Plugins support (#46)

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2026-09-01 15:24:53 +00:00 · 2019-07-25 13:54:42 +08:00
parent daf4a0e0f5
commit c6b1f1db42
770 changed files with 213077 additions and 2659 deletions
@@ -0,0 +1,95 @@
+package dnsutils
+
+import (
+	"math/rand"
+	"net"
+	"sort"
+)
+
+// OrderedSRV returns a count of the results and a map keyed on the order they should be used.
+// This based on the records' priority and randomised selection based on their relative weighting.
+// The function's inputs are the same as those for net.LookupSRV
+// To use in the correct order:
+//
+// count, orderedSRV, err := OrderedSRV(service, proto, name)
+// i := 1
+// for  i <= count {
+//   srv := orderedSRV[i]
+//   // Do something such as dial this SRV. If fails move on the the next or break if it succeeds.
+//   i += 1
+// }
+func OrderedSRV(service, proto, name string) (int, map[int]*net.SRV, error) {
+	_, addrs, err := net.LookupSRV(service, proto, name)
+	if err != nil {
+		return 0, make(map[int]*net.SRV), err
+	}
+	index, osrv := orderSRV(addrs)
+	return index, osrv, nil
+}
+
+func orderSRV(addrs []*net.SRV) (int, map[int]*net.SRV) {
+	// Initialise the ordered map
+	var o int
+	osrv := make(map[int]*net.SRV)
+
+	prioMap := make(map[int][]*net.SRV, 0)
+	for _, srv := range addrs {
+		prioMap[int(srv.Priority)] = append(prioMap[int(srv.Priority)], srv)
+	}
+
+	priorities := make([]int, 0)
+	for p := range prioMap {
+		priorities = append(priorities, p)
+	}
+
+	var count int
+	sort.Ints(priorities)
+	for _, p := range priorities {
+		tos := weightedOrder(prioMap[p])
+		for i, s := range tos {
+			count += 1
+			osrv[o+i] = s
+		}
+		o += len(tos)
+	}
+	return count, osrv
+}
+
+func weightedOrder(srvs []*net.SRV) map[int]*net.SRV {
+	// Get the total weight
+	var tw int
+	for _, s := range srvs {
+		tw += int(s.Weight)
+	}
+
+	// Initialise the ordered map
+	o := 1
+	osrv := make(map[int]*net.SRV)
+
+	// Whilst there are still entries to be ordered
+	l := len(srvs)
+	for l > 0 {
+		i := rand.Intn(l)
+		s := srvs[i]
+		var rw int
+		if tw > 0 {
+			// Greater the weight the more likely this will be zero or less
+			rw = rand.Intn(tw) - int(s.Weight)
+		}
+		if rw <= 0 {
+			// Put entry in position
+			osrv[o] = s
+			if len(srvs) > 1 {
+				// Remove the entry from the source slice by swapping with the last entry and truncating
+				srvs[len(srvs)-1], srvs[i] = srvs[i], srvs[len(srvs)-1]
+				srvs = srvs[:len(srvs)-1]
+				l = len(srvs)
+			} else {
+				l = 0
+			}
+			o += 1
+			tw = tw - int(s.Weight)
+		}
+	}
+	return osrv
+}