mirror of
https://github.com/moby/moby.git
synced 2022-11-09 12:21:53 -05:00
369 lines
11 KiB
Go
369 lines
11 KiB
Go
// Package parser implements a parser and parse tree dumper for Dockerfiles.
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package parser // import "github.com/docker/docker/builder/dockerfile/parser"
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import (
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"bufio"
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"bytes"
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"fmt"
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"io"
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"regexp"
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"runtime"
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"strconv"
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"strings"
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"unicode"
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"github.com/docker/docker/builder/dockerfile/command"
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"github.com/docker/docker/pkg/system"
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"github.com/pkg/errors"
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)
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// Node is a structure used to represent a parse tree.
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//
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// In the node there are three fields, Value, Next, and Children. Value is the
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// current token's string value. Next is always the next non-child token, and
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// children contains all the children. Here's an example:
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//
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// (value next (child child-next child-next-next) next-next)
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//
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// This data structure is frankly pretty lousy for handling complex languages,
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// but lucky for us the Dockerfile isn't very complicated. This structure
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// works a little more effectively than a "proper" parse tree for our needs.
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//
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type Node struct {
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Value string // actual content
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Next *Node // the next item in the current sexp
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Children []*Node // the children of this sexp
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Attributes map[string]bool // special attributes for this node
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Original string // original line used before parsing
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Flags []string // only top Node should have this set
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StartLine int // the line in the original dockerfile where the node begins
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endLine int // the line in the original dockerfile where the node ends
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}
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// Dump dumps the AST defined by `node` as a list of sexps.
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// Returns a string suitable for printing.
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func (node *Node) Dump() string {
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str := ""
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str += node.Value
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if len(node.Flags) > 0 {
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str += fmt.Sprintf(" %q", node.Flags)
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}
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for _, n := range node.Children {
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str += "(" + n.Dump() + ")\n"
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}
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for n := node.Next; n != nil; n = n.Next {
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if len(n.Children) > 0 {
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str += " " + n.Dump()
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} else {
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str += " " + strconv.Quote(n.Value)
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}
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}
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return strings.TrimSpace(str)
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}
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func (node *Node) lines(start, end int) {
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node.StartLine = start
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node.endLine = end
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}
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// AddChild adds a new child node, and updates line information
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func (node *Node) AddChild(child *Node, startLine, endLine int) {
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child.lines(startLine, endLine)
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if node.StartLine < 0 {
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node.StartLine = startLine
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}
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node.endLine = endLine
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node.Children = append(node.Children, child)
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}
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var (
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dispatch map[string]func(string, *Directive) (*Node, map[string]bool, error)
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tokenWhitespace = regexp.MustCompile(`[\t\v\f\r ]+`)
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tokenEscapeCommand = regexp.MustCompile(`^#[ \t]*escape[ \t]*=[ \t]*(?P<escapechar>.).*$`)
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tokenPlatformCommand = regexp.MustCompile(`^#[ \t]*platform[ \t]*=[ \t]*(?P<platform>.*)$`)
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tokenComment = regexp.MustCompile(`^#.*$`)
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)
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// DefaultEscapeToken is the default escape token
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const DefaultEscapeToken = '\\'
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// Directive is the structure used during a build run to hold the state of
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// parsing directives.
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type Directive struct {
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escapeToken rune // Current escape token
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platformToken string // Current platform token
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lineContinuationRegex *regexp.Regexp // Current line continuation regex
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processingComplete bool // Whether we are done looking for directives
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escapeSeen bool // Whether the escape directive has been seen
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platformSeen bool // Whether the platform directive has been seen
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}
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// setEscapeToken sets the default token for escaping characters in a Dockerfile.
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func (d *Directive) setEscapeToken(s string) error {
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if s != "`" && s != "\\" {
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return fmt.Errorf("invalid ESCAPE '%s'. Must be ` or \\", s)
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}
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d.escapeToken = rune(s[0])
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d.lineContinuationRegex = regexp.MustCompile(`\` + s + `[ \t]*$`)
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return nil
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}
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// setPlatformToken sets the default platform for pulling images in a Dockerfile.
