nss.go

Documentation: net

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