Include data captured in another flow

Problem

You want to respond to an HTTP request using data captured by another flow.

Solution

Store data using flow context so that it can be retrieved within the HTTP flow.

Example

[{"id":"92eaf6c0.6d1508","type":"inject","z":"3045204d.cfbae","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"x":100,"y":480,"wires":[["8055b557.7faa48"]]},{"id":"8055b557.7faa48","type":"change","z":"3045204d.cfbae","name":"Store time","rules":[{"t":"set","p":"timestamp","pt":"flow","to":"payload","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":270,"y":480,"wires":[[]]},{"id":"93bf2335.6c40e","type":"http in","z":"3045204d.cfbae","name":"","url":"/hello-data","method":"get","swaggerDoc":"","x":120,"y":520,"wires":[["9e3aa25e.61c56"]]},{"id":"9e3aa25e.61c56","type":"change","z":"3045204d.cfbae","name":"Copy time","rules":[{"t":"set","p":"timestamp","pt":"msg","to":"timestamp","tot":"flow"}],"action":"","property":"","from":"","to":"","reg":false,"x":310,"y":520,"wires":[["f2c385a.f0d3c78"]]},{"id":"f2c385a.f0d3c78","type":"template","z":"3045204d.cfbae","name":"page","field":"payload","fieldType":"msg","format":"handlebars","syntax":"mustache","template":"<html>\n    <head></head>\n    <body>\n        <h1>Time: {{ timestamp }}</h1>\n    </body>\n</html>","x":470,"y":520,"wires":[["def756a1.2108a8"]]},{"id":"def756a1.2108a8","type":"http response","z":"3045204d.cfbae","name":"","x":610,"y":520,"wires":[]}]
[~]$ curl http://localhost:1880/hello-data
<html>
    <head></head>
    <body>
        <h1>Time: 1480201022517</h1>
    </body>
</html>

Discussion

There are many different ways data can be stored and retrieved within a flow. For example, using an external database.

Node-RED provides the flow context as a simple key/value store that is accessible to all nodes on the same tab.

The example above stores a timestamp generated by an Inject node into flow context using a Change node. The flow that handles the HTTP request then uses another Change node to retrieve the value, attaching it to the message which is then passed to a Template node to generate the response.