[chore] update otel libraries (#3740)

* chore: update otel dependencies

* refactor: combine tracing & metrics in observability package

* chore: update example tracing compose file

1 files changed, 911 insertions, 0 deletions

diff --git a/vendor/google.golang.org/grpc/balancer/pickfirst/pickfirstleaf/pickfirstleaf.go b/vendor/google.golang.org/grpc/balancer/pickfirst/pickfirstleaf/pickfirstleaf.go
new file mode 100644
index 000000000..2fc0a71f9
--- /dev/null
+++ b/vendor/google.golang.org/grpc/balancer/pickfirst/pickfirstleaf/pickfirstleaf.go
@@ -0,0 +1,911 @@
+/*
+ *
+ * Copyright 2024 gRPC authors.
+ *
+ * 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 pickfirstleaf contains the pick_first load balancing policy which
+// will be the universal leaf policy after dualstack changes are implemented.
+//
+// # Experimental
+//
+// Notice: This package is EXPERIMENTAL and may be changed or removed in a
+// later release.
+package pickfirstleaf
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net"
+	"net/netip"
+	"sync"
+	"time"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/balancer/pickfirst/internal"
+	"google.golang.org/grpc/connectivity"
+	expstats "google.golang.org/grpc/experimental/stats"
+	"google.golang.org/grpc/grpclog"
+	"google.golang.org/grpc/internal/envconfig"
+	internalgrpclog "google.golang.org/grpc/internal/grpclog"
+	"google.golang.org/grpc/internal/pretty"
+	"google.golang.org/grpc/resolver"
+	"google.golang.org/grpc/serviceconfig"
+)
+
+func init() {
+	if envconfig.NewPickFirstEnabled {
+		// Register as the default pick_first balancer.
+		Name = "pick_first"
+	}
+	balancer.Register(pickfirstBuilder{})
+}
+
+// enableHealthListenerKeyType is a unique key type used in resolver attributes
+// to indicate whether the health listener usage is enabled.
+type enableHealthListenerKeyType struct{}
+
+var (
+	logger = grpclog.Component("pick-first-leaf-lb")
+	// Name is the name of the pick_first_leaf balancer.
+	// It is changed to "pick_first" in init() if this balancer is to be
+	// registered as the default pickfirst.
+	Name                 = "pick_first_leaf"
+	disconnectionsMetric = expstats.RegisterInt64Count(expstats.MetricDescriptor{
+		Name:        "grpc.lb.pick_first.disconnections",
+		Description: "EXPERIMENTAL. Number of times the selected subchannel becomes disconnected.",
+		Unit:        "disconnection",
+		Labels:      []string{"grpc.target"},
+		Default:     false,
+	})
+	connectionAttemptsSucceededMetric = expstats.RegisterInt64Count(expstats.MetricDescriptor{
+		Name:        "grpc.lb.pick_first.connection_attempts_succeeded",
+		Description: "EXPERIMENTAL. Number of successful connection attempts.",
+		Unit:        "attempt",
+		Labels:      []string{"grpc.target"},
+		Default:     false,
+	})
+	connectionAttemptsFailedMetric = expstats.RegisterInt64Count(expstats.MetricDescriptor{
+		Name:        "grpc.lb.pick_first.connection_attempts_failed",
+		Description: "EXPERIMENTAL. Number of failed connection attempts.",
+		Unit:        "attempt",
+		Labels:      []string{"grpc.target"},
+		Default:     false,
+	})
+)
+
+const (
+	// TODO: change to pick-first when this becomes the default pick_first policy.
+	logPrefix = "[pick-first-leaf-lb %p] "
+	// connectionDelayInterval is the time to wait for during the happy eyeballs
+	// pass before starting the next connection attempt.
+	connectionDelayInterval = 250 * time.Millisecond
+)
+
+type ipAddrFamily int
+
+const (
+	// ipAddrFamilyUnknown represents strings that can't be parsed as an IP
+	// address.
+	ipAddrFamilyUnknown ipAddrFamily = iota
+	ipAddrFamilyV4
+	ipAddrFamilyV6
+)
+
+type pickfirstBuilder struct{}
+
+func (pickfirstBuilder) Build(cc balancer.ClientConn, bo balancer.BuildOptions) balancer.Balancer {
+	b := &pickfirstBalancer{
+		cc:              cc,
+		target:          bo.Target.String(),
+		metricsRecorder: bo.MetricsRecorder, // ClientConn will always create a Metrics Recorder.
