blob: 4c9d425f9bcb53afbf37d274950cb50bd3ab5fa0 [file] [log] [blame]
// Package dockerfile is the evaluation step in the Dockerfile parse/evaluate pipeline.
// It incorporates a dispatch table based on the parser.Node values (see the
// parser package for more information) that are yielded from the parser itself.
// Calling NewBuilder with the BuildOpts struct can be used to customize the
// experience for execution purposes only. Parsing is controlled in the parser
// package, and this division of responsibility should be respected.
// Please see the jump table targets for the actual invocations, most of which
// will call out to the functions in internals.go to deal with their tasks.
// ONBUILD is a special case, which is covered in the onbuild() func in
// dispatchers.go.
// The evaluator uses the concept of "steps", which are usually each processable
// line in the Dockerfile. Each step is numbered and certain actions are taken
// before and after each step, such as creating an image ID and removing temporary
// containers and images. Note that ONBUILD creates a kinda-sorta "sub run" which
// includes its own set of steps (usually only one of them).
package dockerfile
import (
// Environment variable interpolation will happen on these statements only.
var replaceEnvAllowed = map[string]bool{
command.Env: true,
command.Label: true,
command.Add: true,
command.Copy: true,
command.Workdir: true,
command.Expose: true,
command.Volume: true,
command.User: true,
command.StopSignal: true,
command.Arg: true,
// Certain commands are allowed to have their args split into more
// words after env var replacements. Meaning:
// ENV foo="123 456"
// EXPOSE $foo
// should result in the same thing as:
// EXPOSE 123 456
// and not treat "123 456" as a single word.
// Note that: EXPOSE "$foo" and EXPOSE $foo are not the same thing.
// Quotes will cause it to still be treated as single word.
var allowWordExpansion = map[string]bool{
command.Expose: true,
var evaluateTable map[string]func(*Builder, []string, map[string]bool, string) error
func init() {
evaluateTable = map[string]func(*Builder, []string, map[string]bool, string) error{
command.Add: add,
command.Arg: arg,
command.Cmd: cmd,
command.Copy: dispatchCopy, // copy() is a go builtin
command.Entrypoint: entrypoint,
command.Env: env,
command.Expose: expose,
command.From: from,
command.Healthcheck: healthcheck,
command.Label: label,
command.Maintainer: maintainer,
command.Onbuild: onbuild,
command.Run: run,
command.Shell: shell,
command.StopSignal: stopSignal,
command.User: user,
command.Volume: volume,
command.Workdir: workdir,
// This method is the entrypoint to all statement handling routines.
// Almost all nodes will have this structure:
// Child[Node, Node, Node] where Child is from parser.Node.Children and each
// node comes from parser.Node.Next. This forms a "line" with a statement and
// arguments and we process them in this normalized form by hitting
// evaluateTable with the leaf nodes of the command and the Builder object.
// ONBUILD is a special case; in this case the parser will emit:
// Child[Node, Child[Node, Node...]] where the first node is the literal
// "onbuild" and the child entrypoint is the command of the ONBUILD statement,
// such as `RUN` in ONBUILD RUN foo. There is special case logic in here to
// deal with that, at least until it becomes more of a general concern with new
// features.
func (b *Builder) dispatch(stepN int, ast *parser.Node) error {
cmd := ast.Value
upperCasedCmd := strings.ToUpper(cmd)
// To ensure the user is given a decent error message if the platform
// on which the daemon is running does not support a builder command.
if err := platformSupports(strings.ToLower(cmd)); err != nil {
return err
attrs := ast.Attributes
original := ast.Original
flags := ast.Flags
strList := []string{}
msg := fmt.Sprintf("Step %d : %s", stepN+1, upperCasedCmd)
if len(ast.Flags) > 0 {
msg += " " + strings.Join(ast.Flags, " ")
if cmd == "onbuild" {
if ast.Next == nil {
return fmt.Errorf("ONBUILD requires at least one argument")
ast = ast.Next.Children[0]
strList = append(strList, ast.Value)
msg += " " + ast.Value
if len(ast.Flags) > 0 {
msg += " " + strings.Join(ast.Flags, " ")
// count the number of nodes that we are going to traverse first
// so we can pre-create the argument and message array. This speeds up the
// allocation of those list a lot when they have a lot of arguments
cursor := ast
var n int
for cursor.Next != nil {
cursor = cursor.Next
msgList := make([]string, n)
var i int
// Append the build-time args to config-environment.
// This allows builder config to override the variables, making the behavior similar to
// a shell script i.e. `ENV foo bar` overrides value of `foo` passed in build
// context. But `ENV foo $foo` will use the value from build context if one
// isn't already been defined by a previous ENV primitive.
// Note, we get this behavior because we know that ProcessWord() will
// stop on the first occurrence of a variable name and not notice
// a subsequent one. So, putting the buildArgs list after the Config.Env
// list, in 'envs', is safe.
envs := b.runConfig.Env
for key, val := range b.options.BuildArgs {
if !b.isBuildArgAllowed(key) {
// skip build-args that are not in allowed list, meaning they have
// not been defined by an "ARG" Dockerfile command yet.
// This is an error condition but only if there is no "ARG" in the entire
// Dockerfile, so we'll generate any necessary errors after we parsed
// the entire file (see 'leftoverArgs' processing in evaluator.go )
envs = append(envs, fmt.Sprintf("%s=%s", key, val))
for ast.Next != nil {
ast = ast.Next
var str string
str = ast.Value
if replaceEnvAllowed[cmd] {
var err error
var words []string
if allowWordExpansion[cmd] {
words, err = ProcessWords(str, envs)
if err != nil {
return err
strList = append(strList, words...)
} else {
str, err = ProcessWord(str, envs)
if err != nil {
return err
strList = append(strList, str)
} else {
strList = append(strList, str)
msgList[i] = ast.Value
msg += " " + strings.Join(msgList, " ")
fmt.Fprintln(b.Stdout, msg)
// XXX yes, we skip any cmds that are not valid; the parser should have
// picked these out already.
if f, ok := evaluateTable[cmd]; ok {
b.flags = NewBFlags()
b.flags.Args = flags
return f(b, strList, attrs, original)
return fmt.Errorf("Unknown instruction: %s", upperCasedCmd)