What WebSocket is, in plain terms
WebSocket is a communication method that keeps a two-way connection open between a client and a server. Once the connection is established, both sides can send messages without repeatedly opening new requests. In many trading or market-data contexts, WebSocket is used to receive streaming updates.
A common mistake is treating WebSocket as “a guarantee of fresh, complete, ordered data.” The protocol provides a persistent channel, but it does not automatically make the content you receive accurate, timely, or suitable for a specific calculation.
How common mistakes happen (and what they can affect)
1) Confusing connection health with data quality
People often check only whether the connection “is up,” then assume the data is usable. In reality, you may still receive incomplete updates, delayed messages, or messages that no longer match your expectations. Connection state and message semantics are related but not identical.
Material consequence: downstream logic can compute results from stale or mismatched information.
2) Assuming message ordering and completeness
Another misunderstanding is expecting that messages always arrive in the same order as they were produced, or that you will always receive a complete sequence. Network behavior, server load, reconnection, and resubscription can create gaps.
Material consequence: client-side state can drift, especially if it applies updates incrementally without recovery.
3) Rigid parsing and “format confidence”
WebSocket payloads are typically encoded as JSON or another structured format. A frequent mistake is writing parsers that assume fields are always present, that types never change, or that one message type always looks like another. When a provider adds a field, omits one, or sends an error/heartbeat differently, rigid code may fail silently or misinterpret content.
Material consequence: incorrect state updates or repeated crashes.
4) Subscription mistakes and wrong filtering
Many systems use subscriptions (for example, selecting symbols, channels, or message categories). A common error is assuming the server is sending what you asked for, without validating subscription confirmations and verifying that incoming messages match the intended scope.
Material consequence: you may process unrelated updates or miss the updates you need.
5) Reconnection logic that doesn’t restore state
WebSocket clients often reconnect after a disconnect, but forget that reconnection usually requires resynchronizing state. If you resume from your previous in-memory values without a recovery step, gaps can remain.
Material consequence: persistent errors that are hard to detect because the connection looks healthy.
Limitations and risks to keep in mind
- Timing is variable. Even with a live connection, delivery timing can fluctuate; therefore, calculations based on arrival time can be misleading.
- Historical behavior doesn’t ensure future results. If a feed seemed consistent before, that does not prove it will stay consistent.
- Provider and network conditions vary. Costs, execution behavior in connected systems, and jurisdiction-specific constraints can change outcomes even when the WebSocket layer is unchanged.
- No single message is necessarily trustworthy alone. Without validation checks, one unexpected payload can corrupt your local state.
Neutral checks you can perform independently
Use a control-style checklist to avoid confirmation bias:
- Define assumptions: What does “fresh” mean for your use case (for example, “received within X seconds”)? If X is not defined, you cannot test it.
- Validate semantics: Confirm message types, required fields, and how errors/heartbeats are represented.
- Test failure modes: Simulate disconnects, slow networks, and malformed messages to see whether your client recovers safely.
- Verify subscription scope: Log the subscription request and confirm that received messages match your intended symbols and channels.
- Track sequence/gaps if available: If your payloads include sequence identifiers or timestamps, detect missing ranges and decide how to resync.
A “finished” WebSocket setup is not just one that stays connected. It is one that can explain what data it is receiving, what assumptions it depends on, and how it behaves when those assumptions fail.