Sequences Of Method Calls Research Articles

A Java typestate checker supporting inheritance

Detecting programming errors in software is increasingly important, and building tools that help developers with this task is a crucial area of investigation on which the industry depends. Leveraging on the observation that in Object-Oriented Programming ( OOP ) it is natural to define stateful objects where the safe use of methods depends on their internal state, we present Java Typestate Checker ( JATYC ), a tool that verifies Java source code with respect to typestates. A typestate defines the object's states, the methods that can be called in each state, and the states resulting from the calls. The tool statically verifies that when a Java program runs: sequences of method calls obey to object's protocols; objects' protocols are completed; null-pointer exceptions are not raised; subclasses' instances respect the protocol of their superclasses. To the best of our knowledge, this is the first OOP tool that simultaneously tackles all these aspects. • Java Typestate Checker is a tool that verifies Java code with respect to typestates. • It verifies that sequences of method calls obey to object's protocols. • It verifies that objects' protocols are completed. • It verifies that null-pointer exceptions are not raised. • It verifies that subclasses' instances respect the protocol of their superclasses.

Fine-Grained Software Defect Prediction Based on the Method-Call Sequence.

Currently, software defect-prediction technology is being extensively researched in the design of metrics. However, the research objects are mainly limited to coarse-grained entities such as classes, files, and packages, and there is a wide range of defects that are difficult to predict in actual situations. To further explore the information between sequences of method calls and to learn the code semantics and syntactic structure between methods, we generated a method-call sequence that retains the code context structure information and the token sequence representing semantic information. We embedded the token sequence into the method-call sequence and encoded it into a fixed-length real-valued vector. We then built a defect-prediction model based on the transformer, which maps the code-vector representation containing the method-call sequences to a low-dimensional vector space to generate semantic features and syntactic structure features and also predicts the defect density of the method-call sequence. We conducted experiments on 10 open-source projects using the ELFF dataset. The experimental results show that the method-call sequence-level prediction effect is better than the class-level effect, and the prediction results are more stable than those of the method level. The mean absolute error (MAE) value of our approach was 8% lower than that of the other deep-learning methods.

C4: verified transactional objects

Transactional objects combine the performance of classical concurrent objects with the high-level programmability of transactional memory. However, verifying the correctness of transactional objects is tricky, requiring reasoning simultaneously about classical concurrent objects, which guarantee the atomicity of individual methods—the property known as linearizability—and about software-transactional-memory libraries, which guarantee the atomicity of user-defined sequences of method calls—or serializability. We present a formal-verification framework called C4, built up from the familiar notion of linearizability and its compositional properties, that allows proof of both kinds of libraries, along with composition of theorems from both styles to prove correctness of applications or further libraries. We apply the framework in a significant case study, verifying a transactional set object built out of both classical and transactional components following the technique of transactional predication ; the proof is modular, reasoning separately about the transactional and nontransactional parts of the implementation. Central to our approach is the use of syntactic transformers on interaction trees —i.e., transactional libraries that transform client code to enforce particular synchronization disciplines. Our framework and case studies are mechanized in Coq.

Search‐based crash reproduction using behavioural model seeding

SummarySearch‐based crash reproduction approaches assist developers during debugging by generating a test case, which reproduces a crash given its stack trace. One of the fundamental steps of this approach is creating objects needed to trigger the crash. One way to overcome this limitation is seeding: using information about the application during the search process. With seeding, the existing usages of classes can be used in the search process to produce realistic sequences of method calls, which create the required objects. In this study, we introduce behavioural model seeding: a new seeding method that learns class usages from both the system under test and existing test cases. Learned usages are then synthesized in a behavioural model (state machine). Then, this model serves to guide the evolutionary process. To assess behavioural model seeding, we evaluate it against test seeding (the state‐of‐the‐art technique for seeding realistic objects) and no seeding (without seeding any class usage). For this evaluation, we use a benchmark of 122 hard‐to‐reproduce crashes stemming from six open‐source projects. Our results indicate that behavioural model seeding outperforms both test seeding and no seeding by a minimum of 6% without any notable negative impact on efficiency.

