# How can i allow join-node after captured two payloads in a datastream?

**URL:** <https://discourse.nodered.org/t/how-can-i-allow-join-node-after-captured-two-payloads-in-a-datastream/71402>\
**Category:** General\
**Created:** [28 November 2022 21:41 UTC](https://discourse.nodered.org/t/how-can-i-allow-join-node-after-captured-two-payloads-in-a-datastream/71402 "2022-11-28T21:41:35Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![syma33](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/syma33/32/30665_2.png) [@syma33](https://discourse.nodered.org/u/syma33)\
**Post date:** [28 November 2022 21:41 UTC](https://discourse.nodered.org/t/how-can-i-allow-join-node-after-captured-two-payloads-in-a-datastream/71402/1 "2022-11-28T21:41:36Z")

</div>

not sure how to explain this but... i got 10byte, 8bits, dec value like this:

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/1/2/12e23b45f67a8e309c98c6d1b23c43b1005ddec1.png)  
and i use join node to split them into array.  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/7/5/75e03f252e87f241c112f0b1f17336b51fb1a0de.png)  
but..sometimes i get glitzes in the communication and the split array just wont work...  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/c/f/cf8d25728d17ee9fbe45b127d01336c717264e23.png)  
i want to somehow watch the data-stream for  
payload[0] == 171 && payload[0] == 205 and then start the "join node" to split into array.

Something like..  
If(payload[0]==171 && payload[0]==205){start count payload[0]'s up to 8 and then merge into one array output}

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<div class="post-metadata">

**Author:** ![Trying\_to\_learn](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/trying_to_learn/32/28400_2.png) [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)\
**Post date:** [28 November 2022 21:49 UTC](https://discourse.nodered.org/t/how-can-i-allow-join-node-after-captured-two-payloads-in-a-datastream/71402/2 "2022-11-28T21:49:09Z")

</div>

Ok, kind of getting what you are saying, but also not. Sorry.

If there is a _glitze_ and the array is _spli_ I fear you have bigger problems.

But, sticking to what you say/ask:

You may need to post the actual message rather than screen shots. (May help)  
_Spit balling_ (throwing ideas to consider)  
~~You will need two `SWITCH` nodes.  
One set to look at `payload[0]` and the next to look at `payload~~

In your example you are testing `payload[0]` for two different variables.  
That can't happen unless you mean check two subsequent messages and check their conditions.

Can you post a GOOD payload and then the BAD payload/s.

---

<div class="post-metadata">

**Author:** ![Colin](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/colin/32/17040_2.png) [@Colin](https://discourse.nodered.org/u/Colin)\
**Post date:** [29 November 2022 09:16 UTC](https://discourse.nodered.org/t/how-can-i-allow-join-node-after-captured-two-payloads-in-a-datastream/71402/3 "2022-11-29T09:16:51Z")

</div>

Where is that data coming from, and through what node?

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<div class="post-metadata">

**Author:** ![syma33](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/syma33/32/30665_2.png) [@syma33](https://discourse.nodered.org/u/syma33)\
**Post date:** [29 November 2022 17:10 UTC](https://discourse.nodered.org/t/how-can-i-allow-join-node-after-captured-two-payloads-in-a-datastream/71402/4 "2022-11-29T17:10:28Z")

</div>

> [@Trying\_to\_learn](#):
>
> In your example you are testing `payload[0]` for two different variables.  
> That can't happen unless you mean check two subsequent messages and check their conditions.
> 
> Can you post a GOOD payload and then the BAD payload/s.

> [@Colin](#):
>
> Where is that data coming from, and through what node?

![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/0/f/0ff53d09dc4322ab57171ae967005412057642db.png)

as i cannot change the stream of correct values, i need to observe when value 171, 205 and then start count the rest of the string, im unsure how.  
this might work if i could put all values inside one payload...

