Multipart uploads with FULL_OBJECT CRC32 not working

[cbornet]

Expected Behavior

Multipart uploads with FULL_OBJECT CRC32 should work

Current Behavior

Multipart uploads with FULL_OBJECT CRC32 don't work with current Minio.

They do work with real S3.

Steps to Reproduce (for bugs)

Run the following script:

import boto3
import zlib
import base64
import tempfile
import os
from botocore.exceptions import ClientError

CHUNK_SIZE = 8 * 1024 * 1024  # 8 MB

AWS_REGION = "us-east-1"
BUCKET_NAME = "your-unique-bucket-name-2039750257079"


def crc32_to_base64(crc):
    crc &= 0xFFFFFFFF
    return base64.b64encode(crc.to_bytes(4, "big")).decode("utf-8")


def create_s3_client():
    return boto3.client(
        "s3",
        endpoint_url="http://localhost:9000",
        aws_access_key_id="minioadmin",
        aws_secret_access_key="minioadmin",
        region_name=AWS_REGION
    )


def create_bucket_if_not_exists(s3, bucket_name):
    try:
        s3.head_bucket(Bucket=bucket_name)
        print(f"Bucket already exists: {bucket_name}")
    except ClientError:
        print(f"Creating bucket: {bucket_name}")

        if AWS_REGION == "us-east-1":
            s3.create_bucket(Bucket=bucket_name)
        else:
            s3.create_bucket(
                Bucket=bucket_name,
                CreateBucketConfiguration={
                    "LocationConstraint": AWS_REGION
                }
            )


def create_temp_file():
    tmp = tempfile.NamedTemporaryFile(delete=False)
    target_size = CHUNK_SIZE * 3  # 3 parts
    chunk = b"A" * (1024 * 1024)  # write in 1 MB blocks

    written = 0
    while written < target_size:
        to_write = min(len(chunk), target_size - written)
        tmp.write(chunk[:to_write])
        written += to_write
    tmp.close()
    return tmp.name


def multipart_upload(s3, file_path, bucket, key):
    resp = s3.create_multipart_upload(
        Bucket=bucket,
        Key=key,
        ChecksumAlgorithm="CRC32",
        ChecksumType="FULL_OBJECT",
    )
    upload_id = resp["UploadId"]

    parts = []
    full_crc32 = 0

    try:
        with open(file_path, "rb") as f:
            part_number = 1

            while True:
                chunk = f.read(CHUNK_SIZE)
                if not chunk:
                    break

                full_crc32 = zlib.crc32(chunk, full_crc32)

                response = s3.upload_part(
                    Bucket=bucket,
                    Key=key,
                    PartNumber=part_number,
                    UploadId=upload_id,
                    Body=chunk
                )

                parts.append({
                    "ETag": response["ETag"],
                    "PartNumber": part_number
                })

                print(f"Uploaded part {part_number}")
                part_number += 1

        full_crc32_b64 = crc32_to_base64(full_crc32)

        result = s3.complete_multipart_upload(
            Bucket=bucket,
            Key=key,
            UploadId=upload_id,
            MultipartUpload={"Parts": parts},
            ChecksumCRC32=full_crc32_b64,
            ChecksumType="FULL_OBJECT",
        )

        print("Upload complete ✅")
        print("S3 checksum:", result.get("ChecksumCRC32"))

    except Exception as e:
        print("Error:", e)
        s3.abort_multipart_upload(
            Bucket=bucket,
            Key=key,
            UploadId=upload_id
        )
        raise


if __name__ == "__main__":
    s3 = create_s3_client()

    # 1. Ensure bucket exists
    create_bucket_if_not_exists(s3, BUCKET_NAME)

    # 2. Create temp file
    temp_file = create_temp_file()

    try:
        # 3. Upload
        multipart_upload(
            s3,
            file_path=temp_file,
            bucket=BUCKET_NAME,
            key="uploads/temp-example.txt"
        )
    finally:
        os.remove(temp_file)
        print("Temp file deleted")

It works with S3.

With Minio, you get:

botocore.exceptions.ClientError: An error occurred (InvalidPart) when calling the CompleteMultipartUpload operation: One or more of the specified parts could not be found.  The part may not have been uploaded, or the specified entity tag may not match the part's entity tag.

Note: the same happens with the S3 Java SDK.

Regression

No

Your Environment

• Version used (minio --version): RELEASE.2026-04-17T00-00-00Z (go1.26.2 linux/arm64)
• Server setup and configuration:
• Operating System and version (uname -a):