Program synthesis with algebraic library specifications

A key challenge in program synthesis is synthesizing programs that use libraries, which most real-world software does. The current state of the art is to model libraries with mock library implementations that perform the same function in a simpler way. However, mocks may still be large and complex, and must include many implementation details, both of which could limit synthesis performance. To address this problem, we introduce JLibSketch, a Java program synthesis tool that allows library behavior to be described with algebraic specifications, which are rewrite rules for sequences of method calls, e.g., encryption followed by decryption (with the same key) is the identity. JLibSketch implements rewrite rules by compiling JLibSketch problems into problems for the Sketch program synthesis tool. More specifically, after compilation, library calls are represented by abstract data types (ADTs), and rewrite rules manipulate those ADTs. We formalize compilation and prove it sound and complete if the rewrite rules are ordered and non-unifiable. We evaluated JLibSketch by using it to synthesize nine programs that use libraries from three domains: data structures, cryptography, and file systems. We found that algebraic specifications are, on average, about half the size of mocks. We also found that algebraic specifications perform better than mocks on seven of the nine programs, sometimes significantly so, and perform equally well on the last two programs. Thus, we believe that JLibSketch takes an important step toward synthesis of programs that use libraries.

Typechecking protocols with Mungo and StMungo: A session type toolchain for Java

Static typechecking is an important feature of many standard programming languages. However, static typing focuses on data rather than communication, and therefore does not help programmers correctly implement communication protocols in distributed systems. The theory of session types provides a basis for tackling this problem; we use it to develop two tools that support static typechecking of communication protocols in Java. The first tool, Mungo, extends Java with typestate definitions, which allow classes to be associated with state machines defining permitted sequences of method calls: for example, communication methods. The second tool, StMungo, takes a session type describing a communication protocol, and generates a typestate specification of the permitted sequences of messages in the protocol. Protocol implementations can be validated by Mungo against their typestate definitions and then compiled with a standard Java compiler. The result is a toolchain for static typechecking of communication protocols in Java. We formalise and prove soundness of the typestate inference system used by Mungo, and show that our toolchain can be used to typecheck a client for the standard Simple Mail Transfer Protocol (SMTP).

GK-Tail+ An Efficient Approach to Learn Software Models

Inferring models of program behavior from execution samples can provide useful information about a system, also in the increasingly common case of systems that evolve and adapt in their lifetime, and without requiring large developers’ effort. Techniques for learning models of program behavior from execution traces shall address conflicting challenges of recall, specificity and performance: They shall generate models that comprehensively represent the system behavior (recall) while limiting the amount of illegal behaviors that may be erroneously accepted by the model (specificity), and should infer the models within a reasonable time budget to process industrial scale systems (performance). In our early work, we designed GK-tail, an approach that can infer guarded finite state machines that model the behavior of object-oriented programs in terms of sequences of method calls and constraints on the parameter values. GK-tail addresses well two of the three main challenges, since it infers guarded finite state machines with a high level of recall and specificity, but presents severe limitations in terms of performance that reduce its scalability. In this paper, we present GK-tail+, a new approach to infer guarded finite state machines from execution traces of object-oriented programs. GK-tail+ proposes a new set of inference criteria that represent the core element of the inference process: It largely reduces the inference time of GK-tail while producing guarded finite state machines with a comparable level of recall and specificity. Thus, GK-tail+ advances the preliminary results of GK-tail by addressing all the three main challenges of learning models of program behavior from execution traces.

Component-based synthesis for complex APIs

Component-based approaches to program synthesis assemble programs from a database of existing components, such as methods provided by an API. In this paper, we present a novel type-directed algorithm for component-based synthesis. The key novelty of our approach is the use of a compact Petri-net representation to model relationships between methods in an API. Given a target method signature S, our approach performs reachability analysis on the underlying Petri-net model to identify sequences of method calls that could be used to synthesize an implementation of S. The programs synthesized by our algorithm are guaranteed to type check and pass all test cases provided by the user. We have implemented this approach in a tool called SyPet, and used it to successfully synthesize real-world programming tasks extracted from on-line forums and existing code repositories. We also compare SyPet with two state-of-the-art synthesis tools, namely InSynth and CodeHint, and demonstrate that SyPet can synthesize more programs in less time. Finally, we compare our approach with an alternative solution based on hypergraphs and demonstrate its advantages.

