apache/beam · error · UnsupportedOperationException

AUTO is applicable only to reading files

Error message

AUTO is applicable only to reading files

What it means

Compression.AUTO only applies when reading (compression detection by extension). Its writeCompressed() therefore always throws UnsupportedOperationException, since there is no concrete codec to compress with when writing.

Solutions

1. Use a concrete compression for writing (GZIP, BZIP2, ZSTD, or UNCOMPRESSED).
2. Special-case AUTO in writing code by substituting UNCOMPRESSED or a detected/appropriate type.
3. Validate user-provided compression options at pipeline construction time and reject AUTO for sinks.

Example fix

// before
Compression.AUTO.writeCompressed(channel);
// after
Compression.GZIP.writeCompressed(channel);

if (compression == Compression.AUTO) {
  compression = Compression.UNCOMPRESSED; // or GZIP
}

try {
  out = compression.writeCompressed(channel);
} catch (UnsupportedOperationException e) {
  out = Compression.UNCOMPRESSED.writeCompressed(channel);
}

When it happens

Trigger: Calling Compression.AUTO.writeCompressed(channel) directly, or configuring a sink's write compression to AUTO (e.g., FileIO.write().withCompression(AUTO) reaching CompressionType.fromCanonical or the enum's write path).

Common situations: Reusing a read-side Compression value for writing; pipeline options where compression=AUTO was meant for reads but applied to an output sink.

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

• Must resolve compression into a concrete value before…
• Writing ZIP files is currently unsupported
• AUTO is not supported for writing
• Caller does not own the underlying input stream and should…
• Caller does not own the underlying output stream and…

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/247b43e642afc200. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/core/src/main/java/org/apache/beam/sdk/io/Compression.java:60

import org.apache.commons.compress.compressors.zstandard.ZstdCompressorOutputStream;

/** Various compression types for reading/writing files. */
@SuppressWarnings("ImmutableEnumChecker")
public enum Compression {
  /**
   * When reading a file, automatically determine the compression type based on filename extension.
   * Not applicable when writing files.
   */
  AUTO("") {
    @Override
    public ReadableByteChannel readDecompressed(ReadableByteChannel channel) {
      throw new UnsupportedOperationException(
          "Must resolve compression into a concrete value before calling readDecompressed()");
    }

    @Override
    public WritableByteChannel writeCompressed(WritableByteChannel channel) {
      throw new UnsupportedOperationException("AUTO is applicable only to reading files");
    }
  },

  /** No compression. */
  UNCOMPRESSED("") {
    @Override
    public ReadableByteChannel readDecompressed(ReadableByteChannel channel) {
      return channel;
    }

    @Override
    public WritableByteChannel writeCompressed(WritableByteChannel channel) {
      return channel;
    }
  },

  /** GZip compression. */
  GZIP(".gz", ".gz") {

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