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