How to pub/sub binary data? about nats.c HOT 18 CLOSED

To send binary data, please use natsConnection_Publish(natsConnection *nc, const char *subj, const void *data, int dataLen).

If you have downloaded the source, please check the documentation by opening doc/html/index.html. Otherwise, you can try the following link that displays the doc directly from the repository:

https://htmlpreview.github.io/?https://raw.githubusercontent.com/nats-io/cnats/master/doc/html/group__conn_pub_group.html#gac0b9f7759ecc39b8d77807b94254f9b4

from nats.c.

Thank you. I read the readme.md and example only. Wonderful job and happy new year.

from nats.c.

No problem. I have added documentation online (the previous was not working well). Give it a try:

http://nats-io.github.io/cnats/

Thanks and Happy New Year to you too!

from nats.c.

@kozlovic is there any way to receive binary data? No matter what I do, the message received is always NULL when subscribing to a subject that broadcasts binary data.

@metalwood did you find a way to subscribe to binary data?

sorry if this is obvious, I can't seem to find any documentation or tests as examples.

from nats.c.

@elimist You simply call natsConnection_Publish with data pointing to your byte array. You need to specify the length with parameter dataLen.

Check the doc for this API here

Let me know if you still have issues.

from nats.c.

@kozlovic thanks for the reply. I'm not sure I understand what you mean by using natsConnection_Publish to subscribe to binary data.

I'm only using the cnats client to receive incoming data, and on the publishing side, I'm using the nats go client with default encoding (which supposedly sends byte arrays untouched).

When I telnet into my gnatsd server and subscribe to the binary channel, I can receive the binary data sent from my go client, so I don't think it's an issue with the sending side.

from nats.c.

Then can you show code for your subscriber? That would be the easiest way to see what's wrong.

from nats.c.

The problem can be demonstrated with the simple onMsg callback from the example code. When receiving binary data, both natsMsg_GetDataLength and natsMsg_GetData return nothing.

from nats.c.

Which version of cnats are you using? I just tested and works fine for me (using a go client with EncodedConn to send a byte array). If the callback is invoked, I would think that Data and DataLength should return something, unless you are sending an empty array. Can you show me how you are sending (the go client side)?

from nats.c.

For example, this works:

ec, _ := nats.NewEncodedConn(nc, "default")
defer ec.Close()

msg := []byte{1, 2, 3, 4}
ec.Publish(subj, msg)

from nats.c.

With the above sender, my C callback could look something like:

if (natsMsg_GetDataLength(msg) != 4)
{
    printf("Wrong size\n");
    abort();
}
else
{
    char *pbytes = (char*) natsMsg_GetData(msg);
    int i, b;

    for (i=0; i<4; i++)
    {
        b = (int)(*pbytes);
        if (b != (i+1))
        {
            printf("Expected %d, got %d\n", (i+1), b);
            abort();
        }
        pbytes++;
    }
}

and it will work.

from nats.c.

hm, that's very interesting. This is the code i've been testing with:

package main

import (
    "fmt"

    "github.com/elimist/flatbuffers-pub-test/fbs"
    flatbuffers "github.com/google/flatbuffers/go"
    "github.com/nats-io/nats"
)

func main() {
    nc, _ := nats.Connect("nats://localhost:4222")
    c, _ := nats.NewEncodedConn(nc, nats.DEFAULT_ENCODER)
    defer c.Close()

    oLat := float64(7.419505)
    oLng := float64(43.736825)

    dLat := float64(7.419758)
    dLng := float64(43.731142)

    b := flatbuffers.NewBuilder(0)

    aid := b.CreateString("test0")
    uid := b.CreateString("test1")

    fbs.LocationUpdateStart(b)
    fbs.LocationUpdateAddOrig(b, fbs.CreateCoords(b, oLat, oLng))
    fbs.LocationUpdateAddOrig(b, fbs.CreateCoords(b, dLat, dLng))
    fbs.LocationUpdateAddApptID(b, aid)
    fbs.LocationUpdateAddUserID(b, uid)
    fbs.LocationUpdateAddSpeed(b, float64(123.321))
    u := fbs.LocationUpdateEnd(b)
    b.Finish(u)
    bts := b.Bytes

    c.Publish("foo", bts)
    c.Close()
}

I'll try the above cb code and see if it works

from nats.c.

The doc about EncodedConn that you pointed out specified this:

// DefaultEncoder implementation for EncodedConn.
// This encoder will leave []byte and string untouched, but will attempt to
// turn numbers into appropriate strings that can be decoded. It will also
// propely encoded and decode bools. If will encode a struct, but if you want
// to properly handle structures you should use JsonEncoder.

So only []byte and string are left untouched. That being said, could you print bts content before the call to publish?

fmt.Printf("bts=%v\n", bts)

Thanks!

from nats.c.

With the above cb code, get the wrong size message. Also, I'm using the latest cnats.
When I print the byte slice, I can see that it's non-zero.

Well, since you are obviously able to receive the binary data it seems this is most likely a problem on my end and has nothing to do with cnats. I'm calling cnats from my c++ code so it might have something to do with that, I'm not sure... time to do more investigating!

from nats.c.

Well, the code I showed was assuming I was sending a byte array of length 4. But clearly, that shows that I was able to send from EncodedConn a byte array and receive it (and verify the content) in the C client.

from nats.c.

right, sorry I just blindly c/p'd that code into my callback hah

from nats.c.

I hope I can get this resolved, but regardless, thanks for all your help!

from nats.c.

I hope too. I know that the C client can receive bytes. Actually, this is the normal behavior. The String APIs are just a convenience, but really, you are sending a byte array of a given length. Receiving is the same. When receiving a message on a given subject, the message has a pointer to a byte array of a given length. I have tested that you can send byte arrays from any client and receive them from the C client.
Anything I can do to help, let me know.

from nats.c.