The runtime fails to provide users sufficient feedback to investigate issues on their own

[silvestrpredko]

Describe the bug
Added library to a smart contract that is compatible with wasm32-unknown-unknown.
Deploy it to the blockchain and call a single method. Virtual machine initialization failed with a FunctionCallError(CompilationError(PrepareError(Instantiate)))

To Reproduce

// lib.rs
use near_sdk::{
    borsh::{self, BorshDeserialize, BorshSerialize},
};

use vodozemac::megolm::{GroupSession, InboundGroupSession, SessionKey};
#[near_bindgen]
#[derive(BorshDeserialize, BorshSerialize, Default)]
pub struct Key {}

#[near_bindgen]
impl Key {
    pub fn key(&self) -> String {
        "Name".to_owned()
    }
}

# Cargo.toml

[package]
name = "key"
version = "0.1.0"
edition = "2021"

[lib]
crate-type = ["cdylib", "rlib"]

[dependencies]
near-sdk = "4.0.0"
near-contract-standards = "4.0.0"
near-units = "0.2.0"
serde = { version = "1", features = ["derive"] }
vodozemac = { version = "0.2.0", features = ["js"] }

Deploy a smart contract and call a key function.

near view <accountId> key

Output: wasm execution failed with error: FunctionCallError(CompilationError(PrepareError(Instantiate)))

Expected behavior
At least tell where exactly the error happens, which part of the used libraries is not compatible

Version (please complete the following information):

• rust version 1.62.1
• testnet

[akhi3030]

CC: @austinabell , @nagisa . Maybe one of you has some hints here?

[nagisa]

Last time I had to investigate something similar, I ended up looking at the wasm itself, in some instances minimizing it using wasm-shrink. There are currently two reasons why PrepareError::Instantiate error could be raised:

1. Module imports names that are not in the allow-list of defined host functions (env namespace is the only permitted);
2. Module is malformed and some of the imports refer to non-existent type indices.

If you were to post the failing .wasm contract, I’d be happy to take a look at it.

The error messages are indeed terrible, and I would love to see them improved. Unfortunately, doing so is going to be somewhat non-trivial – the current errors are set up in a way that enables development of the underlying code without accidental reproducibility breaks. This is primarily achieved by making errors not necessarily super straightforward to interpret.

Having some better developer tooling that could aid in investigating these sorts of problems is definitely on the roadmap, but the priority on that work is tad a bit lower than some other tasks at the moment, so it probably isn’t going to materialize very soon, unfortunately.

[austinabell]

CC: @austinabell , @nagisa . Maybe one of you has some hints here?

My assumption is that rand 0.7 with wasm-bindgen feature (what is enabled by vodozemac) uses some host function exposed when using in a JS context but not available to our runtime. My assumption would be that it's how it's pulling in its entropy for the randomness you are using, and it seems like it's pulling in getrandom which I believe is incompatible because of what they call into.

Seems as if pulling the js feature of vodozemac might be, but not limited to, the issue.

[akhi3030]

@nagisa: I wonder if it would be possible to offer some sort of stand-alone wasm validator. Something that a contract developer could use to validate that their wasm would indeed pass the checks if uploaded to the network. Does something like this make sense?

[nagisa]

Yes, it would make sense and be possible to implement, though at that point it is half-way there to re-introducing the standalone wasm runner binary which we just removed. I know I definitely would love a tool like this personally, as obtaining post-preparation WASM, and working around that area of code base in general, is quite painful today.

I’d see that sort of work ideally as a sub-task in implementing a larger debugging and introspection tool that I’ve been briefly mentioning at some points in the past. But we might end up having no choice if the pain points end up being too unbearable…

[Ekleog]

For this specific instance, for "offering a standalone wasm validator" I think the same solution as the one I suggested in #7220 (comment) might work? As just having additional logs would probably be enough to know why the validation is failing.

[nagisa]

More observability is usually never a bad thing, but devex wise it is not really a tenable long term solution I feel.

[akhi3030]

@silvestrpredko : Based on the discussions above, I wonder in this specific case, if you can reproduce the problem on localnet. If you are able to, you can add some printfs around where we throw the specific error and then you can figure out what is going wrong.

[silvestrpredko]

Last time I had to investigate something similar, I ended up looking at the wasm itself, in some instances minimizing it using wasm-shrink. There are currently two reasons why PrepareError::Instantiate error could be raised:

1. Module imports names that are not in the allow-list of defined host functions (env namespace is the only permitted);
2. Module is malformed and some of the imports refer to non-existent type indices.

