Add new TmpPath public function (#306)

* Add new TmpPath public function to return a custom tmp path to the given integration's file.
* Fix possible JMX nil pointer

jmx/jmx.go

@@ -1,7 +1,8 @@
 /*
 Package jmx is a library to get metrics through JMX. It requires additional
 setup. Read https://github.com/newrelic/infra-integrations-sdk#jmx-support for
-instructions. */
+instructions.
+*/
 package jmx
 
 import (
@@ -242,8 +243,10 @@ func openConnection(config *connectionConfig) (err error) {
 	}
 
 	go func() {
-		if err = cmd.Wait(); err != nil {
-			cmdErrC <- jmxClientError(fmt.Sprintf("nrjmx error: %s [proc-state: %s]", err, cmd.ProcessState))
+		if cmd != nil {
+			if err = cmd.Wait(); err != nil {
+				cmdErrC <- jmxClientError(fmt.Sprintf("nrjmx error: %s [proc-state: %s]", err, cmd.ProcessState))
+			}
 		}
 
 		cmd = nil

persist/storer.go

@@ -83,6 +83,15 @@ func DefaultPath(integrationName string) string {
 	return file
 }
 
+// TmpPath returns the temp folder/filename dir to a Storer for an integration using the given tmpDir or will use the default if not set.
+// The name of the file will be the given name of the integration with the .json extension.
+func TmpPath(tempDir, integrationName string) string {
+	dir := tmpIntegrationDir(tempDir)
+	file := filepath.Join(dir, integrationName+".json")
+
+	return file
+}
+
 func tmpIntegrationDir(tempDir string) string {
 	if tempDir == "" {
 		tempDir = os.TempDir()

persist/storer_test.go

@@ -516,6 +516,48 @@ func TestFileStore_DeleteOldEntriesUponSaving(t *testing.T) {
 	assert.EqualError(t, err, ErrNotFound.Error())
 }
 
+func TestFileStoreTmpPath_Save_and_Delete(t *testing.T) {
+	// Reset global variable affected by other tests to the original
+	// value used by the library.
+	SetNow(time.Now)
+
+	tempDir := path.Join(t.TempDir(), "custom")
+
+	// Given a file storer
+	// filePath includes integrationsDir conetant because the call to TmpPath sets that subFolder.
+	filePath := path.Join(tempDir, integrationsDir, "test.json")
+	ttl := 1 * time.Second
+
+	storer, err := NewFileStore(TmpPath(tempDir, "test"), log.NewStdErr(true), ttl)
+
+	// When a valid storer contains keys with timestamp greater than TTL
+	storer.Set("expiredKey", "val")
+	time.Sleep(ttl + time.Second)
+
+	storer.Set("recentKey", "v")
+
+	assert.NoError(t, storer.Save())
+
+	var val interface{}
+
+	_, err = storer.Get("recentKey", &val)
+	assert.NoError(t, err)
+
+	// Expired keys are removed from the storer on saving.
+	_, err = storer.Get("expiredKey", &val)
+	assert.EqualError(t, err, ErrNotFound.Error())
+
+	storer, err = NewFileStore(filePath, log.NewStdErr(true), ttl)
+	assert.NoError(t, err)
+
+	_, err = storer.Get("recentKey", &val)
+	assert.NoError(t, err)
+
+	// Expired keys have been removed from the file.
+	_, err = storer.Get("expiredKey", &val)
+	assert.EqualError(t, err, ErrNotFound.Error())
+}
+
 var data = []byte(`{"Timestamp":1650971736,"Value":["1","2","3","4"]}`)
 
 func Benchmark_UnmashalEntireStruct(b *testing.B) {