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func (d *Directive) setPlatformToken(s string) error {
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s = strings.ToLower(s)
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valid := []string{runtime.GOOS}
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if system.LCOWSupported() {
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valid = append(valid, "linux")
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}
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for _, item := range valid {
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if s == item {
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d.platformToken = s
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return nil
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}
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}
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return fmt.Errorf("invalid PLATFORM '%s'. Must be one of %v", s, valid)
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}
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// possibleParserDirective looks for one or more parser directives '# escapeToken=<char>' and
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// '# platform=<string>'. Parser directives must precede any builder instruction
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// or other comments, and cannot be repeated.
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func (d *Directive) possibleParserDirective(line string) error {
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if d.processingComplete {
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return nil
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}
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tecMatch := tokenEscapeCommand.FindStringSubmatch(strings.ToLower(line))
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if len(tecMatch) != 0 {
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for i, n := range tokenEscapeCommand.SubexpNames() {
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if n == "escapechar" {
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if d.escapeSeen {
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return errors.New("only one escape parser directive can be used")
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}
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d.escapeSeen = true
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return d.setEscapeToken(tecMatch[i])
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}
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}
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}
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// Only recognise a platform token if LCOW is supported
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if system.LCOWSupported() {
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tpcMatch := tokenPlatformCommand.FindStringSubmatch(strings.ToLower(line))
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if len(tpcMatch) != 0 {
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for i, n := range tokenPlatformCommand.SubexpNames() {
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if n == "platform" {
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if d.platformSeen {
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return errors.New("only one platform parser directive can be used")
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}
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d.platformSeen = true
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return d.setPlatformToken(tpcMatch[i])
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}
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}
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}
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}
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d.processingComplete = true
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return nil
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}
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// NewDefaultDirective returns a new Directive with the default escapeToken token
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func NewDefaultDirective() *Directive {
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directive := Directive{}
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directive.setEscapeToken(string(DefaultEscapeToken))
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return &directive
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}
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func init() {
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// Dispatch Table. see line_parsers.go for the parse functions.
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// The command is parsed and mapped to the line parser. The line parser
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// receives the arguments but not the command, and returns an AST after
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// reformulating the arguments according to the rules in the parser
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// functions. Errors are propagated up by Parse() and the resulting AST can
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// be incorporated directly into the existing AST as a next.
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dispatch = map[string]func(string, *Directive) (*Node, map[string]bool, error){
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command.Add: parseMaybeJSONToList,
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command.Arg: parseNameOrNameVal,
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command.Cmd: parseMaybeJSON,
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command.Copy: parseMaybeJSONToList,
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command.Entrypoint: parseMaybeJSON,
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command.Env: parseEnv,
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command.Expose: parseStringsWhitespaceDelimited,
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command.From: parseStringsWhitespaceDelimited,
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command.Healthcheck: parseHealthConfig,
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command.Label: parseLabel,
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command.Maintainer: parseString,
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command.Onbuild: parseSubCommand,
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command.Run: parseMaybeJSON,
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command.Shell: parseMaybeJSON,
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command.StopSignal: parseString,
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command.User: parseString,
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command.Volume: parseMaybeJSONToList,
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command.Workdir: parseString,
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}
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}
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// newNodeFromLine splits the line into parts, and dispatches to a function
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// based on the command and command arguments. A Node is created from the
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// result of the dispatch.
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func newNodeFromLine(line string, directive *Directive) (*Node, error) {
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cmd, flags, args, err := splitCommand(line)
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if err != nil {
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return nil, err
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}
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fn := dispatch[cmd]
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// Ignore invalid Dockerfile instructions
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if fn == nil {
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fn = parseIgnore
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}
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next, attrs, err := fn(args, directive)
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if err != nil {
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return nil, err
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}
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return &Node{
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Value: cmd,
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Original: line,
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Flags: flags,
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Next: next,
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Attributes: attrs,
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}, nil
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}
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// Result is the result of parsing a Dockerfile
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type Result struct {
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AST *Node
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EscapeToken rune
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// TODO @jhowardmsft - see https://github.com/moby/moby/issues/34617
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// This next field will be removed in a future update for LCOW support.
