docker-parser

Dockerfile parser and deparser for JavaScript/TypeScript.

Installation

npm install docker-parser

Usage

Parsing

import { parse } from 'docker-parser';

const source = `
FROM node:18-alpine
WORKDIR /app
COPY package.json .
RUN npm install
COPY . .
EXPOSE 3000
CMD ["node", "server.js"]
`;

const ast = parse(source);
console.log(JSON.stringify(ast, null, 2));

Deparsing

import { parse, deparse } from 'docker-parser';

const source = 'FROM node:18-alpine';
const ast = parse(source);
const output = deparse(ast);
console.log(output); // FROM node:18-alpine

Comments

A comment belongs to the instruction below it, as leadingComments, and a blank line above a node is blankBefore. Both are emitted by the deparser, so a parsed Dockerfile keeps its comments and section spacing through a round-trip, and a generated one can carry its own:

deparse({
  type: 'Dockerfile',
  directives: [],
  comments: [],
  stages: [
    {
      type: 'Stage',
      from: { type: 'FromInstruction', instruction: 'FROM', image: 'node:22-alpine' },
      instructions: [
        {
          type: 'CopyInstruction',
          instruction: 'COPY',
          sources: ['package.json'],
          destination: './',
          blankBefore: true,
          leadingComments: [{ type: 'Comment', value: 'manifests only: cache the install layer' }],
        },
      ],
    },
  ],
});
// FROM node:22-alpine
// # manifests only: cache the install layer
//
// COPY package.json ./

Dockerfile.comments holds every comment in source order, and comments below the last instruction land in Dockerfile.trailingComments.

Line continuations are not preserved: a RUN written across several lines with \ deparses as one line.

AST Comparison

import { parse, cleanTree } from 'docker-parser';

const ast1 = parse('FROM node:18');
const ast2 = parse('FROM node:18');

const clean1 = cleanTree(ast1);
const clean2 = cleanTree(ast2);

// Compare ASTs without position information
console.log(JSON.stringify(clean1) === JSON.stringify(clean2)); // true

Supported Instructions

• FROM (with platform, AS alias, digest)
• RUN (shell and exec form, with mount flags)
• CMD (shell and exec form)
• ENTRYPOINT (shell and exec form)
• COPY (with --from, --chown, --chmod, --link)
• ADD (with --chown, --chmod, --checksum)
• ENV
• ARG
• WORKDIR
• USER
• EXPOSE
• VOLUME
• LABEL
• SHELL
• HEALTHCHECK
• STOPSIGNAL
• ONBUILD
• MAINTAINER (deprecated)

License

MIT