| // Copyright 2011 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| //go:build unix || fuchsia |
| |
| package net |
| |
| import ( |
| "context" |
| "internal/bytealg" |
| "sync" |
| ) |
| |
| var onceReadProtocols sync.Once |
| |
| // readProtocols loads contents of /etc/protocols into protocols map |
| // for quick access. |
| func readProtocols() { |
| file, err := open("/etc/protocols") |
| if err != nil { |
| return |
| } |
| defer file.close() |
| |
| for line, ok := file.readLine(); ok; line, ok = file.readLine() { |
| // tcp 6 TCP # transmission control protocol |
| if i := bytealg.IndexByteString(line, '#'); i >= 0 { |
| line = line[0:i] |
| } |
| f := getFields(line) |
| if len(f) < 2 { |
| continue |
| } |
| if proto, _, ok := dtoi(f[1]); ok { |
| if _, ok := protocols[f[0]]; !ok { |
| protocols[f[0]] = proto |
| } |
| for _, alias := range f[2:] { |
| if _, ok := protocols[alias]; !ok { |
| protocols[alias] = proto |
| } |
| } |
| } |
| } |
| } |
| |
| // lookupProtocol looks up IP protocol name in /etc/protocols and |
| // returns correspondent protocol number. |
| func lookupProtocol(_ context.Context, name string) (int, error) { |
| onceReadProtocols.Do(readProtocols) |
| return lookupProtocolMap(name) |
| } |
| |
| func (r *Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) { |
| order, conf := systemConf().hostLookupOrder(r, host) |
| if !r.preferGo() && order == hostLookupCgo { |
| if addrs, err, ok := cgoLookupHost(ctx, host); ok { |
| return addrs, err |
| } |
| // cgo not available (or netgo); fall back to Go's DNS resolver |
| order = hostLookupFilesDNS |
| } |
| return r.goLookupHostOrder(ctx, host, order, conf) |
| } |
| |
| func (r *Resolver) lookupIP(ctx context.Context, network, host string) (addrs []IPAddr, err error) { |
| if r.preferGo() { |
| return r.goLookupIP(ctx, network, host) |
| } |
| order, conf := systemConf().hostLookupOrder(r, host) |
| if order == hostLookupCgo { |
| if addrs, err, ok := cgoLookupIP(ctx, network, host); ok { |
| return addrs, err |
| } |
| // cgo not available (or netgo); fall back to Go's DNS resolver |
| order = hostLookupFilesDNS |
| } |
| ips, _, err := r.goLookupIPCNAMEOrder(ctx, network, host, order, conf) |
| return ips, err |
| } |
| |
| func (r *Resolver) lookupPort(ctx context.Context, network, service string) (int, error) { |
| if !r.preferGo() && systemConf().canUseCgo() { |
| if port, err, ok := cgoLookupPort(ctx, network, service); ok { |
| if err != nil { |
| // Issue 18213: if cgo fails, first check to see whether we |
| // have the answer baked-in to the net package. |
| if port, err := goLookupPort(network, service); err == nil { |
| return port, nil |
| } |
| } |
| return port, err |
| } |
| } |
| return goLookupPort(network, service) |
| } |
| |
| func (r *Resolver) lookupCNAME(ctx context.Context, name string) (string, error) { |
| order, conf := systemConf().hostLookupOrder(r, name) |
| if !r.preferGo() && order == hostLookupCgo { |
| if cname, err, ok := cgoLookupCNAME(ctx, name); ok { |
| return cname, err |
| } |
| } |
| return r.goLookupCNAME(ctx, name, order, conf) |
| } |
| |
| func (r *Resolver) lookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) { |
| return r.goLookupSRV(ctx, service, proto, name) |
| } |
| |
| func (r *Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) { |
| return r.goLookupMX(ctx, name) |
| } |
| |
| func (r *Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) { |
| return r.goLookupNS(ctx, name) |
| } |
| |
| func (r *Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) { |
| return r.goLookupTXT(ctx, name) |
| } |
| |
| func (r *Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error) { |
| order, conf := systemConf().hostLookupOrder(r, "") |
| if !r.preferGo() && order == hostLookupCgo { |
| if ptrs, err, ok := cgoLookupPTR(ctx, addr); ok { |
| return ptrs, err |
| } |
| } |
| return r.goLookupPTR(ctx, addr, conf) |
| } |