local-server/vendor/github.com/kevinburke/ssh_config/config.go
2019-02-28 19:27:09 +11:00

640 lines
17 KiB
Go

// Package ssh_config provides tools for manipulating SSH config files.
//
// Importantly, this parser attempts to preserve comments in a given file, so
// you can manipulate a `ssh_config` file from a program, if your heart desires.
//
// The Get() and GetStrict() functions will attempt to read values from
// $HOME/.ssh/config, falling back to /etc/ssh/ssh_config. The first argument is
// the host name to match on ("example.com"), and the second argument is the key
// you want to retrieve ("Port"). The keywords are case insensitive.
//
// port := ssh_config.Get("myhost", "Port")
//
// You can also manipulate an SSH config file and then print it or write it back
// to disk.
//
// f, _ := os.Open(filepath.Join(os.Getenv("HOME"), ".ssh", "config"))
// cfg, _ := ssh_config.Decode(f)
// for _, host := range cfg.Hosts {
// fmt.Println("patterns:", host.Patterns)
// for _, node := range host.Nodes {
// fmt.Println(node.String())
// }
// }
//
// // Write the cfg back to disk:
// fmt.Println(cfg.String())
//
// BUG: the Match directive is currently unsupported; parsing a config with
// a Match directive will trigger an error.
package ssh_config
import (
"bytes"
"errors"
"fmt"
"io"
"os"
osuser "os/user"
"path/filepath"
"regexp"
"runtime"
"strings"
"sync"
)
const version = "0.5"
type configFinder func() string
// UserSettings checks ~/.ssh and /etc/ssh for configuration files. The config
// files are parsed and cached the first time Get() or GetStrict() is called.
type UserSettings struct {
IgnoreErrors bool
systemConfig *Config
systemConfigFinder configFinder
userConfig *Config
userConfigFinder configFinder
loadConfigs sync.Once
onceErr error
}
func homedir() string {
user, err := osuser.Current()
if err == nil {
return user.HomeDir
} else {
return os.Getenv("HOME")
}
}
func userConfigFinder() string {
return filepath.Join(homedir(), ".ssh", "config")
}
// DefaultUserSettings is the default UserSettings and is used by Get and
// GetStrict. It checks both $HOME/.ssh/config and /etc/ssh/ssh_config for keys,
// and it will return parse errors (if any) instead of swallowing them.
var DefaultUserSettings = &UserSettings{
IgnoreErrors: false,
systemConfigFinder: systemConfigFinder,
userConfigFinder: userConfigFinder,
}
func systemConfigFinder() string {
return filepath.Join("/", "etc", "ssh", "ssh_config")
}
func findVal(c *Config, alias, key string) (string, error) {
if c == nil {
return "", nil
}
val, err := c.Get(alias, key)
if err != nil || val == "" {
return "", err
}
if err := validate(key, val); err != nil {
return "", err
}
return val, nil
}
// Get finds the first value for key within a declaration that matches the
// alias. Get returns the empty string if no value was found, or if IgnoreErrors
// is false and we could not parse the configuration file. Use GetStrict to
// disambiguate the latter cases.
//
// The match for key is case insensitive.
//
// Get is a wrapper around DefaultUserSettings.Get.
func Get(alias, key string) string {
return DefaultUserSettings.Get(alias, key)
}
// GetStrict finds the first value for key within a declaration that matches the
// alias. If key has a default value and no matching configuration is found, the
// default will be returned. For more information on default values and the way
// patterns are matched, see the manpage for ssh_config.
//
// error will be non-nil if and only if a user's configuration file or the
// system configuration file could not be parsed, and u.IgnoreErrors is false.
//
// GetStrict is a wrapper around DefaultUserSettings.GetStrict.
func GetStrict(alias, key string) (string, error) {
return DefaultUserSettings.GetStrict(alias, key)
}
// Get finds the first value for key within a declaration that matches the
// alias. Get returns the empty string if no value was found, or if IgnoreErrors
// is false and we could not parse the configuration file. Use GetStrict to
// disambiguate the latter cases.
//
// The match for key is case insensitive.
func (u *UserSettings) Get(alias, key string) string {
val, err := u.GetStrict(alias, key)
if err != nil {
return ""
}
return val
}
// GetStrict finds the first value for key within a declaration that matches the
// alias. If key has a default value and no matching configuration is found, the
// default will be returned. For more information on default values and the way
// patterns are matched, see the manpage for ssh_config.
