Make every ask id end in a digest of its key so two keys never share an id (issue 1201)

go/delivery/gate.go

@@ -94,16 +94,18 @@ func ParseAskKey(key string) (kind, group, hash string, err error) {
 func AnswerKey(askKey string) string { return askKey }
 
 // AskID is the id the teller gives the router for the ask at askKey. The router's ids refuse dots (asks.UsableID),
-// so a dot becomes `-` and a slash `_`; a key too long for an id is cut and ends in a digest of the whole key.
-// It cannot be read back: the teller keeps the key beside it.
+// so in the readable part a dot becomes `-` and a slash `_`; that part is cut to fit, and every id ends in `-` and
+// the first 12 hex digits of the sha256 of the whole key, so two keys never give one id. It cannot be read back:
+// the teller keeps the key beside it.
 func AskID(askKey string) string {
-	id := strings.NewReplacer(".", "-", "/", "_").Replace(askKey)
-	const most = 64
-	if len(id) > most {
-		sum := sha256.Sum256([]byte(askKey))
-		id = id[:most-13] + "-" + hex.EncodeToString(sum[:])[:12]
+	const most = 64 // the router's bound on an id
+	const tail = 13 // "-" and 12 hex digits
+	readable := strings.NewReplacer(".", "-", "/", "_").Replace(askKey)
+	if len(readable) > most-tail {
+		readable = readable[:most-tail]
 	}
-	return id
+	sum := sha256.Sum256([]byte(askKey))
+	return readable + "-" + hex.EncodeToString(sum[:])[:12]
 }
 
 func checkOwedAct(act string) (kind, context string, err error) {

go/delivery/gate_test.go

@@ -55,8 +55,10 @@ func TestAskID(t *testing.T) { // 1201/AC2
 	k3, _ := MergeAskKey("feat/x", gateHeads()[:1])
 	long, _ := MergeAskKey("feat/"+strings.Repeat("long-", 20), gateHeads())
 	long2, _ := MergeAskKey("feat/"+strings.Repeat("long-", 20)+"2", gateHeads())
+	slash, _ := MergeAskKey("a/b", gateHeads())
+	under, _ := MergeAskKey("a_b", gateHeads())
 	seen := map[string]string{}
-	for _, k := range []string{k1, k2, k3, long, long2} {
+	for _, k := range []string{k1, k2, k3, long, long2, slash, under} {
 		id := AskID(k)
 		if strings.Contains(id, ".") {
 			t.Errorf("id %q holds a dot", id)