Modular session types for objects

Session types allow communication protocols to be specified type-theoretically so that protocol implementations can be verified by static type checking. We extend previous work on session types for distributed object-oriented languages in three ways. (1) We attach a session type to a class definition, to specify the possible sequences of method calls. (2) We allow a session type (protocol) implementation to be modularized, i.e. partitioned into separately-callable methods. (3) We treat session-typed communication channels as objects, integrating their session types with the session types of classes. The result is an elegant unification of communication channels and their session types, distributed object-oriented programming, and a form of typestate supporting non-uniform objects, i.e. objects that dynamically change the set of available methods. We define syntax, operational se-mantics, a sound type system, and a sound and complete type checking algorithm for a small distributed class-based object-oriented language with structural subtyping. Static typing guarantees that both sequences of messages on channels, and sequences of method calls on objects, conform to type-theoretic specifications, thus ensuring type-safety. The language includes expected features of session types, such as delegation, and expected features of object-oriented programming, such as encapsulation of local state.

Instance Generator and Problem Representation to Improve Object Oriented Code Coverage

Search-based approaches have been extensively applied to solve the problem of software test-data generation. Yet, test-data generation for object-oriented programming (OOP) is challenging due to the features of OOP, e.g., abstraction, encapsulation, and visibility that prevent direct access to some parts of the source code. To address this problem we present a new automated search-based software test-data generation approach that achieves high code coverage for unit-class testing. We first describe how we structure the test-data generation problem for unit-class testing to generate relevant sequences of method calls. Through a static analysis, we consider only methods or constructors changing the state of the class-under-test or that may reach a test target. Then we introduce a generator of instances of classes that is based on a family of means-of-instantiation including subclasses and external factory methods. It also uses a seeding strategy and a diversification strategy to increase the likelihood to reach a test target. Using a search heuristic to reach all test targets at the same time, we implement our approach in a tool, JTExpert, that we evaluate on more than a hundred Java classes from different open-source libraries. JTExpert gives better results in terms of search time and code coverage than the state of the art, EvoSuite, which uses traditional techniques.

On piggyback runtime monitoring of object-oriented programs

A runtime monitor enforcing a constraint on sequences of method calls on an object involves the implementation of an independent piece of code called a monitor. This monitor intercepts relevant events in the program and must keep track of the state of the sequence by updating an appropriate state machine. The present paper stems from the observation that an object's member fields must already contain an encoding of that state machine and that a monitor essentially duplicates operations that the object performs internally. Rather than maintaining a state machine in parallel, the paper puts forward the concept of "piggyback" runtime monitoring, where the monitor relies as much as possible on the object's own state variables to perform its task. Experiments on real-world benchmarks show that this approach greatly simplifies the monitoring process and drastically reduces the incurred runtime overhead compared to classical solutions.

Code completion with statistical language models

We address the problem of synthesizing code completions for programs using APIs. Given a program with holes, we synthesize completions for holes with the most likely sequences of method calls. Our main idea is to reduce the problem of code completion to a natural-language processing problem of predicting probabilities of sentences. We design a simple and scalable static analysis that extracts sequences of method calls from a large codebase, and index these into a statistical language model. We then employ the language model to find the highest ranked sentences, and use them to synthesize a code completion. Our approach is able to synthesize sequences of calls across multiple objects together with their arguments. Experiments show that our approach is fast and effective. Virtually all computed completions typecheck, and the desired completion appears in the top 3 results in 90% of the cases.