//
// error will be non-nil if and only if a user's configuration file or the
// system configuration file could not be parsed, and u.IgnoreErrors is false.
func (u *UserSettings) GetStrict(alias, key string) (string, error) {
u.loadConfigs.Do(func() {
// can't parse user file, that's ok.
var filename string
if u.userConfigFinder == nil {
filename = userConfigFinder()
} else {
filename = u.userConfigFinder()
}
var err error
u.userConfig, err = parseFile(filename)
if err != nil && os.IsNotExist(err) == false {
u.onceErr = err
return
}
if u.systemConfigFinder == nil {
filename = systemConfigFinder()
} else {
filename = u.systemConfigFinder()
}
u.systemConfig, err = parseFile(filename)
if err != nil && os.IsNotExist(err) == false {
u.onceErr = err
return
}
})
if u.onceErr != nil && u.IgnoreErrors == false {
return "", u.onceErr
}
val, err := findVal(u.userConfig, alias, key)
if err != nil || val != "" {
return val, err
}
val2, err2 := findVal(u.systemConfig, alias, key)
if err2 != nil || val2 != "" {
return val2, err2
}
return Default(key), nil
}
func parseFile(filename string) (*Config, error) {
return parseWithDepth(filename, 0)
}
func parseWithDepth(filename string, depth uint8) (*Config, error) {
f, err := os.Open(filename)
if err != nil {
return nil, err
}
defer f.Close()
return decode(f, isSystem(filename), depth)
}
func isSystem(filename string) bool {
// TODO i'm not sure this is the best way to detect a system repo
return strings.HasPrefix(filepath.Clean(filename), "/etc/ssh")
}
// Decode reads r into a Config, or returns an error if r could not be parsed as
// an SSH config file.
func Decode(r io.Reader) (*Config, error) {
return decode(r, false, 0)
}
func decode(r io.Reader, system bool, depth uint8) (c *Config, err error) {
defer func() {
if r := recover(); r != nil {
if _, ok := r.(runtime.Error); ok {
panic(r)
}
if e, ok := r.(error); ok && e == ErrDepthExceeded {
err = e
return
}
err = errors.New(r.(string))
}
}()
c = parseSSH(lexSSH(r), system, depth)
return c, err
}
// Config represents an SSH config file.
type Config struct {
// A list of hosts to match against. The file begins with an implicit
// "Host *" declaration matching all hosts.
Hosts []*Host
depth uint8
position Position
}
// Get finds the first value in the configuration that matches the alias and
// contains key. Get returns the empty string if no value was found, or if the
// Config contains an invalid conditional Include value.
//
// The match for key is case insensitive.
func (c *Config) Get(alias, key string) (string, error) {
lowerKey := strings.ToLower(key)
for _, host := range c.Hosts {
if !host.Matches(alias) {
continue
}
for _, node := range host.Nodes {
switch t := node.(type) {
case *Empty:
continue
case *KV:
// "keys are case insensitive" per the spec
lkey := strings.ToLower(t.Key)
if lkey == "match" {
panic("can't handle Match directives")
}
if lkey == lowerKey {
return t.Value, nil
}
case *Include:
val := t.Get(alias, key)
if val != "" {
return val, nil
}
default:
return "", fmt.Errorf("unknown Node type %v", t)
}
}
}
return "", nil
}
// String returns a string representation of the Config file.
func (c Config) String() string {
return marshal(c).String()
}
func (c Config) MarshalText() ([]byte, error) {
return marshal(c).Bytes(), nil
}
func marshal(c Config) *bytes.Buffer {
var buf bytes.Buffer
for i := range c.Hosts {
buf.WriteString(c.Hosts[i].String())
}
return &buf
}
// Pattern is a pattern in a Host declaration. Patterns are read-only values;
// create a new one with NewPattern().
type Pattern struct {
str string // Its appearance in the file, not the value that gets compiled.
regex *regexp.Regexp
not bool // True if this is a negated match
}
// String prints the string representation of the pattern.
func (p Pattern) String() string {
return p.str
}
// Copied from regexp.go with * and ? removed.
var specialBytes = []byte(`\.+()|[]{}^$`)
func special(b byte) bool {
return bytes.IndexByte(specialBytes, b) >= 0
}
// NewPattern creates a new Pattern for matching hosts. NewPattern("*") creates
// a Pattern that matches all hosts.