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OS string
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Warnings []string
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}
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// PrintWarnings to the writer
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func (r *Result) PrintWarnings(out io.Writer) {
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if len(r.Warnings) == 0 {
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return
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}
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fmt.Fprintf(out, strings.Join(r.Warnings, "\n")+"\n")
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}
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// Parse reads lines from a Reader, parses the lines into an AST and returns
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// the AST and escape token
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func Parse(rwc io.Reader) (*Result, error) {
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d := NewDefaultDirective()
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currentLine := 0
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root := &Node{StartLine: -1}
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scanner := bufio.NewScanner(rwc)
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warnings := []string{}
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var err error
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for scanner.Scan() {
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bytesRead := scanner.Bytes()
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if currentLine == 0 {
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// First line, strip the byte-order-marker if present
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bytesRead = bytes.TrimPrefix(bytesRead, utf8bom)
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}
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bytesRead, err = processLine(d, bytesRead, true)
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if err != nil {
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return nil, err
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}
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currentLine++
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startLine := currentLine
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line, isEndOfLine := trimContinuationCharacter(string(bytesRead), d)
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if isEndOfLine && line == "" {
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continue
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}
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var hasEmptyContinuationLine bool
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for !isEndOfLine && scanner.Scan() {
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bytesRead, err := processLine(d, scanner.Bytes(), false)
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if err != nil {
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return nil, err
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}
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currentLine++
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if isComment(scanner.Bytes()) {
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// original line was a comment (processLine strips comments)
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continue
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}
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if isEmptyContinuationLine(bytesRead) {
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hasEmptyContinuationLine = true
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continue
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}
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continuationLine := string(bytesRead)
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continuationLine, isEndOfLine = trimContinuationCharacter(continuationLine, d)
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line += continuationLine
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}
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if hasEmptyContinuationLine {
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warning := "[WARNING]: Empty continuation line found in:\n " + line
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warnings = append(warnings, warning)
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}
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child, err := newNodeFromLine(line, d)
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if err != nil {
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return nil, err
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}
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root.AddChild(child, startLine, currentLine)
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}
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if len(warnings) > 0 {
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warnings = append(warnings, "[WARNING]: Empty continuation lines will become errors in a future release.")
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}
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return &Result{
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AST: root,
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Warnings: warnings,
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EscapeToken: d.escapeToken,
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OS: d.platformToken,
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}, handleScannerError(scanner.Err())
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}
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func trimComments(src []byte) []byte {
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return tokenComment.ReplaceAll(src, []byte{})
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}
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func trimWhitespace(src []byte) []byte {
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return bytes.TrimLeftFunc(src, unicode.IsSpace)
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}
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func isComment(line []byte) bool {
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return tokenComment.Match(trimWhitespace(line))
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}
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func isEmptyContinuationLine(line []byte) bool {
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return len(trimWhitespace(line)) == 0
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}
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var utf8bom = []byte{0xEF, 0xBB, 0xBF}
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func trimContinuationCharacter(line string, d *Directive) (string, bool) {
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if d.lineContinuationRegex.MatchString(line) {
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line = d.lineContinuationRegex.ReplaceAllString(line, "")
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return line, false
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}
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return line, true
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}
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// TODO: remove stripLeftWhitespace after deprecation period. It seems silly
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// to preserve whitespace on continuation lines. Why is that done?
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func processLine(d *Directive, token []byte, stripLeftWhitespace bool) ([]byte, error) {
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if stripLeftWhitespace {
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token = trimWhitespace(token)
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}
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return trimComments(token), d.possibleParserDirective(string(token))
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}
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func handleScannerError(err error) error {
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switch err {
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case bufio.ErrTooLong:
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return errors.Errorf("dockerfile line greater than max allowed size of %d", bufio.MaxScanTokenSize-1)
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default:
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return err
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}
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}
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