Monitoring method call sequences using annotations

In this paper we introduce JMSeq, a Java-based tool for monitoring sequences of method calls. JMSeq provides a simple but expressive language to specify the observables of a Java program in terms of sequences of possibly nested method calls. Similar to many monitoring-oriented environments, verification in JMSeq is done at runtime; unlike all other approaches based on aspect-oriented programming, JMSeq uses code annotation rather than instrumentation, and therefore is suitable for component-based software verification.

Enabledness-based program abstractions for behavior validation

Code artifacts that have nontrivial requirements with respect to the ordering in which their methods or procedures ought to be called are common and appear, for instance, in the form of API implementations and objects. This work addresses the problem of validating if API implementations provide their intended behavior when descriptions of this behavior are informal, partial, or nonexistent. The proposed approach addresses this problem by generating abstract behavior models which resemble typestates. These models are statically computed and encode all admissible sequences of method calls. The level of abstraction at which such models are constructed has shown to be useful for validating code artifacts and identifying findings which led to the discovery of bugs, adjustment of the requirements expected by the engineer to the requirements implicit in the code, and the improvement of available documentation.

Handling test length bloat

SUMMARYThe length of test cases is a little investigated topic in search‐based test generation for object‐oriented software, where test cases are sequences of method calls. Although intuitively longer tests can achieve higher overall code coverage, there is always the threat of bloat – a complex phenomenon in evolutionary computation, where the length abnormally grows over time. In this paper, we show that bloat indeed also occurs in the context of test generation for object‐oriented software. We present different techniques to overcome the problem of length bloat, and evaluate all possible combinations of these techniques using different starting lengths for the search. Experiments on a set of difficult search targets, selected from several open source and industrial projects, show that controlling bloat with the appropriate techniques can significantly improve the search performance. Copyright © 2013 John Wiley & Sons, Ltd.

Modular session types for distributed object-oriented programming

Session types allow communication protocols to be specified type-theoretically so that protocol implementations can be verified by static type-checking. We extend previous work on session types for distributed object-oriented languages in three ways. (1) We attach a session type to a class definition, to specify the possible sequences of method calls. (2) We allow a session type (protocol) implementation to be modularized , i.e. partitioned into separately-callable methods. (3) We treat session-typed communication channels as objects, integrating their session types with the session types of classes. The result is an elegant unification of communication channels and their session types, distributed object-oriented programming, and a form of typestates supporting non-uniform objects, i.e. objects that dynamically change the set of available methods. We define syntax, operational semantics, a sound type system, and a correct and complete type checking algorithm for a small distributed class-based object-oriented language. Static typing guarantees that both sequences of messages on channels, and sequences of method calls on objects, conform to type-theoretic specifications, thus ensuring type-safety. The language includes expected features of session types, such as delegation, and expected features of object-oriented programming, such as encapsulation of local state. We also describe a prototype implementation as an extension of Java.

Specifying and checking method call sequences of Java programs

In a pre and postcondition-style specification, it is difficult to specify the allowed sequences of method calls, referred to as protocols. The protocols are essential properties of reusable object-oriented classes and application frameworks, and the approaches based on the pre and postconditions, such as design by contracts (DBC) and formal behavioral interface specification languages (BISL), are being accepted as a practical and effective tool for describing precise interfaces of (reusable) program modules. We propose a simple extension to the Java Modeling Language (JML), a BISL for Java, to specify protocol properties in an intuitive and concise manner. The key idea of our approach is to separate protocol properties from functional properties written in pre and post-conditions and to specify them in a regular expression-like notation. The semantics of our extension is formally defined and provides a foundation for implementing runtime checks. Case studies have been performed to show the effectiveness our approach. We believe that our approach can be adopted by other BISLs.

