[ruby/net-http] Update the content-length heading when decoding bodies

Previously, the content-encoding header was removed and the body
was modified, but the content-length header was not modified,
resulting in the content-length header not matching the body
length.

Fixes [Bug #16672]

a7cb30124c

lib/net/http/response.rb

@@ -263,6 +263,7 @@ class Net::HTTPResponse
     case v&.downcase
     when 'deflate', 'gzip', 'x-gzip' then
       self.delete 'content-encoding'
+      had_content_length = self.delete 'content-length'
 
       inflate_body_io = Inflater.new(@socket)
 
@@ -272,6 +273,9 @@ class Net::HTTPResponse
       ensure
         begin
           inflate_body_io.finish
+          if had_content_length
+            self['content-length'] = inflate_body_io.bytes_inflated.to_s
+          end
         rescue => err
           # Ignore #finish's error if there is an exception from yield
           raise err if success
@@ -373,6 +377,14 @@ class Net::HTTPResponse
       @inflate.finish
     end
 
+    ##
+    # The number of bytes inflated, used to update the Content-Length of
+    # the response.
+
+    def bytes_inflated
+      @inflate.total_out
+    end
+
     ##
     # Returns a Net::ReadAdapter that inflates each read chunk into +dest+.
     #