Fixes #2 by removing all panics and replacing it with reasonable beha…

…vior (writing to log, or stdout)

cmd/ax/alert.go

@@ -43,7 +43,8 @@ func watchAlerts(ctx context.Context, rc config.RuntimeConfig, alertConfig confi
 	case "slack":
 		alerter = slack.New(alertConfig.Name, rc.DataDir, alertConfig.Service)
 	default:
-		panic("No such backend")
+		fmt.Printf("Back-end type not supported: %s\n", alertConfig.Service["backend"])
+		return
 	}
 	query := querySelectorsToQuery(&alertConfig.Selector)
 	query.Follow = true

pkg/backend/common/client.go

@@ -5,6 +5,7 @@ import (
 	"crypto/sha1"
 	"encoding/json"
 	"fmt"
+	"log"
 	"strings"
 	"time"
 )
@@ -88,7 +89,8 @@ func NewLogMessage() LogMessage {
 func MustJsonEncode(obj interface{}) string {
 	buf, err := json.Marshal(obj)
 	if err != nil {
-		panic(err)
+		log.Printf("Could not JSON encode: %+v\n", obj)
+		return "{}"
 	}
 	return string(buf)
 }
@@ -97,7 +99,7 @@ func MustJsonDecode(jsonString string, dst interface{}) {
 	decoder := json.NewDecoder(strings.NewReader(jsonString))
 	err := decoder.Decode(dst)
 	if err != nil {
-		panic(err)
+		log.Fatal(err)
 	}
 }
 
@@ -141,7 +143,8 @@ func (f QueryFilter) Matches(m LogMessage) bool {
 	case "!=":
 		return !ok || (ok && f.Value != fmt.Sprintf("%v", val))
 	default:
-		panic("Not supported operator")
+		fmt.Printf("Not supported operatior: %s\n", f.Operator)
+		return false
 	}
 }
 

pkg/backend/docker/client.go

@@ -3,6 +3,7 @@ package docker
 import (
 	"context"
 	"fmt"
+	"log"
 	"os/exec"
 	"strings"
 
@@ -21,7 +22,8 @@ func GetRunningContainers(pattern string) []string {
 	}
 	allContainers, err := exec.Command("docker", flags...).Output()
 	if err != nil {
-		panic(err)
+		log.Printf("Retrieving all containers failed: %v\n", err)
+		return []string{}
 	}
 	return strings.Split(strings.TrimSpace(string(allContainers)), "\n")
 }

pkg/backend/subprocess/client.go

@@ -2,6 +2,8 @@ package subprocess
 
 import (
 	"context"
+	"fmt"
+	"log"
 	"os/exec"
 
 	"github.com/egnyte/ax/pkg/backend/common"
@@ -13,21 +15,27 @@ type SubprocessClient struct {
 }
 
 func (client *SubprocessClient) Query(ctx context.Context, query common.Query) <-chan common.LogMessage {
+	resultChan := make(chan common.LogMessage)
 	cmd := exec.Command(client.command[0], client.command[1:]...)
 	stdOut, err := cmd.StdoutPipe()
 	if err != nil {
-		panic(err)
+		log.Printf("Could not get stdout pipe: %v", err)
+		close(resultChan)
+		return resultChan
 	}
 	stdOutStream := stream.New(stdOut)
 	stdErr, err := cmd.StderrPipe()
 	if err != nil {
-		panic(err)
+		log.Printf("Could not get stderr pipe: %v", err)
+		close(resultChan)
+		return resultChan
 	}
 	stdErrStream := stream.New(stdErr)
 	if err := cmd.Start(); err != nil {
-		panic(err)
+		fmt.Printf("Could not start process: %s because: %v\n", client.command[0], err)
+		close(resultChan)
+		return resultChan
 	}
-	resultChan := make(chan common.LogMessage)
 	go func() {
 		stdOutQuery := stdOutStream.Query(ctx, query)
 		stdErrQuery := stdErrStream.Query(ctx, query)
@@ -57,7 +65,7 @@ func (client *SubprocessClient) Query(ctx context.Context, query common.Query) <
 		}
 		close(resultChan)
 		if err := cmd.Wait(); err != nil {
-			panic(err)
+			fmt.Printf("Process exited with error: %v\n", err)
 		}
 	}()
 	return resultChan

pkg/config/config.go

@@ -306,9 +306,11 @@ func init() {
 	}
 
 	// Set up logging
-	f, err := os.Create(fmt.Sprintf("%s/ax.log", dataDir))
+	logPath := fmt.Sprintf("%s/ax.log", dataDir)
+	f, err := os.Create(logPath)
 	if err != nil {
-		panic(err)
+		fmt.Printf("Could not use %s for logging, logging to stdout instead\n", logPath)
+		return // Skips log.SetOutput, defaults to stdout
 	}
 	log.SetOutput(f)
 }