Exception Example Triggers Host Panic in extism-py 0.1.4

[bradyjoslin]

I'm encountering a panic when running the example from the readme using version 0.1.4.

Running the documented example:

import extism

@extism.plugin_fn
def greet():
  name = extism.input_str()
  if name == "Benjamin":
    raise Exception("Sorry, we don't greet Benjamins!")
  extism.output_str(f"Hello, {name}")

...results in a panic when called from the host:

$ extism call plugin.wasm greet --input="Benjamin" --wasi
thread '<unnamed>' panicked at src/lib.rs:58:6:
called `Result::unwrap()` on an `Err` value: PyErr { type: <class 'Exception'>, value: Exception("Sorry, we don't greet Benjamins!"), traceback: Some(<traceback object at...
...

[G4Vi]

I think this is working as intended, this is not a host panic, but a panic from rust in wasm which is used to run the python interpreter https://github.com/extism/python-pdk/blob/main/lib/src/lib.rs , the extism cli is written in go and I don't see any go error above. An uncaught exception triggering a panic in wasm doesn't seem surprising to me as long as it isn't breaking out of the wasm runtime.

If you run with --loop 10 after --wasi I'd expect it to run 10 times, proving that the cli itself is not panicking.

In one of the last few updates, the extism cli now sets the environment variable EXTISM_ENABLE_WASI_OUTPUT=1 which sets the host to print the wasi stdout and stderr. If you'd prefer it didn't you can override it by run the cli with the environment variable set as EXTISM_ENABLE_WASI_OUTPUT=0

An improvement could be to report the python exception when raised instead of lazily letting unwrap deal with it.

[bradyjoslin]

The panic from wasm seems abrupt, compared to the README example.

extism call plugin.wasm greet --input="Benjamin" --wasi
# => Error: Sorry, we don't greet Benjamins!:
# =>  File "<source>", line 17, in __invoke
# =>  File "<source>", line 9, in greet

Hoping for something like set error in the other pdks (e.g. go, dotnet) which allows sending a msg to stderr with nonzero exit code.

[zshipko]

I agree, we should be catching unwrap and setting the Extism error - I am working on a fix right now.

[zshipko]

Fix is up here: #53

It now gives similar closer to your example:

$ extism call a.wasm greet --input="Benjamin" --wasi
Error: Sorry, we don't greet Benjamins!
Traceback (most recent call last):
  File "<source>", line 39, in __invoke
  File "<source>", line 28, in __invoke
  File "<source>", line 7, in greet

returned non-zero exit code: 4294967295

[bradyjoslin]

Nice! Checkout out the PR and confirm the same result here.

❯ extism call examples/greet.wasm greet --input "Benjamin" --wasi
Error: Benjamin is not allowed
Traceback (most recent call last):
  File "<source>", line 40, in __invoke
  File "<source>", line 29, in __invoke
  File "<source>", line 7, in greet

returned non-zero exit code: 4294967295

Appreciate it!