Improve go docs (#168)

* Improve go docs

* Update apm-lambda-extension/extension/apm_server.go

Co-authored-by: Jean-Louis Voiseux <48380853+jlvoiseux@users.noreply.github.com>

* Update apm-lambda-extension/extension/apm_server.go

Co-authored-by: Jean-Louis Voiseux <48380853+jlvoiseux@users.noreply.github.com>

Co-authored-by: Jean-Louis Voiseux <48380853+jlvoiseux@users.noreply.github.com>

Author: estolfo

apm-lambda-extension/extension/apm_server.go

@@ -38,24 +38,36 @@ var bufferPool = sync.Pool{New: func() interface{} {
 
 type ApmServerTransportStatusType string
 
+// Constants for the state of the transport used in
+// the backoff implementation.
 const (
 	Failing ApmServerTransportStatusType = "Failing"
 	Pending ApmServerTransportStatusType = "Pending"
 	Healthy ApmServerTransportStatusType = "Healthy"
 )
 
+// A struct to track the state and status of sending
+// to the APM server. Used in the backoff implementation.
 type ApmServerTransportStateType struct {
 	sync.Mutex
 	Status            ApmServerTransportStatusType
 	ReconnectionCount int
 	GracePeriodTimer  *time.Timer
 }
 
+// The status of transport to the APM server.
+//
+// This instance of the ApmServerTransportStateType is public for use in tests.
 var ApmServerTransportState = ApmServerTransportStateType{
 	Status:            Healthy,
 	ReconnectionCount: -1,
 }
 
+// PostToApmServer takes a chunk of APM agent data and posts it to the APM server.
+//
+// The function compresses the APM agent data, if it's not already compressed.
+// It sets the APM transport status to failing upon errors, as part of the backoff
+// strategy.
 func PostToApmServer(client *http.Client, agentData AgentData, config *extensionConfig, ctx context.Context) error {
 	// todo: can this be a streaming or streaming style call that keeps the
 	//       connection open across invocations?
@@ -123,10 +135,21 @@ func PostToApmServer(client *http.Client, agentData AgentData, config *extension
 	return nil
 }
 
+// IsTransportStatusHealthyOrPending returns true if the APM server transport status is 
+// healthy or pending, and false otherwise.
+//
+// This function is public for use in tests.
 func IsTransportStatusHealthyOrPending() bool {
 	return ApmServerTransportState.Status != Failing
 }
 
+// SetApmServerTransportState takes a state of the APM server transport and updates
+// the current state of the transport. For a change to a failing state, the grace period
+// is calculated and a go routine is started that waits for that period to complete
+// before changing the status to "pending". This would allow a subsequent send attempt
+// to the APM server.
+//
+// This function is public for use in tests.
 func SetApmServerTransportState(status ApmServerTransportStatusType, ctx context.Context) {
 	switch status {
 	case Healthy:
@@ -165,6 +188,8 @@ func computeGracePeriod() time.Duration {
 	return time.Duration((gracePeriodWithoutJitter + jitter*gracePeriodWithoutJitter) * float64(time.Second))
 }
 
+// EnqueueAPMData adds a AgentData struct to the agent data channel, effectively queueing for a send
+// to the APM server.
 func EnqueueAPMData(agentDataChannel chan AgentData, agentData AgentData) {
 	select {
 	case agentDataChannel <- agentData:

apm-lambda-extension/extension/http_server.go

@@ -25,6 +25,7 @@ import (
 
 var agentDataServer *http.Server
 
+// StartHttpServer starts the server listening for APM agent data.
 func StartHttpServer(agentDataChan chan AgentData, config *extensionConfig) (err error) {
 	mux := http.NewServeMux()
 	mux.HandleFunc("/", handleInfoRequest(config.apmServerUrl))

apm-lambda-extension/extension/process_env.go

@@ -63,7 +63,7 @@ func getIntFromEnv(name string) (int, error) {
 	return value, nil
 }
 
-// ProcessEnv : pull env into globals
+// ProcessEnv extracts ENV variables into globals
 func ProcessEnv() *extensionConfig {
 	dataReceiverTimeoutSeconds, err := getIntFromEnv("ELASTIC_APM_DATA_RECEIVER_TIMEOUT_SECONDS")
 	if err != nil {

apm-lambda-extension/extension/process_events.go

@@ -23,11 +23,14 @@ import (
 	"net/http"
 )
 
+// ProcessShutdown processes the Shutdown event received from the
+// Lambda runtime API.
 func ProcessShutdown() {
 	Log.Info("Received SHUTDOWN event, exiting")
 	agentDataServer.Close()
 }
 
+// FlushAPMData reads all the apm data in the apm data channel and sends it to the APM server.
 func FlushAPMData(client *http.Client, dataChannel chan AgentData, config *extensionConfig, ctx context.Context) {
 	if !IsTransportStatusHealthyOrPending() {
 		Log.Debug("Flush skipped - Transport unhealthy")
@@ -48,6 +51,7 @@ func FlushAPMData(client *http.Client, dataChannel chan AgentData, config *exten
 	}
 }
 
+// PrettyPrint prints formatted, legible json data.
 func PrettyPrint(v interface{}) string {
 	data, err := json.MarshalIndent(v, "", "\t")
 	if err != nil {

apm-lambda-extension/logsapi/client.go

@@ -55,6 +55,7 @@ const (
 	Extension EventType = "extension"
 )
 
+// SubEventType is a Logs API sub event type
 type SubEventType string
 
 const (
@@ -108,6 +109,7 @@ type Destination struct {
 	Encoding   HttpEncoding `json:"encoding"`
 }
 
+// SchemaVersion is the Lambda runtime API schema version
 type SchemaVersion string
 
 const (

apm-lambda-extension/logsapi/subscribe.go

@@ -33,13 +33,15 @@ var ListenerHost = "sandbox"
 var Server *http.Server
 var Listener net.Listener
 
+// LogEvent represents an event received from the Logs API
 type LogEvent struct {
 	Time         time.Time    `json:"time"`
 	Type         SubEventType `json:"type"`
 	StringRecord string
 	Record       LogEventRecord
 }
 
+// LogEventRecord is a sub-object in a Logs API event
 type LogEventRecord struct {
 	RequestId string `json:"requestId"`
 	Status    string `json:"status"`
@@ -63,7 +65,7 @@ func subscribe(extensionID string, eventTypes []EventType) error {
 	return err
 }
 
-// Subscribe : Starts the HTTP server listening for log events and subscribes to the Logs API
+// Subscribe starts the HTTP server listening for log events and subscribes to the Logs API
 func Subscribe(ctx context.Context, extensionID string, eventTypes []EventType, out chan LogEvent) (err error) {
 	if checkAWSSamLocal() {
 		return errors.New("Detected sam local environment")