fix: manage write error during the display of the DNS help. (#923)

cmd/cmd_dnshelp.go

@@ -2,6 +2,7 @@ package cmd
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"strings"
 	"text/tabwriter"
@@ -27,22 +28,46 @@ func dnsHelp(ctx *cli.Context) error {
 	code := ctx.String("code")
 	if code == "" {
 		w := tabwriter.NewWriter(os.Stdout, 0, 0, 2, ' ', 0)
+		ew := &errWriter{w: w}
 
-		fmt.Fprintln(w, `Credentials for DNS providers must be passed through environment variables.`)
-		fmt.Fprintln(w)
-		fmt.Fprintln(w, `To display the documentation for a DNS providers:`)
-		fmt.Fprintln(w)
-		fmt.Fprintln(w, "\t$ lego dnshelp -c code")
-		fmt.Fprintln(w)
-		fmt.Fprintln(w, "All DNS codes:")
-		fmt.Fprintf(w, "\t%s\n", allDNSCodes())
-		fmt.Fprintln(w)
-		fmt.Fprintln(w, "More information: https://go-acme.github.io/lego/dns")
+		ew.writeln(`Credentials for DNS providers must be passed through environment variables.`)
+		ew.writeln()
+		ew.writeln(`To display the documentation for a DNS providers:`)
+		ew.writeln()
+		ew.writeln("\t$ lego dnshelp -c code")
+		ew.writeln()
+		ew.writeln("All DNS codes:")
+		ew.writef("\t%s\n", allDNSCodes())
+		ew.writeln()
+		ew.writeln("More information: https://go-acme.github.io/lego/dns")
+
+		if ew.err != nil {
+			return ew.err
+		}
 
 		return w.Flush()
 	}
 
-	displayDNSHelp(strings.ToLower(code))
-
-	return nil
+	return displayDNSHelp(strings.ToLower(code))
+}
+
+type errWriter struct {
+	w   io.Writer
+	err error
+}
+
+func (ew *errWriter) writeln(a ...interface{}) {
+	if ew.err != nil {
+		return
+	}
+
+	_, ew.err = fmt.Fprintln(ew.w, a...)
+}
+
+func (ew *errWriter) writef(format string, a ...interface{}) {
+	if ew.err != nil {
+		return
+	}
+
+	_, ew.err = fmt.Fprintf(ew.w, format, a...)
 }