nss.go

     1  // Copyright 2015 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 aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris
     6  
     7  package net
     8  
     9  import (
    10  	"errors"
    11  	"internal/bytealg"
    12  	"io"
    13  	"os"
    14  )
    15  
    16  // nssConf represents the state of the machine's /etc/nsswitch.conf file.
    17  type nssConf struct {
    18  	err     error                  // any error encountered opening or parsing the file
    19  	sources map[string][]nssSource // keyed by database (e.g. "hosts")
    20  }
    21  
    22  type nssSource struct {
    23  	source   string // e.g. "compat", "files", "mdns4_minimal"
    24  	criteria []nssCriterion
    25  }
    26  
    27  // standardCriteria reports all specified criteria have the default
    28  // status actions.
    29  func (s nssSource) standardCriteria() bool {
    30  	for i, crit := range s.criteria {
    31  		if !crit.standardStatusAction(i == len(s.criteria)-1) {
    32  			return false
    33  		}
    34  	}
    35  	return true
    36  }
    37  
    38  // nssCriterion is the parsed structure of one of the criteria in brackets
    39  // after an NSS source name.
    40  type nssCriterion struct {
    41  	negate bool   // if "!" was present
    42  	status string // e.g. "success", "unavail" (lowercase)
    43  	action string // e.g. "return", "continue" (lowercase)
    44  }
    45  
    46  // standardStatusAction reports whether c is equivalent to not
    47  // specifying the criterion at all. last is whether this criteria is the
    48  // last in the list.
    49  func (c nssCriterion) standardStatusAction(last bool) bool {
    50  	if c.negate {
    51  		return false
    52  	}
    53  	var def string
    54  	switch c.status {
    55  	case "success":
    56  		def = "return"
    57  	case "notfound", "unavail", "tryagain":
    58  		def = "continue"
    59  	default:
    60  		// Unknown status
    61  		return false
    62  	}
    63  	if last && c.action == "return" {
    64  		return true
    65  	}
    66  	return c.action == def
    67  }
    68  
    69  func parseNSSConfFile(file string) *nssConf {
    70  	f, err := os.Open(file)
    71  	if err != nil {
    72  		return &nssConf{err: err}
    73  	}
    74  	defer f.Close()
    75  	return parseNSSConf(f)
    76  }
    77  
    78  func parseNSSConf(r io.Reader) *nssConf {
    79  	slurp, err := readFull(r)
    80  	if err != nil {
    81  		return &nssConf{err: err}
    82  	}
    83  	conf := new(nssConf)
    84  	conf.err = foreachLine(slurp, func(line []byte) error {
    85  		line = trimSpace(removeComment(line))
    86  		if len(line) == 0 {
    87  			return nil
    88  		}
    89  		colon := bytealg.IndexByte(line, ':')
    90  		if colon == -1 {
    91  			return errors.New("no colon on line")
    92  		}
    93  		db := string(trimSpace(line[:colon]))
    94  		srcs := line[colon+1:]
    95  		for {
    96  			srcs = trimSpace(srcs)
    97  			if len(srcs) == 0 {
    98  				break
    99  			}
   100  			sp := bytealg.IndexByte(srcs, ' ')
   101  			var src string
   102  			if sp == -1 {
   103  				src = string(srcs)
   104  				srcs = nil // done
   105  			} else {
   106  				src = string(srcs[:sp])
   107  				srcs = trimSpace(srcs[sp+1:])
   108  			}
   109  			var criteria []nssCriterion
   110  			// See if there's a criteria block in brackets.
   111  			if len(srcs) > 0 && srcs[0] == '[' {
   112  				bclose := bytealg.IndexByte(srcs, ']')
   113  				if bclose == -1 {
   114  					return errors.New("unclosed criterion bracket")
   115  				}
   116  				var err error
   117  				criteria, err = parseCriteria(srcs[1:bclose])
   118  				if err != nil {
   119  					return errors.New("invalid criteria: " + string(srcs[1:bclose]))
   120  				}
   121  				srcs = srcs[bclose+1:]
   122  			}
   123  			if conf.sources == nil {
   124  				conf.sources = make(map[string][]nssSource)
   125  			}
   126  			conf.sources[db] = append(conf.sources[db], nssSource{
   127  				source:   src,
   128  				criteria: criteria,
   129  			})
   130  		}
   131  		return nil
   132  	})
   133  	return conf
   134  }
   135  
   136  // parses "foo=bar !foo=bar"
   137  func parseCriteria(x []byte) (c []nssCriterion, err error) {
   138  	err = foreachField(x, func(f []byte) error {
   139  		not := false
   140  		if len(f) > 0 && f[0] == '!' {
   141  			not = true
   142  			f = f[1:]
   143  		}
   144  		if len(f) < 3 {
   145  			return errors.New("criterion too short")
   146  		}
   147  		eq := bytealg.IndexByte(f, '=')
   148  		if eq == -1 {
   149  			return errors.New("criterion lacks equal sign")
   150  		}
   151  		lowerASCIIBytes(f)
   152  		c = append(c, nssCriterion{
   153  			negate: not,
   154  			status: string(f[:eq]),
   155  			action: string(f[eq+1:]),
   156  		})
   157  		return nil
   158  	})
   159  	return
   160  }
   161
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