Move code to pkg

pkg/tracing/operation_name.go

@@ -0,0 +1,65 @@
+package tracing
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"strings"
+
+	"github.com/containous/traefik/pkg/log"
+)
+
+// TraceNameHashLength defines the number of characters to use from the head of the generated hash.
+const TraceNameHashLength = 8
+
+// OperationNameMaxLengthNumber defines the number of static characters in a Span Trace name:
+// 8 chars for hash + 2 chars for '_'.
+const OperationNameMaxLengthNumber = 10
+
+func generateOperationName(prefix string, parts []string, sep string, spanLimit int) string {
+	name := prefix + " " + strings.Join(parts, sep)
+
+	maxLength := OperationNameMaxLengthNumber + len(prefix) + 1
+
+	if spanLimit > 0 && len(name) > spanLimit {
+		if spanLimit < maxLength {
+			log.WithoutContext().Warnf("SpanNameLimit cannot be lesser than %d: falling back on %d, maxLength, maxLength+3", maxLength)
+			spanLimit = maxLength + 3
+		}
+
+		limit := (spanLimit - maxLength) / 2
+
+		var fragments []string
+		for _, value := range parts {
+			fragments = append(fragments, truncateString(value, limit))
+		}
+		fragments = append(fragments, computeHash(name))
+
+		name = prefix + " " + strings.Join(fragments, sep)
+	}
+
+	return name
+}
+
+// truncateString reduces the length of the 'str' argument to 'num' - 3 and adds a '...' suffix to the tail.
+func truncateString(str string, num int) string {
+	text := str
+	if len(str) > num {
+		if num > 3 {
+			num -= 3
+		}
+		text = str[0:num] + "..."
+	}
+	return text
+}
+
+// computeHash returns the first TraceNameHashLength character of the sha256 hash for 'name' argument.
+func computeHash(name string) string {
+	data := []byte(name)
+	hash := sha256.New()
+	if _, err := hash.Write(data); err != nil {
+		// Impossible case
+		log.WithoutContext().WithField("OperationName", name).Errorf("Failed to create Span name hash for %s: %v", name, err)
+	}
+
+	return fmt.Sprintf("%x", hash.Sum(nil))[:TraceNameHashLength]
+}