Move SIP rules from LiveKit server. (#534)

sip/sip.go

@@ -0,0 +1,301 @@
+// Copyright 2023 LiveKit, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sip
+
+import (
+	"fmt"
+	"math"
+	"regexp"
+	"sort"
+
+	"github.com/livekit/protocol/livekit"
+	"github.com/livekit/protocol/logger"
+	"github.com/livekit/protocol/rpc"
+)
+
+// DispatchRulePriority returns sorting priority for dispatch rules. Lower value means higher priority.
+func DispatchRulePriority(info *livekit.SIPDispatchRuleInfo) int32 {
+	// In all these cases, prefer pin-protected rules.
+	// Thus, the order will be the following:
+	// - 0: Direct or Pin (both pin-protected)
+	// - 1: Individual (pin-protected)
+	// - 100: Direct (open)
+	// - 101: Individual (open)
+	const (
+		last = math.MaxInt32
+	)
+	// TODO: Maybe allow setting specific priorities for dispatch rules?
+	switch rule := info.GetRule().GetRule().(type) {
+	default:
+		return last
+	case *livekit.SIPDispatchRule_DispatchRuleDirect:
+		if rule.DispatchRuleDirect.GetPin() != "" {
+			return 0
+		}
+		return 100
+	case *livekit.SIPDispatchRule_DispatchRuleIndividual:
+		if rule.DispatchRuleIndividual.GetPin() != "" {
+			return 1
+		}
+		return 101
+	}
+}
+
+// SortDispatchRules predictably sorts dispatch rules by priority (first one is highest).
+func SortDispatchRules(rules []*livekit.SIPDispatchRuleInfo) {
+	sort.Slice(rules, func(i, j int) bool {
+		p1, p2 := DispatchRulePriority(rules[i]), DispatchRulePriority(rules[j])
+		if p1 < p2 {
+			return true
+		} else if p1 > p2 {
+			return false
+		}
+		// For predictable sorting order.
+		room1, _, _ := GetPinAndRoom(rules[i])
+		room2, _, _ := GetPinAndRoom(rules[j])
+		return room1 < room2
+	})
+}
+
+// SelectDispatchRule takes a list of dispatch rules, and takes the decision which one should be selected.
+// It returns an error if there are conflicting rules. Returns nil if no rules match.
+func SelectDispatchRule(rules []*livekit.SIPDispatchRuleInfo, req *rpc.EvaluateSIPDispatchRulesRequest) (*livekit.SIPDispatchRuleInfo, error) {
+	if len(rules) == 0 {
+		return nil, nil
+	}
+	// Sorting will do the selection for us. We already filtered out irrelevant ones in matchSIPDispatchRule.
+	SortDispatchRules(rules)
+	byPin := make(map[string]*livekit.SIPDispatchRuleInfo)
+	var (
+		pinRule  *livekit.SIPDispatchRuleInfo
+		openRule *livekit.SIPDispatchRuleInfo
+	)
+	openCnt := 0
+	for _, r := range rules {
+		_, pin, err := GetPinAndRoom(r)
+		if err != nil {
+			return nil, err
+		}
+		if pin == "" {
+			openRule = r // last one
+			openCnt++
+		} else if r2 := byPin[pin]; r2 != nil {
+			return nil, fmt.Errorf("Conflicting SIP Dispatch Rules: Same PIN for %q and %q",
+				r.SipDispatchRuleId, r2.SipDispatchRuleId)
+		} else {
+			byPin[pin] = r
+			// Pick the first one with a Pin. If Pin was provided in the request, we already filtered the right rules.
+			// If not, this rule will just be used to send RequestPin=true flag.
+			if pinRule == nil {
+				pinRule = r
+			}
+		}
+	}
+	if req.GetPin() != "" {
+		// If it's still nil that's fine. We will report "no rules matched" later.
