Process certificate signing request in the right event loop

Summary:
To ensure that no deadlocks take place, it is important that there are no re-entrant calls from within the callbacks or event handlers.

For the most part, this was already the case. Event and message handlers run critical sections into a Folly event scheduler.

The only exception was the sendExpectResponse used during the certificate exchange. Once the response was received, the non-secure socket was disconnected.
The solution was to put that operation in the Folly event scheduler as it should've been from the beginning.

changelog: Certificate signing request response to be processed on the right event loop.

Reviewed By: fabiomassimo

Differential Revision: D35548148

fbshipit-source-id: cea2476ad66137f376acda66cdbc27801c0c47e1

xplat/Flipper/FlipperConnectionManagerImpl.cpp

@@ -233,7 +233,7 @@ bool FlipperConnectionManagerImpl::connectAndExchangeCertificate() {
   contextStore_->resetState();
   resettingState->complete();
 
-  requestSignedCertFromFlipper();
+  requestSignedCertificate();
   return true;
 }
 
@@ -377,33 +377,17 @@ bool FlipperConnectionManagerImpl::isCertificateExchangeNeeded() {
   return !hasRequiredFiles;
 }
 
-void FlipperConnectionManagerImpl::requestSignedCertFromFlipper() {
-  auto generatingCSR = flipperState_->start("Generate CSR");
-  std::string csr = contextStore_->getCertificateSigningRequest();
-  generatingCSR->complete();
-  int medium = certProvider_ != nullptr
-      ? certProvider_->getCertificateExchangeMedium()
-      : FlipperCertificateExchangeMedium::FS_ACCESS;
-  folly::dynamic message = folly::dynamic::object("method", "signCertificate")(
-      "csr", csr.c_str())(
-      "destination",
-      contextStore_->getCertificateDirectoryPath().c_str())("medium", medium);
-  auto gettingCert = flipperState_->start("Getting cert from desktop");
-
-  certificateExchangeCompleted_ = false;
-
-  flipperEventBase_->add([this, message, gettingCert, medium]() {
-    client_->sendExpectResponse(
-        folly::toJson(message),
-        [this, message, gettingCert, medium](
-            const std::string& response, bool isError) {
+void FlipperConnectionManagerImpl::processSignedCertificateResponse(
+    std::shared_ptr<FlipperStep> gettingCert,
+    std::string response,
+    bool isError) {
   /**
-            Need to keep track of whether the response has been handled.
-            On success, the completion handler deallocates the socket which in
-            turn triggers a disconnect. A disconnect is called within the
-            context of a subscription handler. This means that the completion
-            handler can be called again to notify that the stream has been
-            interrupted because we are effectively still handing the response
+     Need to keep track of whether the response has been
+     handled. On success, the completion handler deallocates the socket which in
+     turn triggers a disconnect. A disconnect is called within
+     the context of a subscription handler. This means that the completion
+     handler can be called again to notify that the stream has
+     been interrupted because we are effectively still handing the response
      read. So, if already handled, ignore and return;
   */
   if (certificateExchangeCompleted_)
@@ -418,6 +402,10 @@ void FlipperConnectionManagerImpl::requestSignedCertFromFlipper() {
     client_ = nullptr;
     return;
   }
+  int medium = certProvider_ != nullptr
+      ? certProvider_->getCertificateExchangeMedium()
+      : FlipperCertificateExchangeMedium::FS_ACCESS;
+
   if (!response.empty()) {
     folly::dynamic config = folly::parseJson(response);
     config["medium"] = medium;
@@ -456,6 +444,32 @@ void FlipperConnectionManagerImpl::requestSignedCertFromFlipper() {
   // which will be handled by Flipper which will initiate
   // a reconnect sequence.
   client_ = nullptr;
+}
+
+void FlipperConnectionManagerImpl::requestSignedCertificate() {
+  auto generatingCSR = flipperState_->start("Generate CSR");
+  std::string csr = contextStore_->getCertificateSigningRequest();
+  generatingCSR->complete();
+
+  int medium = certProvider_ != nullptr
+      ? certProvider_->getCertificateExchangeMedium()
+      : FlipperCertificateExchangeMedium::FS_ACCESS;
+  folly::dynamic message = folly::dynamic::object("method", "signCertificate")(
+      "csr", csr.c_str())(
+      "destination",
+      contextStore_->getCertificateDirectoryPath().c_str())("medium", medium);
+
+  auto gettingCert = flipperState_->start("Getting cert from desktop");
+
+  certificateExchangeCompleted_ = false;
+  flipperEventBase_->add([this, message, gettingCert]() {
+    client_->sendExpectResponse(
+        folly::toJson(message),
+        [this, gettingCert](const std::string& response, bool isError) {
+          flipperEventBase_->add([this, gettingCert, response, isError]() {
+            this->processSignedCertificateResponse(
+                gettingCert, response, isError);
+          });
         });
   });
   failedConnectionAttempts_ = 0;

xplat/Flipper/FlipperConnectionManagerImpl.h

@@ -82,7 +82,11 @@ class FlipperConnectionManagerImpl : public FlipperConnectionManager {
   bool connectAndExchangeCertificate();
   bool connectSecurely();
   bool isCertificateExchangeNeeded();
-  void requestSignedCertFromFlipper();
+  void requestSignedCertificate();
+  void processSignedCertificateResponse(
+      std::shared_ptr<FlipperStep> gettingCertificateStep,
+      std::string response,
+      bool isError);
   bool isRunningInOwnThread();
   void reevaluateSocketProvider();
   std::string getDeviceId();