[spinel] return error from SaveFrame if not enough space is available (#9244)

src/lib/spinel/multi_frame_buffer.hpp

@@ -309,14 +309,27 @@ public:
      *
      * Saved frame can be retrieved later using `GetNextSavedFrame()`.
      *
+     * @retval OT_ERROR_NONE     Successfully saved the buffer and prepared the write pointer for the next frame.
+     * @retval OT_ERROR_NO_BUFS  Insufficient buffer space.
      */
-    void SaveFrame(void)
+    otError SaveFrame(void)
     {
-        Encoding::LittleEndian::WriteUint16(GetSkipLength() + GetLength(), mWriteFrameStart + kHeaderTotalLengthOffset);
-        mWriteFrameStart = mWritePointer;
-        IgnoreError(SetSkipLength(0));
-        mWritePointer    = GetFrame();
-        mRemainingLength = static_cast<uint16_t>(mBuffer + kSize - mWritePointer);
+        otError error = OT_ERROR_NONE;
+
+        // If the next header will overflow the buffer, we can't save the frame.
+        if (!CanWrite(kHeaderSize))
+        {
+            error = OT_ERROR_NO_BUFS;
+        }
+        else
+        {
+            Encoding::LittleEndian::WriteUint16(GetSkipLength() + GetLength(),
+                                                mWriteFrameStart + kHeaderTotalLengthOffset);
+            mWriteFrameStart = mWritePointer;
+            IgnoreError(SetSkipLength(0));
+        }
+
+        return error;
     }
 
     /**

src/lib/spinel/radio_spinel_impl.hpp

@@ -530,13 +530,14 @@ void RadioSpinel<InterfaceType>::HandleNotification(SpinelInterface::RxFrameBuff
     }
 
 exit:
-    if (shouldSaveFrame)
-    {
-        aFrameBuffer.SaveFrame();
-    }
-    else
+    if (!shouldSaveFrame || aFrameBuffer.SaveFrame() != OT_ERROR_NONE)
     {
         aFrameBuffer.DiscardFrame();
+
+        if (shouldSaveFrame)
+        {
+            otLogCritPlat("RX Spinel buffer full, dropped incoming frame");
+        }
     }
 
     UpdateParseErrorCount(error);