Update config schema API to not use WASI (#964)

Author: jeffcharles

crates/cli/src/js_config.rs

@@ -1,8 +1,8 @@
-use anyhow::Result;
+use anyhow::{anyhow, Result};
 use serde::Deserialize;
 use std::{collections::HashMap, str};
-use wasmtime::{AsContextMut, Engine, Linker};
-use wasmtime_wasi::{pipe::MemoryOutputPipe, WasiCtxBuilder};
+use wasmtime::{AsContext, AsContextMut, Engine, Linker};
+use wasmtime_wasi::WasiCtxBuilder;
 
 use crate::{CliPlugin, PluginKind};
 
@@ -21,18 +21,23 @@ impl ConfigSchema {
                 let module = wasmtime::Module::new(&engine, cli_plugin.as_plugin().as_bytes())?;
                 let mut linker = Linker::new(&engine);
                 wasmtime_wasi::preview1::add_to_linker_sync(&mut linker, |s| s)?;
-                let stdout = MemoryOutputPipe::new(usize::MAX);
-                let wasi = WasiCtxBuilder::new()
-                    .inherit_stderr()
-                    .stdout(stdout.clone())
-                    .build_p1();
+                let wasi = WasiCtxBuilder::new().inherit_stderr().build_p1();
                 let mut store = wasmtime::Store::new(&engine, wasi);
                 let instance = linker.instantiate(store.as_context_mut(), &module)?;
-                instance
-                    .get_typed_func::<(), ()>(store.as_context_mut(), "config_schema")?
+
+                let ret_area = instance
+                    .get_typed_func::<(), i32>(store.as_context_mut(), "config-schema")?
                     .call(store.as_context_mut(), ())?;
-                drop(store);
-                let config_json = stdout.try_into_inner().unwrap().to_vec();
+                let memory = instance
+                    .get_memory(store.as_context_mut(), "memory")
+                    .ok_or_else(|| anyhow!("Missing memory export"))?;
+                let mut buf = [0; 8];
+                memory.read(store.as_context(), ret_area as usize, &mut buf)?;
+                let offset = u32::from_le_bytes(buf[0..4].try_into().unwrap());
+                let len = u32::from_le_bytes(buf[4..8].try_into().unwrap());
+                let mut config_json = vec![0; len as usize];
+                memory.read(store.as_context(), offset as usize, &mut config_json)?;
+
                 let config_schema = serde_json::from_slice::<ConfigSchema>(&config_json)?;
                 let mut configs = Vec::with_capacity(config_schema.supported_properties.len());
                 for config in config_schema.supported_properties {

crates/plugin/src/shared_config/mod.rs

@@ -1,14 +1,19 @@
 //! APIs and data structures for receiving runtime configuration from the Javy CLI.
 
+use std::cell::OnceCell;
+
 use anyhow::Result;
 use javy_plugin_api::Config;
 use serde::Deserialize;
-use std::io::{stdout, Write};
 
 mod runtime_config;
 
 use crate::runtime_config;
 
+thread_local! {
+    static CONFIG_RET_AREA: OnceCell<[u32; 2]> = const { OnceCell::new() };
+}
+
 runtime_config! {
     #[derive(Debug, Default, Deserialize)]
     #[serde(deny_unknown_fields, rename_all = "kebab-case")]
@@ -48,14 +53,17 @@ impl SharedConfig {
     }
 }
 
-#[export_name = "config_schema"]
-pub fn config_schema() {
-    stdout()
-        .write_all(
-            serde_json::to_string(&SharedConfig::config_schema())
-                .unwrap()
-                .as_bytes(),
-        )
-        .unwrap();
-    stdout().flush().unwrap();
+#[export_name = "config-schema"]
+pub fn config_schema() -> *const u32 {
+    let schema = serde_json::to_string(&SharedConfig::config_schema())
+        .unwrap()
+        .into_bytes();
+    let len = schema.len();
+    // Leak the config schema. This should be fine since the Wasm instance will
+    // be torn down right after by the Javy CLI.
+    let bytecode_ptr = Box::leak(schema.into_boxed_slice()).as_ptr();
+    CONFIG_RET_AREA.with(|v| {
+        v.set([bytecode_ptr as u32, len as u32]).unwrap();
+        v.get().unwrap().as_ptr()
+    })
 }