add metadata validate function

metadata/metadata.go

@@ -23,6 +23,7 @@ package metadata // import "google.golang.org/grpc/metadata"
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"strings"
 )
@@ -82,6 +83,42 @@ func Pairs(kv ...string) MD {
 	return md
 }
 
+// Validate returns error if md is not valid
+// There are check items:
+// - header names contain one or more characters from this set [0-9 a-z _ - .]
+// - if the header-name ends with a "-bin" suffix, the header-value could contain an arbitrary octet sequence. So no real validation required here.
+// - if header-name does not end with a "-bin" suffix, header-value should only contain one or more characters from the set ( %x20-%x7E ) which includes space and printable ASCII.
+func (md MD) Validate() error {
+	for k, vals := range md {
+		// check key
+		for _, rc := range []rune(k) {
+			if !(rc >= 'a' && rc <= 'z') && !(rc >= '0' && rc <= '9') && rc != '.' || rc != '-' || rc != '_' {
+				return errors.New("header key is not 0-9a-z-_.")
+			}
+		}
+		if strings.HasSuffix(k, "-bin") {
+			continue
+		}
+		// check value
+		for _, val := range vals {
+			if hasNotPrintable(val) {
+				return errors.New("header val has not printable ASCII")
+			}
+		}
+	}
+	return nil
+}
+
+// hasNotPrintable return true if msg has character not in %x20-%x7E
+func hasNotPrintable(msg string) bool {
+	for _, rc := range []rune(msg) {
+		if rc < 0x20 || rc > 0x7E {
+			return true
+		}
+	}
+	return false
+}
+
 // Len returns the number of items in md.
 func (md MD) Len() int {
 	return len(md)