Continued scaffolding and interface definitions

services/data_service/internal/control/fingerprint.go

@@ -0,0 +1,43 @@
+package control
+
+import (
+	"encoding/binary"
+	"encoding/hex"
+	"sort"
+
+	"lukechampine.com/blake3"
+)
+
+func StreamFingerprint(templateFP, outPort string, inMap map[string]string) string {
+	// Sort input keys for determinism.
+	keys := make([]string, 0, len(inMap))
+	for k := range inMap {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+
+	h := blake3.New(32, nil)
+
+	write := func(s string) {
+		var lenbuf [4]byte
+		binary.LittleEndian.PutUint32(lenbuf[:], uint32(len(s)))
+		_, _ = h.Write(lenbuf[:])
+		_, _ = h.Write([]byte(s))
+	}
+
+	// templateFP, outPort, input count, then pairs.
+	write(templateFP)
+	write(outPort)
+
+	var nbuf [4]byte
+	binary.LittleEndian.PutUint32(nbuf[:], uint32(len(keys)))
+	_, _ = h.Write(nbuf[:])
+
+	for _, k := range keys {
+		write(k)
+		write(inMap[k])
+	}
+
+	sum := h.Sum(nil)
+	return hex.EncodeToString(sum)
+}