Sanitize docker labels when used as journald field names

This fix tries to address the issue raised in #23528 where
docker labels caused journald log error because journald
has special requirements on field names.

This fix addresses this issue by sanitize the labels per
requirements of journald.

Additional unit tests have been added to cover the changes.

This fix fixes #23528.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
Upstream-commit: 9528ea930cdb90f906230a6d4cab179001255927
Component: engine

components/engine/daemon/logger/journald/journald.go

@@ -6,8 +6,8 @@ package journald
 
 import (
 	"fmt"
-	"strings"
 	"sync"
+	"unicode"
 
 	"github.com/Sirupsen/logrus"
 	"github.com/coreos/go-systemd/journal"
@@ -36,6 +36,26 @@ func init() {
 	}
 }
 
+// sanitizeKeyMode returns the sanitized string so that it could be used in journald.
+// In journald log, there are special requirements for fields.
+// Fields must be composed of uppercase letters, numbers, and underscores, but must
+// not start with an underscore.
+func sanitizeKeyMod(s string) string {
+	n := ""
+	for _, v := range s {
+		if 'a' <= v && v <= 'z' {
+			v = unicode.ToUpper(v)
+		} else if ('Z' < v || v < 'A') && ('9' < v || v < '0') {
+			v = '_'
+		}
+		// If (n == "" && v == '_'), then we will skip as this is the beginning with '_'
+		if !(n == "" && v == '_') {
+			n += string(v)
+		}
+	}
+	return n
+}
+
 // New creates a journald logger using the configuration passed in on
 // the context.
 func New(ctx logger.Context) (logger.Logger, error) {
@@ -61,7 +81,7 @@ func New(ctx logger.Context) (logger.Logger, error) {
 		"CONTAINER_NAME":    name,
 		"CONTAINER_TAG":     tag,
 	}
-	extraAttrs := ctx.ExtraAttributes(strings.ToTitle)
+	extraAttrs := ctx.ExtraAttributes(sanitizeKeyMod)
 	for k, v := range extraAttrs {
 		vars[k] = v
 	}

components/engine/daemon/logger/journald/journald_test.go

@@ -0,0 +1,23 @@
+// +build linux
+
+package journald
+
+import (
+	"testing"
+)
+
+func TestSanitizeKeyMod(t *testing.T) {
+	entries := map[string]string{
+		"io.kubernetes.pod.name":      "IO_KUBERNETES_POD_NAME",
+		"io?.kubernetes.pod.name":     "IO__KUBERNETES_POD_NAME",
+		"?io.kubernetes.pod.name":     "IO_KUBERNETES_POD_NAME",
+		"io123.kubernetes.pod.name":   "IO123_KUBERNETES_POD_NAME",
+		"_io123.kubernetes.pod.name":  "IO123_KUBERNETES_POD_NAME",
+		"__io123_kubernetes.pod.name": "IO123_KUBERNETES_POD_NAME",
+	}
+	for k, v := range entries {
+		if sanitizeKeyMod(k) != v {
+			t.Fatalf("Failed to sanitize %s, got %s, expected %s", k, sanitizeKeyMod(k), v)
+		}
+	}
+}