Embryonic object versus mature object

Traditional approaches to object-oriented style emphasize classes with a basic set of constructors and a minimal set of methods that when combined permit the full potential of the instance objects to be realized. This object-oriented style is probably modeled on the style used in mathematics and logic to develop a system based on a minimal set of axioms and operations. The consequences of this style both in practice and in pedagogy are that objects enter into existence in an embryonic state and must be nurtured to maturity by a sequence of method calls that tweak behavior and/or add data. Although this minimalist approach is useful in the first stages of teaching objects and in exploratory design, we suggest that most designs should evolve towards building classes with a rich set of constructors and methods so that the instance objects may be born mature , that is, ready to use in the program without further tweaking. In particular, we believe that if students are taught to design in this manner, then they will be more effective both as students and as computing professionals.The ideas in this article have developed from our experience in designing the Java Power Tools (JPT) and in applying these tools to build many labs and demo programs. We found that using the traditional minimalist design approach hindered our ability to rapidly develop interesting applications. Gradually, we evolved both the tools and the examples to be far richer and have found that our development time has been dramatically reduced. We believe that those who teach objects may be interested in these principles even if they choose to work with entirely different tools and examples.

Automatic component protocol adaptation with the CoConut/J tool suite

While industrial middleware platforms such as CORBA, EJB, or .NET facilitate the development of distributed applications by providing certain infra-structural services required in many distributed systems (such as name services, remote method calls, parameter marshalling, etc.), these industrial platforms fail to support the development of distributed systems with independent components. In particular, their component models do not provide sufficient information for component interoperability checks or automated component adaptation. Especially when considering the personal and institutional separation between component developer and component vendor as one of the prerequisites of an independent component market, finding automatically as many component interoperability errors as possible is crucial. Hence, it is of practical concern that component interfaces not only model the correct way of calling the single methods but also the valid sequences of method calls. Likewise, practice clearly shows that component reuse usually requires component adaptation. This directly shows that only detecting incompatibilities is of limited use, but advocates for techniques of automated component adaptation.In this paper we describe algorithms and tools for specifying and analysing component interfaces in order to check interoperability and to generate adapted component interfaces automatically. Therefore, we introduce the concept of parameterised contracts and a new component interface model.

정적 분석을 이용한 알려지지 않은 악성 스크립트 감지

정적 휴리스틱 분석은 알려지지 않은 악성 코드를 감지하는데 널리 사용되는 기법으로, 악성 코드에 보편적으로 존재하는 코드 조각들을 탐색하여 대상 코드의 악성 여부를 판단한다. 그러나, 스크립트로 작성된 악성 코드에서는 정형화된 코드 조각들을 찾아내기 어려우므로, 특정한 메소드 호출들의 존재만을 검사하는 것이 보편적이다. 이러한 감지 방식은 높은 감지 오류율을 보이게 되는데, 이는 많은 메소드들이 일반 스크립트에서도 빈번하게 사용될 수 있는 것들임에 기인한다. 따라서, 현재 정적 휴리스틱 분석은 일반 스크립트에서 거의 사용되지 않는 특별한 메소드 호출들로 이루어진 악성 행위만을 감지하는데 제한적으로 사용되고 있다. 본 논문에서는 메소드 호출 뿐 아니라 이에 관련된 파라미터와 리턴 값까지 고려하여 악성 행위 패턴을 정확하게 감지함으로써 이러한 단점을 극복할 수 있는 정적 분석 기법을 제안하고 그 구현을 제시한다. 또한, 구현된 시스템 상에서의 실험을 통해, 높은 긍정 오류 때문에 기존 기법의 적용이 어려웠던 악성 행위가 제안된 기법으로 감지될 수 있음을 보인다. Analyzing the code using static heuristics is a widely used technique for detecting unknown malicious codes. It decides the maliciousness of a code by searching for some fragments that had been frequently found in known malicious codes. However, in script codes, it tries to search for sequences of method calls, not code fragments, because finding such fragments is much difficult. This technique makes many false alarms because such method calls can be also used in normal scripts. Thus, static heuristics for scripts are used only to detect malicious behavior consisting of specific method calls which is seldom used in normal scripts. In this paper. we suggest a static analysis that can detect malicious behavior more accurately, by concerning not only the method calls but also parameters and return values. The result of experiments show that malicious behaviors, which were difficult to detect by previous works, due to high false positive, will be detected by our method.