//
// From the manpage, a pattern consists of zero or more non-whitespace
// characters, `*' (a wildcard that matches zero or more characters), or `?' (a
// wildcard that matches exactly one character). For example, to specify a set
// of declarations for any host in the ".co.uk" set of domains, the following
// pattern could be used:
//
// Host *.co.uk
//
// The following pattern would match any host in the 192.168.0.[0-9] network range:
//
// Host 192.168.0.?
func NewPattern(s string) (*Pattern, error) {
if s == "" {
return nil, errors.New("ssh_config: empty pattern")
}
negated := false
if s[0] == '!' {
negated = true
s = s[1:]
}
var buf bytes.Buffer
buf.WriteByte('^')
for i := 0; i < len(s); i++ {
// A byte loop is correct because all metacharacters are ASCII.
switch b := s[i]; b {
case '*':
buf.WriteString(".*")
case '?':
buf.WriteString(".?")
default:
// borrowing from QuoteMeta here.
if special(b) {
buf.WriteByte('\\')
}
buf.WriteByte(b)
}
}
buf.WriteByte('$')
r, err := regexp.Compile(buf.String())
if err != nil {
return nil, err
}
return &Pattern{str: s, regex: r, not: negated}, nil
}
// Host describes a Host directive and the keywords that follow it.
type Host struct {
// A list of host patterns that should match this host.
Patterns []*Pattern
// A Node is either a key/value pair or a comment line.
Nodes []Node
// EOLComment is the comment (if any) terminating the Host line.
EOLComment string
hasEquals bool
leadingSpace uint16 // TODO: handle spaces vs tabs here.
// The file starts with an implicit "Host *" declaration.
implicit bool
}
// Matches returns true if the Host matches for the given alias. For
// a description of the rules that provide a match, see the manpage for
// ssh_config.
func (h *Host) Matches(alias string) bool {
found := false
for i := range h.Patterns {
if h.Patterns[i].regex.MatchString(alias) {
if h.Patterns[i].not == true {
// Negated match. "A pattern entry may be negated by prefixing
// it with an exclamation mark (`!'). If a negated entry is
// matched, then the Host entry is ignored, regardless of
// whether any other patterns on the line match. Negated matches
// are therefore useful to provide exceptions for wildcard
// matches."
return false
}
found = true
}
}
return found
}
// String prints h as it would appear in a config file. Minor tweaks may be
// present in the whitespace in the printed file.
func (h *Host) String() string {
var buf bytes.Buffer
if h.implicit == false {
buf.WriteString(strings.Repeat(" ", int(h.leadingSpace)))
buf.WriteString("Host")
if h.hasEquals {
buf.WriteString(" = ")
} else {
buf.WriteString(" ")
}
for i, pat := range h.Patterns {
buf.WriteString(pat.String())
if i < len(h.Patterns)-1 {
buf.WriteString(" ")
}
}
if h.EOLComment != "" {
buf.WriteString(" #")
buf.WriteString(h.EOLComment)
}
buf.WriteByte('\n')
}
for i := range h.Nodes {
buf.WriteString(h.Nodes[i].String())
buf.WriteByte('\n')
}
return buf.String()
}
// Node represents a line in a Config.
type Node interface {
Pos() Position
String() string
}
// KV is a line in the config file that contains a key, a value, and possibly
// a comment.
type KV struct {
Key string
Value string
Comment string
hasEquals bool
leadingSpace uint16 // Space before the key. TODO handle spaces vs tabs.
position Position
}
// Pos returns k's Position.
func (k *KV) Pos() Position {
return k.position
}
// String prints k as it was parsed in the config file. There may be slight
// changes to the whitespace between values.
func (k *KV) String() string {
if k == nil {
return ""
}
equals := " "
if k.hasEquals {
equals = " = "
}
line := fmt.Sprintf("%s%s%s%s", strings.Repeat(" ", int(k.leadingSpace)), k.Key, equals, k.Value)
if k.Comment != "" {
line += " #" + k.Comment
}
return line
}
// Empty is a line in the config file that contains only whitespace or comments.
