cluster: introduce Cluster.ReadLines()

reading a file, splitting and trimming lines, and
allowing # to comment a line out

Signed-off-by: Alejandro Mery <amery@jpi.io>

pkg/cluster/cluster_file.go

@@ -1,10 +1,12 @@
 package cluster
 
 import (
+	"bufio"
 	"bytes"
 	"fmt"
 	"io"
 	"os"
+	"strings"
 
 	fs "github.com/hack-pad/hackpadfs"
 )
@@ -65,6 +67,31 @@ func (m *Cluster) ReadFile(name string, args ...any) ([]byte, error) {
 	return fs.ReadFile(m.dir, name)
 }
 
+// ReadLines reads a file from the cluster's config directory,
+// split by lines, trimmed, and accepting `#` to comment lines out.
+func (m *Cluster) ReadLines(name string, args ...any) ([]string, error) {
+	var out []string
+
+	data, err := m.ReadFile(name, args...)
+	if err != nil {
+		return nil, err
+	}
+
+	sc := bufio.NewScanner(bytes.NewReader(data))
+	for sc.Scan() {
+		s := strings.TrimSpace(sc.Text())
+		switch {
+		case s == "", strings.HasPrefix(s, "#"):
+			// ignore
+		default:
+			// accepted
+			out = append(out, s)
+		}
+	}
+
+	return out, nil
+}
+
 // WriteStringFile writes the given content to a file on the machine's config directory
 func (m *Cluster) WriteStringFile(value string, name string, args ...any) error {
 	f, err := m.CreateTruncFile(name, args...)