+		return pinRule, nil
+	}
+	if pinRule != nil {
+		return pinRule, nil
+	}
+	if openCnt > 1 {
+		return nil, fmt.Errorf("Conflicting SIP Dispatch Rules: Matched %d open rules for %q", openCnt, req.CallingNumber)
+	}
+	return openRule, nil
+}
+
+// GetPinAndRoom returns a room name/prefix and the pin for a dispatch rule. Just a convenience wrapper.
+func GetPinAndRoom(info *livekit.SIPDispatchRuleInfo) (room, pin string, err error) {
+	// TODO: Could probably add methods on SIPDispatchRuleInfo struct instead.
+	switch rule := info.GetRule().GetRule().(type) {
+	default:
+		return "", "", fmt.Errorf("Unsupported SIP Dispatch Rule: %T", rule)
+	case *livekit.SIPDispatchRule_DispatchRuleDirect:
+		pin = rule.DispatchRuleDirect.GetPin()
+		room = rule.DispatchRuleDirect.GetRoomName()
+	case *livekit.SIPDispatchRule_DispatchRuleIndividual:
+		pin = rule.DispatchRuleIndividual.GetPin()
+		room = rule.DispatchRuleIndividual.GetRoomPrefix()
+	}
+	return room, pin, nil
+}
+
+// MatchTrunk finds a SIP Trunk definition matching the request.
+// Returns nil if no rules matched or an error if there are conflicting definitions.
+func MatchTrunk(trunks []*livekit.SIPTrunkInfo, calling, called string) (*livekit.SIPTrunkInfo, error) {
+	var (
+		selectedTrunk   *livekit.SIPTrunkInfo
+		defaultTrunk    *livekit.SIPTrunkInfo
+		defaultTrunkCnt int // to error in case there are multiple ones
+	)
+	for _, tr := range trunks {
+		// Do not consider it if regexp doesn't match.
+		matches := len(tr.InboundNumbersRegex) == 0
+		for _, reStr := range tr.InboundNumbersRegex {
+			// TODO: we should cache it
+			re, err := regexp.Compile(reStr)
+			if err != nil {
+				logger.Errorw("cannot parse SIP trunk regexp", err, "trunkID", tr.SipTrunkId)
+				continue
+			}
+			if re.MatchString(calling) {
+				matches = true
+				break
+			}
+		}
+		if !matches {
+			continue
+		}
+		if tr.OutboundNumber == "" {
+			// Default/wildcard trunk.
+			defaultTrunk = tr
+			defaultTrunkCnt++
+		} else if tr.OutboundNumber == called {
+			// Trunk specific to the number.
+			if selectedTrunk != nil {
+				return nil, fmt.Errorf("Multiple SIP Trunks matched for %q", called)
+			}
+			selectedTrunk = tr
+			// Keep searching! We want to know if there are any conflicting Trunk definitions.
+		}
+	}
+	if selectedTrunk != nil {
+		return selectedTrunk, nil
+	}
+	if defaultTrunkCnt > 1 {
+		return nil, fmt.Errorf("Multiple default SIP Trunks matched for %q", called)
+	}
+	// Could still be nil here.
+	return defaultTrunk, nil
+}
+
+// MatchDispatchRule finds the best dispatch rule matching the request parameters. Returns an error if no rule matched.
+// Trunk parameter can be nil, in which case only wildcard dispatch rules will be effective (ones without Trunk IDs).
+func MatchDispatchRule(trunk *livekit.SIPTrunkInfo, rules []*livekit.SIPDispatchRuleInfo, req *rpc.EvaluateSIPDispatchRulesRequest) (*livekit.SIPDispatchRuleInfo, error) {
+	// Trunk can still be nil here in case none matched or were defined.
+	// This is still fine, but only in case we'll match exactly one wildcard dispatch rule.
+	if len(rules) == 0 {
+		return nil, fmt.Errorf("No SIP Dispatch Rules defined")
+	}
+	// We split the matched dispatch rules into two sets: specific and default (aka wildcard).
+	// First, attempt to match any of the specific rules, where we did match the Trunk ID.
+	// If nothing matches there - fallback to default/wildcard rules, where no Trunk IDs were mentioned.