+
+		subConns:              resolver.NewAddressMap(),
+		state:                 connectivity.Connecting,
+		cancelConnectionTimer: func() {},
+	}
+	b.logger = internalgrpclog.NewPrefixLogger(logger, fmt.Sprintf(logPrefix, b))
+	return b
+}
+
+func (b pickfirstBuilder) Name() string {
+	return Name
+}
+
+func (pickfirstBuilder) ParseConfig(js json.RawMessage) (serviceconfig.LoadBalancingConfig, error) {
+	var cfg pfConfig
+	if err := json.Unmarshal(js, &cfg); err != nil {
+		return nil, fmt.Errorf("pickfirst: unable to unmarshal LB policy config: %s, error: %v", string(js), err)
+	}
+	return cfg, nil
+}
+
+// EnableHealthListener updates the state to configure pickfirst for using a
+// generic health listener.
+func EnableHealthListener(state resolver.State) resolver.State {
+	state.Attributes = state.Attributes.WithValue(enableHealthListenerKeyType{}, true)
+	return state
+}
+
+type pfConfig struct {
+	serviceconfig.LoadBalancingConfig `json:"-"`
+
+	// If set to true, instructs the LB policy to shuffle the order of the list
+	// of endpoints received from the name resolver before attempting to
+	// connect to them.
+	ShuffleAddressList bool `json:"shuffleAddressList"`
+}
+
+// scData keeps track of the current state of the subConn.
+// It is not safe for concurrent access.
+type scData struct {
+	// The following fields are initialized at build time and read-only after
+	// that.
+	subConn balancer.SubConn
+	addr    resolver.Address
+
+	rawConnectivityState connectivity.State
+	// The effective connectivity state based on raw connectivity, health state
+	// and after following sticky TransientFailure behaviour defined in A62.
+	effectiveState              connectivity.State
+	lastErr                     error
+	connectionFailedInFirstPass bool
+}
+
+func (b *pickfirstBalancer) newSCData(addr resolver.Address) (*scData, error) {
+	sd := &scData{
+		rawConnectivityState: connectivity.Idle,
+		effectiveState:       connectivity.Idle,
+		addr:                 addr,
+	}
+	sc, err := b.cc.NewSubConn([]resolver.Address{addr}, balancer.NewSubConnOptions{
+		StateListener: func(state balancer.SubConnState) {
+			b.updateSubConnState(sd, state)
+		},
+	})
+	if err != nil {
+		return nil, err
+	}
+	sd.subConn = sc
+	return sd, nil
+}
+
+type pickfirstBalancer struct {
+	// The following fields are initialized at build time and read-only after
+	// that and therefore do not need to be guarded by a mutex.
+	logger          *internalgrpclog.PrefixLogger
+	cc              balancer.ClientConn
+	target          string
+	metricsRecorder expstats.MetricsRecorder // guaranteed to be non nil
+
+	// The mutex is used to ensure synchronization of updates triggered
+	// from the idle picker and the already serialized resolver,
+	// SubConn state updates.
+	mu sync.Mutex
+	// State reported to the channel based on SubConn states and resolver
+	// updates.
+	state connectivity.State
+	// scData for active subonns mapped by address.
+	subConns              *resolver.AddressMap
+	addressList           addressList
+	firstPass             bool
+	numTF                 int
+	cancelConnectionTimer func()
+	healthCheckingEnabled bool
+}
+
+// ResolverError is called by the ClientConn when the name resolver produces
+// an error or when pickfirst determined the resolver update to be invalid.
+func (b *pickfirstBalancer) ResolverError(err error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.resolverErrorLocked(err)
+}
+
+func (b *pickfirstBalancer) resolverErrorLocked(err error) {
+	if b.logger.V(2) {
+		b.logger.Infof("Received error from the name resolver: %v", err)
+	}
+
+	// The picker will not change since the balancer does not currently
+	// report an error. If the balancer hasn't received a single good resolver
+	// update yet, transition to TRANSIENT_FAILURE.
+	if b.state != connectivity.TransientFailure && b.addressList.size() > 0 {
+		if b.logger.V(2) {
+			b.logger.Infof("Ignoring resolver error because balancer is using a previous good update.")
+		}
+		return
+	}
+
+	b.updateBalancerState(balancer.State{
+		ConnectivityState: connectivity.TransientFailure,
+		Picker:            &picker{err: fmt.Errorf("name resolver error: %v", err)},
+	})
+}
+
+func (b *pickfirstBalancer) UpdateClientConnState(state balancer.ClientConnState) error {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.cancelConnectionTimer()
+	if len(state.ResolverState.Addresses) == 0 && len(state.ResolverState.Endpoints) == 0 {
+		// Cleanup state pertaining to the previous resolver state.
