Function validate_upload 

pub fn validate_upload(
    filename: Option<&str>,
    content: &[u8],
    expected_format: FileFormat,
) -> Result<Option<String>, ValidationError>

Comprehensive input validation combining filename and content checks

Performs complete security validation for file uploads:

• Filename sanitization and security checks
• File format validation via magic numbers
• Content integrity validation

Errors

Returns a ValidationError if filename validation fails, the file format doesn’t match the expected format, or content validation fails.