From b3fc0e21b29fc17ccf81ed6a7919321443b0caf6 Mon Sep 17 00:00:00 2001
From: Shizuo Fujita <fujita@clear-code.com>
Date: Thu, 19 Jun 2025 14:51:28 +0900
Subject: [PATCH] compressable: fix RuntimeError with large zstd compressed
 data

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>
---
 lib/fluent/plugin/compressable.rb |  4 ++--
 test/plugin/test_compressable.rb  | 24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/lib/fluent/plugin/compressable.rb b/lib/fluent/plugin/compressable.rb
index 00aa915ba5..2ec2122931 100644
--- a/lib/fluent/plugin/compressable.rb
+++ b/lib/fluent/plugin/compressable.rb
@@ -79,9 +79,9 @@ def string_decompress_gzip(compressed_data)
 
       def string_decompress_zstd(compressed_data)
         io = StringIO.new(compressed_data)
+        reader = Zstd::StreamReader.new(io)
         out = ''
         loop do
-          reader = Zstd::StreamReader.new(io)
           # Zstd::StreamReader needs to specify the size of the buffer
           out << reader.read(1024)
           # Zstd::StreamReader doesn't provide unused data, so we have to manually adjust the position
@@ -117,8 +117,8 @@ def io_decompress_gzip(input, output)
       end
 
       def io_decompress_zstd(input, output)
+        reader = Zstd::StreamReader.new(input)
         loop do
-          reader = Zstd::StreamReader.new(input)
           # Zstd::StreamReader needs to specify the size of the buffer
           v = reader.read(1024)
           output.write(v)
diff --git a/test/plugin/test_compressable.rb b/test/plugin/test_compressable.rb
index 96dfa318df..1c6788f6c5 100644
--- a/test/plugin/test_compressable.rb
+++ b/test/plugin/test_compressable.rb
@@ -83,5 +83,29 @@ def compress_assert_equal(expected, actual)
       assert_equal '', decompress('')
       assert_equal '', decompress('', output_io: StringIO.new)
     end
+
+    test 'decompress large zstd compressed data' do
+      src1 = SecureRandom.random_bytes(1024)
+      src2 = SecureRandom.random_bytes(1024)
+      src3 = SecureRandom.random_bytes(1024)
+
+      zstd_compressed_data = compress(src1, type: :zstd) + compress(src2, type: :zstd) + compress(src3, type: :zstd)
+      assert_equal src1 + src2 + src3, decompress(zstd_compressed_data, type: :zstd)
+    end
+
+    test 'decompress large zstd compressed data with input_io and output_io' do
+      src1 = SecureRandom.random_bytes(1024)
+      src2 = SecureRandom.random_bytes(1024)
+      src3 = SecureRandom.random_bytes(1024)
+
+      zstd_compressed_data = compress(src1, type: :zstd) + compress(src2, type: :zstd) + compress(src3, type: :zstd)
+
+      input_io = StringIO.new(zstd_compressed_data)
+      output_io = StringIO.new
+      output_io.set_encoding(src1.encoding)
+
+      decompress(input_io: input_io, output_io: output_io, type: :zstd)
+      assert_equal src1 + src2 + src3, output_io.string
+    end
   end
 end