Fix segfault by ensuring that we have created the context in the VM. (i…

…stio#189)

* Fix segfault by ensuring that we have created the context in the VM.
envoyproxy/envoy-wasm#180

Signed-off-by: John Plevyak <jplevyak@gmail.com>

source/extensions/common/wasm/wasm.cc

@@ -1943,6 +1943,7 @@ void Context::onCreate(uint32_t root_context_id) {
 
 Http::FilterHeadersStatus Context::onRequestHeaders() {
   onCreate(root_context_id_);
+  in_vm_context_created_ = true;
   // Store the stream id so that we can use it in log().
   auto& stream_info = decoder_callbacks_->streamInfo();
   auto& metadata = (*stream_info.dynamicMetadata()
@@ -1992,8 +1993,17 @@ Http::FilterMetadataStatus Context::onRequestMetadata() {
 }
 
 Http::FilterHeadersStatus Context::onResponseHeaders() {
-  if (!wasm_->onResponseHeaders_)
+  if (!in_vm_context_created_) {
+    // If the request is invalid then onRequestHeaders() will not be called and neither will
+    // onCreate() then sendLocalReply be called which will call this function. In this case we
+    // need to call onCreate() so that the Context inside the VM is created before the
+    // onResponseHeaders() call.
+    onCreate(root_context_id_);
+    in_vm_context_created_ = true;
+  }
+  if (!wasm_->onResponseHeaders_) {
     return Http::FilterHeadersStatus::Continue;
+  }
   if (wasm_->onResponseHeaders_(this, id_) == 0) {
     return Http::FilterHeadersStatus::Continue;
   }

source/extensions/common/wasm/wasm.h

@@ -397,6 +397,7 @@ class Context : public Http::StreamFilter,
   Context* root_context_{nullptr}; // set in all contexts.
   const std::string root_id_;      // set only in roots.
   std::string log_prefix_;
+  bool in_vm_context_created_ = false;
   bool destroyed_ = false;
 
   uint32_t next_http_call_token_ = 1;

source/extensions/filters/http/wasm/wasm_filter.h

@@ -28,7 +28,7 @@ class FilterConfig : Logger::Loggable<Logger::Id::wasm> {
     if (!root_context_id_) {
       root_context_id_ = wasm.getRootContext(root_id_)->id();
     }
-    return std::make_shared<Context>(&tls_slot_->getTyped<Wasm>(), root_context_id_);
+    return std::make_shared<Context>(&wasm, root_context_id_);
   }
 
 private: