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moby--moby/builder/dockerfile/shell_parser.go

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package dockerfile
import (
"bytes"
"strings"
"text/scanner"
"unicode"
"github.com/pkg/errors"
)
// ShellLex performs shell word splitting and variable expansion.
//
// ShellLex takes a string and an array of env variables and
// process all quotes (" and ') as well as $xxx and ${xxx} env variable
// tokens. Tries to mimic bash shell process.
// It doesn't support all flavors of ${xx:...} formats but new ones can
// be added by adding code to the "special ${} format processing" section
type ShellLex struct {
escapeToken rune
}
// NewShellLex creates a new ShellLex which uses escapeToken to escape quotes.
func NewShellLex(escapeToken rune) *ShellLex {
return &ShellLex{escapeToken: escapeToken}
}
// ProcessWord will use the 'env' list of environment variables,
// and replace any env var references in 'word'.
func (s *ShellLex) ProcessWord(word string, env []string) (string, error) {
word, _, err := s.process(word, env)
return word, err
}
// ProcessWords will use the 'env' list of environment variables,
// and replace any env var references in 'word' then it will also
// return a slice of strings which represents the 'word'
// split up based on spaces - taking into account quotes. Note that
// this splitting is done **after** the env var substitutions are done.
// Note, each one is trimmed to remove leading and trailing spaces (unless
// they are quoted", but ProcessWord retains spaces between words.
func (s *ShellLex) ProcessWords(word string, env []string) ([]string, error) {
_, words, err := s.process(word, env)
return words, err
}
func (s *ShellLex) process(word string, env []string) (string, []string, error) {
sw := &shellWord{
envs: env,
escapeToken: s.escapeToken,
}
sw.scanner.Init(strings.NewReader(word))
return sw.process(word)
}
type shellWord struct {
scanner scanner.Scanner
envs []string
escapeToken rune
}
func (sw *shellWord) process(source string) (string, []string, error) {
word, words, err := sw.processStopOn(scanner.EOF)
if err != nil {
err = errors.Wrapf(err, "failed to process %q", source)
}
return word, words, err
}
type wordsStruct struct {
word string
words []string
inWord bool
}
func (w *wordsStruct) addChar(ch rune) {
if unicode.IsSpace(ch) && w.inWord {
if len(w.word) != 0 {
w.words = append(w.words, w.word)
w.word = ""
w.inWord = false
}
} else if !unicode.IsSpace(ch) {
w.addRawChar(ch)
}
}
func (w *wordsStruct) addRawChar(ch rune) {
w.word += string(ch)
w.inWord = true
}
func (w *wordsStruct) addString(str string) {
var scan scanner.Scanner
scan.Init(strings.NewReader(str))
for scan.Peek() != scanner.EOF {
w.addChar(scan.Next())
}
}
func (w *wordsStruct) addRawString(str string) {
w.word += str
w.inWord = true
}
func (w *wordsStruct) getWords() []string {
if len(w.word) > 0 {
w.words = append(w.words, w.word)
// Just in case we're called again by mistake
w.word = ""
w.inWord = false
}
return w.words
}
// Process the word, starting at 'pos', and stop when we get to the
// end of the word or the 'stopChar' character
func (sw *shellWord) processStopOn(stopChar rune) (string, []string, error) {
var result bytes.Buffer
var words wordsStruct
var charFuncMapping = map[rune]func() (string, error){
'\'': sw.processSingleQuote,
'"': sw.processDoubleQuote,
'$': sw.processDollar,
}
for sw.scanner.Peek() != scanner.EOF {
ch := sw.scanner.Peek()
if stopChar != scanner.EOF && ch == stopChar {
sw.scanner.Next()
break
}
if fn, ok := charFuncMapping[ch]; ok {
// Call special processing func for certain chars
tmp, err := fn()
if err != nil {
return "", []string{}, err
}
result.WriteString(tmp)
if ch == rune('$') {
words.addString(tmp)
} else {
words.addRawString(tmp)
}
} else {
// Not special, just add it to the result
ch = sw.scanner.Next()
if ch == sw.escapeToken {
// '\' (default escape token, but ` allowed) escapes, except end of line
ch = sw.scanner.Next()
if ch == scanner.EOF {
break
}
words.addRawChar(ch)
} else {
words.addChar(ch)
}
result.WriteRune(ch)
}
}
return result.String(), words.getWords(), nil
}
func (sw *shellWord) processSingleQuote() (string, error) {
// All chars between single quotes are taken as-is
// Note, you can't escape '
//
// From the "sh" man page:
// Single Quotes
// Enclosing characters in single quotes preserves the literal meaning of
// all the characters (except single quotes, making it impossible to put
// single-quotes in a single-quoted string).
