Holochain Forum

Passing AgentPubKey from UI to backend

Hi all -

I’m experimenting with UI development a bit more, and have made pretty good progress using the awesome RAD scaffolding tools.

Something I’m a bit confused about is how to handle different data types, and how to correctly call Holochain functions from values obtained in the UI. The example I currently have is as follows:

  • I have a list of all current users in my UI. The data from my ‘list_users’ function returns:
    nickname: string
    playerId: Uint8array
  • My console output shows the playerId value as base64:
    Profile { player_id: AgentPubKey(uhCAklmrhG4uKAWJsJI64rqOTBj47L1fDbRuqsM82BbcwQ6WFDqbY), nickname: "alex" }
  • In my UI I want to select a player to issue a cap grant to. This selection will either give me a JSON object or a string.
  • Now I need to pass this value in to my ‘create_capgrant’ function:
await appWs.callZome({
          cap: null,
          cell_id: cell_id,
          zome_name: 'myzome',
          fn_name: 'create_capgrant',
          payload: {
            function: "some_function",
            agent: var_containing_selected_agent_pubkey,
          provenance: cell_id[1],

But this is giving me errors and I think it’s about the way that the UI is sending back a valid AgentPubKey for the function to use.

So - in the UI I can see all AgentPubKey’s as Uint8Arrays. I have tried to convert these to Base 64 before sending back, but the resulting value is quite long and doesn’t look similar to what I see in the console.

What is the correct way for me to send AgentPubKey back to the create_capgrant function?

Thanks for your help - alex.

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actually I just noticed in Holochain Gym on Capability Tokens page (Intermediate: Capability Tokens: Holochain Gym) it says:

  • Calls from the UI (this is not working yet)

So does this mean it’s not even possible ??

Thanks for asking this question! I’m actually trying to do something very similar at the moment,. Passing a header hash to the UI, then back to the DNA, but can’t get the DNA to recognize it as a header hash when it comes back…

yeah, same issue!
I have a feeling it’s something to do with base64 vs not-base64. I recall there were some changes in approach to this (?) over the last few versions of holochain.

My app is in 0.0.115, and doesn’t use any base64 entries. I was looking at GitHub - holochain-open-dev/profiles: Profile management with at least a nickname as a reference, which is 0.0.118 and seems to explicitly use base64 for agentpubkey - which is used to pass from UI to backend for some functions.

Might be a red herring, but I’ll try and follow that pattern to see if it makes a difference.

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I came across this wiki page describing one way to get the hash (HeaderHash in my case) from the dna to the ui as a string, not a byte array: How To Pass A String to a Client Instead of A Buffer for Hashes · holochain-open-dev/wiki Wiki · GitHub

This worked, but it’s the other direction that’s my actual problem (ui to dna), and this library did not seem to help me there.

I tried another approach: pass a base64 string to the client and pass the same string back to the DNA and manually convert it to a header hash. For this I used holo_hash, something like this example:

But none of the string to hash conversions from holo_hash were available, even when I copied one verbatim from the holo_hash unit tests.

Then I noticed in the hc_utils cargo.toml they specify that they want the encoding feature of holo_hash:

holo_hash = { version = "=0.0.12", features = ["encoding"] }

…so I’ll try this next — adding the same to my cargo.toml — and see if it helps.

I wrote that old article, the modern incarnation is HeaderHashB64, such as : syn/commit.rs at 198e9d7a84472ce6071b6372d38b1038be573868 · holochain/syn · GitHub

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Yup, that worked, thanks @Connoropolous .

@robot5x does this fix your issues as well?

this will solve things when dealing with HeaderHash, AgentPubKey, EntryHash, etc, in your own Zome/DNA/happ codebase, but won’t solve for you if you have to convert back to a Buffer/Uint8Array and call non-zome AppWebsocket (appInfo) or AdminWebsocket calls… those will all expect Buffer/Uint8Array style hash encodings… so…

to read deeper into how those conversions can work, here’s a couple pointers…

While writing up a section of the happ-client-call-tutorial @jost.schulte and I tried to inquire into the situation. You can see here we tried to diagnose it: Add TypeScript example & update readme by jost-s · Pull Request #2 · holochain/happ-client-call-tutorial · GitHub

One of the references for that discussion, and a utility that Holo uses a lot in its client side code is GitHub - Holo-Host/cryptolib-js: Cross-compatible cryptographic utilities for node/web which handles these holochain specific conversions between string hashes and Buffers.

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Great info Connor, thanks! On the last point, there is another client side lib for converting hashes between strings and bytes: GitHub - mjbrisebois/js-holo-hash: A Javascript library for managing Holochain's HoloHash types — mentioning in case it helps readers of this thread.

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Ok good to know, I’d missed that one. I know @brisebom has a bunch of good stuff though that I’m not sure many people know about yet!

it turns out this issue was ‘related’ to the very dumb mistake I made in another thread. The cause was very stupid but, because I didn’t think I could make such a stupid mistake, I went down a rabbit hole thinking it was about all these other things. Phew.

Once I’d sorted my profile management out, it turns out I can just pass the UInt8Array straight back to holochain from the UI and it works fine. :woman_shrugging:t5:

on the plus side, your issue is fixed and I learnt A LOT more about holochain data types :upside_down_face:

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coding, 25% of the time

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