Handle incomplete sequences at end of input

src/IO/WriteBufferValidUTF8.cpp

@@ -149,9 +149,27 @@ void WriteBufferValidUTF8::finalizeImpl()
     /// Write all complete sequences from buffer.
     nextImpl();
 
-    /// If unfinished sequence at end, then write replacement.
+    /// Handle remaining bytes if we have an incomplete sequence
-    if (working_buffer.begin() != memory.data())
+    if (working_buffer.begin() != memory.data()) {
+        char * p = memory.data();
+
+        while (p < pos) {
+            UInt8 len = length_of_utf8_sequence[static_cast<unsigned char>(*p)];
+            if (p + len > pos) {
+                // Incomplete sequence. Skip one byte.
                 putReplacement();
+                ++p;
+            } else if (Poco::UTF8Encoding::isLegal(reinterpret_cast<unsigned char *>(p), len)) {
+                // Valid sequence
+                putValid(p, len);
+                p += len;
+            } else {
+                // Invalid sequence, skip first byte.
+                putReplacement();
+                ++p;
+            }
+        }
+    }
 }
 
 }