What causes "Cannot process the URI %s: scheme not supported." in kestra-io/kestra?

Reference an internal storage object via its kestra:// URI (e.g. from outputs).

kestra-io/kestra · error · IllegalArgumentException

Cannot process the URI %s: scheme not supported.

Error message

Cannot process the URI %s: scheme not supported.

What it means

Thrown by the 'fileSize' function when the resolved URI scheme is not kestra://, file:// (local), or the namespace file scheme. It mirrors fileExists() but reads file attributes to return a size; the unsupported-scheme default branch throws IllegalArgumentException surfaced via getErrorMessage().

Source

Thrown at core/src/main/java/io/kestra/core/runners/pebble/functions/FileSizeFunction.java:40

    @Override
    protected Object fileFunction(EvaluationContext context, URI path, String namespace, String tenantId, Map<String, Object> args) throws IOException {
        return switch (path.getScheme()) {
            case StorageContext.KESTRA_SCHEME -> {
                FileAttributes fileAttributes = storageInterface.get().getAttributes(tenantId, namespace, path);
                yield fileAttributes.getSize();
            }
            case LocalPath.FILE_SCHEME -> {
                BasicFileAttributes fileAttributes = localPathFactory.get().createLocalPath().getAttributes(path);
                yield fileAttributes.size();
            }
            case Namespace.NAMESPACE_FILE_SCHEME -> {
                FileAttributes fileAttributes = namespaceFactory.get()
                    .of(tenantId, namespace, storageInterface.get())
                    .getFileMetadata(NamespaceFile.normalize(Path.of(path.getPath())));
                yield fileAttributes.getSize();
            }
            default -> throw new IllegalArgumentException(SCHEME_NOT_SUPPORTED_ERROR.formatted(path));
        };
    }

    @Override
    protected String getErrorMessage() {
        return ERROR_MESSAGE;
    }
}

View on GitHub (pinned to 823fada927)

Solutions

Reference an internal storage object via its kestra:// URI (e.g. from outputs).
Reference a namespace file using the namespace scheme, or a local file via file:// where supported.
For remote files, download into internal storage first, then call fileSize() on the resulting URI.

Example fix

# before
size: "{{ fileSize('s3://bucket/key') }}"
# after
size: "{{ fileSize(outputs.download.uri) }}"

Defensive patterns

Strategy: validation

Validate before calling

# Validate the scheme before calling fileSize().
# {{ (uri starts with 'kestra://' or uri starts with 'file://' or uri starts with 'namespace://') ? fileSize(uri) : null }}

Prevention

Pass only kestra://, file://, or namespace file URIs to fileSize().
Download remote files into internal storage before measuring size.
Reference outputs that resolve to internal storage URIs.
Do not use fileSize() for arbitrary remote URLs.

When it happens

Trigger: Passing fileSize() an external URL (http/https/s3/gs) or any URI whose scheme is not one of the three handled. Also triggered by a malformed URI whose scheme parses as null/empty.

Common situations: Treating fileSize() as a generic remote-file size checker; passing an output reference that resolved to a non-storage URI; misconfiguring a path expression so it resolves to a plain string.

Related errors

AI-assisted analysis of kestra-io/kestra@823fada927 (2026-08-14). Data as JSON: /api/errors/08baac08e876a867. Report an issue: GitHub.