[WASMFS] Switch to using out and err (emscripten-core#15629)

Add `emscripten_out` and `emscripten_err` along with `f` versions.
Replaced `emscripten_console_log`/`error` with those two functions respectively in `streams.cpp`.

src/library.js

@@ -3494,6 +3494,22 @@ LibraryManager.library = {
 #endif
   },
 
+  _emscripten_out__sig: 'vi',
+  _emscripten_out: function(str) {
+#if ASSERTIONS
+    assert(typeof str === 'number');
+#endif
+    out(UTF8ToString(str));
+  },
+
+  _emscripten_err__sig: 'vi',
+  _emscripten_err: function(str) {
+#if ASSERTIONS
+    assert(typeof str === 'number');
+#endif
+    err(UTF8ToString(str));
+  },
+
   emscripten_console_log__sig: 'vi',
   emscripten_console_log: function(str) {
 #if ASSERTIONS

system/include/emscripten/console.h

@@ -15,10 +15,23 @@ void emscripten_console_log(const char *utf8String);
 void emscripten_console_warn(const char *utf8String);
 void emscripten_console_error(const char *utf8String);
 
+// Write to the out() and err() hooks directly (defined in shell.js).
+// These have different behavior compared to console.log/err.
+// Under node, they write to stdout and stderr which is a more direct way to
+// write output especially in worker threads.
+// The default behavior of these functions can be overridden by print and
+// printErr, if provided on the Module object.
+// These functions are mainly intended for internal use.
+// See https://github.com/emscripten-core/emscripten/issues/14804
+void _emscripten_out(const char *utf8String);
+void _emscripten_err(const char *utf8String);
+
 // Similar to the above functions but operate with printf-like semantics.
 void emscripten_console_logf(const char *utf8String, ...) __attribute__((__format__(printf, 1, 2)));
 void emscripten_console_warnf(const char *utf8String, ...) __attribute__((__format__(printf, 1, 2)));
 void emscripten_console_errorf(const char *utf8String, ...)__attribute__((__format__(printf, 1, 2)));
+void _emscripten_outf(const char *utf8String, ...) __attribute__((__format__(printf, 1, 2)));
+void _emscripten_errf(const char *utf8String, ...) __attribute__((__format__(printf, 1, 2)));
 
 #ifdef __cplusplus
 }

system/lib/libc/emscripten_console.c

@@ -40,3 +40,17 @@ void emscripten_console_warnf(const char* fmt, ...) {
   vlogf(fmt, ap, &emscripten_console_warn);
   va_end(ap);
 }
+
+void _emscripten_outf(const char* fmt, ...) {
+  va_list ap;
+  va_start(ap, fmt);
+  vlogf(fmt, ap, &_emscripten_out);
+  va_end(ap);
+}
+
+void _emscripten_errf(const char* fmt, ...) {
+  va_list ap;
+  va_start(ap, fmt);
+  vlogf(fmt, ap, &_emscripten_err);
+  va_end(ap);
+}

system/lib/wasmfs/streams.cpp

@@ -34,7 +34,10 @@ std::shared_ptr<StdinFile> StdinFile::getSingleton() {
 }
 
 __wasi_errno_t StdoutFile::write(const uint8_t* buf, size_t len, off_t offset) {
-  return writeStdBuffer(buf, len, &emscripten_console_log, writeBuffer);
+  // Due to this issue with node and worker threads:
+  // https://github.com/emscripten-core/emscripten/issues/14804. This function
+  // will write to out(), which will write directly to stdout in node.
+  return writeStdBuffer(buf, len, &_emscripten_out, writeBuffer);
 }
 
 std::shared_ptr<StdoutFile> StdoutFile::getSingleton() {
@@ -44,7 +47,8 @@ std::shared_ptr<StdoutFile> StdoutFile::getSingleton() {
 }
 
 __wasi_errno_t StderrFile::write(const uint8_t* buf, size_t len, off_t offset) {
-  return writeStdBuffer(buf, len, &emscripten_console_error, writeBuffer);
+  // Similar issue with node and worker threads as emscripten_out.
+  return writeStdBuffer(buf, len, &_emscripten_err, writeBuffer);
 }
 
 std::shared_ptr<StderrFile> StderrFile::getSingleton() {