add option to retain fetchEvent handler

README.md

@@ -130,6 +130,10 @@ Setting `disableFeatures: ['random', 'stdio', 'clocks']` will disable all featur
 
 Note that pure components **will not report errors and will instead trap**, so that this should only be enabled after very careful testing.
 
+The features that are not included by default are:
+* `'http'` - Support for sending and receiving HTTP requests, depends on `wasi:io` 
+* `'fetch-event'` - Enables using `fetchEvent` to respond to `wasi:http/[email protected]#handle`. If the target world does note export `wasi:http/[email protected]`, this will be ignored.
+
 Note that features explicitly imported by the target world cannot be disabled - if you target a component to a world
 that imports `wasi:clocks`, then `disableFeatures: ['clocks']` will not be supported.
 

crates/spidermonkey-embedding-splicer/src/bindgen.rs

@@ -124,7 +124,12 @@ pub struct Componentization {
     pub resource_imports: Vec<(String, String, u32)>,
 }
 
-pub fn componentize_bindgen(resolve: &Resolve, id: WorldId, name: &str) -> Componentization {
+pub fn componentize_bindgen(
+    resolve: &Resolve,
+    id: WorldId,
+    name: &str,
+    retain_fetch_event: bool,
+) -> Componentization {
     let mut bindgen = JsBindgen {
         src: Source::default(),
         esm_bindgen: EsmBindgen::default(),
@@ -342,6 +347,7 @@ pub fn componentize_bindgen(resolve: &Resolve, id: WorldId, name: &str) -> Compo
         "$source_mod",
         &mut bindgen.local_names,
         name,
+        retain_fetch_event,
     );
 
     let js_intrinsics = render_intrinsics(&mut bindgen.all_intrinsics, false, true);
@@ -1001,6 +1007,7 @@ impl EsmBindgen {
         imports_object: &str,
         _local_names: &mut LocalNames,
         source_name: &str,
+        retain_fetch_event: bool,
     ) {
         // TODO: bring back these validations of imports
         // including using the flattened bindings
@@ -1043,6 +1050,10 @@ impl EsmBindgen {
                 ");
         }
         for (export_name, binding) in &self.exports {
+            // If we are retaining the fetch event, then we should just let StarlingMonkey handle the event directly.
+            if retain_fetch_event && export_name == "wasi:http/[email protected]" {
+                continue;
+            }
             match binding {
                 Binding::Interface(bindings) => {
                     uwrite!(output, "const ");

crates/spidermonkey-embedding-splicer/src/lib.rs

@@ -1,6 +1,9 @@
 use anyhow::{bail, Context, Result};
 use bindgen::BindingItem;
-use std::path::{Path, PathBuf};
+use std::{
+    collections::HashSet,
+    path::{Path, PathBuf},
+};
 
 mod bindgen;
 mod splice;
@@ -111,6 +114,7 @@ impl Guest for SpidermonkeyEmbeddingSplicerComponent {
         wit_path: Option<String>,
         world_name: Option<String>,
         debug: bool,
+        mut retain_fetch_event: bool,
     ) -> Result<SpliceResult, String> {
         let source_name = source_name.unwrap_or("source.js".to_string());
 
@@ -131,7 +135,22 @@ impl Guest for SpidermonkeyEmbeddingSplicerComponent {
             .map_err(|e| e.to_string())?;
 
         let mut wasm_bytes = wit_component::dummy_module(&resolve, world);
-        let componentized = bindgen::componentize_bindgen(&resolve, world, &source_name);
+        let componentized =
+            bindgen::componentize_bindgen(&resolve, world, &source_name, retain_fetch_event);
+
+        let target_world = &resolve.worlds[world];
+        let mut target_world_exports = HashSet::new();
+
+        for (key, _) in &target_world.exports {
+            target_world_exports.insert(resolve.name_world_key(key));
+        }
+
+        // Do not retain fetch event if the target world does not export the
+        // incomingHandler Interface as that would make it incompatible with the
+        // target world
+        if !target_world_exports.contains("wasi:http/[email protected]") {
+            retain_fetch_event = false;
+        }
 
