[ruby/zlib] Raise InProgressError from Zlib::Inflate#sync during inflate

Called from the block of Zlib::Inflate#inflate, #sync pointed next_in at its argument, and the inflate loop kept reading from there after the block returned.

https://github.com/ruby/zlib/commit/f7822c93e7

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ext/zlib/zlib.c

@@ -1282,6 +1282,10 @@ zstream_sync(struct zstream *z, Bytef *src, rb_len_t len)
     /* VALUE rest; */
     int err;
 
+    if (z->flags & ZSTREAM_IN_PROGRESS) {
+	rb_raise(cInProgressError, "zlib stream is in progress");
+    }
+
     if (!NIL_P(z->input)) {
 	err = zstream_inflate_sync(z, (Bytef*)RSTRING_PTR(z->input),
 				   RSTRING_LEN(z->input));

test/zlib/test_zlib.rb

@@ -647,6 +647,19 @@ if defined? Zlib
       assert_equal(true, z.sync("\0" * 100 + s))
     end
 
+    def test_sync_in_progress
+      src = "x" * 100_000
+      z = Zlib::Inflate.new
+      inflated = "".dup
+      z.inflate(Zlib.deflate(src)) do |chunk|
+        if inflated.empty?
+          assert_raise(Zlib::InProgressError) { z.sync("\0\0\xff\xff".b) }
+        end
+        inflated << chunk
+      end
+      assert_equal src, inflated
+    end
+
     def test_set_dictionary
       z = Zlib::Inflate.new
       assert_raise(Zlib::StreamError) { z.set_dictionary("foo") }