fix: html5 encoding detection case insensitive re: meta tag

CHANGELOG.md

@@ -44,6 +44,7 @@ This version of Nokogiri uses [`jar-dependencies`](https://github.com/mkristian/
 * [CRuby] The HTML5 parser now correctly handles text at the end of `form` elements.
 * [CRuby] `HTML5::Document#fragment` now always uses `body` as the parsing context. Previously, fragments were parsed in the context of the associated document's root node, which allowed for inconsistent parsing. [[#2553](https://github.com/sparklemotion/nokogiri/issues/2553)]
 * [CRuby] `Nokogiri::HTML5::Document#url` now correctly returns the URL passed to the constructor method. Previously it always returned `nil`. [[#2583](https://github.com/sparklemotion/nokogiri/issues/2583)]
+* [CRuby] `HTML5` encoding detection is now case-insensitive with respect to `meta` tag charset declaration. [[#2693](https://github.com/sparklemotion/nokogiri/issues/2693)]
 * [JRuby] Fixed a bug with adding the same namespace to multiple nodes via `#add_namespace_definition`. [[#1247](https://github.com/sparklemotion/nokogiri/issues/1247)]
 * [JRuby] `NodeSet#[]` now raises a TypeError if passed an invalid parameter type. [[#2211](https://github.com/sparklemotion/nokogiri/issues/2211)]
 * [CRuby+OSX] Compiling from source on MacOS will use the clang option `-Wno-unknown-warning-option` to avoid errors when Ruby injects options that clang doesn't know about. [[#2689](https://github.com/sparklemotion/nokogiri/issues/2689)]

lib/nokogiri/html5.rb

@@ -363,7 +363,7 @@ def reencode(body, content_type = nil)
           # look for a charset in a meta tag in the first 1024 bytes
           unless encoding
             data = body[0..1023].gsub(/<!--.*?(-->|\Z)/m, "")
-            data.scan(/<meta.*?>/m).each do |meta|
+            data.scan(/<meta.*?>/im).each do |meta|
               encoding ||= meta[/charset=["']?([^>]*?)($|["'\s>])/im, 1]
             end
           end

test/html5/test_encoding.rb

@@ -17,13 +17,20 @@ def test_iso8859_encoding
       assert_equal("<span>Señor</span>", doc.at("span").to_xml)
     end
 
-    def test_charset_encoding
+    def test_meta_charset_encoding
       utf8 = (+"<meta charset='utf-8'><span>Se\xC3\xB1or</span>")
         .force_encoding(Encoding::ASCII_8BIT)
       doc = Nokogiri::HTML5(utf8)
       assert_equal("<span>Señor</span>", doc.at("span").to_xml)
     end
 
+    def test_META_CHARSET_encoding
+      utf8 = (+"<META CHARSET='utf-8'><SPAN>Se\xC3\xB1or</SPAN>")
+        .force_encoding(Encoding::ASCII_8BIT)
+      doc = Nokogiri::HTML5(utf8)
+      assert_equal("<span>Señor</span>", doc.at("span").to_xml)
+    end
+
     def test_bogus_encoding
       bogus = (+"<meta charset='bogus'><span>Se\xF1or</span>")
         .force_encoding(Encoding::ASCII_8BIT)