WebSocket Keep-Alive #44611
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WebSocket Keep-Alive #44611
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dotnet-policy-service
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dotnet-fundamentals/svc
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antonfirsov
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Jan 29, 2025
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| 1. Keep-Alive is **OFF**, if | ||
| - `KeepAliveInterval` is `TimeSpan.Zero` or `Timeout.InfiniteTimeSpan` | ||
| 2. **Unsolicited PONG**, if | ||
| - `KeepAliveInterval` is a positive finite `TimeSpan`, -AND- | ||
| - `KeepAliveTimeout` is `TimeSpan.Zero` or `Timeout.InfiniteTimeSpan` | ||
| 3. **PING/PONG**, if | ||
| - `KeepAliveInterval` is a positive finite `TimeSpan`, -AND- | ||
| - `KeepAliveTimeout` is a positive finite `TimeSpan` |
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It would be better to use <xref> here instead of code blocks.
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| If you use `ClientWebSocket`, the default <xref:System.Net.WebSockets.ClientWebSocketOptions.KeepAliveInterval?displayProperty=nameWithType> value is <xref:System.Net.WebSockets.WebSocket.DefaultKeepAliveInterval?displayProperty=nameWithType> (typically 30 seconds). That means, `ClientWebSocket` has the Keep-Alive ON by default, with Unsolicited PONG as the default strategy. | ||
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| If you want to switch to the PING/PONG strategy, overriding <xref:System.Net.WebSockets.ClientWebSocketOptions.KeepAliveTimeout?displayProperty=nameWithType> is enough: |
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Would be good suggest that this is an implication of the behavior described before.
Suggested change
| If you want to switch to the PING/PONG strategy, overriding <xref:System.Net.WebSockets.ClientWebSocketOptions.KeepAliveTimeout?displayProperty=nameWithType> is enough: | |
| As a result, overriding <xref:System.Net.WebSockets.ClientWebSocketOptions.KeepAliveTimeout?displayProperty=nameWithType> is enough to switch to the PING/PONG strategy if you keep the default value for <xref:System.Net.WebSockets.WebSocket.DefaultKeepAliveInterval?displayProperty=nameWithType>: |
| ### Keep Reading To Process PONGs | ||
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| > [!NOTE] | ||
| > Currently, `WebSocket` ONLY processes incoming frames while there's a `ReceiveAsync` pending. |
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Suggested change
| > Currently, `WebSocket` ONLY processes incoming frames while there's a `ReceiveAsync` pending. | |
| > Currently, `WebSocket` ONLY processes incoming frames while there's a <xref:System.Net.WebSockets.WebSocket.ReceiveAsync%2A> task pending. |
| var result = await _webSocket.ReceiveAsync(buffer, cts.Token); | ||
| ``` | ||
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| If the timeout elapses, an outstanding `ReceiveAsync` throws an `OperationCanceledException`: |
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Suggested change
| If the timeout elapses, an outstanding `ReceiveAsync` throws an `OperationCanceledException`: | |
| If the timeout elapses, an outstanding <xref:System.Net.WebSockets.WebSocket.ReceiveAsync%2A> throws an <xref:System.OperationCanceledException>: |
| > Currently, `WebSocket` ONLY processes incoming frames while there's a `ReceiveAsync` pending. | ||
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| > [!IMPORTANT] | ||
| > If you want to use Keep-Alive Timeout, it's _crucial_ that PONG responses are _promptly processed_. Even if the remote endpoint is alive and properly sends the PONG response, but the `WebSocket` isn't processing the incoming frames, the Keep-Alive mechanism can issue a "false-positive" Abort. This problem can happen if the PONG frame is never picked up from the transport stream before the timeout elapsed. |
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Suggested change
| > If you want to use Keep-Alive Timeout, it's _crucial_ that PONG responses are _promptly processed_. Even if the remote endpoint is alive and properly sends the PONG response, but the `WebSocket` isn't processing the incoming frames, the Keep-Alive mechanism can issue a "false-positive" Abort. This problem can happen if the PONG frame is never picked up from the transport stream before the timeout elapsed. | |
| > If you want to use Keep-Alive Timeout, it's _crucial_ that PONG responses are _promptly processed_. Even when the remote endpoint is alive and properly sends the PONG response, if the `WebSocket` isn't processing the incoming frames, the Keep-Alive mechanism can issue a "false-positive" Abort. This problem can happen if the PONG frame is never picked up from the transport stream before the timeout elapsed. |
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Moving all the details from the blogpost to the dedicated conceptual doc.
cc @dotnet/ncl
Acrolinx section score 85
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