+		// Treat an empty address list like an error by calling b.ResolverError.
+		b.closeSubConnsLocked()
+		b.addressList.updateAddrs(nil)
+		b.resolverErrorLocked(errors.New("produced zero addresses"))
+		return balancer.ErrBadResolverState
+	}
+	b.healthCheckingEnabled = state.ResolverState.Attributes.Value(enableHealthListenerKeyType{}) != nil
+	cfg, ok := state.BalancerConfig.(pfConfig)
+	if state.BalancerConfig != nil && !ok {
+		return fmt.Errorf("pickfirst: received illegal BalancerConfig (type %T): %v: %w", state.BalancerConfig, state.BalancerConfig, balancer.ErrBadResolverState)
+	}
+
+	if b.logger.V(2) {
+		b.logger.Infof("Received new config %s, resolver state %s", pretty.ToJSON(cfg), pretty.ToJSON(state.ResolverState))
+	}
+
+	var newAddrs []resolver.Address
+	if endpoints := state.ResolverState.Endpoints; len(endpoints) != 0 {
+		// Perform the optional shuffling described in gRFC A62. The shuffling
+		// will change the order of endpoints but not touch the order of the
+		// addresses within each endpoint. - A61
+		if cfg.ShuffleAddressList {
+			endpoints = append([]resolver.Endpoint{}, endpoints...)
+			internal.RandShuffle(len(endpoints), func(i, j int) { endpoints[i], endpoints[j] = endpoints[j], endpoints[i] })
+		}
+
+		// "Flatten the list by concatenating the ordered list of addresses for
+		// each of the endpoints, in order." - A61
+		for _, endpoint := range endpoints {
+			newAddrs = append(newAddrs, endpoint.Addresses...)
+		}
+	} else {
+		// Endpoints not set, process addresses until we migrate resolver
+		// emissions fully to Endpoints. The top channel does wrap emitted
+		// addresses with endpoints, however some balancers such as weighted
+		// target do not forward the corresponding correct endpoints down/split
+		// endpoints properly. Once all balancers correctly forward endpoints
+		// down, can delete this else conditional.
+		newAddrs = state.ResolverState.Addresses
+		if cfg.ShuffleAddressList {
+			newAddrs = append([]resolver.Address{}, newAddrs...)
+			internal.RandShuffle(len(endpoints), func(i, j int) { endpoints[i], endpoints[j] = endpoints[j], endpoints[i] })
+		}
+	}
+
+	// If an address appears in multiple endpoints or in the same endpoint
+	// multiple times, we keep it only once. We will create only one SubConn
+	// for the address because an AddressMap is used to store SubConns.
+	// Not de-duplicating would result in attempting to connect to the same
+	// SubConn multiple times in the same pass. We don't want this.
+	newAddrs = deDupAddresses(newAddrs)
+	newAddrs = interleaveAddresses(newAddrs)
+
+	prevAddr := b.addressList.currentAddress()
+	prevSCData, found := b.subConns.Get(prevAddr)
+	prevAddrsCount := b.addressList.size()
+	isPrevRawConnectivityStateReady := found && prevSCData.(*scData).rawConnectivityState == connectivity.Ready
+	b.addressList.updateAddrs(newAddrs)
+
+	// If the previous ready SubConn exists in new address list,
+	// keep this connection and don't create new SubConns.
+	if isPrevRawConnectivityStateReady && b.addressList.seekTo(prevAddr) {
+		return nil
+	}
+
+	b.reconcileSubConnsLocked(newAddrs)
+	// If it's the first resolver update or the balancer was already READY
+	// (but the new address list does not contain the ready SubConn) or
+	// CONNECTING, enter CONNECTING.
+	// We may be in TRANSIENT_FAILURE due to a previous empty address list,
+	// we should still enter CONNECTING because the sticky TF behaviour
+	//  mentioned in A62 applies only when the TRANSIENT_FAILURE is reported
+	// due to connectivity failures.
+	if isPrevRawConnectivityStateReady || b.state == connectivity.Connecting || prevAddrsCount == 0 {
+		// Start connection attempt at first address.
+		b.forceUpdateConcludedStateLocked(balancer.State{
+			ConnectivityState: connectivity.Connecting,
+			Picker:            &picker{err: balancer.ErrNoSubConnAvailable},
+		})
+		b.startFirstPassLocked()
+	} else if b.state == connectivity.TransientFailure {
+		// If we're in TRANSIENT_FAILURE, we stay in TRANSIENT_FAILURE until
+		// we're READY. See A62.
