apache/seatunnel · error · IOException

Not supported

Error message

Not supported

What it means

SeaTunnelFTPFileSystem explicitly does not implement append(); any call throws this IOException. The FTP-backed filesystem only supports creating new files and overwriting, not appending to an existing file.

Solutions

1. Rewrite the logic to create a new file per run instead of appending
2. Buffer data locally and write a complete new file via fs.create(path, overwrite=true)
3. Switch to a filesystem/connector that supports append (e.g. HDFS, S3 with appropriate setup)
4. Check the connector's write-mode configuration and remove append-oriented settings

Example fix

// before
FSDataOutputStream out = fs.append(path);
out.write(data);
// after
FSDataOutputStream out = fs.create(path, true); // overwrite instead of append
out.write(data);

// detect append support before calling
boolean supportsAppend = !(fs instanceof org.apache.seatunnel.connectors.seatunnel.file.ftp.system.SeaTunnelFTPFileSystem);

boolean supportsAppend(org.apache.hadoop.fs.FileSystem fs) {
    return !(fs instanceof org.apache.seatunnel.connectors.seatunnel.file.ftp.system.SeaTunnelFTPFileSystem);
}

try {
    out = fs.append(path);
} catch (IOException e) {
    if (e.getMessage().equals("Not supported")) {
        out = fs.create(path, true); // fallback: rewrite file instead of appending
    } else { throw e; }
}

When it happens

Trigger: Calling fs.append(path, bufferSize, progress) on a SeaTunnelFTPFileSystem instance, e.g. from code that assumes Hadoop-compatible append semantics or a sink configured in append mode.

Common situations: Streaming writes that rely on append to an existing file on FTP; migrating a job from HDFS (which supports append) to the FTP connector; sink configurations that set append/write-mode options.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Not supported
• A decoding format must override this method to apply…
• Can't create JdbcDialect without compatible mode for…
• Can't make directory for path
• can't support custom load jar

AI-assisted analysis of apache/seatunnel@cf67b549a7 (2026-09-10). Data as JSON: /api/errors/5cfabaed422bd853. Report an issue: GitHub.

Appendix: source

Thrown at seatunnel-connectors-v2/connector-file/connector-file-ftp/src/main/java/org/apache/seatunnel/connectors/seatunnel/file/ftp/system/SeaTunnelFTPFileSystem.java:408

                                    "Could not complete transfer, Reply Code - "
                                            + client.getReplyCode());
                        }
                    }
                };
        if (!FTPReply.isPositivePreliminary(client.getReplyCode())) {
            // The ftpClient is an inconsistent state. Must close the stream
            // which in turn will logout and disconnect from FTP server
            fos.close();
            throw new IOException("Unable to create file: " + file + ", Aborting");
        }
        return fos;
    }

    /** This optional operation is not yet supported. */
    @Override
    public FSDataOutputStream append(Path f, int bufferSize, Progressable progress)
            throws IOException {
        throw new IOException("Not supported");
    }

    /**
     * Convenience method, so that we don't open a new connection when using this method from within
     * another method. Otherwise every API invocation incurs the overhead of opening/closing a TCP
     * connection.
     *
     * @throws IOException on IO problems other than FileNotFoundException
     */
    private boolean exists(FTPClient client, Path file) throws IOException {
        try {
            return getFileStatus(client, file) != null;
        } catch (FileNotFoundException fnfe) {
            LOG.debug("File does not exist: " + file, fnfe);
            return false;
        }
    }

View on GitHub (pinned to cf67b549a7)