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ast.go
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ast.go
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package dockerfile
import (
"bytes"
"fmt"
"io"
"sort"
"strings"
"github.com/docker/distribution/reference"
"github.com/moby/buildkit/frontend/dockerfile/command"
"github.com/moby/buildkit/frontend/dockerfile/dockerfile2llb"
"github.com/moby/buildkit/frontend/dockerfile/instructions"
"github.com/moby/buildkit/frontend/dockerfile/parser"
"github.com/moby/buildkit/frontend/dockerfile/shell"
"github.com/pkg/errors"
"github.com/windmilleng/tilt/internal/container"
)
type AST struct {
directives map[string]string
result *parser.Result
}
func ParseAST(df Dockerfile) (AST, error) {
result, err := parser.Parse(newReader(df))
if err != nil {
return AST{}, errors.Wrap(err, "dockerfile.ParseAST")
}
return AST{
directives: dockerfile2llb.ParseDirectives(newReader(df)),
result: result,
}, nil
}
func (a AST) extractBaseNameInFromCommand(node *parser.Node, shlex *shell.Lex, metaArgs []instructions.ArgCommand) string {
if node.Next == nil {
return ""
}
inst, err := instructions.ParseInstruction(node)
if err != nil {
return node.Next.Value // if there's a parsing error, fallback to the first arg
}
fromInst, ok := inst.(*instructions.Stage)
if !ok || fromInst.BaseName == "" {
return ""
}
// The base image name may have ARG expansions in it. Do the default
// substitution.
argsMap := fakeArgsMap(shlex, metaArgs)
baseName, err := shlex.ProcessWordWithMap(fromInst.BaseName, argsMap)
if err != nil {
// If anything fails, just use the hard-coded BaseName.
return fromInst.BaseName
}
return baseName
}
// Find all images referenced in this dockerfile and call the visitor function.
// If the visitor function returns a new image, subsitute that image into the dockerfile.
func (a AST) traverseImageRefs(visitor func(node *parser.Node, ref reference.Named) reference.Named) error {
// Parse the instructions for ARG expansions. It's not a big deal if it doesn't parse.
_, metaArgs, _ := instructions.Parse(a.result.AST)
shlex := shell.NewLex(a.result.EscapeToken)
return a.Traverse(func(node *parser.Node) error {
switch node.Value {
case command.From:
baseName := a.extractBaseNameInFromCommand(node, shlex, metaArgs)
if baseName == "" {
return nil // ignore parsing error
}
ref, err := container.ParseNamed(baseName)
if err != nil {
return nil // drop the error, we don't care about malformed images
}
newRef := visitor(node, ref)
if newRef != nil {
node.Next.Value = container.FamiliarString(newRef)
}
case command.Copy:
if len(node.Flags) == 0 {
return nil
}
inst, err := instructions.ParseInstruction(node)
if err != nil {
return nil // ignore parsing error
}
copyCmd, ok := inst.(*instructions.CopyCommand)
if !ok {
return nil
}
ref, err := container.ParseNamed(copyCmd.From)
if err != nil {
return nil // drop the error, we don't care about malformed images
}
newRef := visitor(node, ref)
if newRef != nil {
for i, flag := range node.Flags {
if strings.HasPrefix(flag, "--from=") {
node.Flags[i] = fmt.Sprintf("--from=%s", container.FamiliarString(newRef))
}
}
}
}
return nil
})
}
func (a AST) InjectImageDigest(selector container.RefSelector, ref reference.NamedTagged) (bool, error) {
modified := false
err := a.traverseImageRefs(func(node *parser.Node, toReplace reference.Named) reference.Named {
if selector.Matches(toReplace) {
modified = true
return ref
}
return nil
})
return modified, err
}
// Post-order traversal of the Dockerfile AST.
