Logs: Fix creating of detected fields for each letter in log line (#40507)

* Logs: Fix using of JSON parser for strings

* Update packages/grafana-data/src/utils/logs.ts

* Update packages/grafana-data/src/utils/logs.ts

* Update parser typing and documentation

packages/grafana-data/src/types/logs.ts

@@ -132,9 +132,9 @@ export interface LogsParser {
   getValueFromField: (field: string) => string;
   /**
    * Function to verify if this is a valid parser for the given line.
-   * The parser accepts the line unless it returns undefined.
+   * The parser accepts the line if it returns true.
    */
-  test: (line: string) => any;
+  test: (line: string) => boolean;
 }
 
 export enum LogsDedupDescription {

packages/grafana-data/src/utils/logs.test.ts

@@ -165,6 +165,7 @@ describe('LogsParsers', () => {
 
     test('should detect format', () => {
       expect(parser.test('foo')).toBeFalsy();
+      expect(parser.test('"foo"')).toBeFalsy();
       expect(parser.test('{"foo":"bar"}')).toBeTruthy();
     });
 

packages/grafana-data/src/utils/logs.ts

@@ -83,9 +83,13 @@ export const LogsParsers: { [name: string]: LogsParser } = {
     getLabelFromField: (field) => (field.match(/^"([^"]+)"\s*:/) || [])[1],
     getValueFromField: (field) => (field.match(/:\s*(.*)$/) || [])[1],
     test: (line) => {
+      let parsed;
       try {
-        return JSON.parse(line);
+        parsed = JSON.parse(line);
       } catch (error) {}
+      // The JSON parser should only be used for log lines that are valid serialized JSON objects.
+      // If it would be used for a string, detected fields would include each letter as a separate field.
+      return typeof parsed === 'object';
     },
   },