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Developer Fixes Chat App Bug That Falsely Marked Online Users as Offline

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A developer building a real-time chat application called ChatSphere discovered a presence-tracking bug when logging in as the same user across two browser tabs. The flaw occurred because the server tracked online status by socket ID rather than by username, so closing one tab removed the user from the online list even if they remained connected elsewhere. The fix involved mapping each username to a set of active socket connections, marking a user offline only when all their connections drop. The developer also identified a related vulnerability allowing clients to flood the server with messages unchecked, and addressed it with an in-memory sliding-window rate limiter. Both fixes highlight how multi-device usage represents normal behavior rather than an edge case in modern chat applications.

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Developer Fixes Chat App Bug That Falsely Marked Online Users as Offline · ShortSingh