apple/pkl · error · RuntimeException

Failed to parse hostname in no-proxy rule: ${repr}

Error message

Failed to parse hostname in no-proxy rule: ${repr}

What it means

Pkl failed to parse the hostname portion of an entry in the NO_PROXY / no_proxy environment value. NoProxyRule parses each comma-separated rule and throws this RuntimeException when a rule does not match the expected host[:port] pattern syntax.

Source

Thrown at pkl-core/src/main/java/org/pkl/core/http/NoProxyRule.java:107

          hostname = repr;
          return;
        }
        ipv6Mask = new BigInteger(1, maskBuffer.array()).not().shiftRight(prefixLength);
      }
      if (ipv6Matcher.group("port") != null) {
        port = Integer.parseInt(ipv6Matcher.group("port"));
      }
      return;
    }
    var hostnameMatcher = hostnamePattern.matcher(repr);
    if (hostnameMatcher.matches()) {
      hostname = hostnameMatcher.group("host");
      if (hostnameMatcher.group("port") != null) {
        port = Integer.parseInt(hostnameMatcher.group("port"));
      }
      return;
    }
    throw new RuntimeException("Failed to parse hostname in no-proxy rule: " + repr);
  }

  public boolean matches(URI uri) {
    if (allNoProxy) {
      return true;
    }
    if (!hostMatches(uri)) {
      return false;
    }
    if (port == 0) {
      return true;
    }
    var thatPort = uri.getPort();
    if (thatPort == -1) {
      thatPort =
          switch (uri.getScheme()) {
            case "http" -> 80;
            case "https" -> 443;

View on GitHub (pinned to f3efcbfc9b)

Solutions

1. Print the no_proxy value (`echo $NO_PROXY` / `echo $no_proxy`) and find the malformed entry mentioned in `${repr}`.
2. Rewrite each entry as `host` or `host:port` only — no scheme (https://) or path.
3. Remove or fix the invalid entry and retry the Pkl command.
4. Keep the value to comma-separated hostnames, domains (with leading dot), and optional numeric ports.
5. Prefer a library-managed or generated no_proxy list rather than manual edits.

Example fix

// before (shell)
export NO_PROXY="https://internal.example.com,localhost:8080x"
// after (shell)
export NO_PROXY="internal.example.com,localhost:8080"

for (String rule : System.getenv("NO_PROXY").split(",")) {
  String r = rule.strip();
  if (r.contains("://") || !r.matches("(\\*|\\.?[^:,\\s]+)(:\\d+)?")) {
    throw new IllegalStateException("Malformed NO_PROXY entry: " + r);
  }
}

try {
  // run Pkl
} catch (RuntimeException e) {
  if (e.getMessage().startsWith("Failed to parse hostname in no-proxy rule")) {
    // fix the offending entry printed in the message
  }
}

When it happens

Trigger: Setting NO_PROXY (or http.noProxy config) with an entry whose hostname part cannot be parsed by the rule regex, e.g. malformed URL-ish entries like `https://host`, brackets/whitespace oddities, or an invalid port (`host:port`, non-numeric port). NoProxyRule's public constructor throws this.

Common situations: Hand-edited NO_PROXY values with typos (`host::8080`, `host:notaport`), pasting full URLs instead of hostnames, copy-pasting rules with stray characters or scheme prefixes.

Understand the failure class

Background: "is not a valid" / "Invalid ... value" environment variable errors: how libraries validate env vars and what to do when they reject yours — this error's family across 48 libraries.

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• cannotParseCertFile
• malformedProxyAddress
• `%s` is too large to fit into a Version.
• `%s` could not be parsed as a semantic version number.
• invalidUri

AI-assisted analysis of apple/pkl@f3efcbfc9b (2026-09-08). Data as JSON: /api/errors/0c60fb23dd836b8c. Report an issue: GitHub.