2021-12-02 22:27:31 +00:00
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# Subscribe via API
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## Fetching cached messages
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Messages may be cached for a couple of hours (see [message caching](../config.md#message-cache)) to account for network
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interruptions of subscribers. If the server has configured message caching, you can read back what you missed by using
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the `since=` query parameter. It takes either a duration (e.g. `10m` or `30s`), a Unix timestamp (e.g. `1635528757`)
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or `all` (all cached messages).
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```
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curl -s "ntfy.sh/mytopic/json?since=10m"
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```
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## Polling
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You can also just poll for messages if you don't like the long-standing connection using the `poll=1`
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query parameter. The connection will end after all available messages have been read. This parameter can be
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combined with `since=` (defaults to `since=all`).
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```
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curl -s "ntfy.sh/mytopic/json?poll=1"
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```
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## Subscribing to multiple topics
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It's possible to subscribe to multiple topics in one HTTP call by providing a
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comma-separated list of topics in the URL. This allows you to reduce the number of connections you have to maintain:
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```
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$ curl -s ntfy.sh/mytopic1,mytopic2/json
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{"id":"0OkXIryH3H","time":1637182619,"event":"open","topic":"mytopic1,mytopic2,mytopic3"}
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{"id":"dzJJm7BCWs","time":1637182634,"event":"message","topic":"mytopic1","message":"for topic 1"}
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{"id":"Cm02DsxUHb","time":1637182643,"event":"message","topic":"mytopic2","message":"for topic 2"}
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```
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