From 5924737c636018e781da324c53289cc23b8f535c Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Mon, 26 Oct 2026 13:18:14 +0900
Subject: [PATCH 1/2] Clear next_in once the rest of the input is buffered

Zlib::Deflate#params after breaking out of the block of #deflate compressed the input left by the break a second time, and the output no longer inflated to the original. Zlib::Inflate#inflate now checks the buffered input instead of avail_in to decide whether an empty string has anything to process.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 ext/zlib/zlib.c        |  8 +++++++-
 test/zlib/test_zlib.rb | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/ext/zlib/zlib.c b/ext/zlib/zlib.c
index f13ef4d..d51ac30 100644
--- a/ext/zlib/zlib.c
+++ b/ext/zlib/zlib.c
@@ -1216,6 +1216,8 @@ zstream_run_try(VALUE value_arg)
 		}
 	    }
 	}
+	z->stream.next_in = Z_NULL;
+	z->stream.avail_in = 0;
 	raise_zlib_error(err, z->stream.msg);
     }
 
@@ -1225,6 +1227,9 @@ zstream_run_try(VALUE value_arg)
     if (!NIL_P(old_input)) {
 	rb_str_resize(old_input, 0);
     }
+    /* the rest is in z->input now; do not leave next_in in old_input */
+    z->stream.next_in = Z_NULL;
+    z->stream.avail_in = 0;
 
     return Qnil;
 }
@@ -2144,7 +2149,8 @@ do_inflate(struct zstream *z, VALUE src)
 	return;
     }
     StringValue(src);
-    if (RSTRING_LEN(src) > 0 || z->stream.avail_in > 0) { /* prevent Z_BUF_ERROR */
+    if (RSTRING_LEN(src) > 0 ||
+	(!NIL_P(z->input) && RSTRING_LEN(z->input) > 0)) { /* prevent Z_BUF_ERROR */
 	zstream_run(z, (Bytef*)RSTRING_PTR(src), RSTRING_LEN(src), Z_SYNC_FLUSH);
     }
 }
diff --git a/test/zlib/test_zlib.rb b/test/zlib/test_zlib.rb
index e1ecbf8..986d7df 100644
--- a/test/zlib/test_zlib.rb
+++ b/test/zlib/test_zlib.rb
@@ -102,6 +102,27 @@ def test_deflate_chunked_break
       assert_equal input, original
     end
 
+    def test_params_after_chunked_break
+      chunks = []
+      r = Random.new 0
+
+      # small enough that params can flush what zlib holds without Z_BUF_ERROR
+      z = Zlib::Deflate.new(Zlib::DEFAULT_COMPRESSION, 9, 1)
+
+      input = r.bytes(20000)
+      z.deflate(input) do |chunk|
+        chunks << chunk
+        break
+      end
+
+      assert_operator 0, :<, z.avail_in
+
+      z.params(Zlib::BEST_SPEED, Zlib::FILTERED)
+      chunks << z.finish
+
+      assert_equal input, Zlib.inflate(chunks.join)
+    end
+
     def test_addstr
       z = Zlib::Deflate.new
       z << "foo"
@@ -620,6 +641,24 @@ def test_inflate_dictionary
       assert_equal "foofoofoo", out
     end
 
+    def test_inflate_empty_after_chunked_break
+      chunks = []
+      input = Random.new(0).bytes(20000)
+
+      z = Zlib::Inflate.new
+
+      z.inflate(Zlib.deflate(input)) do |chunk|
+        chunks << chunk
+        break
+      end
+
+      assert_operator 0, :<, z.avail_in
+
+      chunks << z.inflate("")
+
+      assert_equal input, chunks.join
+    end
+
     def test_sync
       z = Zlib::Deflate.new
       s = z.deflate("foo" * 1000, Zlib::FULL_FLUSH)

From 7b2736f4f598a06a4e109465b5e80168e3ca5647 Mon Sep 17 00:00:00 2001
From: Hiroshi SHIBATA <hsbt@ruby-lang.org>
Date: Mon, 26 Oct 2026 13:22:24 +0900
Subject: [PATCH 2/2] Test Zlib::Deflate#params after a failed deflate

The chunked break test does not reach the reset of next_in on the error path.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 test/zlib/test_zlib.rb | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/test/zlib/test_zlib.rb b/test/zlib/test_zlib.rb
index 986d7df..fd85f01 100644
--- a/test/zlib/test_zlib.rb
+++ b/test/zlib/test_zlib.rb
@@ -123,6 +123,17 @@ def test_params_after_chunked_break
       assert_equal input, Zlib.inflate(chunks.join)
     end
 
+    def test_params_after_failed_deflate
+      z = Zlib::Deflate.new
+      z << "foo"
+      assert_raise(Zlib::StreamError) { z.deflate("bar", 10000) }
+      assert_equal "bar", z.flush_next_in
+
+      z.params(Zlib::BEST_SPEED, Zlib::FILTERED)
+
+      assert_equal "foo", Zlib::Inflate.inflate(z.finish)
+    end
+
     def test_addstr
       z = Zlib::Deflate.new
       z << "foo"