Flush stdout unconditionally (#668)

This commit ensures that `stdout` is always correctly flushed after
reading from it. This is critical for dynamic use-cases of Javy

crates/cli/tests/dynamic_linking_test.rs

@@ -4,7 +4,7 @@ use std::io::{Cursor, Read, Write};
 use std::process::Command;
 use std::str;
 use uuid::Uuid;
-use wasi_common::pipe::WritePipe;
+use wasi_common::pipe::{ReadPipe, WritePipe};
 use wasi_common::sync::WasiCtxBuilder;
 use wasi_common::WasiCtx;
 use wasmtime::{Config, Engine, ExternType, Linker, Module, Store};
@@ -14,7 +14,7 @@ mod common;
 #[test]
 pub fn test_dynamic_linking() -> Result<()> {
     let js_src = "console.log(42);";
-    let log_output = invoke_fn_on_generated_module(js_src, "_start", None)?;
+    let log_output = invoke_fn_on_generated_module(js_src, "_start", None, None, None)?;
     assert_eq!("42\n", &log_output);
     Ok(())
 }
@@ -29,15 +29,16 @@ pub fn test_dynamic_linking_with_func() -> Result<()> {
             export foo-bar: func()
         }
     ";
-    let log_output = invoke_fn_on_generated_module(js_src, "foo-bar", Some((wit, "foo-test")))?;
+    let log_output =
+        invoke_fn_on_generated_module(js_src, "foo-bar", Some((wit, "foo-test")), None, None)?;
     assert_eq!("Toplevel\nIn foo\n", &log_output);
     Ok(())
 }
 
 #[test]
 pub fn test_dynamic_linking_with_func_without_flag() -> Result<()> {
     let js_src = "export function foo() { console.log('In foo'); }; console.log('Toplevel');";
-    let res = invoke_fn_on_generated_module(js_src, "foo", None);
+    let res = invoke_fn_on_generated_module(js_src, "foo", None, None, None);
     assert_eq!(
         "failed to find function export `foo`",
         res.err().unwrap().to_string()
@@ -50,7 +51,7 @@ pub fn check_for_new_imports() -> Result<()> {
     // If you need to change this test, then you've likely made a breaking change.
     let js_src = "console.log(42);";
     let wasm = create_dynamically_linked_wasm_module(js_src, None)?;
-    let (engine, _linker, _store) = create_wasm_env(WritePipe::new_in_memory())?;
+    let (engine, _linker, _store) = create_wasm_env(WritePipe::new_in_memory(), None, None)?;
     let module = Module::from_binary(&engine, &wasm)?;
     for import in module.imports() {
         match (import.module(), import.name(), import.ty()) {
@@ -78,7 +79,7 @@ pub fn check_for_new_imports_for_exports() -> Result<()> {
         }
     ";
     let wasm = create_dynamically_linked_wasm_module(js_src, Some((wit, "foo-test")))?;
-    let (engine, _linker, _store) = create_wasm_env(WritePipe::new_in_memory())?;
+    let (engine, _linker, _store) = create_wasm_env(WritePipe::new_in_memory(), None, None)?;
     let module = Module::from_binary(&engine, &wasm)?;
     for import in module.imports() {
         match (import.module(), import.name(), import.ty()) {
@@ -107,8 +108,13 @@ pub fn test_dynamic_linking_with_arrow_fn() -> Result<()> {
             export default: func()
         }
     ";
-    let log_output =
-        invoke_fn_on_generated_module(js_src, "default", Some((wit, "exported-arrow")))?;
+    let log_output = invoke_fn_on_generated_module(
+        js_src,
+        "default",
+        Some((wit, "exported-arrow")),
+        None,
+        None,
+    )?;
     assert_eq!("42\n", log_output);
     Ok(())
 }
@@ -120,6 +126,28 @@ fn test_producers_section_present() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn javy_json_identity() -> Result<()> {
+    let src = r#"
+        console.log(Javy.JSON.toStdout(Javy.JSON.fromStdin()));
+    "#;
+
+    let input = "{\"x\":5}";
+
+    let bytes = String::from(input).into_bytes();
+    let stdin = Some(ReadPipe::from(bytes));
+    let stdout = WritePipe::new_in_memory();
+    let out = invoke_fn_on_generated_module(src, "_start", None, stdin, Some(stdout.clone()))?;
+
+    assert_eq!(out, "undefined\n");
+    assert_eq!(
+        String::from(input),
+        String::from_utf8(stdout.try_into_inner().unwrap().into_inner()).unwrap(),
+    );
+
+    Ok(())
+}
+
 fn create_dynamically_linked_wasm_module(
     js_src: &str,
     wit: Option<(&str, &str)>,
@@ -164,11 +192,13 @@ fn invoke_fn_on_generated_module(
     js_src: &str,
     func: &str,
     wit: Option<(&str, &str)>,
+    stdin: Option<ReadPipe<Cursor<Vec<u8>>>>,
+    stdout: Option<WritePipe<Cursor<Vec<u8>>>>,
 ) -> Result<String> {
     let js_wasm = create_dynamically_linked_wasm_module(js_src, wit)?;
 
     let stderr = WritePipe::new_in_memory();
-    let (engine, mut linker, mut store) = create_wasm_env(stderr.clone())?;
+    let (engine, mut linker, mut store) = create_wasm_env(stderr.clone(), stdin, stdout)?;
     let quickjs_provider_module = common::create_quickjs_provider_module(&engine)?;
     let js_module = Module::from_binary(&engine, &js_wasm)?;
 
@@ -190,11 +220,19 @@ fn invoke_fn_on_generated_module(
 
 fn create_wasm_env(
     stderr: WritePipe<Cursor<Vec<u8>>>,
+    stdin: Option<ReadPipe<Cursor<Vec<u8>>>>,
+    stdout: Option<WritePipe<Cursor<Vec<u8>>>>,
 ) -> Result<(Engine, Linker<WasiCtx>, Store<WasiCtx>)> {
     let engine = Engine::new(Config::new().wasm_multi_memory(true))?;
     let mut linker = Linker::new(&engine);
     wasi_common::sync::add_to_linker(&mut linker, |s| s)?;
     let wasi = WasiCtxBuilder::new().stderr(Box::new(stderr)).build();
+    if let Some(stdout) = stdout {
+        wasi.set_stdout(Box::new(stdout));
+    }
+    if let Some(stdin) = stdin {
+        wasi.set_stdin(Box::new(stdin));
+    }
     let store = Store::new(&engine, wasi);
     Ok((engine, linker, store))
 }

crates/javy/src/apis/json.rs

@@ -230,5 +230,6 @@ fn to_stdout(args: Args<'_>) -> Result<()> {
     let (_, args) = args.release();
     let mut fd = std::io::stdout();
     let buffer = json::stringify(args[0].clone())?;
-    fd.write_all(&buffer).map_err(Into::into)
+    fd.write_all(&buffer)?;
+    fd.flush().map_err(Into::into)
 }