tls.parseCertString()

Description

Since tls.parseCertString() is deprecated (DEP0076) and has reached End-of-Life status in Node.js v18.0.0, we should provide a codemod to replace it.

• The codemod should remove usage of tls.parseCertString().
• The codemod should suggest using proper certificate parsing libraries instead.
• The codemod should add comments explaining why the function was removed.
• The codemod should handle both CommonJS and ESM import patterns.

Additional Information

Note that tls.parseCertString() was removed in Node.js v18.0.0. This function was a trivial parsing helper that was made public by mistake. While it was supposed to parse certificate subject and issuer strings, it never handled multi-value Relative Distinguished Names (RDNs) correctly.

Earlier versions of the documentation suggested using querystring.parse() as an alternative, but that also does not handle all certificate subjects correctly. Instead, developers should use proper certificate parsing libraries or the crypto module's X509Certificate API for working with certificates.

Examples

Example 1: Basic usage with CommonJS

Before:

const tls = require("node:tls");

const subject = "C=US/ST=California/L=San Francisco/O=Example/CN=example.com";
const parsed = tls.parseCertString(subject);
console.log(parsed);

After:

// tls.parseCertString() has been removed
// For certificate parsing, use the X509Certificate API from node:crypto
const { X509Certificate } = require("node:crypto");

// If you have a certificate object, use its subject property directly
// const cert = new X509Certificate(certPem);
// const subject = cert.subject;

// For simple string parsing (not recommended for production):
const subject = "C=US/ST=California/L=San Francisco/O=Example/CN=example.com";
const parsed = Object.fromEntries(
  subject.split("/")
    .filter(Boolean)
    .map(pair => pair.split("="))
);
console.log(parsed);

Example 2: Parsing certificate subject

Before:

const tls = require("node:tls");

const socket = tls.connect(443, "example.com", () => {
  const cert = socket.getPeerCertificate();
  const subject = tls.parseCertString(cert.subject);
  console.log("Subject:", subject);
});

After:

const tls = require("node:tls");

const socket = tls.connect(443, "example.com", () => {
  const cert = socket.getPeerCertificate();
  // cert.subject is already a parsed object, no parsing needed
  console.log("Subject:", cert.subject);
});

Example 3: Parsing certificate issuer

Before:

const tls = require("node:tls");

const cert = socket.getPeerCertificate();
const issuer = tls.parseCertString(cert.issuer);

After:

const tls = require("node:tls");

const cert = socket.getPeerCertificate();
// cert.issuer is already a parsed object
const issuer = cert.issuer;

Example 4: ESM import

Before:

import tls from "node:tls";

const parsed = tls.parseCertString("CN=example.com/O=Example");

After:

// tls.parseCertString() has been removed
// Use the X509Certificate API for proper certificate handling
import { X509Certificate } from "node:crypto";

// For certificate objects, access properties directly:
// const cert = new X509Certificate(certPem);
// const commonName = cert.subject;

// Manual parsing (simplified, may not handle all cases):
const certString = "CN=example.com/O=Example";
const parsed = Object.fromEntries(
  certString.split("/")
    .filter(Boolean)
    .map(pair => pair.split("="))
);

Example 5: Using X509Certificate API

Before:

const tls = require("node:tls");
const fs = require("node:fs");

const certPem = fs.readFileSync("cert.pem");
const certStr = extractSubjectString(certPem);
const parsed = tls.parseCertString(certStr);

After:

const { X509Certificate } = require("node:crypto");
const fs = require("node:fs");

const certPem = fs.readFileSync("cert.pem");
const cert = new X509Certificate(certPem);
// Access certificate properties directly
const subject = cert.subject;
const issuer = cert.issuer;
const commonName = cert.subjectAltName;

Example 6: Destructured import

Before:

const { parseCertString } = require("node:tls");

const result = parseCertString("C=US/CN=test");

After:

// parseCertString has been removed
// Use X509Certificate for proper certificate handling
const { X509Certificate } = require("node:crypto");

// For manual parsing (not recommended):
const certString = "C=US/CN=test";
const result = Object.fromEntries(
  certString.split("/")
    .filter(Boolean)
    .map(pair => pair.split("="))
);

Example 7: Extracting specific fields

Before:

const tls = require("node:tls");

const certString = "C=US/ST=CA/L=SF/O=Acme/CN=example.com";
const parsed = tls.parseCertString(certString);
const commonName = parsed.CN;

After:

// tls.parseCertString() has been removed
// If working with actual certificates, use X509Certificate
const { X509Certificate } = require("node:crypto");

// For a PEM certificate:
// const cert = new X509Certificate(certPem);
// const commonName = cert.subject.split('\n')
//   .find(line => line.startsWith('CN='))
//   ?.substring(3);

// For simple string parsing:
const certString = "C=US/ST=CA/L=SF/O=Acme/CN=example.com";
const parsed = Object.fromEntries(
  certString.split("/")
    .filter(Boolean)
    .map(pair => pair.split("="))
);
const commonName = parsed.CN;

Caveats

• The simple string parsing approach shown in examples does not handle multi-value RDNs correctly
• For production use, always use proper certificate parsing with the X509Certificate API
• The querystring.parse() alternative mentioned in older documentation is also not recommended
• Certificate subject and issuer in getPeerCertificate() are already parsed objects

Refs

• DEP0076: tls.parseCertString()
• tls.parseCertString() removal node#41479

Begin at the project's codemod entry point and use the CommonJS, ESM, and destructured-import examples as the required cases. Check the replacement guidance against node:crypto's X509Certificate API and the documented subject and issuer caveats. Done means each listed import and call pattern is handled with explanatory comments and tests cover the examples.