What causes "${className} does not support positioned readFully." in apache/hadoop?

Use seek() plus sequential readFully when the stream is Seekable

apache/hadoop · error · UnsupportedOperationException

does not support positioned readFully.

Error message

${className} does not support positioned readFully.

What it means

The byte[] positioned readFully on CryptoInputStream requires `in instanceof PositionedReadable`. If the wrapped stream supports only sequential reads, UnsupportedOperationException naming the wrapped class is thrown up front, before any decryption happens.

Solutions

Use seek() plus sequential readFully when the stream is Seekable
Wrap the source stream in a PositionedReadable implementation before building the CryptoInputStream
Catch UnsupportedOperationException and use a sequential copy strategy

Example fix

// before
cryptoIn.readFully(pos, buf, 0, len); // UOE without PositionedReadable

// after
try {
  cryptoIn.readFully(pos, buf, 0, len);
} catch (UnsupportedOperationException e) {
  cryptoIn.seek(pos);
  IOUtils.readFully(cryptoIn, buf, 0, len);
}

Defensive patterns

Strategy: try-catch

Try / catch

try {
  in.readFully(pos, buf, off, len);
} catch (UnsupportedOperationException e) {
  in.seek(pos);
  IOUtils.readFully(in, buf, off, len);
}

Prevention

Do not assume FSDataInputStream positional APIs work on every FileSystem; probe once per filesystem type and cache the result
Prefer seek+sequential reads in reader loops that already track a current offset
For custom streams, implement PositionedReadable so wrapped/encrypted views inherit the capability

When it happens

Trigger: readFully(position, buffer, offset, length) on a CryptoInputStream wrapping a non-PositionedReadable stream — e.g. wrapped local streams, some connector streams, or mocks.

Common situations: Split-based record readers doing positional readFully on encrypted files backed by incompatible stream types; libraries assuming every FSDataInputStream supports positional reads.

Related errors

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/e62d6c6fd8fbec64. Report an issue: GitHub.

Appendix: source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/crypto/CryptoInputStream.java:507

        } finally {
          localPadding = afterDecryption(localDecryptor, localInBuffer,
                                         filePosition + length, localIV);
        }
      }
    } finally {
      returnBuffer(localInBuffer);
      returnBuffer(localOutBuffer);
      returnDecryptor(localDecryptor);
    }
  }

  /** Positioned read fully. It is thread-safe */
  @Override
  public void readFully(long position, byte[] buffer, int offset, int length)
      throws IOException {
    checkStream();
    if (!(in instanceof PositionedReadable)) {
      throw new UnsupportedOperationException(in.getClass().getCanonicalName()
          + " does not support positioned readFully.");
    }
    ((PositionedReadable) in).readFully(position, buffer, offset, length);
    if (length > 0) {
      // This operation does not change the current offset of the file
      decrypt(position, buffer, offset, length);
    }
  }

  @Override
  public void readFully(long position, byte[] buffer) throws IOException {
    readFully(position, buffer, 0, buffer.length);
  }

  /** Seek to a position. */
  @Override
  public void seek(long pos) throws IOException {
    if (pos < 0) {

View on GitHub (pinned to 2add963021)