+		b.startFirstPassLocked()
+	}
+	return nil
+}
+
+// UpdateSubConnState is unused as a StateListener is always registered when
+// creating SubConns.
+func (b *pickfirstBalancer) UpdateSubConnState(subConn balancer.SubConn, state balancer.SubConnState) {
+	b.logger.Errorf("UpdateSubConnState(%v, %+v) called unexpectedly", subConn, state)
+}
+
+func (b *pickfirstBalancer) Close() {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.closeSubConnsLocked()
+	b.cancelConnectionTimer()
+	b.state = connectivity.Shutdown
+}
+
+// ExitIdle moves the balancer out of idle state. It can be called concurrently
+// by the idlePicker and clientConn so access to variables should be
+// synchronized.
+func (b *pickfirstBalancer) ExitIdle() {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.state == connectivity.Idle {
+		b.startFirstPassLocked()
+	}
+}
+
+func (b *pickfirstBalancer) startFirstPassLocked() {
+	b.firstPass = true
+	b.numTF = 0
+	// Reset the connection attempt record for existing SubConns.
+	for _, sd := range b.subConns.Values() {
+		sd.(*scData).connectionFailedInFirstPass = false
+	}
+	b.requestConnectionLocked()
+}
+
+func (b *pickfirstBalancer) closeSubConnsLocked() {
+	for _, sd := range b.subConns.Values() {
+		sd.(*scData).subConn.Shutdown()
+	}
+	b.subConns = resolver.NewAddressMap()
+}
+
+// deDupAddresses ensures that each address appears only once in the slice.
+func deDupAddresses(addrs []resolver.Address) []resolver.Address {
+	seenAddrs := resolver.NewAddressMap()
+	retAddrs := []resolver.Address{}
+
+	for _, addr := range addrs {
+		if _, ok := seenAddrs.Get(addr); ok {
+			continue
+		}
+		retAddrs = append(retAddrs, addr)
+	}
+	return retAddrs
+}
+
+// interleaveAddresses interleaves addresses of both families (IPv4 and IPv6)
+// as per RFC-8305 section 4.
+// Whichever address family is first in the list is followed by an address of
+// the other address family; that is, if the first address in the list is IPv6,
+// then the first IPv4 address should be moved up in the list to be second in
+// the list. It doesn't support configuring "First Address Family Count", i.e.
+// there will always be a single member of the first address family at the
+// beginning of the interleaved list.
+// Addresses that are neither IPv4 nor IPv6 are treated as part of a third
+// "unknown" family for interleaving.
+// See: https://datatracker.ietf.org/doc/html/rfc8305#autoid-6
+func interleaveAddresses(addrs []resolver.Address) []resolver.Address {
+	familyAddrsMap := map[ipAddrFamily][]resolver.Address{}
+	interleavingOrder := []ipAddrFamily{}
+	for _, addr := range addrs {
+		family := addressFamily(addr.Addr)
+		if _, found := familyAddrsMap[family]; !found {
+			interleavingOrder = append(interleavingOrder, family)
+		}
+		familyAddrsMap[family] = append(familyAddrsMap[family], addr)
+	}
+
+	interleavedAddrs := make([]resolver.Address, 0, len(addrs))
+
+	for curFamilyIdx := 0; len(interleavedAddrs) < len(addrs); curFamilyIdx = (curFamilyIdx + 1) % len(interleavingOrder) {
+		// Some IP types may have fewer addresses than others, so we look for
+		// the next type that has a remaining member to add to the interleaved
+		// list.
+		family := interleavingOrder[curFamilyIdx]
+		remainingMembers := familyAddrsMap[family]
+		if len(remainingMembers) > 0 {
+			interleavedAddrs = append(interleavedAddrs, remainingMembers[0])
+			familyAddrsMap[family] = remainingMembers[1:]
+		}
+	}
+
+	return interleavedAddrs
+}
+
+// addressFamily returns the ipAddrFamily after parsing the address string.
+// If the address isn't of the format "ip-address:port", it returns
+// ipAddrFamilyUnknown. The address may be valid even if it's not an IP when
+// using a resolver like passthrough where the address may be a hostname in
+// some format that the dialer can resolve.
+func addressFamily(address string) ipAddrFamily {
+	// Parse the IP after removing the port.
