package tracing import ( "crypto/sha256" "encoding/hex" "strings" "github.com/rs/zerolog/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.Warn().Msgf("SpanNameLimit cannot be lesser than %d: falling back on %d", maxLength, maxLength+3) 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.Error().Str("OperationName", name).Err(err).Msgf("Failed to create Span name hash for %s", name) } return hex.EncodeToString(hash.Sum(nil))[:TraceNameHashLength] }