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Inspecting server-sent events
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`Server-sent events <https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events>`_ allow for an inversion of the traditional client-initiated web request model, with a server sending new data to a web page at any time by pushing messages. From Firefox 82 onwards, you can inspect server-sent events and their message contents using the :doc:`Network Monitor <../index>`. This article shows you how.
Inspecting the SSE network activity
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When you are viewing a document that is receiving server-sent events, you can go to the Network Monitor, select the file that is sending the server-sent events, and view the received messages in the *Response* tab on the right-hand panel.
.. image:: basic-sse-message-view.png
:class: border
At the top of the panel there is a trash can icon, which allows you to trash the messages sent so far, and a filter field in which you can enter a text string to filter the displayed messages by.
Viewing the message contents
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Select one of the messages listed in the *Response* tab, and you'll see the message contents displayed at the bottom of that same tab.
.. image:: see-message-detail-view.png
:class: border
In the above example, you can see that JSON and raw data representations of the content are shown. For a plain text message, you'd just see a raw data section.
The supported data formats are as follows:
- Mercure protocol
- JSON
Customizing the displayed columns
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For each message, you'll see *Data* and Time columns by default, but you can right-click on the table header to bring up a context menu in which you can toggle columns on and off, and reset it back to its original state.
.. image:: customize-columns.png
:class: border
The available columns are as follows:
- *Data*: A summary of the contained message data.
- *Size*: The size of the message.
- *Time*: A timestamp representing when the message was sent.
- *Event Name*: The name of the event type that resulted in the message being sent (e.g. ```message``` or ```ping```).
- *Last Event ID*: The ID of the last event that was fired.
- *Retry*: The interval after which failed message will be resent.
Network Monitor features
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The following articles cover different aspects of using the network monitor:
- :doc:`Toolbar <../toolbar/index>`
- :doc:`Network request list <../request_list/index>`
- :doc:`Network request details <../request_details/index>`
- :doc:`Network traffic recording <../performance_analysis/index>`
- :doc:`Throttling <../throttling/index>`
- :doc:`Inspecting web sockets <../inspecting_web_sockets/index>`