// Halts immediately on error.
func (a AST) Traverse(visit func(*parser.Node) error) error {
return a.traverseNode(a.result.AST, visit)
}
func (a AST) traverseNode(node *parser.Node, visit func(*parser.Node) error) error {
for _, c := range node.Children {
err := a.traverseNode(c, visit)
if err != nil {
return err
}
}
return visit(node)
}
func (a AST) Print() (Dockerfile, error) {
buf := bytes.NewBuffer(nil)
currentLine := 1
directiveFmt := "# %s = %s\n"
for _, k := range sortedKeys(a.directives) {
// order of directives in a docker makes no semantic difference; we
// rehydrate directives in sorted order so output is deterministic
v := a.directives[k]
_, err := fmt.Fprintf(buf, directiveFmt, k, v)
if err != nil {
return "", err
}
currentLine++
}
for _, node := range a.result.AST.Children {
for currentLine < node.StartLine {
_, err := buf.Write([]byte("\n"))
if err != nil {
return "", err
}
currentLine++
}
err := a.printNode(node, buf)
if err != nil {
return "", err
}
currentLine = node.StartLine + 1
if node.Next != nil && node.Next.StartLine != 0 {
currentLine = node.Next.StartLine + 1
}
}
return Dockerfile(buf.String()), nil
}
// Loosely adapted from
// https://github.com/jessfraz/dockfmt/blob/master/format.go
func (a AST) printNode(node *parser.Node, writer io.Writer) error {
var v string
// format per directive
switch node.Value {
// all the commands that use parseMaybeJSON
// https://github.com/moby/buildkit/blob/2ec7d53b00f24624cda0adfbdceed982623a93b3/frontend/dockerfile/parser/parser.go#L152
case command.Cmd, command.Entrypoint, command.Run, command.Shell:
v = fmtCmd(node)
case command.Label:
v = fmtLabel(node)
default:
v = fmtDefault(node)
}
_, err := fmt.Fprintln(writer, v)
if err != nil {
return err
}
return nil
}
func getCmd(n *parser.Node) []string {
if n == nil {
return nil
}
cmd := []string{strings.ToUpper(n.Value)}
if len(n.Flags) > 0 {
cmd = append(cmd, n.Flags...)
}
return append(cmd, getCmdArgs(n)...)
}
func getCmdArgs(n *parser.Node) []string {
if n == nil {
return nil
}
cmd := []string{}
for node := n.Next; node != nil; node = node.Next {
cmd = append(cmd, node.Value)
if len(node.Flags) > 0 {
cmd = append(cmd, node.Flags...)
}
}
return cmd
}
func fmtCmd(node *parser.Node) string {
if node.Attributes["json"] {
cmd := []string{strings.ToUpper(node.Value)}
if len(node.Flags) > 0 {
cmd = append(cmd, node.Flags...)
}
encoded := []string{}
for _, c := range getCmdArgs(node) {
encoded = append(encoded, fmt.Sprintf("%q", c))
}
return fmt.Sprintf("%s [%s]", strings.Join(cmd, " "), strings.Join(encoded, ", "))
}
cmd := getCmd(node)
return strings.Join(cmd, " ")
}
func fmtDefault(node *parser.Node) string {
cmd := getCmd(node)
return strings.Join(cmd, " ")
}
func fmtLabel(node *parser.Node) string {
cmd := getCmd(node)
assignments := []string{cmd[0]}
for i := 1; i < len(cmd); i += 2 {
if i+1 < len(cmd) {
assignments = append(assignments, fmt.Sprintf("%s=%s", cmd[i], cmd[i+1]))
} else {
assignments = append(assignments, cmd[i])
}
}
return strings.Join(assignments, " ")
}
func newReader(df Dockerfile) io.Reader {
return bytes.NewBufferString(string(df))
}
func sortedKeys(m map[string]string) []string {
var keys []string
for k := range m {
keys = append(keys, k)
}
sort.Strings(keys)
return keys
}
// Loosely adapted from the buildkit code for turning args into a map.
// Iterate through them and do substitutions in order.
func fakeArgsMap(shlex *shell.Lex, args []instructions.ArgCommand) map[string]string {
m := make(map[string]string)
for _, a := range args {
val := ""
if a.Value != nil {
val, _ = shlex.ProcessWordWithMap(*(a.Value), m)
}
m[a.Key] = val
}
return m
}