From e7f8a88033a8f8f8d6d2606f24ea392de95fde61 Mon Sep 17 00:00:00 2001
From: Lucas Dohmen <lucas@dohmen.io>
Date: Wed, 30 Sep 2026 13:05:54 +0200
Subject: [PATCH] Fix Interoperability with Zlib::GzipReader

GzipReader offers both a read and to_io method. The read method returns
the uncompressed file as a string. The to_io method returns the
compressed file. The JSON.load method first tests for the to_io method
and uses it before testing for the read method. This results in reading
the compressed file, which is invalid JSON.

Instead, we now test for the read method first.
---
 lib/json/common.rb                      |  4 ++--
 test/json/json_common_interface_test.rb | 14 ++++++++++++--
 test/json/test_helper.rb                |  1 +
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/lib/json/common.rb b/lib/json/common.rb
index 3b5e3157a..a1603c06c 100644
--- a/lib/json/common.rb
+++ b/lib/json/common.rb
@@ -699,10 +699,10 @@ def load(source, proc = nil, allow_blank: true, **options)
     unless source.is_a?(String)
       if source.respond_to? :to_str
         source = source.to_str
+      elsif source.respond_to? :read
+        source = source.read
       elsif source.respond_to? :to_io
         source = source.to_io.read
-      elsif source.respond_to?(:read)
-        source = source.read
       end
     end
 
diff --git a/test/json/json_common_interface_test.rb b/test/json/json_common_interface_test.rb
index e4bf958d4..4fb161569 100644
--- a/test/json/json_common_interface_test.rb
+++ b/test/json/json_common_interface_test.rb
@@ -122,15 +122,25 @@ def o.to_s
 
   def test_load
     assert_equal @hash, JSON.load(@json)
+    assert_equal nil, JSON.load(nil)
+    assert_equal nil, JSON.load('')
+
     tempfile = Tempfile.open('@json')
     tempfile.write @json
     tempfile.rewind
     assert_equal @hash, JSON.load(tempfile)
+
     stringio = StringIO.new(@json)
     stringio.rewind
     assert_equal @hash, JSON.load(stringio)
-    assert_equal nil, JSON.load(nil)
-    assert_equal nil, JSON.load('')
+
+    tempfile = Tempfile.open('@json.gzip')
+    gzw = Zlib::GzipWriter.new(tempfile)
+    gzw.write(@json)
+    gzw.close
+    tempfile.open
+    gzr = Zlib::GzipReader.new(tempfile)
+    assert_equal @hash, JSON.load(gzr)
   ensure
     tempfile.close!
   end
diff --git a/test/json/test_helper.rb b/test/json/test_helper.rb
index a30885c40..222ba86df 100644
--- a/test/json/test_helper.rb
+++ b/test/json/test_helper.rb
@@ -31,6 +31,7 @@
 require 'test/unit'
 require 'stringio'
 require 'tempfile'
+require 'zlib'
 begin
   require 'bigdecimal'
 rescue LoadError