Set size limit for user agent and accept language. (#493)

CHANGELOG.md

@@ -18,6 +18,10 @@
 - Fix QQ detection.
 - Fix Alipay detection.
 - Add Sougou Browser detection.
+- User agent has a size limit of 512 bytes. This can be customized through 
+  `Browser.user_agent_size_limit`.
+- Accept-Language has a size limit of 256 bytes. This can be customized through
+  `Browser.accept_language_size_limit`.
 
 ## 4.2.0
 

README.md

@@ -350,6 +350,20 @@ Rails.configuration.middleware.use Browser::Middleware do
 end
 ```
 
+### Restrictions
+
+- User agent has a size limit of 512 bytes. This can be customized through 
+  `Browser.user_agent_size_limit=(size)`.
+- Accept-Language has a size limit of 256 bytes. This can be customized through
+  `Browser.accept_language_size_limit=(size)`.
+
+If size is not respected, then `Browser::Error` is raised.
+
+```ruby
+Browser.user_agent_size_limit = 1024
+Browser.accept_language_size_limit = 150
+```
+
 ## Development
 
 ### Versioning

lib/browser/base.rb

@@ -10,6 +10,9 @@ class Base
     attr_reader :accept_language
 
     def initialize(ua, accept_language: nil)
+      validate_size(:user_agent, ua.to_s)
+      validate_size(:accept_language, accept_language.to_s)
+
       @ua = ua
       @accept_language = AcceptLanguage.parse(accept_language)
     end
@@ -251,5 +254,16 @@ def proxy?
     def electron?(expected_version = nil)
       Electron.new(ua).match? && detect_version?(full_version, expected_version)
     end
+
+    private def validate_size(subject, input)
+      actual_bytesize = input.bytesize
+      size_limit = Browser.public_send("#{subject}_size_limit")
+
+      return if actual_bytesize < size_limit
+
+      raise Error,
+            "#{subject} cannot be larger than #{size_limit} bytes; " \
+            "actual size is #{actual_bytesize}"
+    end
   end
 end

lib/browser/browser.rb

@@ -51,10 +51,20 @@
 module Browser
   EMPTY_STRING = ""
 
+  Error = Class.new(StandardError)
+
   def self.root
     @root ||= Pathname.new(File.expand_path("../..", __dir__))
   end
 
+  class << self
+    attr_accessor :user_agent_size_limit
+    attr_accessor :accept_language_size_limit
+  end
+
+  self.user_agent_size_limit = 512
+  self.accept_language_size_limit = 256
+
   # Hold the list of browser matchers.
   # Order is important.
   def self.matchers

test/browser_test.rb

@@ -154,4 +154,22 @@ class BrowserTest < Minitest::Test
     browser = Browser.new("Fancy new browser")
     refute browser.known?
   end
+
+  test "rejects user agent larger than 512 bytes" do
+    message = "user_agent cannot be larger than 512 bytes; actual size is " \
+              "513 bytes"
+
+    assert_raises(Browser::Error, message) do
+      Browser.new("a" * 513)
+    end
+  end
+
+  test "rejects accept language larger than 256 bytes" do
+    message = "accept_language cannot be larger than 256 bytes; actual size " \
+              "is 257 bytes"
+
+    assert_raises(Browser::Error, message) do
+      Browser.new("Chrome", accept_language: "a" * 257)
+    end
+  end
 end