From 8d8999d2e7ea84b62dd075f975a39b4156d71d82 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Brynjar=20Magn=C3=BAsson?= <brynjar@brynjar.is>
Date: Thu, 9 Oct 2025 21:01:18 +0000
Subject: [PATCH 1/2] Fix S3 COPY CSV FILE_SIZE_BYTES

---
 src/s3fs.cpp                                 |  1 +
 test/sql/copy/s3/csv_s3_file_size_bytes.test | 46 ++++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 test/sql/copy/s3/csv_s3_file_size_bytes.test

diff --git a/src/s3fs.cpp b/src/s3fs.cpp
index 2a92f22..88f7575 100644
--- a/src/s3fs.cpp
+++ b/src/s3fs.cpp
@@ -1003,6 +1003,7 @@ void S3FileSystem::Write(FileHandle &handle, void *buffer, int64_t nr_bytes, idx
 			FlushBuffer(s3fh, write_buffer);
 		}
 		s3fh.file_offset += bytes_to_write;
+		s3fh.length += bytes_to_write;
 		bytes_written += bytes_to_write;
 	}
 
diff --git a/test/sql/copy/s3/csv_s3_file_size_bytes.test b/test/sql/copy/s3/csv_s3_file_size_bytes.test
new file mode 100644
index 0000000..b1c6415
--- /dev/null
+++ b/test/sql/copy/s3/csv_s3_file_size_bytes.test
@@ -0,0 +1,46 @@
+# name: test/sql/copy/s3/csv_s3_file_size_bytes.test
+# description: Test FILE_SIZE_BYTES parameter for csv copy over s3
+# group: [s3]
+
+require httpfs
+
+require-env S3_TEST_SERVER_AVAILABLE 1
+
+# Require that these environment variables are also set
+
+require-env AWS_DEFAULT_REGION
+
+require-env AWS_ACCESS_KEY_ID
+
+require-env AWS_SECRET_ACCESS_KEY
+
+require-env DUCKDB_S3_ENDPOINT
+
+require-env DUCKDB_S3_USE_SSL
+
+# override the default behaviour of skipping HTTP errors and connection failures: this test fails on connection issues
+set ignore_error_messages
+
+# different vector sizes result in different number of files
+require no_vector_verification
+
+statement ok
+CREATE TABLE bigdata AS SELECT i AS col_a, i AS col_b FROM range(0,10000) tbl(i);
+
+statement ok
+set threads=1
+
+# parameter in bytes
+statement ok
+COPY (FROM bigdata) TO 's3://test-bucket/file_size_bytes_csv1' (FORMAT CSV, FILE_SIZE_BYTES 1000);
+
+query I
+SELECT COUNT(*) FROM read_csv_auto('s3://test-bucket/file_size_bytes_csv1/*.csv')
+----
+10000
+
+# should lead to 3 files
+query I
+SELECT count(*) FROM glob('s3://test-bucket/file_size_bytes_csv1/*.csv')
+----
+3
\ No newline at end of file

From 7262e98627abf90d2c37f8f2edaee6f176618456 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Brynjar=20Magn=C3=BAsson?= <brynjar@brynjar.is>
Date: Thu, 9 Oct 2025 21:02:58 +0000
Subject: [PATCH 2/2] Fix S3 COPY CSV FILE_SIZE_BYTES

---
 test/sql/copy/s3/csv_s3_file_size_bytes.test | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/sql/copy/s3/csv_s3_file_size_bytes.test b/test/sql/copy/s3/csv_s3_file_size_bytes.test
index b1c6415..cd730f5 100644
--- a/test/sql/copy/s3/csv_s3_file_size_bytes.test
+++ b/test/sql/copy/s3/csv_s3_file_size_bytes.test
@@ -43,4 +43,4 @@ SELECT COUNT(*) FROM read_csv_auto('s3://test-bucket/file_size_bytes_csv1/*.csv'
 query I
 SELECT count(*) FROM glob('s3://test-bucket/file_size_bytes_csv1/*.csv')
 ----
-3
\ No newline at end of file
+3