Expound on HIDL Return errors. am: 94c4374133

am: 83d1790b25

Change-Id: I2183ead0d214500ef2c18c2924d923ea5f9490c0

2 files changed, 20 insertions, 8 deletions

diff --git a/base/Status.cpp b/base/Status.cpp
index 90474a0..08631cc 100644
--- a/base/Status.cpp
+++ b/base/Status.cpp
@@ -149,19 +149,28 @@ void setProcessHidlReturnRestriction(HidlReturnRestriction restriction) {
 }
 
 namespace details {
-    void return_status::assertOk() const {
+    void return_status::onValueRetrieval() const {
         if (!isOk()) {
             LOG(FATAL) << "Attempted to retrieve value from failed HIDL call: " << description();
         }
     }
 
+    void return_status::assertOk() const {
+        if (!isOk()) {
+            LOG(FATAL) << "Failed HIDL return status not checked. Usually this happens because of "
+                          "a transport error (error parceling, binder driver, or from unparceling)"
+                          ". If you see this in code calling into \"Bn\" classes in for a HAL "
+                          "server process, then it is likely that the code there is returning "
+                          "transport errors there (as opposed to errors defined within its "
+                          "protocol). Error is: " << description();
+        }
+    }
+
     return_status::~return_status() {
         // mCheckedStatus must be checked before isOk since isOk modifies mCheckedStatus
         if (mCheckedStatus) return;
 
-        if (!isOk()) {
-            LOG(FATAL) << "Failed HIDL return status not checked: " << description();
-        }
+        assertOk();
 
         if (gReturnRestriction == HidlReturnRestriction::NONE) {
             return;
@@ -176,9 +185,10 @@ namespace details {
     }
 
     return_status& return_status::operator=(return_status&& other) noexcept {
-        if (!mCheckedStatus && !isOk()) {
-            LOG(FATAL) << "Failed HIDL return status not checked: " << description();
+        if (!mCheckedStatus) {
+            assertOk();
         }
+
         std::swap(mStatus, other.mStatus);
         std::swap(mCheckedStatus, other.mCheckedStatus);
         return *this;
diff --git a/base/include/hidl/Status.h b/base/include/hidl/Status.h
index 817277f..07d352f 100644
--- a/base/include/hidl/Status.h
+++ b/base/include/hidl/Status.h
@@ -143,6 +143,8 @@ namespace details {
 
         template <typename T, typename U>
         friend Return<U> StatusOf(const Return<T> &other);
+    protected:
+        void onValueRetrieval() const;
     public:
         void assertOk() const;
         return_status() {}
@@ -224,7 +226,7 @@ public:
     ~Return() = default;
 
     operator T() const {
-        assertOk();
+        onValueRetrieval();  // assert okay
         return mVal;
     }
 
@@ -253,7 +255,7 @@ public:
     ~Return() = default;
 
     operator sp<T>() const {
-        assertOk();
+        onValueRetrieval();  // assert okay
         return mVal;
     }