var result bytes.Buffer
sw.scanner.Next()
for {
ch := sw.scanner.Next()
switch ch {
case scanner.EOF:
return "", errors.New("unexpected end of statement while looking for matching single-quote")
case '\'':
return result.String(), nil
}
result.WriteRune(ch)
}
}
func (sw *shellWord) processDoubleQuote() (string, error) {
// All chars up to the next " are taken as-is, even ', except any $ chars
// But you can escape " with a \ (or ` if escape token set accordingly)
//
// From the "sh" man page:
// Double Quotes
// Enclosing characters within double quotes preserves the literal meaning
// of all characters except dollarsign ($), backquote (`), and backslash
// (\). The backslash inside double quotes is historically weird, and
// serves to quote only the following characters:
// $ ` " \ <newline>.
// Otherwise it remains literal.
var result bytes.Buffer
sw.scanner.Next()
for {
switch sw.scanner.Peek() {
case scanner.EOF:
return "", errors.New("unexpected end of statement while looking for matching double-quote")
case '"':
sw.scanner.Next()
return result.String(), nil
case '$':
value, err := sw.processDollar()
if err != nil {
return "", err
}
result.WriteString(value)
default:
ch := sw.scanner.Next()
if ch == sw.escapeToken {
switch sw.scanner.Peek() {
case scanner.EOF:
// Ignore \ at end of word
continue
case '"', '$', sw.escapeToken:
// These chars can be escaped, all other \'s are left as-is
// Note: for now don't do anything special with ` chars.
// Not sure what to do with them anyway since we're not going
// to execute the text in there (not now anyway).
ch = sw.scanner.Next()
}
}
result.WriteRune(ch)
}
}
}
func (sw *shellWord) processDollar() (string, error) {
sw.scanner.Next()
// $xxx case
if sw.scanner.Peek() != '{' {
name := sw.processName()
if name == "" {
return "$", nil
}
return sw.getEnv(name), nil
}
sw.scanner.Next()
name := sw.processName()
ch := sw.scanner.Peek()
if ch == '}' {
// Normal ${xx} case
sw.scanner.Next()
return sw.getEnv(name), nil
}
if ch == ':' {
// Special ${xx:...} format processing
// Yes it allows for recursive $'s in the ... spot
sw.scanner.Next() // skip over :
modifier := sw.scanner.Next()
word, _, err := sw.processStopOn('}')
if err != nil {
return "", err
}
// Grab the current value of the variable in question so we
// can use to to determine what to do based on the modifier
newValue := sw.getEnv(name)
switch modifier {
case '+':
if newValue != "" {
newValue = word
}
return newValue, nil
case '-':
if newValue == "" {
newValue = word
}
return newValue, nil
default:
return "", errors.Errorf("unsupported modifier (%c) in substitution", modifier)
}
}
return "", errors.Errorf("missing ':' in substitution")
}
func (sw *shellWord) processName() string {
// Read in a name (alphanumeric or _)
// If it starts with a numeric then just return $#
var name bytes.Buffer
for sw.scanner.Peek() != scanner.EOF {
ch := sw.scanner.Peek()
if name.Len() == 0 && unicode.IsDigit(ch) {
ch = sw.scanner.Next()
return string(ch)
}
if !unicode.IsLetter(ch) && !unicode.IsDigit(ch) && ch != '_' {
break
}
ch = sw.scanner.Next()
name.WriteRune(ch)
}
return name.String()
}
func (sw *shellWord) getEnv(name string) string {
for _, env := range sw.envs {
i := strings.Index(env, "=")
if i < 0 {
if equalEnvKeys(name, env) {
// Should probably never get here, but just in case treat
// it like "var" and "var=" are the same
return ""
}
continue
}
compareName := env[:i]
if !equalEnvKeys(name, compareName) {
continue
}
return env[i+1:]
}
return ""
}