Querying EventHandle Events using API: "message": "Deserialization error, field(message) type is not a EventHandle struct: unexpected end of input"

[kshitijc1506]

Asked by gftea10086 on Discord (#dev-discussion).

Hi, I publish the hello_blockchain example to my local net using aptos-node-1.9.7, and try to query the event after set_message call.
Have read the v1 rest api spec, but it is not working using below syntax
curl http://127.0.0.1:8080/v1/accounts/0xff89ee9ccec5cf2009c846b2b645af112b581725f57c7d30e92a0d012dd00051/events/0xff89ee9ccec5cf2009c846b2b645af112b581725f57c7d30e92a0d012dd00051::message::MessageChange/from_message
curl http://127.0.0.1:8080/v1/accounts/0xff89ee9ccec5cf2009c846b2b645af112b581725f57c7d30e92a0d012dd00051/events/0xff89ee9ccec5cf2009c846b2b645af112b581725f57c7d30e92a0d012dd00051::message::MessageHolder/message | jq
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 159 100 159 0 0 124k 0 --:--:-- --:--:-- --:--:-- 155k
{
"message": "Deserialization error, field(message) type is not a EventHandle struct: unexpected end of input",
"error_code": "invalid_input",
"vm_error_code": null

keywords: API, Events

[kshitijc1506]

The error message suggests that the expected type for the message field is not an EventHandle struct.

The format should be http://<API_ENDPOINT>/v1/accounts/<ACCOUNT_ADDRESS>/events/<EVENT_KEY>::<MODULE_NAME>::<RESOURCE_NAME>/<EVENT_NAME>

Can you try running this?
curl http://127.0.0.1:8080/v1/accounts/0xff89ee9ccec5cf2009c846b2b645af112b581725f57c7d30e92a0d012dd00051/events/0xff89ee9ccec5cf2009c846b2b645af112b581725f57c7d30e92a0d012dd00051::message::MessageHolder/message_change_events

These steps can be seen on the "Your First Move Module" page, under step 5.

[gftea]

• the output of resource MessageHolder dose NOT include events

curl http://127.0.0.1:8080/v1/accounts/45b868338b69eceed4f3dc5ef1dce3fb7c591e10cdda9f79db55acfefeadc8fc/resourc│
e/0x45b868338b69eceed4f3dc5ef1dce3fb7c591e10cdda9f79db55acfefeadc8fc::message::MessageHolder | jq                                                                              │
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current                                                                                                │
                                 Dload  Upload   Total   Spent    Left  Speed                                                                                                  │
100   140  100   140    0     0  76211      0 --:--:-- --:--:-- --:--:--  136k                                                                                                 │
{                                                                                                                                                                              │
  "type": "0x45b868338b69eceed4f3dc5ef1dce3fb7c591e10cdda9f79db55acfefeadc8fc::message::MessageHolder",                                                                        │
  "data": {                                                                                                                                                                    │
    "message": "hello, blockchain"                                                                                                                                             │
  }                                                                                                                                                                            │
}                                                                          

• query events returns struct field not found

curl http://127.0.0.1:8080/v1/accounts/0x45b868338b69eceed4f3dc5ef1dce3fb7c591e10cdda9f7│
9db55acfefeadc8fc/events/0x45b868338b69eceed4f3dc5ef1dce3fb7c591e10cdda9f79db55acfefeadc8fc::message::MessageHolder/message_change_events | jq                                 │
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current                                                                                                │
                                 Dload  Upload   Total   Spent    Left  Speed                                                                                                  │
100   338  100   338    0     0   224k      0 --:--:-- --:--:-- --:--:--  330k                                                                                                 │
{                                                                                                                                                                              │
  "message": "Struct Field not found by Address(0x45b868338b69eceed4f3dc5ef1dce3fb7c591e10cdda9f79db55acfefeadc8fc), Struct tag(0x45b868338b69eceed4f3dc5ef1dce3fb7c591e10cdda9│
f79db55acfefeadc8fc::message::MessageHolder), Field name(message_change_events) and Ledger version(1164)",                                                                     │
  "error_code": "struct_field_not_found",                                                                                                                                      │
  "vm_error_code": null                                                                                                                                                        │
}                                                                                                     

• based on move codes, try to query message field of MessageHolder

curl http://127.0.0.1:8080/v1/accounts/0x45b868338b69eceed4f3dc5ef1dce3fb7c5│
91e10cdda9f79db55acfefeadc8fc/events/0x45b868338b69eceed4f3dc5ef1dce3fb7c591e10cdda9f79db55acfefeadc8fc::message::MessageHolder/message | jq                                   │
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current                                                                                                │
                                 Dload  Upload   Total   Spent    Left  Speed                                                                                                  │
100   159  100   159    0     0  93309      0 --:--:-- --:--:-- --:--:--  155k                                                                                                 │
{                                                                                                                                                                              │
  "message": "Deserialization error, field(message) type is not a EventHandle struct: unexpected end of input",                                                                │
  "error_code": "invalid_input",                                                                                                                                               │
  "vm_error_code": null                                                                                                                                                        │
}                                                                                                      

[kshitijc1506]

Thanks for the detailed explanation. I think I know what the problem you're experiencing is:

The API calls are trying to query the MessageHolder resource for events. However, the resource does not contain any Event Handles. This is likely because 'Event Handles' is deprecated now, and instead we use 'Module Events'. While EventHandle events still work, developers are encouraged to migrate to Module Events.

The tutorial over here needs to be updated, we will have that done soon.

For now, if you'd still like to proceed, you can do this:

1. Change the module itself- add an Event Handle to the MessageHolder, and in the set_message function add the required logic.
2. Compile and Publish.
3. Query the event how you were trying to- http://<API_ENDPOINT>/v1/accounts/<ACCOUNT_ADDRESS>/events/<EVENT_KEY>::<MODULE_NAME>::<RESOURCE_NAME>/<EVENT_NAME> (the other API calls you were making should also work now)

Alternatively, you could use Module Events (recommended):
The GraphQL API supports module events (and EventHandle events).

Let me know if this answers your question!

[gftea]

The document is indeed misleading, it is using module event, but rest api refers to eventhandle
good to know The API for querying Module Events is under construction, I think that explain I can query event curl http://127.0.0.1:8080/v1/accounts/45b868338b69eceed4f3dc5ef1dce3fb7c591e10cdda9f79db55acfefeadc8fc/events/0x1::coin::CoinStore%3C0x1::aptos_coin::AptosCoin%3E/deposit_events but cannot query the module event in example code

[kshitijc1506]

Yes, that is referring to CoinStore, which uses EventHandle events.

[so-schen]

I also want to know where and how the module event is stored?

[kshitijc1506]

Module events are structs with the store and drop abilities. Therefore, they are stored in global storage as a part of the module's bytecode. However, you can also store them as a part of a top-level resource in global storage since you can include them as a field for a resource (since module events have the store ability).

For additional reference, here's an example of how to use Module Events.