signalapp/Signal-Server · error · FieldValidationException

byte array expected to be non-empty

Error message

byte array expected to be non-empty

What it means

NonEmptyFieldValidator.validateBytesValue rejects empty ByteString fields. If the bytes field is empty, it throws FieldValidationException('byte array expected to be non-empty'), enforcing that required binary fields carry data.

Solutions

1. Ensure the byte array is generated/loaded (non-zero length) before placing it in the request
2. Check client-side: if the field is genuinely optional, don't set the field at all rather than setting empty bytes
3. Verify the key-generation step didn't fail silently and return an empty array
4. Log/inspect the value on the client to confirm non-empty content before sending

Example fix

// before
byte[] backupKey = new byte[0];
request.setBackupKey(ByteString.copyFrom(backupKey));
// after
if (backupKey.length > 0) {
  request.setBackupKey(ByteString.copyFrom(backupKey));
}

if (bytes == null || bytes.length == 0) {
  throw new IllegalArgumentException("required byte field must be non-empty");
}

static boolean isNonEmpty(ByteString b) { return b != null && !b.isEmpty(); }

try {
  grpcStub.call(request);
} catch (StatusRuntimeException e) {
  if (e.getStatus().getCode() == Code.INVALID_ARGUMENT && e.getStatus().getDescription().contains("non-empty")) {
    // generate/load the missing key material and retry
  }
}

When it happens

Trigger: gRPC requests where a bytes field (e.g. profile key, backup key, storage manifest) is present but zero-length — typically because the client passed a new byte[0] or an unset/empty value.

Common situations: Client code generating keys before they are ready (no key material available yet); failing to check a byte array before encoding; proto fields defaulting to empty bytes when not explicitly set.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• byte array length is
• field value is [ ] but expected to be within the [ , ] range
• value is not valid base64 url
• value is not in E164 format
• enum field must be specified

AI-assisted analysis of signalapp/Signal-Server@100ab61c82 (2026-09-09). Data as JSON: /api/errors/6f86a78856890b96. Report an issue: GitHub.

Appendix: source

Thrown at service/src/main/java/org/whispersystems/textsecuregcm/grpc/validators/NonEmptyFieldValidator.java:35

    super("nonEmpty", Set.of(
        Descriptors.FieldDescriptor.Type.STRING,
        Descriptors.FieldDescriptor.Type.BYTES
    ), MissingOptionalAction.FAIL, true);
  }

  @Override
  protected Boolean resolveExtensionValue(final Object extensionValue) throws FieldValidationException {
    return requireFlagExtension(extensionValue);
  }

  @Override
  protected void validateBytesValue(
      final Boolean extensionValue,
      final ByteString fieldValue) throws FieldValidationException {
    if (!fieldValue.isEmpty()) {
      return;
    }
    throw new FieldValidationException("byte array expected to be non-empty");
  }

  @Override
  protected void validateStringValue(
      final Boolean extensionValue,
      final String fieldValue) throws FieldValidationException {
    if (StringUtils.isNotEmpty(fieldValue)) {
      return;
    }
    throw new FieldValidationException("string expected to be non-empty");
  }

  @Override
  protected void validateRepeatedField(
      final Boolean extensionValue,
      final Descriptors.FieldDescriptor fd,
      final List<?> repeated) throws FieldValidationException {
    if (repeated.size() > 0) {

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