Convert nil pointer log field value to string "nil" (#230)

* Set nil pointer to string nil when converting key values.

This causes a panic that will be recovered by the fmt package.
Altought on darwin this makes any project using open tracing impossible to debug.

see cortexproject/cortex#1712

Signed-off-by: Cyril Tovena <cyril.tovena@gmail.com>

* Adds some tests for InterleavedKVToFields.

Signed-off-by: Cyril Tovena <cyril.tovena@gmail.com>

log/util.go

@@ -1,6 +1,9 @@
 package log
 
-import "fmt"
+import (
+	"fmt"
+	"reflect"
+)
 
 // InterleavedKVToFields converts keyValues a la Span.LogKV() to a Field slice
 // a la Span.LogFields().
@@ -46,6 +49,10 @@ func InterleavedKVToFields(keyValues ...interface{}) ([]Field, error) {
 		case float64:
 			fields[i] = Float64(key, typedVal)
 		default:
+			if typedVal == nil || (reflect.ValueOf(typedVal).Kind() == reflect.Ptr && reflect.ValueOf(typedVal).IsNil()) {
+				fields[i] = String(key, "nil")
+				continue
+			}
 			// When in doubt, coerce to a string
 			fields[i] = String(key, fmt.Sprint(typedVal))
 		}

log/util_test.go

@@ -0,0 +1,86 @@
+package log
+
+import (
+	"errors"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+var nilInterface io.Reader
+
+func TestInterleavedKVToFields(t *testing.T) {
+
+	tests := []struct {
+		name      string
+		keyValues []interface{}
+		want      []Field
+		wantErr   bool
+	}{
+		{
+			"incorrect pair",
+			[]interface{}{"test"},
+			nil,
+			true,
+		},
+		{
+			"non string key",
+			[]interface{}{struct{}{}, "foo"},
+			nil,
+			true,
+		},
+		{
+			"happy path",
+			[]interface{}{
+				"bool", true,
+				"string", "string",
+				"int", int(1),
+				"int8", int8(2),
+				"int16", int16(3),
+				"int64", int64(4),
+				"uint", uint(5),
+				"uint64", uint64(6),
+				"uint8", uint8(7),
+				"uint16", uint16(8),
+				"uint32", uint32(9),
+				"float32", float32(10),
+				"float64", float64(11),
+				"int32", int32(12),
+				"stringer", errors.New("err"),
+				"nilInterface", nilInterface,
+				"nil", nil,
+			},
+			[]Field{
+				Bool("bool", true),
+				String("string", "string"),
+				Int("int", int(1)),
+				Int32("int8", int32(2)),
+				Int32("int16", int32(3)),
+				Int64("int64", int64(4)),
+				Uint64("uint", uint64(5)),
+				Uint64("uint64", uint64(6)),
+				Uint32("uint8", uint32(7)),
+				Uint32("uint16", uint32(8)),
+				Uint32("uint32", uint32(9)),
+				Float32("float32", float32(10)),
+				Float64("float64", float64(11)),
+				Int32("int32", int32(12)),
+				String("stringer", errors.New("err").Error()),
+				String("nilInterface", "nil"),
+				String("nil", "nil"),
+			},
+			false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := InterleavedKVToFields(tt.keyValues...)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("InterleavedKVToFields() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}