type Empty struct {
Comment string
leadingSpace uint16 // TODO handle spaces vs tabs.
position Position
}
// Pos returns e's Position.
func (e *Empty) Pos() Position {
return e.position
}
// String prints e as it was parsed in the config file.
func (e *Empty) String() string {
if e == nil {
return ""
}
if e.Comment == "" {
return ""
}
return fmt.Sprintf("%s#%s", strings.Repeat(" ", int(e.leadingSpace)), e.Comment)
}
// Include holds the result of an Include directive, including the config files
// that have been parsed as part of that directive. At most 5 levels of Include
// statements will be parsed.
type Include struct {
// Comment is the contents of any comment at the end of the Include
// statement.
Comment string
parsed bool
// an include directive can include several different files, and wildcards
directives []string
mu sync.Mutex
// 1:1 mapping between matches and keys in files array; matches preserves
// ordering
matches []string
// actual filenames are listed here
files map[string]*Config
leadingSpace uint16
position Position
depth uint8
hasEquals bool
}
const maxRecurseDepth = 5
// ErrDepthExceeded is returned if too many Include directives are parsed.
// Usually this indicates a recursive loop (an Include directive pointing to the
// file it contains).
var ErrDepthExceeded = errors.New("ssh_config: max recurse depth exceeded")
func removeDups(arr []string) []string {
// Use map to record duplicates as we find them.
encountered := make(map[string]bool, len(arr))
result := make([]string, 0)
for v := range arr {
if encountered[arr[v]] == false {
encountered[arr[v]] = true
result = append(result, arr[v])
}
}
return result
}
// NewInclude creates a new Include with a list of file globs to include.
// Configuration files are parsed greedily (e.g. as soon as this function runs).
// Any error encountered while parsing nested configuration files will be
// returned.
func NewInclude(directives []string, hasEquals bool, pos Position, comment string, system bool, depth uint8) (*Include, error) {
if depth > maxRecurseDepth {
return nil, ErrDepthExceeded
}
inc := &Include{
Comment: comment,
directives: directives,
files: make(map[string]*Config),
position: pos,
leadingSpace: uint16(pos.Col) - 1,
depth: depth,
hasEquals: hasEquals,
}
// no need for inc.mu.Lock() since nothing else can access this inc
matches := make([]string, 0)
for i := range directives {
var path string
if filepath.IsAbs(directives[i]) {
path = directives[i]
} else if system {
path = filepath.Join("/etc/ssh", directives[i])
} else {
path = filepath.Join(homedir(), ".ssh", directives[i])
}
theseMatches, err := filepath.Glob(path)
if err != nil {
return nil, err
}
matches = append(matches, theseMatches...)
}
matches = removeDups(matches)
inc.matches = matches
for i := range matches {
config, err := parseWithDepth(matches[i], depth)
if err != nil {
return nil, err
}
inc.files[matches[i]] = config
}
return inc, nil
}
// Pos returns the position of the Include directive in the larger file.
func (i *Include) Pos() Position {
return i.position
}
// Get finds the first value in the Include statement matching the alias and the
// given key.
func (inc *Include) Get(alias, key string) string {
inc.mu.Lock()
defer inc.mu.Unlock()
// TODO: we search files in any order which is not correct
for i := range inc.matches {
cfg := inc.files[inc.matches[i]]
if cfg == nil {
panic("nil cfg")
}
val, err := cfg.Get(alias, key)
if err == nil && val != "" {
return val
}
}
return ""
}
// String prints out a string representation of this Include directive. Note
// included Config files are not printed as part of this representation.
func (inc *Include) String() string {
equals := " "
if inc.hasEquals {
equals = " = "
}
line := fmt.Sprintf("%sInclude%s%s", strings.Repeat(" ", int(inc.leadingSpace)), equals, strings.Join(inc.directives, " "))
if inc.Comment != "" {
line += " #" + inc.Comment
}
return line
}
var matchAll *Pattern
func init() {
var err error
matchAll, err = NewPattern("*")
if err != nil {
panic(err)
}
}
func newConfig() *Config {
return &Config{
Hosts: []*Host{
&Host{
implicit: true,
Patterns: []*Pattern{matchAll},
Nodes: make([]Node, 0),
},
},
depth: 0,
}
}