retry

backend/epc_client/_retry.py

@@ -11,6 +11,7 @@ def call_with_retry(
     max_retries: int = 5,
     backoff_base: float = 1.0,
     backoff_multiplier: float = 2.0,
+    max_backoff: float = 60.0,
 ) -> T:
     last_exc: EpcRateLimitError | None = None
     for attempt in range(max_retries + 1):
@@ -19,5 +20,9 @@ def call_with_retry(
         except EpcRateLimitError as exc:
             last_exc = exc
             if attempt < max_retries:
-                time.sleep(backoff_base * (backoff_multiplier ** attempt))
+                if exc.retry_after is not None:
+                    delay = exc.retry_after
+                else:
+                    delay = backoff_base * (backoff_multiplier ** attempt)
+                time.sleep(min(delay, max_backoff))
     raise last_exc  # type: ignore[misc]

backend/epc_client/epc_client_service.py

@@ -18,6 +18,7 @@ from datatypes.epc.search import EpcSearchResult
 
 class EpcClientService:
     BASE_URL = "https://api.get-energy-performance-data.communities.gov.uk"
+    REQUEST_TIMEOUT = 10.0
 
     def __init__(self, auth_token: str) -> None:
         self._headers = {
@@ -25,6 +26,16 @@ class EpcClientService:
             "Accept": "application/json",
         }
 
+    @staticmethod
+    def _parse_retry_after(resp: httpx.Response) -> Optional[float]:
+        header = resp.headers.get("Retry-After")
+        if header is None:
+            return None
+        try:
+            return float(header)
+        except (TypeError, ValueError):
+            return None
+
     def get_by_certificate_number(self, cert_num: str) -> EpcPropertyData:
         raw = call_with_retry(lambda: self._fetch_certificate(cert_num))
         return EpcPropertyDataMapper.from_api_response(raw)
@@ -48,11 +59,15 @@ class EpcClientService:
             f"{self.BASE_URL}/api/certificate",
             params={"certificate_number": cert_num},
             headers=self._headers,
+            timeout=self.REQUEST_TIMEOUT,
         )
         if resp.status_code == 404:
             raise EpcNotFoundError(cert_num)
         if resp.status_code == 429:
-            raise EpcRateLimitError("Rate limited by EPC API")
+            raise EpcRateLimitError(
+                "Rate limited by EPC API",
+                retry_after=self._parse_retry_after(resp),
+            )
         if not resp.is_success:
             raise EpcApiError(f"EPC API error {resp.status_code}: {resp.text}")
         return resp.json()["data"]
@@ -72,11 +87,15 @@ class EpcClientService:
             f"{self.BASE_URL}/api/domestic/search",
             params=params,
             headers=self._headers,
+            timeout=self.REQUEST_TIMEOUT,
         )
         if resp.status_code == 404:
             return []
         if resp.status_code == 429:
-            raise EpcRateLimitError("Rate limited by EPC API")
+            raise EpcRateLimitError(
+                "Rate limited by EPC API",
+                retry_after=self._parse_retry_after(resp),
+            )
         if not resp.is_success:
             raise EpcApiError(f"EPC API error {resp.status_code}: {resp.text}")
 

backend/epc_client/exceptions.py

@@ -1,3 +1,6 @@
+from typing import Optional
+
+
 class EpcApiError(Exception):
     """Base for all EPC client errors."""
 
@@ -8,3 +11,7 @@ class EpcNotFoundError(EpcApiError):
 
 class EpcRateLimitError(EpcApiError):
     """Raised when the API returns 429 and all retries are exhausted."""
+
+    def __init__(self, message: str, retry_after: Optional[float] = None) -> None:
+        super().__init__(message)
+        self.retry_after = retry_after