Add new configuration to preserve headers case

- Add new configuration to preserve headers case in Net::HTTP class
- Add new configuration to preserve headers case in GenericRequest class

lib/net/http.rb

@@ -507,6 +507,10 @@ class HTTPHeaderSyntaxError < StandardError; end
   #   Returns the write timeout.
   # - {write_timeout=}[rdoc-ref:Net::HTTP#write_timeout=]:
   #   Sets the write timeout.
+  # - {:preserve_headers}[rdoc-ref:Net::HTTP#preserve_headers]:
+  #   Returns the open timeout.
+  # - {:preserve_headers=}[rdoc-ref:Net::HTTP#preserve_headers=]:
+  #   Sets the read timeout.
   #
   # === Requests
   #
@@ -1123,6 +1127,7 @@ def initialize(address, port = nil) # :nodoc:
       @ssl_context = nil
       @ssl_session = nil
       @sspi_enabled = false
+      @preserve_headers = false
       SSL_IVNAMES.each do |ivname|
         instance_variable_set ivname, nil
       end
@@ -1532,6 +1537,9 @@ def use_ssl=(flag)
     # See {OpenSSL::SSL::SSLContext#verify_hostname=}[https://docs.ruby-lang.org/en/master/OpenSSL/SSL/SSLContext.html#attribute-i-verify_mode].
     attr_accessor :verify_hostname
 
+    # Sets or returns whether to preserve the headers case
+    attr_accessor :preserve_headers
+
     # Returns the X509 certificate chain (an array of strings)
     # for the session's socket peer,
     # or +nil+ if none.
@@ -2300,6 +2308,7 @@ def request(req, body = nil, &block)  # :yield: +response+
           return request(req, body, &block)
         }
       end
+      req.preserve_headers = preserve_headers
       if proxy_user()
         req.proxy_basic_auth proxy_user(), proxy_pass() unless use_ssl?
       end

lib/net/http/generic_request.rb

@@ -55,6 +55,7 @@ def initialize(m, reqbody, resbody, uri_or_path, initheader = nil) # :nodoc:
     @body = nil
     @body_stream = nil
     @body_data = nil
+    @preserve_headers = false
   end
 
   # Returns the string method name for the request:
@@ -94,6 +95,9 @@ def initialize(m, reqbody, resbody, uri_or_path, initheader = nil) # :nodoc:
   #
   attr_reader :decode_content
 
+  # Sets if will preserve case from headers
+  attr_accessor :preserve_headers
+
   # Returns a string representation of the request:
   #
   #   Net::HTTP::Post.new(uri).inspect # => "#<Net::HTTP::Post POST>"
@@ -403,8 +407,14 @@ def write_header(sock, ver, path)
     end
     buf = +''
     buf << reqline << "\r\n"
-    each_capitalized do |k,v|
-      buf << "#{k}: #{v}\r\n"
+    if preserve_headers
+      each_header do |k,v|
+        buf << "#{k}: #{v}\r\n"
+      end
+    else
+      each_capitalized do |k,v|
+        buf << "#{k}: #{v}\r\n"
+      end
     end
     buf << "\r\n"
     sock.write buf

test/net/http/test_http.rb

@@ -1367,4 +1367,27 @@ def test_partial_response
     http.ignore_eof = false
     assert_raise(EOFError) {http.get('/')}
   end
+
+  def test_no_preserved_headers
+    headers = { accept: '*/*' }
+    expected_raw_header = "Accept: */*\r\n"
+    @server.mount_proc('/') do |req, _res|
+      assert_includes(req.raw_header, expected_raw_header)
+    end
+
+    http = Net::HTTP.new(config('host'), config('port'))
+    http.get('/', headers)
+  end
+
+  def test_preserved_headers
+    headers = { accept: '*/*' }
+    expected_raw_header = "accept: */*\r\n"
+    @server.mount_proc('/') do |req, _res|
+      assert_includes(req.raw_header, expected_raw_header)
+    end
+
+    http = Net::HTTP.new(config('host'), config('port'))
+    http.preserve_headers = true
+    http.get('/', headers)
+  end
 end