brotli is an optional dependency

- move dev deps to the Gemfile
- brotli is not a dev dep for jruby (which it doesn't support)
- test how brotli responses are handled when Brotli is not loaded

Gemfile

@@ -1,3 +1,9 @@
 source "https://rubygems.org"
 
 gemspec
+
+gem "minitest", "~> 5.14"
+gem "rake", "~> 13.0"
+gem "rdoc", "~> 6.3"
+gem "rubocop", "~> 1.12"
+gem "brotli", ">= 0.5" unless RUBY_PLATFORM == "java"

lib/mechanize/http/agent.rb

@@ -2,7 +2,6 @@
 require 'tempfile'
 require 'net/ntlm'
 require 'webrobots'
-require 'brotli'
 
 ##
 # An HTTP (and local disk access) user agent.  This class is an implementation
@@ -498,14 +497,24 @@ def content_encoding_inflate body_io
 
   ##
   # Decodes a Brotli-encoded +body_io+
+  #
+  # Although Mechanize will never request a Brotli-encoded response via `accept-encoding`, buggy
+  # servers may return brotli-encoded responses anyway. Let's try to handle that case if the Brotli
+  # gem is loaded.
 
   def content_encoding_brotli(body_io)
-    log.debug('deflate brotly body') if log
+    log.debug('deflate brotli body') if log
+
+    unless defined?(::Brotli)
+      raise Mechanize::Error, "cannot deflate brotli-encoded response. Please install and require the 'brotli' gem."
+    end
 
-    return StringIO.new(Brotli.inflate(body_io.read))
-  rescue Brotli::Error
-    log.error('unable to brotli-inflate response') if log
-    raise Mechanize::Error, "could not inflate brotli-encoded response"
+    begin
+      return StringIO.new(Brotli.inflate(body_io.read))
+    rescue Brotli::Error
+      log.error("unable to brotli-inflate response") if log
+      raise Mechanize::Error, "error inflating brotli-encoded response."
+    end
   ensure
     body_io.close
   end

mechanize.gemspec

@@ -58,7 +58,6 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency("http-cookie", ">= 1.0.3", "~> 1.0")
   spec.add_runtime_dependency("mime-types", "~> 3.0")
   spec.add_runtime_dependency("net-http-digest_auth", ">= 1.4.1", "~> 1.4")
-  spec.add_runtime_dependency("brotli", ">= 0.5")
 
   # careful! some folks are relying on older versions of net-http-persistent
   # - see the socks proxy patch in use at #507 and #464
@@ -72,9 +71,4 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency("rubyntlm", ">= 0.6.3", "~> 0.6")
   spec.add_runtime_dependency("base64") # removed from bundled gems in 3.4, and needed by rubyntlm (which doesn't declare this dependency)
   spec.add_runtime_dependency("nkf") # removed from bundled gems in 3.4
-
-  spec.add_development_dependency("minitest", "~> 5.14")
-  spec.add_development_dependency("rake", "~> 13.0")
-  spec.add_development_dependency("rdoc", "~> 6.3")
-  spec.add_development_dependency("rubocop", "~> 1.12")
 end

test/test_mechanize_http_agent.rb

@@ -2,6 +2,7 @@
 # frozen_string_literal: true
 
 require 'mechanize/test_case'
+require "brotli" unless RUBY_PLATFORM == "java"
 
 class TestMechanizeHttpAgent < Mechanize::TestCase
 
@@ -924,7 +925,23 @@ def @res.content_length() nil end
     assert_equal 'part', body.read
   end
 
-  def test_response_content_encoding_br
+  def test_response_content_encoding_brotli_when_brotli_not_loaded
+    skip("only test this on jruby which doesn't have brotli support") unless RUBY_ENGINE == 'jruby'
+
+    @res.instance_variable_set :@header, 'content-encoding' => %w[br]
+    body_io = StringIO.new("content doesn't matter for this test")
+
+    e = assert_raises(Mechanize::Error) do
+      @agent.response_content_encoding(@res, body_io)
+    end
+    assert_includes(e.message, "cannot deflate brotli-encoded response")
+
+    assert(body_io.closed?)
+  end
+
+  def test_response_content_encoding_brotli
+    skip("jruby does not have brotli support") if RUBY_ENGINE == 'jruby'
+
     @res.instance_variable_set :@header, 'content-encoding' => %w[br]
     body_io = StringIO.new(Brotli.deflate("this is compressed by brotli"))
 
@@ -934,16 +951,17 @@ def test_response_content_encoding_br
     assert(body_io.closed?)
   end
 
-  def test_response_content_encoding_br_corrupt
+  def test_response_content_encoding_brotli_corrupt
+    skip("jruby does not have brotli support") if RUBY_ENGINE == 'jruby'
+
     @res.instance_variable_set :@header, 'content-encoding' => %w[br]
     body_io = StringIO.new("not a brotli payload")
 
     e = assert_raises(Mechanize::Error) do
       @agent.response_content_encoding(@res, body_io)
     end
-    assert_includes(e.message, "could not inflate brotli-encoded response")
+    assert_includes(e.message, "error inflating brotli-encoded response")
     assert_kind_of(Brotli::Error, e.cause)
-
     assert(body_io.closed?)
   end