+	host, _, err := net.SplitHostPort(address)
+	if err != nil {
+		return ipAddrFamilyUnknown
+	}
+	ip, err := netip.ParseAddr(host)
+	if err != nil {
+		return ipAddrFamilyUnknown
+	}
+	switch {
+	case ip.Is4() || ip.Is4In6():
+		return ipAddrFamilyV4
+	case ip.Is6():
+		return ipAddrFamilyV6
+	default:
+		return ipAddrFamilyUnknown
+	}
+}
+
+// reconcileSubConnsLocked updates the active subchannels based on a new address
+// list from the resolver. It does this by:
+//   - closing subchannels: any existing subchannels associated with addresses
+//     that are no longer in the updated list are shut down.
+//   - removing subchannels: entries for these closed subchannels are removed
+//     from the subchannel map.
+//
+// This ensures that the subchannel map accurately reflects the current set of
+// addresses received from the name resolver.
+func (b *pickfirstBalancer) reconcileSubConnsLocked(newAddrs []resolver.Address) {
+	newAddrsMap := resolver.NewAddressMap()
+	for _, addr := range newAddrs {
+		newAddrsMap.Set(addr, true)
+	}
+
+	for _, oldAddr := range b.subConns.Keys() {
+		if _, ok := newAddrsMap.Get(oldAddr); ok {
+			continue
+		}
+		val, _ := b.subConns.Get(oldAddr)
+		val.(*scData).subConn.Shutdown()
+		b.subConns.Delete(oldAddr)
+	}
+}
+
+// shutdownRemainingLocked shuts down remaining subConns. Called when a subConn
+// becomes ready, which means that all other subConn must be shutdown.
+func (b *pickfirstBalancer) shutdownRemainingLocked(selected *scData) {
+	b.cancelConnectionTimer()
+	for _, v := range b.subConns.Values() {
+		sd := v.(*scData)
+		if sd.subConn != selected.subConn {
+			sd.subConn.Shutdown()
+		}
+	}
+	b.subConns = resolver.NewAddressMap()
+	b.subConns.Set(selected.addr, selected)
+}
+
+// requestConnectionLocked starts connecting on the subchannel corresponding to
+// the current address. If no subchannel exists, one is created. If the current
+// subchannel is in TransientFailure, a connection to the next address is
+// attempted until a subchannel is found.
+func (b *pickfirstBalancer) requestConnectionLocked() {
+	if !b.addressList.isValid() {
+		return
+	}
+	var lastErr error
+	for valid := true; valid; valid = b.addressList.increment() {
+		curAddr := b.addressList.currentAddress()
+		sd, ok := b.subConns.Get(curAddr)
+		if !ok {
+			var err error
+			// We want to assign the new scData to sd from the outer scope,
+			// hence we can't use := below.
+			sd, err = b.newSCData(curAddr)
+			if err != nil {
+				// This should never happen, unless the clientConn is being shut
+				// down.
+				if b.logger.V(2) {
+					b.logger.Infof("Failed to create a subConn for address %v: %v", curAddr.String(), err)
+				}
+				// Do nothing, the LB policy will be closed soon.
+				return
+			}
+			b.subConns.Set(curAddr, sd)
+		}
+
+		scd := sd.(*scData)
+		switch scd.rawConnectivityState {
+		case connectivity.Idle:
+			scd.subConn.Connect()
+			b.scheduleNextConnectionLocked()
+			return
+		case connectivity.TransientFailure:
+			// The SubConn is being re-used and failed during a previous pass
+			// over the addressList. It has not completed backoff yet.
+			// Mark it as having failed and try the next address.
+			scd.connectionFailedInFirstPass = true
+			lastErr = scd.lastErr
+			continue
+		case connectivity.Connecting:
+			// Wait for the connection attempt to complete or the timer to fire
+			// before attempting the next address.
+			b.scheduleNextConnectionLocked()
+			return
+		default:
+			b.logger.Errorf("SubConn with unexpected state %v present in SubConns map.", scd.rawConnectivityState)
+			return
+
+		}
+	}
+
+	// All the remaining addresses in the list are in TRANSIENT_FAILURE, end the
+	// first pass if possible.
+	b.endFirstPassIfPossibleLocked(lastErr)
+}
+
+func (b *pickfirstBalancer) scheduleNextConnectionLocked() {
+	b.cancelConnectionTimer()
+	if !b.addressList.hasNext() {
+		return
+	}
+	curAddr := b.addressList.currentAddress()
+	cancelled := false // Access to this is protected by the balancer's mutex.
+	closeFn := internal.TimeAfterFunc(connectionDelayInterval, func() {
+		b.mu.Lock()
+		defer b.mu.Unlock()
+		// If the scheduled task is cancelled while acquiring the mutex, return.
