Normalize router paths by removing leading slashes

[apapacy]

PR: Normalize router paths by removing leading slashes

Summary

Fixed an issue in the router where filename:join/1 was incorrectly processing paths due to a persistent leading slash. Previously, the leading slash caused the function to treat the segment as an absolute path, effectively discarding the base directory.

The Problem

In Erlang, filename:join/1 has a specific behavior: if an element in the list starts with a directory separator (a leading slash), it is treated as an absolute path. This causes filename:join to ignore all preceding elements in the list.

Example of the bug:

%% If LocalPath is "/static/item.png"
filename:join(["/app/priv", "/static/item.png"]).
%% Result: "/static/item.png" (The "/app/priv" part is lost)

Because of this, the logic was unintentionally biased towards the LocalPath value, bypasssing the intended directory nesting.

Changes

• Implemented leading slash removal for incoming path segments before joining.
• Utilized string:trim(Path, leading, "/") (or pattern matching) to ensure the path is treated as relative to the application's priv_dir.

Impact

• Current Logic: This change has no immediate negative impact on existing functionality, as the resolved paths still point to the correct files in the current environment.
• Future Proofing: This is a preemptive fix. It ensures that future code changes—such as shifting base directories, adding nested prefixes, or modifying how priv_dir is structured—will behave predictably. It resolves a "silent bug" before it becomes a breaking issue.

Technical Notes

By normalizing the path to a relative string, filename:join now correctly concatenates the segments:

%% After fix:
filename:join(["/app/priv", "static/item.png"]).
%% Result: "/app/priv/static/item.png" (Correct)

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Key terms used:

• Leading slash: Слэш на початку рядка.
• Preemptive fix: Виправлення "наперед" (профілактичне).
• Predictably: Передбачувано.
• Discarding: Відкидання (ігнорування) частини шляху.