecycle management. Documentation has improved significantly with the plugin framework migration guides and attribute-level examples.

The main friction point is the learning curve when migrating from SDKv2 to the plugin framework - while migration is well-documented, it requires significant refactoring. Testing utilities are solid with acceptance test helpers, though mocking can be verbose. IDE support is excellent thanks to Go's strong typing, making autocomplete and refactoring reliable.

Working with the Terraform SDK as a provider developer, you'll find a well-structured framework that handles much of the heavy lifting around state management, authentication patterns, and schema validation. The SDK enforces input validation through its schema system with built-in type checking and validation functions, which helps prevent common injection issues. The crypto defaults are solid—TLS certificate validation is strict by default, and the SDK doesn't encourage insecure shortcuts.

Error handling requires attention though. The framework returns errors that can inadvertently expose sensitive data from provider configurations or API responses if you're not careful about what you include in diagnostic messages. You need to consciously sanitize errors before they bubble up to users. The authentication design is flexible but puts responsibility on you to implement secure credential handling—the SDK provides patterns but doesn't enforce them.

Dependency management is reasonable with HashiCorp maintaining the core, though you'll need to stay on top of transitive dependencies in the broader ecosystem. The framework follows secure-by-default principles in most areas, but requires developer discipline around secrets handling and error exposure.

The Terraform core library provides a robust framework for building infrastructure-as-code tooling, particularly custom providers. The plugin protocol is well-designed with gRPC-based communication that enforces structured data flow between core and providers. State management includes encryption-at-rest support through backend configurations, though you need to explicitly enable it.

From a security perspective, the library handles sensitive data marking reasonably well through the schema system, preventing accidental exposure in logs and plan outputs. Input validation is your responsibility at the provider level, which gives flexibility but requires discipline. The error handling can be verbose but generally avoids leaking credentials or internal paths when configured properly. TLS configuration for remote backends defaults to secure settings, requiring explicit opt-out for insecure connections.

Dependency management is straightforward since HashiCorp maintains tight control over the core APIs. Breaking changes are clearly communicated through major version bumps. The biggest challenge is keeping up with provider protocol versions and ensuring backward compatibility when building custom providers.