Feature delay argument for iterator

package.json

@@ -94,6 +94,7 @@
     "millify": "^6.1.0",
     "n3": "^1.17.2",
     "ora": "^7.0.1",
+    "parse-duration": "^1.1.0",
     "pretty-ms": "^8.0.0",
     "sparqljs": "^3.7.1"
   }

src/lib/Generator.class.ts

@@ -99,4 +99,5 @@ class Generator extends EventEmitter {
   }
 }
 
+
 export default Generator

src/lib/Iterator.class.ts

@@ -10,6 +10,7 @@ import getEndpoint from "../utils/getEndpoint.js";
 import type { Endpoint, QueryEngine } from "./types.js";
 import getEngine from "../utils/getEngine.js";
 import getEngineSource from "../utils/getEngineSource.js";
+import parse from 'parse-duration'
 
 const DEFAULT_LIMIT = 10;
 declare interface Iterator {
@@ -26,6 +27,7 @@ class Iterator extends EventEmitter {
   private readonly query: SelectQuery;
   public readonly endpoint: Endpoint;
   private readonly engine: QueryEngine;
+  private readonly delay: number | undefined
   private source: string = "";
   private $offset = 0;
   private totalResults = 0;
@@ -39,52 +41,58 @@ class Iterator extends EventEmitter {
       DEFAULT_LIMIT;
     this.endpoint = getEndpoint(stage);
     this.engine = getEngine(this.endpoint);
+    if (stage.configuration.iterator.delay !== undefined){
+      const delay = parse(stage.configuration.iterator.delay)
+      if (delay === undefined) throw new Error(`Error in stage \`${stage.configuration.name}\`: incorrect delay format was provided.`)
+      this.delay = delay
+    }
   }
 
   public run(): void {
-    let resultsPerPage = 0;
-    if (this.source === "") this.source = getEngineSource(this.endpoint);
-    this.query.offset = this.$offset;
-    const queryString = getSPARQLQueryString(this.query);
-    const error = (e: any): Error => new Error(
-      `The Iterator did not run succesfully, it could not get the results from the endpoint ${this.source} (offset: ${this.$offset}, limit ${this.query.limit}): ${(e as Error).message}`
-    )
-    this.engine
-      .queryBindings(queryString, {
-        sources: [this.source],
-      })
-      .then((stream) => {
-        stream.on("data", (binding: Bindings) => {
-          resultsPerPage++;
-          if (!binding.has("this"))
-            throw new Error("Missing binding $this in the Iterator result.");
-          const $this = binding.get("this")!;
-          if ($this.termType !== "NamedNode") {
-            throw new Error(
-              `Binding $this in the Iterator result must be an Iri/NamedNode, but it is of type ${$this.termType}.`
-            );
-          } else {
-            this.emit("data", $this);
-          }
-        });
-
-        stream.on("end", () => {
-          this.totalResults += resultsPerPage;
-          this.$offset += this.query.limit!;
-          if (resultsPerPage < this.query.limit!) {
-            this.emit("end", this.totalResults);
-          } else {
-            this.run();
-          }
-        });
-
-        stream.on('error', (e) => {
-          this.emit("error", error(e))
+    setTimeout(() => {                
+      let resultsPerPage = 0;
+      if (this.source === "") this.source = getEngineSource(this.endpoint);
+      this.query.offset = this.$offset;
+      const queryString = getSPARQLQueryString(this.query);
+      const error = (e: any): Error => new Error(
+        `The Iterator did not run succesfully, it could not get the results from the endpoint ${this.source} (offset: ${this.$offset}, limit ${this.query.limit}): ${(e as Error).message}`
+      )
+      this.engine
+        .queryBindings(queryString, {
+          sources: [this.source],
+        })
+        .then((stream) => {
+          stream.on("data", (binding: Bindings) => {
+            resultsPerPage++;
+            if (!binding.has("this"))
+              throw new Error("Missing binding $this in the Iterator result.");
+            const $this = binding.get("this")!;
+            if ($this.termType !== "NamedNode") {
+              throw new Error(
+                `Binding $this in the Iterator result must be an Iri/NamedNode, but it is of type ${$this.termType}.`
+              );
+            } else {
+              this.emit("data", $this);
+            }
+          });
+          stream.on("end", () => {
+            this.totalResults += resultsPerPage;
+            this.$offset += this.query.limit!;
+            if (resultsPerPage < this.query.limit!) {
+              this.emit("end", this.totalResults);
+            } else {
+              this.run();
+            }
+          });
+
+          stream.on('error', (e) => {
+            this.emit("error", error(e))
+          })
         })
-      })
-      .catch((e) => {
-        this.emit("error", error(e))
-      });
+        .catch((e) => {
+          this.emit("error", error(e))
+        });
+    }, this.delay ?? 0)
   }
 }
 

src/lib/LDWorkbenchConfiguration.d.ts

@@ -49,6 +49,10 @@ export interface LDWorkbenchConfiguration {
          * Overrule the iterator's behaviour of fetching 10 results per request, regardless of any limit's in your query.
          */
         batchSize?: number;
+        /**
+         * Human readable time delay for the iterator's SPARQL endpoint requests (e.g. '5ms', '100 milliseconds', '1s').
+         */
+        delay?: string;
       };
       /**
        * @minItems 1
@@ -117,6 +121,10 @@ export interface LDWorkbenchConfiguration {
          * Overrule the iterator's behaviour of fetching 10 results per request, regardless of any limit's in your query.
          */
         batchSize?: number;
+        /**
+         * Human readable time delay for the iterator's SPARQL endpoint requests (e.g. '5ms', '100 milliseconds', '1s').
+         */
+        delay?: string;
       };
       /**
        * @minItems 1

static/example/config.yml

@@ -14,6 +14,7 @@ stages:
     iterator:
       query: file://static/example/iterator-stage-1.rq
       endpoint: https://api.triplydb.com/datasets/Triply/iris/services/demo-service/sparql
+      delay: "50ms"
     generator: 
       # First generator
       -  query: file://static/example/generator-stage-1-1.rq 

static/ld-workbench.schema.json

@@ -47,6 +47,10 @@
                 "type": "number",
                 "minimum": 1,
                 "description": "Overrule the iterator's behaviour of fetching 10 results per request, regardless of any limit's in your query."
+              },
+              "delay": {
+                "type": "string",
+                "description": "Human readable time delay for the iterator's SPARQL endpoint requests (e.g. '5ms', '100 milliseconds', '1s'). "
               }
             }
           },