+/**
+ * Copy data to the compression buffer of a connection. We do collect
+ * some data there until it's full so that we can achieve better
+ * compression ratios.
+ * If the (pre-)compression buffer is full, we try to flush it ("actually
+ * compress some data") and to add the new (uncompressed) data afterwards.
+ * This function closes the connection on error.
+ * @param Idx Connection handle.
+ * @param Data Pointer to the data.
+ * @param Len Length of the data to add.
+ * @return true on success, false otherwise.
+ */