> let lines = msg.payload.split(" ");  
> for(let i = 0; i \< lines.length; i++) {  
> let line = lines[i].trim();  
> let parts = line.split(" ");  
> if(parts.length != 2) continue;  
> node.send({ topic: "byte\_nr\_" + parts[0], payload: parts[1]});  
> }  
> node.send({complete:true})

the 10byte value in decimal looks like this.  
171 205 001 019 000 000 000 001 000 021

im trying to find a solution something like this...  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/6/d/6d4ec27e2729d0483532220e0fa0d7ac80c73652.png)

---

<div class="post-metadata">

**Author:** ![Colin](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/colin/32/17040_2.png) [@Colin](https://discourse.nodered.org/u/Colin)\
**Post date:** [29 November 2022 20:41 UTC](https://discourse.nodered.org/t/how-can-i-allow-join-node-after-captured-two-payloads-in-a-datastream/71402/5 "2022-11-29T20:41:23Z")

</div>

Something like this should do it, in a Function node

```auto
let state = context.get("state") || "wait_171"
let buff = context.get("buff") || []
let count = context.get("count") || 0
const maxCount = 8 // number of additional chars to get
switch(state) {
    case "wait_171":
    if (msg.payload[0] == 171) {
        buff = [171]
        state = "wait_205"
    }
    // otherwise ignore this character
    // send nothing back 
    msg = null
    break;

    case "wait_205":
    if (msg.payload[0] == 205) {
        buff.push(205)
        state = "buffering"
        count = 0
    } else {
        // only 205 is valid here, so start again
        state = "wait_171"
    }
    msg = null
    break;
    
    default: // buffering
    buff.push(msg.payload[0])
    count++
    if (count >= maxCount) {
        // have now received a full buffer
        msg.payload = buff
        state = "wait_171"
        count = 0
    } else {
        msg = null
    }
}
context.set("state", state)
context.set("buff", buff)
context.set("count", count)
node.status({ text: `state: ${state}, count: ${count}` });
return msg;

```

Test flow:

```auto
[{"id":"6586e0f3363d2f8f","type":"inject","z":"e672d6322ed2b137","name":"171","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"[171]","payloadType":"bin","x":130,"y":220,"wires":[["31c19a45d4d1ba99"]]},{"id":"5eef4a3f33425859","type":"debug","z":"e672d6322ed2b137","name":"debug 47","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":540,"y":260,"wires":[]},{"id":"6915fc970d0ba5e0","type":"inject","z":"e672d6322ed2b137","name":"205","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"[205]","payloadType":"bin","x":130,"y":260,"wires":[["31c19a45d4d1ba99"]]},{"id":"2c2d25c611fb7c8f","type":"inject","z":"e672d6322ed2b137","name":"1","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"[1]","payloadType":"bin","x":130,"y":340,"wires":[["31c19a45d4d1ba99"]]},{"id":"074de7f8c91057b5","type":"inject","z":"e672d6322ed2b137","name":"22","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"[22]","payloadType":"bin","x":130,"y":380,"wires":[["31c19a45d4d1ba99"]]},{"id":"31c19a45d4d1ba99","type":"function","z":"e672d6322ed2b137","name":"Build message","func":"let state = context.get(\"state\") || \"wait_171\"\nlet buff = context.get(\"buff\") || []\nlet count = context.get(\"count\") || 0\nconst maxCount = 8 // number of additional chars to get\nswitch(state) {\n case \"wait_171\":\n if (msg.payload[0] == 171) {\n buff = [171]\n state = \"wait_205\"\n }\n // otherwise ignore this character\n // send nothing back \n msg = null\n break;\n\n case \"wait_205\":\n if (msg.payload[0] == 205) {\n buff.push(205)\n state = \"buffering\"\n count = 0\n } else {\n // only 205 is valid here, so start again\n state = \"wait_171\"\n }\n msg = null\n break;\n \n default: // buffering\n buff.push(msg.payload[0])\n count++\n if (count >= maxCount) {\n // have now received a full buffer\n msg.payload = buff\n state = \"wait_171\"\n count = 0\n } else {\n msg = null\n }\n}\ncontext.set(\"state\", state)\ncontext.set(\"buff\", buff)\ncontext.set(\"count\", count)\nnode.status({ text: `state: ${state}, count: ${count}` });\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":340,"y":260,"wires":[["5eef4a3f33425859"]]}]

