TestData: stream via fetch (#16963)

Stream from fetch CSV

public/app/plugins/datasource/testdata/StreamHandler.ts

@@ -9,6 +9,7 @@ import {
   DataStreamState,
   LoadingState,
   LogLevel,
+  CSVReader,
 } from '@grafana/ui';
 import { TestDataQuery, StreamingQuery } from './types';
 
@@ -57,6 +58,8 @@ export class StreamHandler {
         this.workers[key] = new SignalWorker(key, query, req, observer);
       } else if (type === 'logs') {
         this.workers[key] = new LogsWorker(key, query, req, observer);
+      } else if (type === 'fetch') {
+        this.workers[key] = new FetchWorker(key, query, req, observer);
       } else {
         throw {
           message: 'Unknown Stream type: ' + type,
@@ -72,6 +75,7 @@ export class StreamHandler {
  * Manages a single stream request
  */
 export class StreamWorker {
+  refId: string;
   query: StreamingQuery;
   stream: DataStreamState;
   observer: DataStreamObserver;
@@ -85,6 +89,7 @@ export class StreamWorker {
       request,
       unsubscribe: this.unsubscribe,
     };
+    this.refId = query.refId;
     this.query = query.stream;
     this.last = Date.now();
     this.observer = observer;
@@ -207,6 +212,56 @@ export class SignalWorker extends StreamWorker {
   };
 }
 
+export class FetchWorker extends StreamWorker {
+  csv: CSVReader;
+  reader: ReadableStreamReader<Uint8Array>;
+
+  constructor(key: string, query: TestDataQuery, request: DataQueryRequest, observer: DataStreamObserver) {
+    super(key, query, request, observer);
+    if (!query.stream.url) {
+      throw new Error('Missing Fetch URL');
+    }
+    if (!query.stream.url.startsWith('http')) {
+      throw new Error('Fetch URL must be absolute');
+    }
+
+    this.csv = new CSVReader({ callback: this });
+    fetch(new Request(query.stream.url)).then(response => {
+      this.reader = response.body.getReader();
+      this.reader.read().then(this.processChunk);
+    });
+  }
+
+  processChunk = (value: ReadableStreamReadResult<Uint8Array>): any => {
+    if (this.observer == null) {
+      return; // Nothing more to do
+    }
+
+    if (value.value) {
+      const text = new TextDecoder().decode(value.value);
+      this.csv.readCSV(text);
+    }
+
+    if (value.done) {
+      console.log('Finished stream');
+      this.stream.state = LoadingState.Done;
+      return;
+    }
+
+    return this.reader.read().then(this.processChunk);
+  };
+
+  onHeader = (series: SeriesData) => {
+    series.refId = this.refId;
+    this.stream.series = [series];
+  };
+
+  onRow = (row: any[]) => {
+    // TODO?? this will send an event for each row, even if the chunk passed a bunch of them
+    this.appendRows([row]);
+  };
+}
+
 export class LogsWorker extends StreamWorker {
   index = 0;