+		if cancelled {
+			return
+		}
+		if b.logger.V(2) {
+			b.logger.Infof("Happy Eyeballs timer expired while waiting for connection to %q.", curAddr.Addr)
+		}
+		if b.addressList.increment() {
+			b.requestConnectionLocked()
+		}
+	})
+	// Access to the cancellation callback held by the balancer is guarded by
+	// the balancer's mutex, so it's safe to set the boolean from the callback.
+	b.cancelConnectionTimer = sync.OnceFunc(func() {
+		cancelled = true
+		closeFn()
+	})
+}
+
+func (b *pickfirstBalancer) updateSubConnState(sd *scData, newState balancer.SubConnState) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	oldState := sd.rawConnectivityState
+	sd.rawConnectivityState = newState.ConnectivityState
+	// Previously relevant SubConns can still callback with state updates.
+	// To prevent pickers from returning these obsolete SubConns, this logic
+	// is included to check if the current list of active SubConns includes this
+	// SubConn.
+	if !b.isActiveSCData(sd) {
+		return
+	}
+	if newState.ConnectivityState == connectivity.Shutdown {
+		sd.effectiveState = connectivity.Shutdown
+		return
+	}
+
+	// Record a connection attempt when exiting CONNECTING.
+	if newState.ConnectivityState == connectivity.TransientFailure {
+		sd.connectionFailedInFirstPass = true
+		connectionAttemptsFailedMetric.Record(b.metricsRecorder, 1, b.target)
+	}
+
+	if newState.ConnectivityState == connectivity.Ready {
+		connectionAttemptsSucceededMetric.Record(b.metricsRecorder, 1, b.target)
+		b.shutdownRemainingLocked(sd)
+		if !b.addressList.seekTo(sd.addr) {
+			// This should not fail as we should have only one SubConn after
+			// entering READY. The SubConn should be present in the addressList.
+			b.logger.Errorf("Address %q not found address list in  %v", sd.addr, b.addressList.addresses)
+			return
+		}
+		if !b.healthCheckingEnabled {
+			if b.logger.V(2) {
+				b.logger.Infof("SubConn %p reported connectivity state READY and the health listener is disabled. Transitioning SubConn to READY.", sd.subConn)
+			}
+
+			sd.effectiveState = connectivity.Ready
+			b.updateBalancerState(balancer.State{
+				ConnectivityState: connectivity.Ready,
+				Picker:            &picker{result: balancer.PickResult{SubConn: sd.subConn}},
+			})
+			return
+		}
+		if b.logger.V(2) {
+			b.logger.Infof("SubConn %p reported connectivity state READY. Registering health listener.", sd.subConn)
+		}
+		// Send a CONNECTING update to take the SubConn out of sticky-TF if
+		// required.
+		sd.effectiveState = connectivity.Connecting
+		b.updateBalancerState(balancer.State{
+			ConnectivityState: connectivity.Connecting,
+			Picker:            &picker{err: balancer.ErrNoSubConnAvailable},
+		})
+		sd.subConn.RegisterHealthListener(func(scs balancer.SubConnState) {
+			b.updateSubConnHealthState(sd, scs)
+		})
+		return
+	}
+
+	// If the LB policy is READY, and it receives a subchannel state change,
+	// it means that the READY subchannel has failed.
+	// A SubConn can also transition from CONNECTING directly to IDLE when
+	// a transport is successfully created, but the connection fails
+	// before the SubConn can send the notification for READY. We treat
+	// this as a successful connection and transition to IDLE.
+	// TODO: https://github.com/grpc/grpc-go/issues/7862 - Remove the second
+	// part of the if condition below once the issue is fixed.
+	if oldState == connectivity.Ready || (oldState == connectivity.Connecting && newState.ConnectivityState == connectivity.Idle) {
+		// Once a transport fails, the balancer enters IDLE and starts from
+		// the first address when the picker is used.
+		b.shutdownRemainingLocked(sd)
+		sd.effectiveState = newState.ConnectivityState
+		// READY SubConn interspliced in between CONNECTING and IDLE, need to
+		// account for that.
+		if oldState == connectivity.Connecting {
+			// A known issue (https://github.com/grpc/grpc-go/issues/7862)
+			// causes a race that prevents the READY state change notification.
+			// This works around it.
