json marshalling handled on server side

main.go

@@ -1,16 +1,13 @@
 package main
 
 import (
-	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"log"
 	"net/http"
 	"os"
 
 	"github.com/c-bata/go-prompt"
 	"github.com/indiependente/autoEqMac/autoeq"
-	"github.com/indiependente/autoEqMac/eqmac"
 	"github.com/indiependente/autoEqMac/eqmac/mapping"
 	"github.com/indiependente/autoEqMac/server"
 	"gopkg.in/alecthomas/kingpin.v2"
@@ -69,19 +66,18 @@ func run() error {
 	if err != nil {
 		return fmt.Errorf("could not find fixed band EQ preset: %w", err)
 	}
-
-	jsonPreset, err := json.Marshal([]eqmac.EQPreset{eqPreset})
-	if err != nil {
-		return fmt.Errorf("could not marshal preset to JSON: %w", err)
-	}
+	out := os.Stdout
 	if *file != "" {
-		err := ioutil.WriteFile(*file, jsonPreset, os.ModePerm)
+		f, err := os.Create(*file)
 		if err != nil {
-			return fmt.Errorf("could not write preset to file: %w", err)
+			return fmt.Errorf("could not create preset file: %w", err)
 		}
-		return nil
+		out = f
+	}
+	err = srv.WritePreset(out, eqPreset)
+	if err != nil {
+		return fmt.Errorf("could not write preset to file: %w", err)
 	}
-	fmt.Printf("%s\n", string(jsonPreset))
 	return nil
 }
 

server/interface.go

@@ -1,6 +1,8 @@
 package server
 
 import (
+	"io"
+
 	"github.com/indiependente/autoEqMac/autoeq"
 	"github.com/indiependente/autoEqMac/eqmac"
 )
@@ -9,4 +11,5 @@ type Server interface {
 	ListEQsMetadata() ([]autoeq.EQMetadata, error)
 	GetFixedBandEQPreset(id string) (eqmac.EQPreset, error)
 	GetEQMetadataByName(name string) (autoeq.EQMetadata, error)
+	WritePreset(w io.Writer, p eqmac.EQPreset) error
 }

server/server.go

@@ -1,7 +1,9 @@
 package server
 
 import (
+	"encoding/json"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"net/http"
 
@@ -103,3 +105,12 @@ func (s HTTPServer) GetEQMetadataByName(name string) (autoeq.EQMetadata, error)
 	}
 	return eqMeta, nil
 }
+
+func (s HTTPServer) WritePreset(w io.Writer, p eqmac.EQPreset) error {
+	jsonPreset, err := json.Marshal([]eqmac.EQPreset{p})
+	if err != nil {
+		return fmt.Errorf("could not marshal preset to JSON: %w", err)
+	}
+	_, err = fmt.Fprintln(w, string(jsonPreset))
+	return err
+}