signalapp/Signal-Server · error · FieldValidationException

string length is [ ] but expected to be one of

Error message

string length is [%d] but expected to be one of %s

What it means

ExactlySizeFieldValidator.validateStringValue checks that a proto string field's length is one of the permitted sizes. If not, it throws FieldValidationException with the actual length and allowed sizes in the message.

Solutions

1. Truncate or otherwise conform the string to one of the lengths listed in the error message
2. Check whether you should be sending base64url rather than hex (or vice versa) — different lengths for the same data
3. Validate string length client-side before building the request
4. Empty string may be the issue: confirm the value is present

Example fix

// before
String deviceId = Hex.toStringCondensed(uuidBytes); // 64 chars
// after
String deviceId = uuid.toString(); // 36 chars, matches permitted size

if (!permittedSizes.contains(value.length())) {
  throw new IllegalArgumentException("expected string length in " + permittedSizes + ", got " + value.length());
}

try {
  grpcStub.call(request);
} catch (StatusRuntimeException e) {
  if (e.getStatus().getCode() == Code.INVALID_ARGUMENT && e.getStatus().getDescription().contains("string length")) {
    // adjust encoding (hex vs base64url) or truncate to permitted size
  }
}

When it happens

Trigger: gRPC requests with string fields (e.g. device names, tokens, encoded identifiers) annotated with exact-size validation whose character count isn't in permittedSizes — e.g. deviceName longer than 50 chars, or a token of unexpected length.

Common situations: Client sending empty strings where a fixed-length token is required; localized names/IDs that exceed the configured length; encoders producing variable-length output (hex vs base64) for the same underlying data.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

• byte array length is
• list size is [ ] but expected to be one of
• 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/becd4555a3f8c49e. Report an issue: GitHub.

Appendix: source

Thrown at service/src/main/java/org/whispersystems/textsecuregcm/grpc/validators/ExactlySizeFieldValidator.java:45

  @Override
  protected void validateBytesValue(
      final Set<Integer> permittedSizes,
      final ByteString fieldValue) throws FieldValidationException {
    if (permittedSizes.contains(fieldValue.size())) {
      return;
    }
    throw new FieldValidationException("byte array length is [%d] but expected to be one of %s".formatted(fieldValue.size(), permittedSizes));
  }

  @Override
  protected void validateStringValue(
      final Set<Integer> permittedSizes,
      final String fieldValue) throws FieldValidationException {
    if (permittedSizes.contains(fieldValue.length())) {
      return;
    }
    throw new FieldValidationException("string length is [%d] but expected to be one of %s".formatted(fieldValue.length(), permittedSizes));
  }

  @Override
  protected void validateRepeatedField(
      final Set<Integer> permittedSizes,
      final Descriptors.FieldDescriptor fd,
      final List<?> repeated) throws FieldValidationException {
    if (permittedSizes.contains(repeated.size())) {
      return;
    }
    throw new FieldValidationException("list size is [%d] but expected to be one of %s".formatted(repeated.size(), permittedSizes));
  }
}

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