fn: introduce agent config and minor ghostreader tweak (#797)

* fn: introduce agent config and minor ghostreader tweak

TODO: move all constants/tweaks in agent to agent config.

* fn: json convention

api/agent/agent.go

@@ -3,10 +3,7 @@ package agent
 import (
 	"context"
 	"io"
-	"math"
 	"net/http"
-	"os"
-	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -98,6 +95,7 @@ type Agent interface {
 }
 
 type agent struct {
+	cfg           AgentConfig
 	da            DataAccess
 	callListeners []fnext.CallListener
 
@@ -112,42 +110,30 @@ type agent struct {
 	shutonce sync.Once
 	shutdown chan struct{}
 
-	freezeIdleMsecs time.Duration
-	ejectIdleMsecs  time.Duration
-
 	// Prometheus HTTP handler
 	promHandler http.Handler
 }
 
 func New(da DataAccess) Agent {
+
+	cfg, err := NewAgentConfig()
+	if err != nil {
+		logrus.WithField("cfg", cfg).WithError(err).Fatal("error in agent config")
+	}
+	logrus.WithField("cfg", cfg).Info("agent starting")
+
 	// TODO: Create drivers.New(runnerConfig)
 	driver := docker.NewDocker(drivers.Config{
 		ServerVersion: "17.06.0-ce",
 	})
 
-	freezeIdleMsecs, err := getEnvMsecs("FN_FREEZE_IDLE_MSECS", 50*time.Millisecond)
-	if err != nil {
-		logrus.WithError(err).Fatal("error initializing freeze idle delay")
-	}
-
-	ejectIdleMsecs, err := getEnvMsecs("FN_EJECT_IDLE_MSECS", 1000*time.Millisecond)
-	if err != nil {
-		logrus.WithError(err).Fatal("error initializing eject idle delay")
-	}
-	if ejectIdleMsecs == time.Duration(0) {
-		logrus.Fatal("eject idle delay cannot be zero")
-	}
-
-	logrus.WithFields(logrus.Fields{"eject_msec": ejectIdleMsecs, "free_msec": freezeIdleMsecs}).Info("agent starting")
-
 	a := &agent{
+		cfg:         *cfg,
 		da:          da,
 		driver:      driver,
 		slotMgr:     NewSlotQueueMgr(),
 		resources:   NewResourceTracker(),
 		shutdown:    make(chan struct{}),
-		freezeIdleMsecs: freezeIdleMsecs,
-		ejectIdleMsecs:  ejectIdleMsecs,
 		promHandler: promhttp.Handler(),
 	}
 
@@ -158,26 +144,6 @@ func New(da DataAccess) Agent {
 	return a
 }
 
-func getEnvMsecs(name string, defaultVal time.Duration) (time.Duration, error) {
-
-	delay := defaultVal
-
-	if dur := os.Getenv(name); dur != "" {
-		durInt, err := strconv.ParseInt(dur, 10, 64)
-		if err != nil {
-			return defaultVal, err
-		}
-		// disable if negative or set to msecs specified.
-		if durInt < 0 || time.Duration(durInt) >= math.MaxInt64/time.Millisecond {
-			delay = math.MaxInt64
-		} else {
-			delay = time.Duration(durInt) * time.Millisecond
-		}
-	}
-
-	return delay, nil
-}
-
 // TODO shuffle this around somewhere else (maybe)
 func (a *agent) Enqueue(ctx context.Context, call *models.Call) error {
 	return a.da.Enqueue(ctx, call)
@@ -747,9 +713,9 @@ func (a *agent) runHotReq(ctx context.Context, call *call, state ContainerState,
 	var err error
 	isFrozen := false
 
-	freezeTimer := time.NewTimer(a.freezeIdleMsecs)
+	freezeTimer := time.NewTimer(a.cfg.FreezeIdleMsecs)
 	idleTimer := time.NewTimer(time.Duration(call.IdleTimeout) * time.Second)
-	ejectTicker := time.NewTicker(a.ejectIdleMsecs)
+	ejectTicker := time.NewTicker(a.cfg.EjectIdleMsecs)
 
 	defer freezeTimer.Stop()
 	defer idleTimer.Stop()
@@ -763,7 +729,7 @@ func (a *agent) runHotReq(ctx context.Context, call *call, state ContainerState,
 	}()
 