If you were to post the failing .wasm contract, I’d be happy to take a look at it.

The error messages are indeed terrible, and I would love to see them improved. Unfortunately, doing so is going to be somewhat non-trivial – the current errors are set up in a way that enables development of the underlying code without accidental reproducibility breaks. This is primarily achieved by making errors not necessarily super straightforward to interpret.

Having some better developer tooling that could aid in investigating these sorts of problems is definitely on the roadmap, but the priority on that work is tad a bit lower than some other tasks at the moment, so it probably isn’t going to materialize very soon, unfortunately.

Hi, thank you for your support. Here is a smart contract that is failing key.wasm.zip Also do you have a specification of NEAR runtime and how does it differs from a JS runtime, what is allowed and what is not. I know that networking isn't allowed, but I was surprised with rand stuff.

[silvestrpredko]

@silvestrpredko : Based on the discussions above, I wonder in this specific case, if you can reproduce the problem on localnet. If you are able to, you can add some printfs around where we throw the specific error and then you can figure out what is going wrong.

Currently, workspaces not working for me(( M1 problem. Or do you mean something else under localnet?

[nagisa]

Also do you have a specification of NEAR runtime and how does it differs from a JS runtime, what is allowed and what is not. I know that networking isn't allowed, but I was surprised with rand stuff.

The various APIs exposed to the NEAR contract are specified in this section of the specification. In JavaScript world the wasm code is allowed to set up and expose whatever APIs they wish. AFAIK usually developers will run their code through tools like wasm-bindgen and wasm-pack to set up these APIs for them automatically.

---

Let us run your contract through the wasm2wat tool first, to get a readable representation of the code. Looking at the imports we can see these:

