feat: Etag cache control for Discovery data store and service #61

doc/discovery-service-openapi.yaml

@@ -31,6 +31,14 @@ paths:
     get:
       summary: Get all backends
       description: Retrieves a list of all registered Lightning node backends.
+      parameters:
+        - name: If-None-Match
+          in: header
+          required: false
+          description: ETag value from a previous response. If it matches the current ETag, returns 304 Not Modified.
+          schema:
+            type: string
+          example: "12345"
       responses:
         '200':
           description: List of backends
@@ -47,12 +55,37 @@ paths:
               schema:
                 type: string
                 example: "no-cache"
+            ETag:
+              schema:
+                type: string
+              description: Current version of the backend list
+              example: "12345"
           content:
             application/json:
               schema:
                 type: array
                 items:
                   $ref: '#/components/schemas/DiscoveryBackendRest'
+        '304':
+          description: Not Modified - backend list hasn't changed since the ETag provided in If-None-Match
+          headers:
+            Cache-Control:
+              schema:
+                type: string
+                example: "no-store, no-cache, must-revalidate"
+            Expires:
+              schema:
+                type: string
+                example: "Thu, 01 Jan 1970 00:00:00 GMT"
+            Pragma:
+              schema:
+                type: string
+                example: "no-cache"
+            ETag:
+              schema:
+                type: string
+              description: Current version of the backend list (same as the If-None-Match value)
+              example: "12345"
   /discovery/{addr_variant}/{addr_value}:
     get:
       summary: Get specific backend

migration/src/lib.rs

@@ -1,5 +1,7 @@
 pub use sea_orm_migration::prelude::*;
 
+pub const DISCOVERY_BACKEND_GET_ALL_ETAG_ID: i32 = 1;
+
 mod m20220101_000001_create_table;
 mod m20250724_182058_create_table;
 

migration/src/m20220101_000001_create_table.rs

@@ -1,3 +1,4 @@
+use crate::DISCOVERY_BACKEND_GET_ALL_ETAG_ID;
 use sea_orm_migration::{prelude::*, schema::*};
 
 #[derive(DeriveMigrationName)]
@@ -31,10 +32,35 @@ impl MigrationTrait for DiscoveryBackendMigration {
                     .primary_key(Index::create().col(DiscoveryBackend::Address))
                     .to_owned(),
             )
-            .await
+            .await?;
+
+        manager
+            .create_table(
+                Table::create()
+                    .table(DiscoveryBackendEtag::Table)
+                    .if_not_exists()
+                    .col(integer(DiscoveryBackendEtag::Id).not_null())
+                    .col(big_integer(DiscoveryBackendEtag::Value).not_null())
+                    .primary_key(Index::create().col(DiscoveryBackendEtag::Id))
+                    .to_owned(),
+            )
+            .await?;
+
+        let insert_stmt = Query::insert()
+            .into_table(DiscoveryBackendEtag::Table)
+            .columns([DiscoveryBackendEtag::Id, DiscoveryBackendEtag::Value])
+            .values([DISCOVERY_BACKEND_GET_ALL_ETAG_ID.into(), 0.into()])
+            .map_err(|e| DbErr::Custom(e.to_string()))?
+            .to_owned();
+
+        manager.exec_stmt(insert_stmt).await
     }
 
     async fn down(&self, manager: &SchemaManager) -> Result<(), DbErr> {
+        manager
+            .drop_table(Table::drop().table(DiscoveryBackendEtag::Table).to_owned())
+            .await?;
+
         manager
             .drop_table(Table::drop().table(DiscoveryBackend::Table).to_owned())
             .await
@@ -54,3 +80,10 @@ enum DiscoveryBackend {
     CreatedAt,
     UpdatedAt,
 }
+
+#[derive(DeriveIden)]
+enum DiscoveryBackendEtag {
+    Table,
+    Id,
+    Value,
+}