kestra-io/kestra · error · IllegalArgumentException

Cannot import file of type

Error message

Cannot import file of type <type>

What it means

Thrown by HasSource.readSourceFile() when the uploaded file is neither a .yaml/.yml file nor a .zip archive. The import endpoint only accepts YAML flow files or ZIP archives of YAML files; any other extension (or no extension) is rejected with the offending type extracted from the filename. This guards the flow import API at the trust boundary.

Solutions

1. Convert the file to YAML (.yaml or .yml) before importing.
2. If importing multiple files, bundle them into a .zip archive of YAML files.
3. Verify the uploaded filename has the correct extension and is not sanitized away by a proxy.
4. Check that the multipart upload preserves the original filename.

Example fix

// before
import file: flow.json
// IllegalArgumentException: Cannot import file of type .json

// after
import file: flow.yaml   // or bundle into flows.zip

String name = fileUpload.getFilename().toLowerCase();
boolean yaml = name.endsWith(".yaml") || name.endsWith(".yml");
boolean zip = name.endsWith(".zip");
if (!yaml && !zip) {
    throw new IllegalArgumentException("Cannot import file of type " + name);
}

try {
    HasSource.readSourceFile(protection, upload, reader);
} catch (IllegalArgumentException e) {
    return ResponseEntity.badRequest().body(Map.of("error", e.getMessage()));
}

When it happens

Trigger: Uploading a .json, .txt, .csv, or extensionless file to a flow import endpoint; uploading a .tar or .gz archive that is not a zip; a misconfigured client sending the wrong Content-Type or filename.

Common situations: User exports a flow as JSON and tries to import it; drag-and-drop of a non-YAML file in the UI; a CI script uploads the wrong artifact.

Related errors

• File type not allowed. Accepted extensions
• Invalid `files` properties with type
• The 'yaml' function expects an argument 'yaml'.
• The 'yaml' function expects an argument 'yaml' with type…
• Both `namespace` and `flowId` must be set when…

AI-assisted analysis of kestra-io/kestra@823fada927 (2026-08-14). Data as JSON: /api/errors/f4b4132daaae8e27. Report an issue: GitHub.

Appendix: source

Thrown at core/src/main/java/io/kestra/core/models/HasSource.java:92

                for (int i = 0; i < sources.size(); i++) {
                    String source = sources.get(i);
                    reader.accept(source, fileName + "(flow number: " + i + ")");
                }
            } else if (fileName.endsWith(".zip")) {

                try (ZipInputStream archive = ProtectedZipInputStream.of(inputStream, zipBombProtection)) {
                    ZipEntry entry;
                    while ((entry = archive.getNextEntry()) != null) {
                        if (entry.isDirectory() || !isYAML(entry.getName())) {
                            continue;
                        }
                        reader.accept(new String(archive.readAllBytes()), entry.getName());
                    }
                }
            } else {
                int extensionIndex = fileName.lastIndexOf('.');
                String type = extensionIndex >= 0 ? fileName.substring(extensionIndex) : fileName;
                throw new IllegalArgumentException("Cannot import file of type " + type);
            }
        }
    }

    private static boolean isYAML(final String fileName) {
        return fileName.endsWith(".yaml") || fileName.endsWith(".yml");
    }
}

View on GitHub (pinned to 823fada927)