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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"
"io"
"regexp"
"strings"
"unicode"
"github.com/docker/docker/builder/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
}
var (
dispatch map[string]func(string) (*Node, map[string]bool, error)
tokenWhitespace = regexp.MustCompile(`[\t\v\f\r ]+`)
tokenLineContinuation = regexp.MustCompile(`\\[ \t]*$`)
tokenComment = regexp.MustCompile(`^#.*$`)
)
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) (*Node, map[string]bool, error){
command.User: parseString,
command.Onbuild: parseSubCommand,
command.Workdir: parseString,
command.Env: parseEnv,
command.Label: parseLabel,
command.Maintainer: parseString,
command.From: parseString,
command.Add: parseMaybeJSONToList,
command.Copy: parseMaybeJSONToList,
command.Run: parseMaybeJSON,
command.Cmd: parseMaybeJSON,
command.Entrypoint: parseMaybeJSON,
command.Expose: parseStringsWhitespaceDelimited,
command.Volume: parseMaybeJSONToList,
command.StopSignal: parseString,
command.Arg: parseNameOrNameVal,
}
}
// parse a line and return the remainder.
func parseLine(line string) (string, *Node, error) {
if line = stripComments(line); line == "" {
return "", nil, nil
}
if tokenLineContinuation.MatchString(line) {
line = tokenLineContinuation.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)
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) (*Node, error) {
currentLine := 0
root := &Node{}
root.StartLine = -1
scanner := bufio.NewScanner(rwc)
for scanner.Scan() {
scannedLine := strings.TrimLeftFunc(scanner.Text(), unicode.IsSpace)
currentLine++
line, child, err := parseLine(scannedLine)
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)
if err != nil {
return nil, err
}
if child != nil {
break
}
}
if child == nil && line != "" {
line, child, err = parseLine(line)
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
}