Avoid using a map for log attributes

Having a map per log entry seemed heavier than necessary. These
attributes end up being sorted and serialized, so storing them in a map
doesn't add anything (there's no random access element). In SwarmKit,
they originate as a slice, so there's an unnecessary conversion to a map
and back.

This also fixes the sort comparator, which used to inefficiently split
the string on each comparison.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>
Upstream-commit: b642b3f21f17cf50c79e464d3aedc93b2dbf0fb0
Component: engine

components/engine/api/server/httputils/write_log_stream.go

@@ -5,7 +5,6 @@ import (
 	"io"
 	"net/url"
 	"sort"
-	"strings"
 
 	"golang.org/x/net/context"
 
@@ -53,7 +52,8 @@ func WriteLogStream(ctx context.Context, w io.Writer, msgs <-chan *backend.LogMe
 		}
 		logLine := msg.Line
 		if config.Details {
-			logLine = append([]byte(stringAttrs(msg.Attrs)+" "), logLine...)
+			logLine = append(attrsByteSlice(msg.Attrs), ' ')
+			logLine = append(logLine, msg.Line...)
 		}
 		if config.Timestamps {
 			// TODO(dperny) the format is defined in
@@ -71,24 +71,26 @@ func WriteLogStream(ctx context.Context, w io.Writer, msgs <-chan *backend.LogMe
 	}
 }
 
-type byKey []string
+type byKey []backend.LogAttr
 
-func (s byKey) Len() int { return len(s) }
-func (s byKey) Less(i, j int) bool {
-	keyI := strings.Split(s[i], "=")
-	keyJ := strings.Split(s[j], "=")
-	return keyI[0] < keyJ[0]
-}
-func (s byKey) Swap(i, j int) {
-	s[i], s[j] = s[j], s[i]
-}
+func (b byKey) Len() int           { return len(b) }
+func (b byKey) Less(i, j int) bool { return b[i].Key < b[j].Key }
+func (b byKey) Swap(i, j int)      { b[i], b[j] = b[j], b[i] }
 
-func stringAttrs(a backend.LogAttributes) string {
-	var ss byKey
-	for k, v := range a {
-		k, v := url.QueryEscape(k), url.QueryEscape(v)
-		ss = append(ss, k+"="+v)
+func attrsByteSlice(a []backend.LogAttr) []byte {
+	// Note this sorts "a" in-place. That is fine here - nothing else is
+	// going to use Attrs or care about the order.
+	sort.Sort(byKey(a))
+
+	var ret []byte
+	for i, pair := range a {
+		k, v := url.QueryEscape(pair.Key), url.QueryEscape(pair.Value)
+		ret = append(ret, []byte(k)...)
+		ret = append(ret, '=')
+		ret = append(ret, []byte(v)...)
+		if i != len(a)-1 {
+			ret = append(ret, ',')
+		}
 	}
-	sort.Sort(ss)
-	return strings.Join(ss, ",")
+	return ret
 }

components/engine/api/types/backend/backend.go

@@ -35,7 +35,7 @@ type LogMessage struct {
 	Line      []byte
 	Source    string
 	Timestamp time.Time
-	Attrs     LogAttributes
+	Attrs     []LogAttr
 	Partial   bool
 
 	// Err is an error associated with a message. Completeness of a message
@@ -44,9 +44,11 @@ type LogMessage struct {
 	Err error
 }
 
-// LogAttributes is used to hold the extra attributes available in the log message
-// Primarily used for converting the map type to string and sorting.
-type LogAttributes map[string]string
+// LogAttr is used to hold the extra attributes available in the log message.
+type LogAttr struct {
+	Key   string
+	Value string
+}
 
 // LogSelector is a list of services and tasks that should be returned as part
 // of a log stream. It is similar to swarmapi.LogSelector, with the difference