+			connectionAttemptsSucceededMetric.Record(b.metricsRecorder, 1, b.target)
+		}
+		disconnectionsMetric.Record(b.metricsRecorder, 1, b.target)
+		b.addressList.reset()
+		b.updateBalancerState(balancer.State{
+			ConnectivityState: connectivity.Idle,
+			Picker:            &idlePicker{exitIdle: sync.OnceFunc(b.ExitIdle)},
+		})
+		return
+	}
+
+	if b.firstPass {
+		switch newState.ConnectivityState {
+		case connectivity.Connecting:
+			// The effective state can be in either IDLE, CONNECTING or
+			// TRANSIENT_FAILURE. If it's  TRANSIENT_FAILURE, stay in
+			// TRANSIENT_FAILURE until it's READY. See A62.
+			if sd.effectiveState != connectivity.TransientFailure {
+				sd.effectiveState = connectivity.Connecting
+				b.updateBalancerState(balancer.State{
+					ConnectivityState: connectivity.Connecting,
+					Picker:            &picker{err: balancer.ErrNoSubConnAvailable},
+				})
+			}
+		case connectivity.TransientFailure:
+			sd.lastErr = newState.ConnectionError
+			sd.effectiveState = connectivity.TransientFailure
+			// Since we're re-using common SubConns while handling resolver
+			// updates, we could receive an out of turn TRANSIENT_FAILURE from
+			// a pass over the previous address list. Happy Eyeballs will also
+			// cause out of order updates to arrive.
+
+			if curAddr := b.addressList.currentAddress(); equalAddressIgnoringBalAttributes(&curAddr, &sd.addr) {
+				b.cancelConnectionTimer()
+				if b.addressList.increment() {
+					b.requestConnectionLocked()
+					return
+				}
+			}
+
+			// End the first pass if we've seen a TRANSIENT_FAILURE from all
+			// SubConns once.
+			b.endFirstPassIfPossibleLocked(newState.ConnectionError)
+		}
+		return
+	}
+
+	// We have finished the first pass, keep re-connecting failing SubConns.
+	switch newState.ConnectivityState {
+	case connectivity.TransientFailure:
+		b.numTF = (b.numTF + 1) % b.subConns.Len()
+		sd.lastErr = newState.ConnectionError
+		if b.numTF%b.subConns.Len() == 0 {
+			b.updateBalancerState(balancer.State{
+				ConnectivityState: connectivity.TransientFailure,
+				Picker:            &picker{err: newState.ConnectionError},
+			})
+		}
+		// We don't need to request re-resolution since the SubConn already
+		// does that before reporting TRANSIENT_FAILURE.
+		// TODO: #7534 - Move re-resolution requests from SubConn into
+		// pick_first.
+	case connectivity.Idle:
+		sd.subConn.Connect()
+	}
+}
+
+// endFirstPassIfPossibleLocked ends the first happy-eyeballs pass if all the
+// addresses are tried and their SubConns have reported a failure.
+func (b *pickfirstBalancer) endFirstPassIfPossibleLocked(lastErr error) {
+	// An optimization to avoid iterating over the entire SubConn map.
+	if b.addressList.isValid() {
+		return
+	}
+	// Connect() has been called on all the SubConns. The first pass can be
+	// ended if all the SubConns have reported a failure.
+	for _, v := range b.subConns.Values() {
+		sd := v.(*scData)
+		if !sd.connectionFailedInFirstPass {
+			return
+		}
+	}
+	b.firstPass = false
+	b.updateBalancerState(balancer.State{
+		ConnectivityState: connectivity.TransientFailure,
+		Picker:            &picker{err: lastErr},
+	})
+	// Start re-connecting all the SubConns that are already in IDLE.
+	for _, v := range b.subConns.Values() {
+		sd := v.(*scData)
+		if sd.rawConnectivityState == connectivity.Idle {
+			sd.subConn.Connect()
+		}
+	}
+}
+
+func (b *pickfirstBalancer) isActiveSCData(sd *scData) bool {
+	activeSD, found := b.subConns.Get(sd.addr)
+	return found && activeSD == sd
+}
+
+func (b *pickfirstBalancer) updateSubConnHealthState(sd *scData, state balancer.SubConnState) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	// Previously relevant SubConns can still callback with state updates.
+	// To prevent pickers from returning these obsolete SubConns, this logic
+	// is included to check if the current list of active SubConns includes
+	// this SubConn.
