178 lines
7.0 KiB
Go
178 lines
7.0 KiB
Go
// Copyright 2015 Matthew Holt and The Caddy Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package network provides transport-neutral DNS-based discovery of upstream
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// targets, with result caching. It lives under modules/internal so it can be
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// shared between Caddy's own proxies (currently the HTTP reverse_proxy) without
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// each copying the resolution and caching logic.
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//
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// The package intentionally returns neutral [Target] values rather than any
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// proxy-specific upstream type; each caller builds its own upstream
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// representation from the targets.
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package network
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import (
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"context"
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"net"
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"strconv"
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"time"
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"go.uber.org/zap"
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"go.uber.org/zap/zapcore"
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)
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// Target is a single discovered upstream endpoint. It carries the SRV priority
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// and weight when available (both zero for non-SRV lookups).
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type Target struct {
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Host string
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Port string
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Priority uint16
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Weight uint16
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}
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// SRVLookupFunc resolves SRV records. It matches the signature of
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// (*net.Resolver).LookupSRV, so callers can pass that directly (and tests can
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// inject a stub).
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type SRVLookupFunc func(ctx context.Context, service, proto, name string) (cname string, addrs []*net.SRV, err error)
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// SRV resolves the given SRV record into targets, caching the result for
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// refresh. lookup is the resolver to use (typically (*net.Resolver).LookupSRV).
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// resolverKey identifies that resolver, so results looked up with different
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// resolvers for the same record are cached separately; pass "" for the default
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// resolver.
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//
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// If the lookup fails but returns some records (e.g. a few invalid names were
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// filtered out), those records are still used. If it fails with no records and
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// grace > 0, the previously cached result keeps being served for up to grace
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// past its refresh instead of returning an error. With no cached result, grace
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// also suppresses the error and returns no targets, preserving the reverse
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// proxy's existing behavior.
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//
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// Concurrent calls for the same record share one lookup, and no lock is held
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// while it runs, so a slow lookup does not delay calls for other records. The
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// shared lookup is detached from ctx (and bounded by its own timeout), so the
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// caller that started it can go away without failing it for the others; ctx
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// still bounds how long this call waits for the result.
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func SRV(ctx context.Context, lookup SRVLookupFunc, resolverKey, service, proto, name string, refresh, grace time.Duration, logger *zap.Logger) ([]Target, error) {
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key := srvKey(resolverKey, service, proto, name)
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return srvCache.get(ctx, key, refresh, grace, logger, func(ctx context.Context) ([]Target, error) {
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if c := logger.Check(zapcore.DebugLevel, "refreshing SRV upstreams"); c != nil {
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c.Write(zap.String("service", service), zap.String("proto", proto), zap.String("name", name))
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}
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_, records, err := lookup(ctx, service, proto, name)
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if err != nil {
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// From LookupSRV docs: invalid names are filtered out and an error is
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// returned alongside any remaining results; only treat it as fatal when
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// nothing usable came back.
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if len(records) == 0 {
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return nil, err
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}
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if c := logger.Check(zapcore.WarnLevel, "SRV records filtered"); c != nil {
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c.Write(zap.Error(err))
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}
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}
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targets := make([]Target, len(records))
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for i, rec := range records {
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if c := logger.Check(zapcore.DebugLevel, "discovered SRV record"); c != nil {
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c.Write(zap.String("target", rec.Target), zap.Uint16("port", rec.Port),
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zap.Uint16("priority", rec.Priority), zap.Uint16("weight", rec.Weight))
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}
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targets[i] = Target{
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Host: rec.Target,
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Port: strconv.Itoa(int(rec.Port)),
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Priority: rec.Priority,
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Weight: rec.Weight,
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}
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}
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return targets, nil
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})
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}
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// ResetSRV removes the cached result for a single SRV record resolved with the
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// given resolver (see [SRV] for resolverKey). A lookup for it that is already
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// in flight will not write its result back.
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func ResetSRV(resolverKey, service, proto, name string) {
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srvCache.reset(srvKey(resolverKey, service, proto, name))
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}
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// ResetAllSRV clears the entire SRV cache. Lookups already in flight will not
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// write their results back.
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func ResetAllSRV() {
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srvCache.resetAll()
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}
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func srvKey(resolverKey, service, proto, name string) string {
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return resolverKey + "\x00" + service + "\x00" + proto + "\x00" + name
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}
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// IPLookupFunc resolves a host's IP addresses. It matches the signature of
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// (*net.Resolver).LookupIP, so callers can pass that directly (and tests can
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// inject a stub). network is one of "ip", "ip4", "ip6".
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type IPLookupFunc func(ctx context.Context, network, host string) ([]net.IP, error)
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// A resolves name's A/AAAA records into targets (one per address, all using the
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// given port), caching the result for refresh. network selects the IP versions
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// ("ip", "ip4" or "ip6"). lookup is the resolver to use (typically
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// (*net.Resolver).LookupIP). resolverKey identifies that resolver, so results
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// looked up with different resolvers for the same name are cached separately;
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// pass "" for the default resolver.
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//
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// Concurrency and cancellation behave as described for [SRV].
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func A(ctx context.Context, lookup IPLookupFunc, resolverKey, network, name, port string, refresh time.Duration, logger *zap.Logger) ([]Target, error) {
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key := aKey(resolverKey, network, name, port)
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return aCache.get(ctx, key, refresh, 0, logger, func(ctx context.Context) ([]Target, error) {
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if c := logger.Check(zapcore.DebugLevel, "refreshing A upstreams"); c != nil {
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c.Write(zap.String("version", network), zap.String("name", name), zap.String("port", port))
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}
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ips, err := lookup(ctx, network, name)
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if err != nil {
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return nil, err
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}
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targets := make([]Target, len(ips))
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for i, ip := range ips {
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if c := logger.Check(zapcore.DebugLevel, "discovered A record"); c != nil {
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c.Write(zap.String("ip", ip.String()))
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}
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targets[i] = Target{Host: ip.String(), Port: port}
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}
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return targets, nil
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})
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}
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// ResetA removes the cached result for a single A/AAAA lookup (see [A] for the
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// parameters). A lookup for it that is already in flight will not write its
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// result back.
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func ResetA(resolverKey, network, name, port string) {
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aCache.reset(aKey(resolverKey, network, name, port))
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}
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// ResetAllA clears the entire A/AAAA cache. Lookups already in flight will not
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// write their results back.
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func ResetAllA() {
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aCache.resetAll()
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}
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func aKey(resolverKey, network, name, port string) string {
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return resolverKey + "\x00" + name + "\x00" + port + "\x00" + network
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}
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var (
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srvCache = newCache("SRV")
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aCache = newCache("A")
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)
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