         // merge the engine world with the target world, retaining the engine producers
         let producers = if let Ok((
@@ -330,8 +349,8 @@ impl Guest for SpidermonkeyEmbeddingSplicerComponent {
         // println!("{:?}", &imports);
         // println!("{:?}", &componentized.imports);
         // println!("{:?}", &exports);
-        let mut wasm =
-            splice::splice(engine, imports, exports, debug).map_err(|e| format!("{:?}", e))?;
+        let mut wasm = splice::splice(engine, imports, exports, debug, retain_fetch_event)
+            .map_err(|e| format!("{:?}", e))?;
 
         // add the world section to the spliced wasm
         wasm.push(section.id());

crates/spidermonkey-embedding-splicer/src/splice.rs

@@ -38,6 +38,7 @@ pub fn splice(
     imports: Vec<(String, String, CoreFn, Option<i32>)>,
     exports: Vec<(String, CoreFn)>,
     debug: bool,
+    retain_fetch_event: bool,
 ) -> Result<Vec<u8>> {
     let mut config = walrus::ModuleConfig::new();
     if debug {
@@ -53,13 +54,16 @@ pub fn splice(
         module.exports.delete(expt.id());
         module.funcs.delete(run);
     }
-    if let Ok(serve) = module
-        .exports
-        .get_func("wasi:http/[email protected]#handle")
-    {
-        let expt = module.exports.get_exported_func(serve).unwrap();
-        module.exports.delete(expt.id());
-        module.funcs.delete(serve);
+
+    if !retain_fetch_event {
+        if let Ok(serve) = module
+            .exports
+            .get_func("wasi:http/[email protected]#handle")
+        {
+            let expt = module.exports.get_exported_func(serve).unwrap();
+            module.exports.delete(expt.id());
+            module.funcs.delete(serve);
+        }
     }
 
     // we reencode the WASI world component data, so strip it out from the
@@ -79,7 +83,7 @@ pub fn splice(
     synthesize_import_functions(&mut module, &imports)?;
 
     // create the exported functions as wrappers around the "cabi_call" function
-    synthesize_export_functions(&mut module, &exports)?;
+    synthesize_export_functions(&mut module, &exports, retain_fetch_event)?;
 
     Ok(module.emit_wasm())
 }
@@ -530,6 +534,7 @@ fn synthesize_import_functions(
 fn synthesize_export_functions(
     module: &mut walrus::Module,
     exports: &Vec<(String, CoreFn)>,
+    retain_fetch_event: bool,
 ) -> Result<()> {
     let cabi_realloc = get_export_fid(
         module,
@@ -561,6 +566,9 @@ fn synthesize_export_functions(
     let arg_ptr = module.locals.add(ValType::I32);
     let ret_ptr = module.locals.add(ValType::I32);
     for (export_num, (expt_name, expt_sig)) in exports.iter().enumerate() {
+        if retain_fetch_event && expt_name == "wasi:http/[email protected]#handle" {
+            continue;
+        }
         // Export function synthesis
         {
             // add the function type

crates/spidermonkey-embedding-splicer/wit/spidermonkey-embedding-splicer.wit

@@ -33,5 +33,5 @@ world spidermonkey-embedding-splicer {
 
   export stub-wasi: func(engine: list<u8>, features: list<features>, wit-world: option<string>, wit-path: option<string>, world-name: option<string>) -> result<list<u8>, string>;
 
-  export splice-bindings: func(source-name: option<string>, spidermonkey-engine: list<u8>, wit-world: option<string>, wit-path: option<string>, world-name: option<string>, debug: bool) -> result<splice-result, string>;
+  export splice-bindings: func(source-name: option<string>, spidermonkey-engine: list<u8>, wit-world: option<string>, wit-path: option<string>, world-name: option<string>, debug: bool, retain-fetch-event: bool ) -> result<splice-result, string>;
 }

src/componentize.js

@@ -47,13 +47,16 @@ export async function componentize(jsSource, witWorld, opts) {
     enableFeatures = [],
   } = opts || {};
 
+  const retainFetchEvent = enableFeatures.includes('fetch-event')
+
   let { wasm, jsBindings, importWrappers, exports, imports } = spliceBindings(
     sourceName,
     await readFile(engine),
     witWorld,
     maybeWindowsPath(witPath),
     worldName,
-    false
+    false,
+    retainFetchEvent
   );
 
   // we never disable a feature that is already in the target world usage