imports

  (import "__wbindgen_placeholder__" "__wbindgen_is_undefined" (func $_ZN12wasm_bindgen23__wbindgen_is_undefined17hd5096780d189d788E (type 1)))
  (import "__wbindgen_placeholder__" "__wbg_self_86b4b13392c7af56" (func $_ZN9getrandom3imp6Global8get_self27__wbg_self_86b4b13392c7af5617h3ab47533c76ae43aE (type 13)))
  (import "__wbindgen_placeholder__" "__wbg_crypto_b8c92eaac23d0d80" (func $_ZN9getrandom3imp5Self_6crypto29__wbg_crypto_b8c92eaac23d0d8017hff605b69df2c41a9E (type 1)))
  (import "__wbindgen_placeholder__" "__wbg_msCrypto_9ad6677321a08dd8" (func $_ZN9getrandom3imp5Self_9ms_crypto31__wbg_msCrypto_9ad6677321a08dd817hf3f8f5dc84af062aE (type 1)))
  (import "__wbindgen_placeholder__" "__wbg_require_f5521a5b85ad2542" (func $_ZN9getrandom3imp10NodeModule7require30__wbg_require_f5521a5b85ad254217hea14bb6263c0c6daE (type 11)))
  (import "__wbindgen_placeholder__" "__wbg_getRandomValues_dd27e6b0652b3236" (func $_ZN9getrandom3imp13BrowserCrypto20get_random_values_fn38__wbg_getRandomValues_dd27e6b0652b323617hfe4b774914f6f3b7E (type 1)))
  (import "__wbindgen_placeholder__" "__wbg_randomFillSync_d2ba53160aec6aba" (func $_ZN9getrandom3imp10NodeCrypto16random_fill_sync37__wbg_randomFillSync_d2ba53160aec6aba17h9abba5b30cc1bb43E (type 3)))
  (import "__wbindgen_placeholder__" "__wbg_getRandomValues_e57c9b75ddead065" (func $_ZN9getrandom3imp13BrowserCrypto17get_random_values38__wbg_getRandomValues_e57c9b75ddead06517h286726fd8a6c66b9E (type 10)))
  (import "__wbindgen_placeholder__" "__wbg_static_accessor_MODULE_452b4680e8614c81" (func $_ZN9getrandom3imp6MODULE4init45__wbg_static_accessor_MODULE_452b4680e8614c8117h15b30e327ca0f032E (type 13)))
  (import "__wbindgen_placeholder__" "__wbindgen_object_drop_ref" (func $_ZN12wasm_bindgen26__wbindgen_object_drop_ref17h2d0c764e483bffa9E (type 0)))
  (import "__wbindgen_placeholder__" "__wbindgen_describe" (func $_ZN12wasm_bindgen19__wbindgen_describe17h1d5dffb576c62f5bE (type 0)))
  (import "__wbindgen_placeholder__" "__wbg_buffer_de1150f91b23aa89" (func $_ZN6js_sys11WebAssembly6Memory6buffer29__wbg_buffer_de1150f91b23aa8917h3aa70f3a6bcb1421E (type 1)))
  (import "__wbindgen_placeholder__" "__wbg_new_97cf52648830a70d" (func $_ZN6js_sys10Uint8Array3new26__wbg_new_97cf52648830a70d17h4241b996df6c6d6eE (type 1)))
  (import "__wbindgen_placeholder__" "__wbg_newwithlength_e833b89f9db02732" (func $_ZN6js_sys10Uint8Array15new_with_length36__wbg_newwithlength_e833b89f9db0273217h937eebccdafba65cE (type 1)))
  (import "__wbindgen_placeholder__" "__wbg_subarray_9482ae5cd5cd99d3" (func $_ZN6js_sys10Uint8Array8subarray31__wbg_subarray_9482ae5cd5cd99d317hfbc4e69e7490de6bE (type 11)))
  (import "__wbindgen_placeholder__" "__wbg_length_e09c0b925ab8de5d" (func $_ZN6js_sys10Uint8Array6length29__wbg_length_e09c0b925ab8de5d17hd53c873ca0d4adf5E (type 1)))
  (import "__wbindgen_placeholder__" "__wbg_set_a0172b213e2469e9" (func $_ZN6js_sys10Uint8Array3set26__wbg_set_a0172b213e2469e917h03d5ec4dbd548c78E (type 3)))
  (import "__wbindgen_placeholder__" "__wbindgen_throw" (func $_ZN12wasm_bindgen16__wbindgen_throw17hf0416b09e9451751E (type 10)))
  (import "__wbindgen_placeholder__" "__wbindgen_memory" (func $_ZN12wasm_bindgen17__wbindgen_memory17hbf7175b901445af8E (type 13)))
  (import "__wbindgen_externref_xform__" "__wbindgen_externref_table_grow" (func $_ZN12wasm_bindgen9externref31__wbindgen_externref_table_grow17hab300b53f6cf602aE (type 1)))
  (import "__wbindgen_externref_xform__" "__wbindgen_externref_table_set_null" (func $_ZN12wasm_bindgen9externref35__wbindgen_externref_table_set_null17h8cc4f9feb9c99eb0E (type 0)))
  (import "env" "read_register" (func $read_register (type 14)))
  (import "env" "register_len" (func $register_len (type 15)))
  (import "env" "value_return" (func $value_return (type 14)))
  (import "env" "panic_utf8" (func $panic_utf8 (type 14)))
  (import "env" "storage_read" (func $storage_read (type 16)))

Notice the two different styles of imports. The "env" "..." ones are importing the NEAR functions, whereas the __wbindgen_* ones are going to be the wasm-bindgen stuff. Unfortunately you won’t be able to use any crates that utilize wasm-bindgen for their webassembly support in NEAR – wasm-bindgen generates code incompatible with the near runtime bindings specification.

[silvestrpredko]

Also do you have a specification of NEAR runtime and how does it differs from a JS runtime, what is allowed and what is not. I know that networking isn't allowed, but I was surprised with rand stuff.

The various APIs exposed to the NEAR contract are specified in this section of the specification. In JavaScript world the wasm code is allowed to set up and expose whatever APIs they wish. AFAIK usually developers will run their code through tools like wasm-bindgen and wasm-pack to set up these APIs for them automatically.

Let us run your contract through the wasm2wat tool first, to get a readable representation of the code. Looking at the imports we can see these:

Notice the two different styles of imports. The "env" "..." ones are importing the NEAR functions, whereas the __wbindgen_* ones are going to be the wasm-bindgen stuff. Unfortunately you won’t be able to use any crates that utilize wasm-bindgen for their webassembly support in NEAR – wasm-bindgen generates code incompatible with the near runtime bindings specification.

Understood, thanks for the support.

[matklad]

Closing as the particular mystery has been solved. The error handling is tracked at #5315.