 	// if an immediate freeze is requested, freeze first before enqueuing at all.
-	if a.freezeIdleMsecs == time.Duration(0) && !isFrozen {
+	if a.cfg.FreezeIdleMsecs == time.Duration(0) && !isFrozen {
 		err = cookie.Freeze(ctx)
 		if err != nil {
 			return false
@@ -846,14 +812,10 @@ type container struct {
 }
 
 func (c *container) swap(stdin io.Reader, stdout, stderr io.Writer, cs *drivers.Stats) func() {
-	ostdin := c.stdin.(*ghostReader).inner
-	ostdout := c.stdout.(*ghostWriter).inner
-	ostderr := c.stderr.(*ghostWriter).inner
-
 	// if tests don't catch this, then fuck me
-	c.stdin.(*ghostReader).swap(stdin)
-	c.stdout.(*ghostWriter).swap(stdout)
-	c.stderr.(*ghostWriter).swap(stderr)
+	ostdin := c.stdin.(*ghostReader).swap(stdin)
+	ostdout := c.stdout.(*ghostWriter).swap(stdout)
+	ostderr := c.stderr.(*ghostWriter).swap(stderr)
 
 	c.statsMu.Lock()
 	ocs := c.stats
@@ -947,11 +909,13 @@ type ghostReader struct {
 	closed bool
 }
 
-func (g *ghostReader) swap(r io.Reader) {
+func (g *ghostReader) swap(r io.Reader) (old io.Reader) {
 	g.cond.L.Lock()
+	old = g.inner
 	g.inner = r
 	g.cond.L.Unlock()
 	g.cond.Broadcast()
+	return old
 }
 
 func (g *ghostReader) Close() {

api/agent/config.go

@@ -0,0 +1,60 @@
+package agent
+
+import (
+	"errors"
+	"math"
+	"os"
+	"strconv"
+	"time"
+)
+
+type AgentConfig struct {
+	MinDockerVersion string        `json:"min_docker_version"`
+	FreezeIdleMsecs  time.Duration `json:"freeze_idle_msecs"`
+	EjectIdleMsecs   time.Duration `json:"eject_idle_msecs"`
+}
+
+func NewAgentConfig() (*AgentConfig, error) {
+
+	var err error
+
+	cfg := &AgentConfig{
+		MinDockerVersion: "17.06.0-ce",
+	}
+
+	cfg.FreezeIdleMsecs, err = getEnvMsecs("FN_FREEZE_IDLE_MSECS", 50*time.Millisecond)
+	if err != nil {
+		return cfg, errors.New("error initializing freeze idle delay")
+	}
+
+	cfg.EjectIdleMsecs, err = getEnvMsecs("FN_EJECT_IDLE_MSECS", 1000*time.Millisecond)
+	if err != nil {
+		return cfg, errors.New("error initializing eject idle delay")
+	}
+
+	if cfg.EjectIdleMsecs == time.Duration(0) {
+		return cfg, errors.New("error eject idle delay cannot be zero")
+	}
+
+	return cfg, nil
+}
+
+func getEnvMsecs(name string, defaultVal time.Duration) (time.Duration, error) {
+
+	delay := defaultVal
+
+	if dur := os.Getenv(name); dur != "" {
+		durInt, err := strconv.ParseInt(dur, 10, 64)
+		if err != nil {
+			return defaultVal, err
+		}
+		// disable if negative or set to msecs specified.
+		if durInt < 0 || time.Duration(durInt) >= math.MaxInt64/time.Millisecond {
+			delay = math.MaxInt64
+		} else {
+			delay = time.Duration(durInt) * time.Millisecond
+		}
+	}
+
+	return delay, nil
+}