Allow `brew audit` to fake a Safari user-agent.

This allows us to detect if homepages such as e.g. `aiccu` which
blocks `curl` are up or not.

Library/Homebrew/dev-cmd/audit.rb

@@ -169,7 +169,7 @@ class FormulaAuditor
     @specs = %w[stable devel head].map { |s| formula.send(s) }.compact
   end
 
-  def url_status_code(url, range: false)
+  def url_status_code(url, range: false, user_agent: :default)
     # The system Curl is too old and unreliable with HTTPS homepages on
     # Yosemite and below.
     return "200" unless DevelopmentTools.curl_handles_most_https_homepages?
@@ -185,7 +185,7 @@ class FormulaAuditor
     args = curl_args(
       extra_args: extra_args,
       show_output: true,
-      default_user_agent: true
+      user_agent: user_agent
     )
     retries = 3
     status_code = nil
@@ -597,7 +597,7 @@ class FormulaAuditor
 
     return unless @online
 
-    status_code = url_status_code(homepage)
+    status_code = url_status_code(homepage, user_agent: :browser)
     return if status_code.start_with? "20"
     problem "The homepage #{homepage} is not reachable (HTTP status code #{status_code})"
   end

Library/Homebrew/global.rb

@@ -26,6 +26,7 @@ RUBY_BIN = RUBY_PATH.dirname
 
 HOMEBREW_USER_AGENT_CURL = ENV["HOMEBREW_USER_AGENT_CURL"]
 HOMEBREW_USER_AGENT_RUBY = "#{ENV["HOMEBREW_USER_AGENT"]} ruby/#{RUBY_VERSION}-p#{RUBY_PATCHLEVEL}".freeze
+HOMEBREW_USER_AGENT_FAKE_SAFARI = "Mozilla/5.0 (#{ENV["HOMEBREW_SYSTEM"]}; #{ENV["HOMEBREW_PROCESSOR"]} #{ENV["HOMEBREW_OS_VERSION"]}) AppleWebKit/602.3.12 (KHTML, like Gecko) Version/10.0.2 Safari/602.3.12".freeze
 
 require "tap_constants"
 

Library/Homebrew/utils/curl.rb

@@ -12,7 +12,10 @@ def curl_args(options = {})
     "--location",
   ]
 
-  unless options[:default_user_agent]
+  case options[:user_agent]
+  when :browser
+    args << "--user-agent" << HOMEBREW_USER_AGENT_FAKE_SAFARI
+  else
     args << "--user-agent" << HOMEBREW_USER_AGENT_CURL
   end