fix: add debug logger that accepts a function

src/logger.ts

@@ -587,6 +587,22 @@ export class Logger {
     return this;
   }
 
+  /**
+   * Logs at `debug` level with filtering applied.
+   *
+   * @param cb A callback that returns on array objects to be logged.
+   */
+  public debugCallback(cb: () => Array<unknown> | string) {
+    if (this.getLevel() === LoggerLevel.DEBUG || process.env.DEBUG) {
+      const result = cb();
+      if (isArray(result)) {
+        this.bunyan.debug(this.applyFilters(LoggerLevel.DEBUG, ...result));
+      } else {
+        this.bunyan.debug(this.applyFilters(LoggerLevel.DEBUG, ...[result]));
+      }
+    }
+  }
+
   /**
    * Logs at `info` level with filtering applied. For convenience `this` object is returned.
    *

test/unit/loggerTest.ts

@@ -168,6 +168,29 @@ describe('Logger', () => {
     });
   });
 
+  describe('debugCallback', () => {
+    it('should log', async () => {
+      const logger = (await Logger.child('testLogger')).useMemoryLogging();
+      logger.setLevel(LoggerLevel.DEBUG);
+      const FOO = 'foo';
+      const BAR = 'bar';
+      const spy = $$.SANDBOX.spy(() => [FOO, BAR]);
+      logger.debugCallback(spy);
+      expect(spy.callCount).to.be.equal(1);
+      expect(logger.readLogContentsAsText())
+        .to.include(FOO)
+        .and.to.include(BAR);
+    });
+
+    it("shouldn't log", async () => {
+      const logger = (await Logger.child('testLogger')).useMemoryLogging();
+      const fooSpy = $$.SANDBOX.spy(() => 'FOO');
+      const cbSpy = $$.SANDBOX.spy(() => `${fooSpy()}`);
+      logger.debugCallback(cbSpy);
+      expect(fooSpy.callCount).to.be.equal(0);
+      expect(cbSpy.callCount).to.be.equal(0);
+    });
+  });
   describe('filters', () => {
     const sid = 'SIDHERE!';
     const simpleString = `sid=${sid}`;