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parser.go
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parser.go
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// Package parser implements a parser and parse tree dumper for Dockerfiles.
package parser
import (
"bufio"
"bytes"
"fmt"
"io"
"regexp"
"strings"
"unicode"
"github.com/wutong-paas/wutong/util/dockerfile/command"
)
// Node is a structure used to represent a parse tree.
//
// In the node there are three fields, Value, Next, and Children. Value is the
// current token's string value. Next is always the next non-child token, and
// children contains all the children. Here's an example:
//
// (value next (child child-next child-next-next) next-next)
//
// This data structure is frankly pretty lousy for handling complex languages,
// but lucky for us the Dockerfile isn't very complicated. This structure
// works a little more effectively than a "proper" parse tree for our needs.
type Node struct {
Value string // actual content
Next *Node // the next item in the current sexp
Children []*Node // the children of this sexp
Attributes map[string]bool // special attributes for this node
Original string // original line used before parsing
Flags []string // only top Node should have this set
StartLine int // the line in the original dockerfile where the node begins
EndLine int // the line in the original dockerfile where the node ends
}
// Directive is the structure used during a build run to hold the state of
// parsing directives.
type Directive struct {
EscapeToken rune // Current escape token
LineContinuationRegex *regexp.Regexp // Current line contination regex
LookingForDirectives bool // Whether we are currently looking for directives
EscapeSeen bool // Whether the escape directive has been seen
}
var (
dispatch map[string]func(string, *Directive) (*Node, map[string]bool, error)
tokenWhitespace = regexp.MustCompile(`[\t\v\f\r ]+`)
tokenEscapeCommand = regexp.MustCompile(`^#[ \t]*escape[ \t]*=[ \t]*(?P<escapechar>.).*$`)
tokenComment = regexp.MustCompile(`^#.*$`)
)
// DefaultEscapeToken is the default escape token
const DefaultEscapeToken = "\\"
// SetEscapeToken sets the default token for escaping characters in a Dockerfile.
func SetEscapeToken(s string, d *Directive) error {
if s != "`" && s != "\\" {
return fmt.Errorf("invalid ESCAPE '%s'. Must be ` or \\", s)
}
d.EscapeToken = rune(s[0])
d.LineContinuationRegex = regexp.MustCompile(`\` + s + `[ \t]*$`)
return nil
}
func init() {
// Dispatch Table. see line_parsers.go for the parse functions.
// The command is parsed and mapped to the line parser. The line parser
// receives the arguments but not the command, and returns an AST after
// reformulating the arguments according to the rules in the parser
// functions. Errors are propagated up by Parse() and the resulting AST can
// be incorporated directly into the existing AST as a next.
dispatch = map[string]func(string, *Directive) (*Node, map[string]bool, error){
command.Add: parseMaybeJSONToList,
command.Arg: parseNameOrNameVal,
command.Cmd: parseMaybeJSON,
command.Copy: parseMaybeJSONToList,
command.Entrypoint: parseMaybeJSON,
command.Env: parseEnv,
command.Expose: parseStringsWhitespaceDelimited,
command.From: parseString,
command.Healthcheck: parseHealthConfig,
command.Label: parseLabel,
command.Maintainer: parseString,
command.Onbuild: parseSubCommand,
command.Run: parseMaybeJSON,
command.Shell: parseMaybeJSON,
command.StopSignal: parseString,
command.User: parseString,
command.Volume: parseMaybeJSONToList,
command.Workdir: parseString,
}
}
// ParseLine parse a line and return the remainder.
func ParseLine(line string, d *Directive) (string, *Node, error) {
// Handle the parser directive '# escape=<char>. Parser directives must precede
// any builder instruction or other comments, and cannot be repeated.
if d.LookingForDirectives {
tecMatch := tokenEscapeCommand.FindStringSubmatch(strings.ToLower(line))
if len(tecMatch) > 0 {
if d.EscapeSeen {
return "", nil, fmt.Errorf("only one escape parser directive can be used")
}
for i, n := range tokenEscapeCommand.SubexpNames() {
if n == "escapechar" {
if err := SetEscapeToken(tecMatch[i], d); err != nil {
return "", nil, err
}
d.EscapeSeen = true
return "", nil, nil
}
}
}
}
d.LookingForDirectives = false
if line = stripComments(line); line == "" {
return "", nil, nil
}
if d.LineContinuationRegex.MatchString(line) {
line = d.LineContinuationRegex.ReplaceAllString(line, "")
return line, nil, nil
}
cmd, flags, args, err := splitCommand(line)
if err != nil {
return "", nil, err
}
node := &Node{}
node.Value = cmd
sexp, attrs, err := fullDispatch(cmd, args, d)
if err != nil {
return "", nil, err
}
node.Next = sexp
node.Attributes = attrs
node.Original = line
node.Flags = flags
return "", node, nil
}
// Parse is the main parse routine.
// It handles an io.ReadWriteCloser and returns the root of the AST.
func Parse(rwc io.Reader, d *Directive) (*Node, error) {
currentLine := 0
root := &Node{}
root.StartLine = -1
scanner := bufio.NewScanner(rwc)
utf8bom := []byte{0xEF, 0xBB, 0xBF}
for scanner.Scan() {
scannedBytes := scanner.Bytes()
// We trim UTF8 BOM
if currentLine == 0 {
scannedBytes = bytes.TrimPrefix(scannedBytes, utf8bom)
}
scannedLine := strings.TrimLeftFunc(string(scannedBytes), unicode.IsSpace)
currentLine++
line, child, err := ParseLine(scannedLine, d)
if err != nil {
return nil, err
}
startLine := currentLine
if line != "" && child == nil {
for scanner.Scan() {
newline := scanner.Text()
currentLine++
if stripComments(strings.TrimSpace(newline)) == "" {
continue
}
line, child, err = ParseLine(line+newline, d)
if err != nil {
return nil, err
}
if child != nil {
break
}
}
if child == nil && line != "" {
_, child, err = ParseLine(line, d)
if err != nil {
return nil, err
}
}
}
if child != nil {
// Update the line information for the current child.
child.StartLine = startLine
child.EndLine = currentLine
// Update the line information for the root. The starting line of the root is always the
// starting line of the first child and the ending line is the ending line of the last child.
if root.StartLine < 0 {
root.StartLine = currentLine
}
root.EndLine = currentLine
root.Children = append(root.Children, child)
}
}
return root, nil
}