...
Run Format

Source file src/net/lookup_unix.go

Documentation: net

  // 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.
  
  // +build darwin dragonfly freebsd linux netbsd openbsd solaris
  
  package net
  
  import (
  	"context"
  	"sync"
  )
  
  var onceReadProtocols sync.Once
  
  // readProtocols loads contents of /etc/protocols into protocols map
  // for quick access.
  func readProtocols() {
  	if file, err := open("/etc/protocols"); err == nil {
  		for line, ok := file.readLine(); ok; line, ok = file.readLine() {
  			// tcp    6   TCP    # transmission control protocol
  			if i := byteIndex(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
  					}
  				}
  			}
  		}
  		file.close()
  	}
  }
  
  // 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 := systemConf().hostLookupOrder(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 goLookupHostOrder(ctx, host, order)
  }
  
  func (r *Resolver) lookupIP(ctx context.Context, host string) (addrs []IPAddr, err error) {
  	if r.PreferGo {
  		return goLookupIP(ctx, host)
  	}
  	order := systemConf().hostLookupOrder(host)
  	if order == hostLookupCgo {
  		if addrs, err, ok := cgoLookupIP(ctx, host); ok {
  			return addrs, err
  		}
  		// cgo not available (or netgo); fall back to Go's DNS resolver
  		order = hostLookupFilesDNS
  	}
  	addrs, _, err = goLookupIPCNAMEOrder(ctx, host, order)
  	return
  }
  
  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) {
  	if !r.PreferGo && systemConf().canUseCgo() {
  		if cname, err, ok := cgoLookupCNAME(ctx, name); ok {
  			return cname, err
  		}
  	}
  	return goLookupCNAME(ctx, name)
  }
  
  func (*Resolver) lookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
  	var target string
  	if service == "" && proto == "" {
  		target = name
  	} else {
  		target = "_" + service + "._" + proto + "." + name
  	}
  	cname, rrs, err := lookup(ctx, target, dnsTypeSRV)
  	if err != nil {
  		return "", nil, err
  	}
  	srvs := make([]*SRV, len(rrs))
  	for i, rr := range rrs {
  		rr := rr.(*dnsRR_SRV)
  		srvs[i] = &SRV{Target: rr.Target, Port: rr.Port, Priority: rr.Priority, Weight: rr.Weight}
  	}
  	byPriorityWeight(srvs).sort()
  	return cname, srvs, nil
  }
  
  func (*Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
  	_, rrs, err := lookup(ctx, name, dnsTypeMX)
  	if err != nil {
  		return nil, err
  	}
  	mxs := make([]*MX, len(rrs))
  	for i, rr := range rrs {
  		rr := rr.(*dnsRR_MX)
  		mxs[i] = &MX{Host: rr.Mx, Pref: rr.Pref}
  	}
  	byPref(mxs).sort()
  	return mxs, nil
  }
  
  func (*Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) {
  	_, rrs, err := lookup(ctx, name, dnsTypeNS)
  	if err != nil {
  		return nil, err
  	}
  	nss := make([]*NS, len(rrs))
  	for i, rr := range rrs {
  		nss[i] = &NS{Host: rr.(*dnsRR_NS).Ns}
  	}
  	return nss, nil
  }
  
  func (r *Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
  	_, rrs, err := lookup(ctx, name, dnsTypeTXT)
  	if err != nil {
  		return nil, err
  	}
  	txts := make([]string, len(rrs))
  	for i, rr := range rrs {
  		txts[i] = rr.(*dnsRR_TXT).Txt
  	}
  	return txts, nil
  }
  
  func (r *Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error) {
  	if !r.PreferGo && systemConf().canUseCgo() {
  		if ptrs, err, ok := cgoLookupPTR(ctx, addr); ok {
  			return ptrs, err
  		}
  	}
  	return goLookupPTR(ctx, addr)
  }
  

View as plain text