jnunemaker/httparty · error · NotImplementedError

#{self.class.name} has not implemented a decompression metho

Error message

#{self.class.name} has not implemented a decompression method for #{encoding.inspect} encoding.

What it means

The Decompressor raises NotImplementedError (from decompress_supported_encoding) when the response's Content-Encoding maps to a method the decompressor class does not define. SupportedEncodings maps 'none'/'identity' to :none, 'br' to :brotli, 'compress' to :lzw and 'zstd' to :zstd; a subclass of HTTParty::Decompressor that omits one of those instance methods will blow up when a server sends that encoding. Note the base class itself deliberately returns nil (not an error) when the optional Brotli gem is missing, so this raise is specifically about a missing method on a custom subclass.

Source

Thrown at lib/httparty/decompressor.rb:64

      if supports_encoding?
        decompress_supported_encoding
      else
        nil
      end
    end

    protected

    def supports_encoding?
      SupportedEncodings.keys.include?(encoding)
    end

    def decompress_supported_encoding
      method = SupportedEncodings[encoding]
      if respond_to?(method, true)
        send(method)
      else
        raise NotImplementedError, "#{self.class.name} has not implemented a decompression method for #{encoding.inspect} encoding."
      end
    end

    def none
      body
    end

    def brotli
      return nil unless defined?(::Brotli)
      begin
        ::Brotli.inflate(body)
      rescue StandardError
        nil
      end
    end

    def lzw
      begin

View on GitHub (pinned to 8f4a09e343)

Solutions

1. Define the missing method on the subclass (`def zstd; ...; end`) or remove the override so it inherits.
2. For brotli/zstd support, add the requisite gem (`brotli`, `zstd-ruby`) to the Gemfile and let the built-in methods work.
3. Strip the Accept-Encoding request header so the server does not negotiate the unsupported encoding.

Example fix

# before
class LoggedDecompressor < HTTParty::Decompressor
  def brotli
    Rails.logger.info('brotli') && super
  end
  # no zstd method -> NotImplementedError on Content-Encoding: zstd
end

# after
class LoggedDecompressor < HTTParty::Decompressor
  def brotli
    Rails.logger.info('brotli'); super
  end

  def zstd
    Rails.logger.info('zstd'); super
  end
end

method = HTTParty::Decompressor::SupportedEncodings[content_encoding]
raise NotImplementedError, "decompressor cannot handle #{content_encoding}" unless method && decompressor.respond_to?(method)

handles_encoding = ->(enc, dec = MyDecompressor) do
  m = HTTParty::Decompressor::SupportedEncodings[enc]
  !m.nil? && dec.method_defined?(m)
end

begin
  Foo.get(url)
rescue NotImplementedError => e
  raise unless e.message.include?('decompression method')
  Foo.get(url, headers: { 'Accept-Encoding' => 'gzip, deflate' })  # avoid unsupported encodings
end

When it happens

Trigger: A custom `class MyDecompressor < HTTParty::Decompressor` that overrides or trims methods, then a server responds with `Content-Encoding: zstd` (or 'compress'/'br') and the decompressor tries to `send(:zstd)` which does not exist.

Common situations: Subclassing Decompressor to add logging or custom decompression and forgetting to keep all SupportedEncodings methods, new encodings (zstd) arriving from upgraded servers/CDNs, and copy-pasted decompressor subclasses from older httparty versions that predate a new encoding entry.

Related errors

• #{self.class.name} has not implemented a parsing method for
• #{response}
• Default params must be an object which responds to #to_hash
• Headers must be an object which responds to #to_hash
• Cookies must be an object which responds to #to_hash

AI-assisted analysis of jnunemaker/httparty@8f4a09e343 (2026-08-21). Data as JSON: /api/errors/d94ea4a70e629cca. Report an issue: GitHub.