ruby/ruby · error · ArgumentError

uri scheme is invalid: #{uri.scheme.inspect}

Error message

uri scheme is invalid: #{uri.scheme.inspect}

What it means

Gem::RemoteFetcher#fetch_path dispatches on the URI scheme to a concrete fetcher: http/https map to fetch_http, s3 to fetch_s3, and file to fetch_file. Any other scheme - including nil, which is what a scheme-less string like "/tmp/specs.4.8.gz" parses to - raises ArgumentError with the inspected scheme. The error is raised by Hash#fetch's default block, so it fires before any download attempt.

Source

Thrown at lib/rubygems/remote_fetcher.rb:259

      error_detail = custom_error || response.message
      raise FetchError.new("Bad response #{error_detail} #{response.code}", uri)
    end
  end

  alias_method :fetch_https, :fetch_http

  ##
  # Downloads +uri+ and returns it as a String.

  def fetch_path(uri, mtime = nil, head = false)
    uri = Gem::Uri.new uri

    method = {
      "http" => "fetch_http",
      "https" => "fetch_http",
      "s3" => "fetch_s3",
      "file" => "fetch_file",
    }.fetch(uri.scheme) { raise ArgumentError, "uri scheme is invalid: #{uri.scheme.inspect}" }

    data = send method, uri, mtime, head

    if data && !head && uri.to_s.end_with?(".gz")
      begin
        data = Gem::Util.gunzip data
      rescue Zlib::GzipFile::Error
        raise FetchError.new("server did not return a valid file", uri)
      end
    end

    data
  rescue Gem::Timeout::Error, IOError, SocketError, SystemCallError,
         *(OpenSSL::SSL::SSLError if Gem::HAVE_OPENSSL) => e
    raise FetchError.new("#{e.class}: #{e}", uri)
  end

  def fetch_s3(uri, mtime = nil, head = false)

View on GitHub (pinned to 0e5b888e1c)

Solutions

1. Pass a proper URI: use http:// or https:// for remote files
2. Prefix local paths with file:// (e.g. URI('file:///tmp/specs.4.8.gz')) so the scheme is 'file'
3. Audit `gem sources -l` and ~/.gemrc for entries whose scheme is not http/https and remove them with `gem sources -r`
4. For s3, keep the s3:// scheme and configure credentials via the standard s3 env vars RubyGems honors

Example fix

# before
fetcher.fetch_path("/var/gem_mirror/specs.4.8.gz")

# after
fetcher.fetch_path(URI("file:///var/gem_mirror/specs.4.8.gz"))

uri = Gem::Uri.new(source)
raise ArgumentError, "scheme must be http/https/s3/file, got #{uri.scheme.inspect}" unless %w[http https s3 file].include?(uri.scheme)
fetcher.fetch_path(uri)

begin
  fetcher.fetch_path(uri)
rescue ArgumentError => e
  # distinguish scheme errors (message contains 'uri scheme is invalid') from other argument errors
  raise if !e.message.include?('uri scheme is invalid')
  warn "skipping unsupported source #{uri}" and nil
end

When it happens

Trigger: Gem::RemoteFetcher.fetcher.fetch_path('ftp://host/file') or fetch_path('/local/path/specs.4.8.gz') (nil scheme). Also hit indirectly by gem commands (gem fetch, gem spec, dependency resolution) when a configured source or spec URI carries a non-http/https/s3/file scheme.

Common situations: Passing a plain filesystem path string where a file:// URI is required; a source left in `gem sources -l` with a bad protocol; tooling that builds URIs by string concatenation and drops the scheme; using fetch_path on git: or ssh: URIs.

Related errors

• unsupported URI scheme #{source_uri.scheme}
• can't open %s. give up.\n
• bad component(expected scheme component): #{v}
• bad URI (absolute but no scheme): #{uri}
• bad URI (absolute but no path): #{uri}

AI-assisted analysis of ruby/ruby@0e5b888e1c (2026-08-21). Data as JSON: /api/errors/f9b4afc0cb5b117e. Report an issue: GitHub.