+	var (
+		specificRules []*livekit.SIPDispatchRuleInfo
+		defaultRules  []*livekit.SIPDispatchRuleInfo
+	)
+	noPin := req.NoPin
+	sentPin := req.GetPin()
+	for _, info := range rules {
+		_, rulePin, err := GetPinAndRoom(info)
+		if err != nil {
+			logger.Errorw("Invalid SIP Dispatch Rule", err, "dispatchRuleID", info.SipDispatchRuleId)
+			continue
+		}
+		// Filter heavily on the Pin, so that only relevant rules remain.
+		if noPin {
+			if rulePin != "" {
+				// Skip pin-protected rules if no pin mode requested.
+				continue
+			}
+		} else if sentPin != "" {
+			if rulePin == "" {
+				// Pin already sent, skip non-pin-protected rules.
+				continue
+			}
+			if sentPin != rulePin {
+				// Pin doesn't match. Don't return an error here, just wait for other rule to match (or none at all).
+				// Note that we will NOT match non-pin-protected rules, thus it will not fallback to open rules.
+				continue
+			}
+		}
+		if len(info.TrunkIds) == 0 {
+			// Default/wildcard dispatch rule.
+			defaultRules = append(defaultRules, info)
+			continue
+		}
+		// Specific dispatch rules. Require a Trunk associated with the number.
+		if trunk == nil {
+			continue
+		}
+		matches := false
+		for _, id := range info.TrunkIds {
+			if id == trunk.SipTrunkId {
+				matches = true
+				break
+			}
+		}
+		if !matches {
+			continue
+		}
+		specificRules = append(specificRules, info)
+	}
+	best, err := SelectDispatchRule(specificRules, req)
+	if err != nil {
+		return nil, err
+	} else if best != nil {
+		return best, nil
+	}
+	best, err = SelectDispatchRule(defaultRules, req)
+	if err != nil {
+		return nil, err
+	} else if best != nil {
+		return best, nil
+	}
+	if trunk == nil {
+		return nil, fmt.Errorf("No SIP Trunk or Dispatch Rules matched for %q", req.CalledNumber)
+	}
+	return nil, fmt.Errorf("No SIP Dispatch Rules matched for %q", req.CalledNumber)
+}
+
+// EvaluateDispatchRule checks a selected Dispatch Rule against the provided request.
+func EvaluateDispatchRule(rule *livekit.SIPDispatchRuleInfo, req *rpc.EvaluateSIPDispatchRulesRequest) (*rpc.EvaluateSIPDispatchRulesResponse, error) {
+	sentPin := req.GetPin()
+
+	from := req.CallingNumber
+	if rule.HidePhoneNumber {
+		// TODO: Decide on the phone masking format.
+		//       Maybe keep regional code, but mask all but 4 last digits?
+		from = from[len(from)-4:]
+	}
+	fromName := "Phone " + from
+
+	room, rulePin, err := GetPinAndRoom(rule)
+	if err != nil {
+		return nil, err
+	}
+	if rulePin != "" {
+		if sentPin == "" {
+			return &rpc.EvaluateSIPDispatchRulesResponse{
+				RequestPin: true,
+			}, nil
+		}
+		if rulePin != sentPin {
+			// This should never happen in practice, because matchSIPDispatchRule should remove rules with the wrong pin.
+			return nil, fmt.Errorf("Incorrect PIN for SIP room")
+		}
+	} else {
+		// Pin was sent, but room doesn't require one. Assume user accidentally pressed phone button.
+	}
+	switch rule := rule.GetRule().GetRule().(type) {
+	case *livekit.SIPDispatchRule_DispatchRuleIndividual:
+		// TODO: Decide on the suffix. Do we need to escape specific characters?
+		room = rule.DispatchRuleIndividual.GetRoomPrefix() + from
+	}
+	return &rpc.EvaluateSIPDispatchRulesResponse{
+		RoomName:            room,
+		ParticipantIdentity: fromName,
+	}, nil
+}