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Build: The Anthropic Client

Maps to: Task 8. Kind: Build.

Objective

Implement AnthropicClient — a concrete ModelClient that builds the request, sends it, and parses the completion into a ModelResponse. Test it entirely against a wiremock mock server, spending no API credits.

Scaffold

Create: crates/panoptes-harness/src/anthropic.rs. Modify: crates/panoptes-harness/src/lib.rs (re-export AnthropicClient).

Dependencies: no manifest changes — reqwest and the dev-only wiremock were declared when you created the crate. The test needs #[tokio::test], which tokio's full features already cover.

Expected result: cargo test -p panoptes-harness anthropic → 1 test passes (parses_a_mocked_completion).

The spec (givens)

  • AnthropicClient fields: api_key, model, base_url (all public String — base_url injectable so tests can point at the mock) plus a private http: reqwest::Client. Constructor new(api_key, model, base_url).
  • Request: POST {base_url}/v1/messages with headers x-api-key: <key> and anthropic-version: 2023-06-01; JSON body {"model": …, "max_tokens": 1024, "messages": [{"role": "user", "content": <prompt>}]}.
  • Response shape to deserialize: {"content": [{"text": …}, …], "usage": {"input_tokens": …, "output_tokens": …}} — concatenate the block texts in order.

Full code: Answer Key, Task 8.

Concepts exercised

  • reqwest JSON POST with headers.
  • Deserializing a nested API response into typed structs.
  • wiremock mock definitions and #[tokio::test].

The build loop (you drive)

  1. Write the failing test parses_a_mocked_completion: mount a mock returning a known completion + usage, call generate, assert the parsed text and token counts.
  2. Predict: the response JSON has a content array of blocks. What does your parsing do if the array is empty? Decide the behavior before implementing.
  3. Run, check.
  4. Implement the client with an injectable base_url.
  5. Run green, commit.
Verify against live docs The request and response shapes here are written to match the API's structure, but API schemas change. When you build this for real, check the current request/response format against the official documentation before trusting the parse. The mock proves your parsing logic; it does not prove the schema is current.

Done when

cargo test -p panoptes-harness anthropic passes. Adding a second provider (OpenAI, a local gateway) is now "copy this file, change the request/response shapes" — the trait makes providers uniform.