write_stdout: add tabulated data format

Add a new write_stdout format called "fields". If specified, write a
tabulated list of fields. It's easier to read than raw json or text
outputs.

Signed-off-by: Adrian Moreno <amorenoz@redhat.com>

docs/api.md

@@ -145,7 +145,7 @@ Following is the supported API format for writing to standard output:
 
 <pre>
  stdout:
-         format: the format of each line: printf (default) or json
+         format: the format of each line: printf (default), fields, or json
 </pre>
 ## Aggregate metrics API
 Following is the supported API format for specifying metrics aggregations:

pkg/api/write_stdout.go

@@ -1,5 +1,5 @@
 package api
 
 type WriteStdout struct {
-	Format string `yaml:"format" json:"format" doc:"the format of each line: printf (default) or json"`
+	Format string `yaml:"format" json:"format" doc:"the format of each line: printf (default), fields, or json"`
 }

pkg/pipeline/write/write_stdout.go

@@ -20,6 +20,8 @@ package write
 import (
 	"encoding/json"
 	"fmt"
+	"os"
+	"text/tabwriter"
 	"time"
 
 	"github.com/netobserv/flowlogs-pipeline/pkg/config"
@@ -39,6 +41,15 @@ func (t *writeStdout) Write(in []config.GenericMap) {
 			txt, _ := json.Marshal(v)
 			fmt.Println(string(txt))
 		}
+	} else if t.format == "fields" {
+		for _, v := range in {
+			fmt.Printf("Flow record at %s:\n", time.Now().Format(time.StampMilli))
+			w := tabwriter.NewWriter(os.Stdout, 0, 0, 1, ' ', 0)
+			for key, val := range v {
+				fmt.Fprintf(w, "%v\t=\t%v\n", key, val)
+			}
+			w.Flush()
+		}
 	} else {
 		for _, v := range in {
 			fmt.Printf("%s: %v\n", time.Now().Format(time.StampMilli), v)