Add Runtime Info API

[posborne]

Overview

Add support for Fastly's Compute Runtime API, providing access to resource usage metrics and runtime environment information.

WIT Interface

interface compute-runtime {
  type vcpu-ms = u64;
  type memory-mib = u32;

  get-vcpu-ms: func() -> vcpu-ms;
  get-heap-mib: func() -> memory-mib;
  get-sandbox-id: func() -> string;
  get-hostname: func() -> string;
  get-pop: func() -> string;
  get-region: func() -> string;
  get-cache-generation: func() -> u64;
  get-customer-id: func() -> string;
  get-is-staging: func() -> bool;
  get-service-id: func() -> string;
  get-service-version: func() -> u64;
  get-namespace-id: func() -> string;
}

WIT bindings: stubs/wit_world/imports/compute_runtime.py

API Design

• Simple function-based module API
• Functions: vcpu_ms(), heap_usage_mib(), sandbox_id(), hostname(), pop(), region(), etc.
• All functions are simple getters returning runtime information
• No resource management needed (stateless queries)
• Values equivalent to environment variables (FASTLY_HOSTNAME, FASTLY_SERVICE_ID, etc.)

Cross-SDK Comparison: All SDKs provide getter functions for CPU/memory/time info. Rust returns structured types, Go returns primitives, JS returns objects. Python should provide simple module-level getters (get_cpu_time_ns()).

Viceroy Testing

Viceroy provides default/mock values for runtime information. Tests can verify:

• Function calls return expected types
• Sandbox ID is a valid UUID format
• Boolean flags work correctly
• Numeric values are reasonable

Actual runtime values will differ between Viceroy and production. Tests should focus on API functionality rather than specific values.

Reference

• Fastly VCL Variables