Merge "libbinder*: clarify setDataPosition constraints"

2 files changed, 10 insertions, 0 deletions

diff --git a/libs/binder/include/binder/Parcel.h b/libs/binder/include/binder/Parcel.h
index e2b2c5128d..39d0c9068f 100644
--- a/libs/binder/include/binder/Parcel.h
+++ b/libs/binder/include/binder/Parcel.h
@@ -76,6 +76,11 @@ public:
     size_t              dataCapacity() const;
 
     status_t            setDataSize(size_t size);
+
+    // this must only be used to set a data position that was previously returned from
+    // dataPosition(). If writes are made, the exact same types of writes must be made (e.g.
+    // auto i = p.dataPosition(); p.writeInt32(0); p.setDataPosition(i); p.writeInt32(1);).
+    // Writing over objects, such as file descriptors and binders, is not supported.
     void                setDataPosition(size_t pos) const;
     status_t            setDataCapacity(size_t size);
 
diff --git a/libs/binder/ndk/include_ndk/android/binder_parcel.h b/libs/binder/ndk/include_ndk/android/binder_parcel.h
index 84575811f0..f68612c3ba 100644
--- a/libs/binder/ndk/include_ndk/android/binder_parcel.h
+++ b/libs/binder/ndk/include_ndk/android/binder_parcel.h
@@ -59,6 +59,11 @@ void AParcel_delete(AParcel* parcel) __INTRODUCED_IN(29);
 /**
  * Sets the position within the parcel.
  *
+ * This must be called with a position that has been previously returned from
+ * AParcel_getDataPosition. If writes are made after setting the data position, they must
+ * be made in the exact same sequence used before resetting data position. Writing over
+ * objects such as binders or file descriptors is not supported.
+ *
  * Available since API level 29.
  *
  * \param parcel The parcel of which to set the position.