abstract the string slice struct to stringutils package

Signed-off-by: Shijiang Wei <mountkin@gmail.com>

stringutils/strslice.go

@@ -0,0 +1,71 @@
+package stringutils
+
+import (
+	"encoding/json"
+	"strings"
+)
+
+// StrSlice representes a string or an array of strings.
+// We need to override the json decoder to accept both options.
+type StrSlice struct {
+	parts []string
+}
+
+// MarshalJSON Marshals (or serializes) the StrSlice into the json format.
+// This method is needed to implement json.Marshaller.
+func (e *StrSlice) MarshalJSON() ([]byte, error) {
+	if e == nil {
+		return []byte{}, nil
+	}
+	return json.Marshal(e.Slice())
+}
+
+// UnmarshalJSON decodes the byte slice whether it's a string or an array of strings.
+// This method is needed to implement json.Unmarshaler.
+func (e *StrSlice) UnmarshalJSON(b []byte) error {
+	if len(b) == 0 {
+		return nil
+	}
+
+	p := make([]string, 0, 1)
+	if err := json.Unmarshal(b, &p); err != nil {
+		var s string
+		if err := json.Unmarshal(b, &s); err != nil {
+			return err
+		}
+		p = append(p, s)
+	}
+
+	e.parts = p
+	return nil
+}
+
+// Len returns the number of parts of the StrSlice.
+func (e *StrSlice) Len() int {
+	if e == nil {
+		return 0
+	}
+	return len(e.parts)
+}
+
+// Slice gets the parts of the StrSlice as a Slice of string.
+func (e *StrSlice) Slice() []string {
+	if e == nil {
+		return nil
+	}
+	return e.parts
+}
+
+// ToString gets space separated string of all the parts.
+func (e *StrSlice) ToString() string {
+	s := e.Slice()
+	if s == nil {
+		return ""
+	}
+	return strings.Join(s, " ")
+}
+
+// NewStrSlice creates an StrSlice based on the specified parts (as strings).
+func NewStrSlice(parts ...string) *StrSlice {
+	return &StrSlice{parts}
+}