lookup_unix.go

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  //go:build unix || js || wasip1
     6  
     7  package net
     8  
     9  import (
    10  	"context"
    11  	"internal/bytealg"
    12  	"sync"
    13  )
    14  
    15  var onceReadProtocols sync.Once
    16  
    17  // readProtocols loads contents of /etc/protocols into protocols map
    18  // for quick access.
    19  func readProtocols() {
    20  	file, err := open("/etc/protocols")
    21  	if err != nil {
    22  		return
    23  	}
    24  	defer file.close()
    25  
    26  	for line, ok := file.readLine(); ok; line, ok = file.readLine() {
    27  		// tcp    6   TCP    # transmission control protocol
    28  		if i := bytealg.IndexByteString(line, '#'); i >= 0 {
    29  			line = line[0:i]
    30  		}
    31  		f := getFields(line)
    32  		if len(f) < 2 {
    33  			continue
    34  		}
    35  		if proto, _, ok := dtoi(f[1]); ok {
    36  			if _, ok := protocols[f[0]]; !ok {
    37  				protocols[f[0]] = proto
    38  			}
    39  			for _, alias := range f[2:] {
    40  				if _, ok := protocols[alias]; !ok {
    41  					protocols[alias] = proto
    42  				}
    43  			}
    44  		}
    45  	}
    46  }
    47  
    48  // lookupProtocol looks up IP protocol name in /etc/protocols and
    49  // returns correspondent protocol number.
    50  func lookupProtocol(_ context.Context, name string) (int, error) {
    51  	onceReadProtocols.Do(readProtocols)
    52  	return lookupProtocolMap(name)
    53  }
    54  
    55  func (r *Resolver) lookupHost(ctx context.Context, host string) (addrs []string, err error) {
    56  	order, conf := systemConf().hostLookupOrder(r, host)
    57  	if order == hostLookupCgo {
    58  		return cgoLookupHost(ctx, host)
    59  	}
    60  	return r.goLookupHostOrder(ctx, host, order, conf)
    61  }
    62  
    63  func (r *Resolver) lookupIP(ctx context.Context, network, host string) (addrs []IPAddr, err error) {
    64  	order, conf := systemConf().hostLookupOrder(r, host)
    65  	if order == hostLookupCgo {
    66  		return cgoLookupIP(ctx, network, host)
    67  	}
    68  	ips, _, err := r.goLookupIPCNAMEOrder(ctx, network, host, order, conf)
    69  	return ips, err
    70  }
    71  
    72  func (r *Resolver) lookupPort(ctx context.Context, network, service string) (int, error) {
    73  	// Port lookup is not a DNS operation.
    74  	// Prefer the cgo resolver if possible.
    75  	if !systemConf().mustUseGoResolver(r) {
    76  		port, err := cgoLookupPort(ctx, network, service)
    77  		if err != nil {
    78  			// Issue 18213: if cgo fails, first check to see whether we
    79  			// have the answer baked-in to the net package.
    80  			if port, err := goLookupPort(network, service); err == nil {
    81  				return port, nil
    82  			}
    83  		}
    84  		return port, err
    85  	}
    86  	return goLookupPort(network, service)
    87  }
    88  
    89  func (r *Resolver) lookupCNAME(ctx context.Context, name string) (string, error) {
    90  	order, conf := systemConf().hostLookupOrder(r, name)
    91  	if order == hostLookupCgo {
    92  		if cname, err, ok := cgoLookupCNAME(ctx, name); ok {
    93  			return cname, err
    94  		}
    95  	}
    96  	return r.goLookupCNAME(ctx, name, order, conf)
    97  }
    98  
    99  func (r *Resolver) lookupSRV(ctx context.Context, service, proto, name string) (string, []*SRV, error) {
   100  	return r.goLookupSRV(ctx, service, proto, name)
   101  }
   102  
   103  func (r *Resolver) lookupMX(ctx context.Context, name string) ([]*MX, error) {
   104  	return r.goLookupMX(ctx, name)
   105  }
   106  
   107  func (r *Resolver) lookupNS(ctx context.Context, name string) ([]*NS, error) {
   108  	return r.goLookupNS(ctx, name)
   109  }
   110  
   111  func (r *Resolver) lookupTXT(ctx context.Context, name string) ([]string, error) {
   112  	return r.goLookupTXT(ctx, name)
   113  }
   114  
   115  func (r *Resolver) lookupAddr(ctx context.Context, addr string) ([]string, error) {
   116  	order, conf := systemConf().addrLookupOrder(r, addr)
   117  	if order == hostLookupCgo {
   118  		return cgoLookupPTR(ctx, addr)
   119  	}
   120  	return r.goLookupPTR(ctx, addr, order, conf)
   121  }
   122
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