Fix some escaping around env var processing

Clarify in the docs that ENV is not recursive

Closes #10391

Signed-off-by: Doug Davis <dug@us.ibm.com>

builder/shell_parser.go

@@ -0,0 +1,209 @@
+package builder
+
+// This will take a single word 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 ${} format processing" section
+
+import (
+	"fmt"
+	"strings"
+	"unicode"
+)
+
+type shellWord struct {
+	word string
+	envs []string
+	pos  int
+}
+
+func ProcessWord(word string, env []string) (string, error) {
+	sw := &shellWord{
+		word: word,
+		envs: env,
+		pos:  0,
+	}
+	return sw.process()
+}
+
+func (sw *shellWord) process() (string, error) {
+	return sw.processStopOn('\000')
+}
+
+// Process the word, starting at 'pos', and stop when we get to the
+// end of the word or the 'stopChar' character
+func (sw *shellWord) processStopOn(stopChar rune) (string, error) {
+	var result string
+	var charFuncMapping = map[rune]func() (string, error){
+		'\'': sw.processSingleQuote,
+		'"':  sw.processDoubleQuote,
+		'$':  sw.processDollar,
+	}
+
+	for sw.pos < len(sw.word) {
+		ch := sw.peek()
+		if stopChar != '\000' && ch == stopChar {
+			sw.next()
+			break
+		}
+		if fn, ok := charFuncMapping[ch]; ok {
+			// Call special processing func for certain chars
+			tmp, err := fn()
+			if err != nil {
+				return "", err
+			}
+			result += tmp
+		} else {
+			// Not special, just add it to the result
+			ch = sw.next()
+			if ch == '\\' {
+				// '\' escapes, except end of line
+				ch = sw.next()
+				if ch == '\000' {
+					continue
+				}
+			}
+			result += string(ch)
+		}
+	}
+
+	return result, nil
+}
+
+func (sw *shellWord) peek() rune {
+	if sw.pos == len(sw.word) {
+		return '\000'
+	}
+	return rune(sw.word[sw.pos])
+}
+
+func (sw *shellWord) next() rune {
+	if sw.pos == len(sw.word) {
+		return '\000'
+	}
+	ch := rune(sw.word[sw.pos])
+	sw.pos++
+	return ch
+}
+
+func (sw *shellWord) processSingleQuote() (string, error) {
+	// All chars between single quotes are taken as-is
+	// Note, you can't escape '
+	var result string
+
+	sw.next()
+
+	for {
+		ch := sw.next()
+		if ch == '\000' || ch == '\'' {
+			break
+		}
+		result += string(ch)
+	}
+	return result, nil
+}
+
+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 \
+	var result string
+
+	sw.next()
+
+	for sw.pos < len(sw.word) {
+		ch := sw.peek()
+		if ch == '"' {
+			sw.next()
+			break
+		}
+		if ch == '$' {
+			tmp, err := sw.processDollar()
+			if err != nil {
+				return "", err
+			}
+			result += tmp
+		} else {
+			ch = sw.next()
+			if ch == '\\' {
+				chNext := sw.peek()
+
+				if chNext == '\000' {
+					// Ignore \ at end of word
+					continue
+				}
+
+				if chNext == '"' || chNext == '$' {
+					// \" and \$ can be escaped, all other \'s are left as-is
+					ch = sw.next()
+				}
+			}
+			result += string(ch)
+		}
+	}
+
+	return result, nil
+}
+
+func (sw *shellWord) processDollar() (string, error) {
+	sw.next()
+	ch := sw.peek()
+	if ch == '{' {
+		sw.next()
+		name := sw.processName()
+		ch = sw.peek()
+		if ch == '}' {
+			// Normal ${xx} case
+			sw.next()
+			return sw.getEnv(name), nil
+		}
+		return "", fmt.Errorf("Unsupported ${} substitution: %s", sw.word)
+	} else {
+		// $xxx case
+		name := sw.processName()
+		if name == "" {
+			return "$", nil
+		}
+		return sw.getEnv(name), nil
+	}
+}
+
+func (sw *shellWord) processName() string {
+	// Read in a name (alphanumeric or _)
+	// If it starts with a numeric then just return $#
+	var name string
+
+	for sw.pos < len(sw.word) {
+		ch := sw.peek()
+		if len(name) == 0 && unicode.IsDigit(ch) {
+			ch = sw.next()
+			return string(ch)
+		}
+		if !unicode.IsLetter(ch) && !unicode.IsDigit(ch) && ch != '_' {
+			break
+		}
+		ch = sw.next()
+		name += string(ch)
+	}
+
+	return name
+}
+
+func (sw *shellWord) getEnv(name string) string {
+	for _, env := range sw.envs {
+		i := strings.Index(env, "=")
+		if i < 0 {
+			if name == env {
+				// Should probably never get here, but just in case treat
+				// it like "var" and "var=" are the same
+				return ""
+			}
+			continue
+		}
+		if name != env[:i] {
+			continue
+		}
+		return env[i+1:]
+	}
+	return ""
+}