```

---

<div class="post-metadata">

**Author:** ![syma33](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/syma33/32/30665_2.png) [@syma33](https://discourse.nodered.org/u/syma33)\
**Post date:** [30 November 2022 21:10 UTC](https://discourse.nodered.org/t/how-can-i-allow-join-node-after-captured-two-payloads-in-a-datastream/71402/6 "2022-11-30T21:10:49Z")

</div>

> [@Colin](#):
>
> Something like this should do it, in a Function node

indeed, it did quite good, there was still some issues and when i observe the tcp-stream, it seems node-red pick up more than one value in the array (sometimes) and that wont count...

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/2/9/29be07ee72d4676eeb186433b3830be4ad9256a1.png)

i added some .hasOwnProperty and it seems to work but unsure if this looks ok, how would you done this?

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/8/f/8fdbbbcf74f2a937dd7aa0d2d23baa294912e973.png)

```auto
[
    {
        "id": "31c19a45d4d1ba99",
        "type": "function",
        "z": "0f9de81aaa0f53ef",
        "name": "Build message",
        "func": "let state = context.get(\"state\") || \"wait_171\"\nlet buff = context.get(\"buff\") || []\nlet count = context.get(\"count\") || 0\nconst maxCount = 8 // number of additional chars to get\nswitch(state) {\n case \"wait_171\":\n if (msg.payload[0] == 171) {\n buff = [171]\n state = \"wait_205\"\n }\n // otherwise ignore this character\n // send nothing back \n msg = null\n break;\n\n case \"wait_205\":\n if (msg.payload[0] == 205) {\n buff.push(205)\n state = \"buffering\"\n count = 0\n } else {\n // only 205 is valid here, so start again\n state = \"wait_171\"\n }\n msg = null\n break;\n \n default: // buffering\n buff.push(msg.payload[0])\n if (msg.payload.hasOwnProperty([1])){\n state = \"count [1]\"\n buff.push(msg.payload[1])\n // if theres a the msg.payload[] contains more than one value, then count this as well..\n count++\n if (msg.payload.hasOwnProperty([2])){\n state = \"count [2]\"\n buff.push(msg.payload[2])\n // if theres a the msg.payload[] contains more than one message, then count this as well..\n count++\n if (msg.payload.hasOwnProperty([3])){\n state = \"count [3]\"\n buff.push(msg.payload[3])\n // if theres a the msg.payload[] contains more than one value, then count this as well..\n count++\n if (msg.payload.hasOwnProperty([4])){\n state = \"count [4]\"\n buff.push(msg.payload[4])\n // if theres a the msg.payload[] contains more than one message, then count this as well..\n count++\n }\n }\n }\n }\n\n \n count++\n if (count >= maxCount) {\n // have now received a full buffer\n msg.payload = buff\n state = \"wait_171\"\n count = 0\n } else {\n msg = null\n }\n}\ncontext.set(\"state\", state)\ncontext.set(\"buff\", buff)\ncontext.set(\"count\", count)\nnode.status({ text: `state: ${state}, count: ${count}` });\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 500,
        "y": 2000,
        "wires": [
            [
                "5eef4a3f33425859"
            ]
        ]
    }
]

```

---

<div class="post-metadata">

**Author:** ![Colin](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/colin/32/17040_2.png) [@Colin](https://discourse.nodered.org/u/Colin)\
**Post date:** [30 November 2022 21:23 UTC](https://discourse.nodered.org/t/how-can-i-allow-join-node-after-captured-two-payloads-in-a-datastream/71402/7 "2022-11-30T21:23:54Z")

</div>

Instead of doing that, insert a split node in front of the function , configured as

![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/f/f/ff71453e538d81131a6cedf75f4ea720c5142572.png)

which will split it up into single bytes for the function to handle.

As you currently have it, if a multibyte buffer arrived near the end then it would overflow the 10 bytes length.

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [29 January 2023 21:24 UTC](https://discourse.nodered.org/t/how-can-i-allow-join-node-after-captured-two-payloads-in-a-datastream/71402/8 "2023-01-29T21:24:25Z")

</div>

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