puppetlabs/puppet · error · Puppet::HTTP::ProtocolError

Content-Type is unsupported

Error message

Content-Type is unsupported

What it means

After resolving a formatter from Content-Type, Puppet::HTTP::Service rejects formats that are excluded from network use: EXCLUDED_FORMATS = [:yaml, :b64_zlib_yaml, :dot] (service.rb:15). Those renderers exist only for local CLI output, so a response advertising e.g. text/yaml or the b64_zlib_yaml/dot mimes raises Puppet::HTTP::ProtocolError — puppet's HTTP services only negotiate pson/json (and msgpack when enabled).

Source

Thrown at lib/puppet/http/service.rb:137

  def build_url(api, server, port)
    URI::HTTPS.build(host: server,
                     port: port,
                     path: api).freeze
  end

  def get_mime_types(model)
    network_formats = model.supported_formats - EXCLUDED_FORMATS
    network_formats.map { |f| model.get_format(f).mime }
  end

  def formatter_for_response(response)
    header = response['Content-Type']
    raise Puppet::HTTP::ProtocolError, _("No content type in http response; cannot parse") unless header

    header.gsub!(/\s*;.*$/, '') # strip any charset

    formatter = Puppet::Network::FormatHandler.mime(header)
    raise Puppet::HTTP::ProtocolError, "Content-Type is unsupported" if EXCLUDED_FORMATS.include?(formatter.name)

    formatter
  end

  def serialize(formatter, object)
    formatter.render(object)
  rescue => err
    raise Puppet::HTTP::SerializationError.new("Failed to serialize #{object.class} to #{formatter.name}: #{err.message}", err)
  end

  def serialize_multiple(formatter, object)
    formatter.render_multiple(object)
  rescue => err
    raise Puppet::HTTP::SerializationError.new("Failed to serialize multiple #{object.class} to #{formatter.name}: #{err.message}", err)
  end

  def deserialize(response, model)
    formatter = formatter_for_response(response)

View on GitHub (pinned to e227c27540)

Solutions

1. Set both agent and server to a network-supported format (pson/json, or msgpack via the proper setting) and remove yaml from route format lists.
2. Remove any proxy rule that rewrites response Content-Type.
3. Align agent and server versions so format negotiation matches.

Example fix

# puppetserver conf (route) - before
provides: [yaml, pson]

# after - yaml is not a network format
provides: [pson, json]

begin
  service.get_facts(name)
rescue Puppet::HTTP::ProtocolError => e
  raise unless e.message.include?('Content-Type is unsupported')
  # server advertised yaml/b64_zlib_yaml/dot — fix route format negotiation
  raise
end

When it happens

Trigger: A server responds with a Content-Type that FormatHandler maps to :yaml, :b64_zlib_yaml, or :dot — e.g. someone force-enabling YAML serialization on puppetserver routes, or a proxy rewriting Content-Type; version/feature skew where one side negotiates a format the other never accepts over HTTP.

Common situations: Operators configuring preferred_serialization_format or format whitelists to yaml thinking it is network-safe; middleboxes 'normalizing' application/json to text/yaml; mismatched agent/server pairs after a partial upgrade.

Related errors

• No content type in http response; cannot parse
• 'put' requires a 'content-type' header
• 'post' requires a 'content-type' header
• Location response header is missing
• Failed to parse Retry-After header '%{retry_after}' as an in

AI-assisted analysis of puppetlabs/puppet@e227c27540 (2026-08-21). Data as JSON: /api/errors/2307c336f884dec3. Report an issue: GitHub.