metadata: make Stringer implementation consistent (#7355)

metadata/metadata.go

@@ -90,19 +90,10 @@ func Pairs(kv ...string) MD {
  return md
 }
 
-// String implements the Stringer interface for pretty-printing a MD.
-// Ordering of the values is non-deterministic as it ranges over a map.
+// String implements fmt.Stringer to allow metadata to be printed when stored
+// in a context. It returns the metadata map as formatted by Go's fmt package.
 func (md MD) String() string {
- var sb strings.Builder
- fmt.Fprintf(&sb, "MD{")
- for k, v := range md {
- if sb.Len() > 3 {
- fmt.Fprintf(&sb, ", ")
- }
- fmt.Fprintf(&sb, "%s=[%s]", k, strings.Join(v, ", "))
- }
- fmt.Fprintf(&sb, "}")
- return sb.String()
+ return fmt.Sprint(map[string][]string(md))
 }
 
 // Len returns the number of items in md.

metadata/metadata_test.go

@@ -22,7 +22,6 @@ import (
  "context"
  "reflect"
  "strconv"
- "strings"
  "testing"
  "time"
 
@@ -342,19 +341,19 @@ func (s) TestAppendToOutgoingContext_FromKVSlice(t *testing.T) {
 func TestStringerMD(t *testing.T) {
  for _, test := range []struct {
  md MD
- want []string
+ want string
  }{
- {MD{}, []string{"MD{}"}},
- {MD{"k1": []string{}}, []string{"MD{k1=[]}"}},
- {MD{"k1": []string{"v1", "v2"}}, []string{"MD{k1=[v1, v2]}"}},
- {MD{"k1": []string{"v1"}}, []string{"MD{k1=[v1]}"}},
- {MD{"k1": []string{"v1", "v2"}, "k2": []string{}, "k3": []string{"1", "2", "3"}}, []string{"MD{", "k1=[v1, v2]", "k2=[]", "k3=[1, 2, 3]", "}"}},
+ {MD{}, "map[]"},
+ {MD{"k1": []string{}}, "map[k1:[]]"},
+ {MD{"k1": []string{"v1", "v2"}}, "map[k1:[v1 v2]]"},
+ {MD{"k1": []string{"v1"}}, "map[k1:[v1]]"},
+ {MD{"k1": []string{"v1", "v2"}, "k2": []string{}, "k3": []string{"1", "2", "3"}}, "map[k1:[v1 v2] k2:[] k3:[1 2 3]]"},
+ {MD{"k2": []string{}, "k3": []string{"1", "2", "3"}, "k1": []string{"v1", "v2"}}, "map[k1:[v1 v2] k2:[] k3:[1 2 3]]"},
+ {MD{"k3": []string{"1", "2", "3"}, "k2": []string{}, "k1": []string{"v1", "v2"}}, "map[k1:[v1 v2] k2:[] k3:[1 2 3]]"},
  } {
  got := test.md.String()
- for _, want := range test.want {
- if !strings.Contains(got, want) {
- t.Fatalf("Metadata string %q is missing %q", got, want)
- }
+ if got != test.want {
+ t.Fatalf("Metadata string %q should be %q", got, test.want)
  }
  }
 }