From 8ca2fd0092d51d1edf3ebd25ccd3884c5c336e5a Mon Sep 17 00:00:00 2001
From: Matthew Evans <git@ml-evs.science>
Date: Tue, 6 Dec 2022 19:14:54 +0000
Subject: [PATCH] Add configurable `request_delay` support to server and models

---
 openapi/index_openapi.json       |  6 ++++++
 openapi/openapi.json             |  6 ++++++
 optimade/models/optimade_json.py | 14 +++++++++++++-
 optimade/server/config.py        | 14 ++++++++++++++
 optimade/server/routers/utils.py |  4 ++++
 5 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/openapi/index_openapi.json b/openapi/index_openapi.json
index 38b883057..264f294e3 100644
--- a/openapi/index_openapi.json
+++ b/openapi/index_openapi.json
@@ -1710,6 +1710,12 @@
             "type": "string",
             "description": "response string from the server"
           },
+          "request_delay": {
+            "title": "Request Delay",
+            "minimum": 0.0,
+            "type": "number",
+            "description": "A non-negative float giving time in seconds that the client is suggested to wait before issuing a subsequent request."
+          },
           "implementation": {
             "title": "Implementation",
             "allOf": [
diff --git a/openapi/openapi.json b/openapi/openapi.json
index 918a2965c..d3498d34e 100644
--- a/openapi/openapi.json
+++ b/openapi/openapi.json
@@ -3280,6 +3280,12 @@
             "type": "string",
             "description": "response string from the server"
           },
+          "request_delay": {
+            "title": "Request Delay",
+            "minimum": 0.0,
+            "type": "number",
+            "description": "A non-negative float giving time in seconds that the client is suggested to wait before issuing a subsequent request."
+          },
           "implementation": {
             "title": "Implementation",
             "allOf": [
diff --git a/optimade/models/optimade_json.py b/optimade/models/optimade_json.py
index bad738057..f611e18b6 100644
--- a/optimade/models/optimade_json.py
+++ b/optimade/models/optimade_json.py
@@ -4,7 +4,14 @@
 from enum import Enum
 from typing import Any, Dict, List, Optional, Type, Union
 
-from pydantic import AnyHttpUrl, AnyUrl, BaseModel, EmailStr, root_validator
+from pydantic import (
+    AnyHttpUrl,
+    AnyUrl,
+    BaseModel,
+    EmailStr,
+    NonNegativeFloat,
+    root_validator,
+)
 
 from optimade.models import jsonapi
 from optimade.models.utils import SemanticVersion, StrictField
@@ -313,6 +320,11 @@ class ResponseMeta(jsonapi.Meta):
         None, description="response string from the server"
     )
 
+    request_delay: Optional[NonNegativeFloat] = StrictField(
+        None,
+        description="A non-negative float giving time in seconds that the client is suggested to wait before issuing a subsequent request.",
+    )
+
     implementation: Optional[Implementation] = StrictField(
         None, description="a dictionary describing the server implementation"
     )
diff --git a/optimade/server/config.py b/optimade/server/config.py
index f763c336d..a5d820a58 100644
--- a/optimade/server/config.py
+++ b/optimade/server/config.py
@@ -292,6 +292,13 @@ class ServerConfig(BaseSettings):
         description="If True, the server will check whether the query parameters given in the request are correct.",
     )
 
+    request_delay: Optional[float] = Field(
+        None,
+        description=(
+            "The value to use for the `meta->request_delay` field, which indicates to clients how long they should leave between success queries."
+        ),
+    )
+
     @validator("implementation", pre=True)
     def set_implementation_version(cls, v):
         """Set defaults and modify bypassed value(s)"""
@@ -299,6 +306,13 @@ def set_implementation_version(cls, v):
         res.update(v)
         return res
 
+    @validator("request_delay", pre=True)
+    def check_request_delay(cls, v):
+        """Check `request_delay` is non-negative."""
+        if v is not None and v < 0:
+            raise ValueError("`request_delay` must be non-negative")
+        return v
+
     @root_validator(pre=True)
     def use_real_mongo_override(cls, values):
         """Overrides the `database_backend` setting with MongoDB and
diff --git a/optimade/server/routers/utils.py b/optimade/server/routers/utils.py
index ac19df72f..152f98370 100644
--- a/optimade/server/routers/utils.py
+++ b/optimade/server/routers/utils.py
@@ -76,6 +76,10 @@ def meta_values(
     if schema is None:
         schema = CONFIG.schema_url if not CONFIG.is_index else CONFIG.index_schema_url
 
+    if CONFIG.request_delay is not None:
+        # Add request delay via **kwargs only so that it is not set to null by default
+        kwargs["request_delay"] = CONFIG.request_delay
+
     return ResponseMeta(
         query=ResponseMetaQuery(representation=f"{url_path}?{url.query}"),
         api_version=__api_version__,