+	if !b.isActiveSCData(sd) {
+		return
+	}
+	sd.effectiveState = state.ConnectivityState
+	switch state.ConnectivityState {
+	case connectivity.Ready:
+		b.updateBalancerState(balancer.State{
+			ConnectivityState: connectivity.Ready,
+			Picker:            &picker{result: balancer.PickResult{SubConn: sd.subConn}},
+		})
+	case connectivity.TransientFailure:
+		b.updateBalancerState(balancer.State{
+			ConnectivityState: connectivity.TransientFailure,
+			Picker:            &picker{err: fmt.Errorf("pickfirst: health check failure: %v", state.ConnectionError)},
+		})
+	case connectivity.Connecting:
+		b.updateBalancerState(balancer.State{
+			ConnectivityState: connectivity.Connecting,
+			Picker:            &picker{err: balancer.ErrNoSubConnAvailable},
+		})
+	default:
+		b.logger.Errorf("Got unexpected health update for SubConn %p: %v", state)
+	}
+}
+
+// updateBalancerState stores the state reported to the channel and calls
+// ClientConn.UpdateState(). As an optimization, it avoids sending duplicate
+// updates to the channel.
+func (b *pickfirstBalancer) updateBalancerState(newState balancer.State) {
+	// In case of TransientFailures allow the picker to be updated to update
+	// the connectivity error, in all other cases don't send duplicate state
+	// updates.
+	if newState.ConnectivityState == b.state && b.state != connectivity.TransientFailure {
+		return
+	}
+	b.forceUpdateConcludedStateLocked(newState)
+}
+
+// forceUpdateConcludedStateLocked stores the state reported to the channel and
+// calls ClientConn.UpdateState().
+// A separate function is defined to force update the ClientConn state since the
+// channel doesn't correctly assume that LB policies start in CONNECTING and
+// relies on LB policy to send an initial CONNECTING update.
+func (b *pickfirstBalancer) forceUpdateConcludedStateLocked(newState balancer.State) {
+	b.state = newState.ConnectivityState
+	b.cc.UpdateState(newState)
+}
+
+type picker struct {
+	result balancer.PickResult
+	err    error
+}
+
+func (p *picker) Pick(balancer.PickInfo) (balancer.PickResult, error) {
+	return p.result, p.err
+}
+
+// idlePicker is used when the SubConn is IDLE and kicks the SubConn into
+// CONNECTING when Pick is called.
+type idlePicker struct {
+	exitIdle func()
+}
+
+func (i *idlePicker) Pick(balancer.PickInfo) (balancer.PickResult, error) {
+	i.exitIdle()
+	return balancer.PickResult{}, balancer.ErrNoSubConnAvailable
+}
+
+// addressList manages sequentially iterating over addresses present in a list
+// of endpoints. It provides a 1 dimensional view of the addresses present in
+// the endpoints.
+// This type is not safe for concurrent access.
+type addressList struct {
+	addresses []resolver.Address
+	idx       int
+}
+
+func (al *addressList) isValid() bool {
+	return al.idx < len(al.addresses)
+}
+
+func (al *addressList) size() int {
+	return len(al.addresses)
+}
+
+// increment moves to the next index in the address list.
+// This method returns false if it went off the list, true otherwise.
+func (al *addressList) increment() bool {
+	if !al.isValid() {
+		return false
+	}
+	al.idx++
+	return al.idx < len(al.addresses)
+}
+
+// currentAddress returns the current address pointed to in the addressList.
+// If the list is in an invalid state, it returns an empty address instead.
+func (al *addressList) currentAddress() resolver.Address {
+	if !al.isValid() {
+		return resolver.Address{}
+	}
+	return al.addresses[al.idx]
+}
+
+func (al *addressList) reset() {
+	al.idx = 0
+}
+
+func (al *addressList) updateAddrs(addrs []resolver.Address) {
+	al.addresses = addrs
+	al.reset()
+}
+
+// seekTo returns false if the needle was not found and the current index was
+// left unchanged.
+func (al *addressList) seekTo(needle resolver.Address) bool {
+	for ai, addr := range al.addresses {
+		if !equalAddressIgnoringBalAttributes(&addr, &needle) {
+			continue
+		}
+		al.idx = ai
+		return true
+	}
+	return false
+}
+
+// hasNext returns whether incrementing the addressList will result in moving
+// past the end of the list. If the list has already moved past the end, it
+// returns false.
+func (al *addressList) hasNext() bool {
+	if !al.isValid() {
+		return false
+	}
+	return al.idx+1 < len(al.addresses)
+}
+
+// equalAddressIgnoringBalAttributes returns true is a and b are considered
+// equal. This is different from the Equal method on the resolver.Address type
+// which considers all fields to determine equality. Here, we only consider
+// fields that are meaningful to the SubConn.
+func equalAddressIgnoringBalAttributes(a, b *resolver.Address) bool {
+	return a.Addr == b.Addr && a.ServerName == b.ServerName &&
+		a.Attributes.Equal(b.Attributes) &&
+		a.Metadata == b.Metadata
+}