fix: ensure ResourceTable contains valid resource upon creation

Author: Sl1mb0

host/src/component.rs

@@ -24,6 +24,24 @@ use crate::{
     state::WasmStateImpl, vfs::VfsState,
 };
 
+/// Sentinel resource for handle 0 in the resource table. This is needed since
+/// wasip2 treats handle 0 as invalid, but wasmtime's resource table starts at
+/// 0. We need to reserve handle 0 to be able to use the resource table as a
+/// source of truth for handle validity in the WASI p2 implementation. The
+/// actual value of the sentinel is not important since we will never access it
+/// (and if we do, it's a bug).
+struct ResourceTableSentinel;
+
+/// Create new resource table with sentinel.
+fn new_resource_table() -> ResourceTable {
+    let mut table = ResourceTable::new();
+    // Reserve handle 0 since wasip2 treats it as invalid.
+    table
+        .push(ResourceTableSentinel)
+        .expect("resource table sentinel insert");
+    table
+}
+
 /// Create WASM engine.
 fn create_engine<F>(flags: &F) -> DataFusionResult<Engine>
 where
@@ -321,7 +339,7 @@ impl WasmComponentInstance {
             stderr,
             wasi_ctx: wasi_ctx_builder.build().into(),
             wasi_http_ctx: WasiHttpCtx::new(),
-            resource_table: ResourceTable::new(),
+            resource_table: new_resource_table(),
             http_validator: Arc::clone(&permissions.http),
             io_rt,
         };