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52 lines
2.8 KiB
Markdown
52 lines
2.8 KiB
Markdown
Websockets are a way of connecting a client and a server without the request response nature of HTTP.<br><br>
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## Routes
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To create a websocket in Crow, you need a websocket route.<br>
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A websocket route differs from a normal route quite a bit. It uses a slightly altered `CROW_WEBSOCKET_ROUTE(app, "/url")` macro, which is then followed by a series of methods (with handlers inside) for each event. These are (sorted by order of execution):
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- `#!cpp onaccept([&](const crow::request& req, void** userdata){handler code goes here})`
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- `#!cpp onopen([&](crow::websocket::connection& conn){handler code goes here})`
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- `#!cpp onmessage([&](crow::websocket::connection& conn, const std::string& message, bool is_binary){handler code goes here})`
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- `#!cpp onerror([&](crow::websocket::connection& conn, const std::string& error_message){handler code goes here})`
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- `#!cpp onclose([&](crow::websocket::connection& conn, const std::string& reason){handler code goes here})`
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!!! note
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`onaccept` must return a boolean. In case `false` is returned, the connection is shut down, deleted, and no further communication is done.
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!!! Warning
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By default, Crow allows clients to send unmasked websocket messages. This is useful for debugging, but goes against the protocol specifications. Production Crow applications should enforce the protocol by adding `#!cpp #define CROW_ENFORCE_WS_SPEC` to their source code.
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These event methods and their handlers can be chained. The full route should look similar to this:
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```cpp
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CROW_WEBSOCKET_ROUTE(app, "/ws")
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.onopen([&](crow::websocket::connection& conn){
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do_something();
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})
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.onclose([&](crow::websocket::connection& conn, const std::string& reason){
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do_something();
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})
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.onmessage([&](crow::websocket::connection& /*conn*/, const std::string& data, bool is_binary){
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if (is_binary)
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do_something(data);
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else
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do_something_else(data);
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});
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```
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## Maximum payload size
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<span class="tag">[:octicons-feed-tag-16: master](https://github.com/CrowCpp/Crow)</span>
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The maximum payload size that a connection accepts can be adjusted either globally by using `#!cpp app.websocket_max_payload(<value in bytes>)` or per route by using `#!cpp CROW_WEBSOCKET_ROUTE(app, "/url").max_payload(<value in bytes>)`. In case a message was sent that exceeded the limit. The connection would be shut down and `onerror` would be triggered.
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!!! note
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By default, this limit is disabled. To disable the global setting in specific routes, you only need to call `#!cpp CROW_WEBSOCKET_ROUTE(app, "/url").max_payload(UINT64_MAX)`.
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For more info about websocket routes go [here](../reference/classcrow_1_1_web_socket_rule.html).
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For more info about websocket connections go [here](../reference/classcrow_1_1websocket_1_1_connection.html).
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