Local port scan/communication connection confirmation tool | ZeroTools

In order to understand the operating status of ports in the local host space without using an external application, it is necessary to make full use of the native communication interface provided by the browser.

This system is equipped with a unique communication inference engine to achieve precise network diagnosis even under the constraints of the same origin policy.

The main communication verification method is a complex combination of the fetch application programming interface that handles asynchronous communication using the hypertext transfer protocol, web sockets that establish bidirectional communication, and the measurement of error latency caused by event handlers when loading images.

These are issued to specific Internet protocol addresses and local host domains, which are loopback addresses, and monitor the success or failure of requests to major well-known ports or alternative ports, as well as behavior when rejected.

For example, requests for these different protocol specifications are simultaneously sent to the port number on which a standard web server runs, the port number that listens for encrypted communication, and the port number occupied by open source databases and document-oriented databases, which are typical relational database management systems.

There is a slight difference in the arrival time of the transmission control protocol reset packet returned to the browser from the operating system's network stack depending on whether a particular port is listening for communication or when it is completely closed.

We have built an advanced mechanism to estimate the presence or absence of a daemon process in the background of the port by measuring the time difference between microseconds and milliseconds, that is, error latency, using a high-precision performance timer and applying statistical threshold processing.

Another important indicator for determining the operating status of a port is the determination of whether the intentionally set connection timeout in milliseconds has been exceeded and the differential analysis of the response patterns obtained from this.

A clear difference in behavior can be observed between when the target port is configured to silently drop socket connection requests from the browser and when it immediately returns a connection refusal signal.

In this algorithm, we intentionally create a race condition in asynchronous processing and utilize the timeout destruction of the promise object to accurately cut out the duration of the unresponsive state.

A port in a listening state tends to complete the connection process itself immediately by waiting for some data stream from the application layer or a handshake after connection establishment.

A non-working port, on the other hand, can result in either the connection not being established and either throwing an immediate error exception or being held up to a timeout limit.

The distribution data on this time axis is collected multiple times in succession, and only the pure communication response time is extracted after eliminating the effects of thread delays due to network fluctuations and browser engine garbage collection.

The extracted data group is matched with a predefined listening state profile model and a normalized score is calculated. A strict judgment logic is in place that confirms that the port is in the listening state only when this score exceeds a specified random variable, achieving state estimation that eliminates false positives to the utmost.

Local network environments are often operated on the assumption that they are protected from direct threats from the outside, but unprotected development services hidden inside and unintentionally opened backdoor ports pose serious security risks.

This tool provides developers with the ability to dynamically check and evaluate the security posture of private networks running on their own devices.

By executing a scan limited to the local loopback interface, it simulates vulnerability diagnosis within a secure closed network without leaking packets to the outside.

In particular, cache servers and in-memory data stores that are left running temporarily during development, or node processes that are waiting with a debugger attached, may allow privileged operations without an authentication mechanism.

By comprehensively scanning endpoints that can be a security blind spot and visualizing unintended port openings, developers can detect in advance the risk that their local environment will become a target of cross-site web socket hijacking or server-side request forgery from external malicious scripts, and take defensive measures such as modifying the bind address appropriately and applying firewall rules.

When performing a sensitive operation called a network scan, it is absolutely necessary to avoid sending data such as the environment information of the scan target and the opening/closing status of ports to an external server from the viewpoint of privacy and security.

This system employs a completely local processing architecture that completes all scan execution logic and result analysis within the client's browser environment.

When a user pulls the trigger to start a scan on the interface, asynchronous probe requests are generated in a web worker independent of the main thread and issued sequentially to each target local host port.

All measured latency data and timeout logs are kept only in the browser's volatile memory space and are never written to a persistent database or sent payloads to external application programming interfaces.

Rendering of analysis results is also done only by synchronizing the state through the virtual document object model, so all scan data is discarded without leaving a trace as soon as you end the session and close the tab.

As a result, the port scanner is designed to be able to be used safely without worrying about the risk of information leakage, even on business terminals where strict enterprise information management policies are applied, or in environments where top-secret development projects are underway.

The extracted local host network status is deployed on the user interface as a port status list table in an intuitive and analysis-optimized data grid format.

This list table not only simply enumerates the port number and the binary state of open/closed, but also comprehensively displays various metadata such as the average number of milliseconds required for a response, the type of probe protocol used, and the frequency of timeouts.

Furthermore, a core feature of this tool is built-in logic that automatically deduces the name of the service or daemon that is most likely to be running on that port based on the port number and response characteristic signature.

In addition to the official port assignment list established by the Internet Assigned Numbers Authority, it has its own database of port numbers that are bound by default to frameworks and container orchestration tools frequently used in modern web development.

For example, based on the combination of request behavior and port number, we can predict with high accuracy whether it is a front-end hot reloading server, a back-end application server, or a remote procedure call endpoint, and highlight it as a badge in a dedicated column of the table.

This allows users to intuitively understand the architectural configuration of the current development environment from a list of numbers.

In modern microservices architectures and environments where multiple containerized applications are developed in parallel, port conflicts can be a major impediment to development progress.

More than just a scanner, this tool serves as a practical investigative guide to help you verify connectivity with your local development server and troubleshoot port conflicts.

If an address already used error message is output when trying to start a specific service, the developer launches this tool and pinpoints the target port number to be scanned.

You can instantly visualize the existence of background processes occupying the port, and get clues to identify the application causing the conflict from the automatically estimated service name.

Furthermore, by using the range scan function that specifies a specific port range, you can grasp the free port area in advance and logically formulate a port allocation plan using environment variables and configuration files before starting multiple services.

Developers can seamlessly debug network layers on the browser, the platform they use every day, without having knowledge of advanced command line tools for deep networking, and gain powerful insights to maintain and build a stable development environment.