Similar to software bugs, configuration errors are also one of the major causes of today's system failures. Many configuration issues manifest themselves in ways similar to software bugs such as crashes, hangs, silent failures. It leaves users clueless and forced to report to developers for technical support, wasting not only users' but also developers' precious time and effort. Unfortunately, unlike software bugs, many software developers take a much less active, responsible role in handling configuration errors because "they are users' faults."This paper advocates the importance for software developers to take an active role in handling misconfigurations. It also makes a concrete first step towards this goal by providing tooling support to help developers improve their configuration design, and harden their systems against configuration errors. Specifically, we build a tool, called SPEX, to automatically infer configuration requirements (referred to as constraints) from software source code, and then use the inferred constraints to: (1) expose misconfiguration vulnerabilities (i.e., bad system reactions to configuration errors such as crashes, hangs, silent failures); and (2) detect certain types of errorprone configuration design and handling.We evaluate SPEX with one commercial storage system and six open-source server applications. SPEX automatically infers a total of 3800 constraints for more than 2500 configuration parameters. Based on these constraints, SPEX further detects 743 various misconfiguration vulnerabilities and at least 112 error-prone constraints in the latest versions of the evaluated systems. To this day, 364 vulnerabilities and 80 inconsistent constraints have been confirmed or fixed by developers after we reported them. Our results have influenced the Squid Web proxy project to improve its configuration parsing library towards a more user-friendly design.
The paper briefly presents some essential concepts and features of light fields with strong spatial inhomogeneity of amplitude, phase, polarization, and other parameters. It contains a characterization of optical vortices, speckle fields, polarization singularities. A special attention is paid to the field dynamical characteristics (energy, momentum, angular momentum, and their derivatives), which are considered not only as mechanical attributes of the field but also as its meaningful and application-oriented descriptive parameters. Peculiar features of the light dynamical characteristics in inhomogeneous and dispersive media are discussed. The dynamical properties of paraxial beams and evanescent waves (including surface plasmon-polaritons) are analyzed in more detail; in particular, a general treatment of the extraordinary spin and momentum, orthogonal to the main propagation direction, is outlined. Applications of structured light fields for optical manipulation, metrology, probing, and data processing are described.
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