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diff --git a/backend/ipc.h b/backend/ipc.h
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+/*  ipc.h -- inter-process communication (IPC) support
+ *  Copyright (C) 2019 SEIKO EPSON Corporation
+ *
+ *  License: EPSON END USER SOFTWARE LICENSE
+ *  Author : SEIKO EPSON Corporation
+ *
+ *  This file is part of Image Scan! for Linux.
+ *  It is distributed under the terms of the EPSON END USER SOFTWARE LICENSE.
+ *
+ *  You should have received a verbatim copy of the EPSON END USER SOFTWARE
+ *  LICENSE along with the software.
+ */
+
+
+#ifndef ipc_h
+#define ipc_h
+
+#include <stdint.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <sane/sane.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+/*! \brief Exceptional return values from ipc_recv() and ipc_send()
+ *  In particular, a return value of zero from read() conflicts with
+ *  our ipc_recv() API where a return value of zero does not indicate
+ *  EOF, but a successful read of zero bytes.
+ */
+#define MERR -1               /*!< read/write error */
+#define MEOF -2               /*!< eof; only returned by ipc_recv() */
+
+enum {
+  TYPE_ESC = 1,
+  TYPE_INIT,
+  TYPE_DIE,
+  TYPE_OPEN,
+  TYPE_CLOSE,
+  TYPE_LIST,
+  TYPE_STATUS,
+
+  TYPE_DIP_CTOR = 0x01,
+  TYPE_DIP_DTOR = 0x02,
+  TYPE_DIP_PARM = 0x03,
+  TYPE_DIP_DATA = 0x04,
+  TYPE_DIP_MASK = 0x0f,
+  TYPE_DIP_FLAG = 0xf0,
+
+  TYPE_DIP_SKEW_FLAG = 0x10,
+  TYPE_DIP_SKEW_CTOR = TYPE_DIP_SKEW_FLAG | TYPE_DIP_CTOR,
+  TYPE_DIP_SKEW_DTOR = TYPE_DIP_SKEW_FLAG | TYPE_DIP_DTOR,
+  TYPE_DIP_SKEW_PARM = TYPE_DIP_SKEW_FLAG | TYPE_DIP_PARM,
+  TYPE_DIP_SKEW_DATA = TYPE_DIP_SKEW_FLAG | TYPE_DIP_DATA,
+  TYPE_DIP_SKEW_MASK = TYPE_DIP_SKEW_FLAG | TYPE_DIP_MASK,
+
+  TYPE_DIP_CROP_FLAG = 0x20,
+  TYPE_DIP_CROP_CTOR = TYPE_DIP_CROP_FLAG | TYPE_DIP_CTOR,
+  TYPE_DIP_CROP_DTOR = TYPE_DIP_CROP_FLAG | TYPE_DIP_DTOR,
+  TYPE_DIP_CROP_PARM = TYPE_DIP_CROP_FLAG | TYPE_DIP_PARM,
+  TYPE_DIP_CROP_DATA = TYPE_DIP_CROP_FLAG | TYPE_DIP_DATA,
+  TYPE_DIP_CROP_MASK = TYPE_DIP_CROP_FLAG | TYPE_DIP_MASK,
+};
+
+enum {
+  STATUS_OK = 0,
+  STATUS_NG
+};
+
+ssize_t ipc_send (int sock, uint16_t id, uint8_t type_status,
+                  size_t size, const void* payload);
+ssize_t ipc_recv (int sock, uint16_t *id, uint8_t *type_status,
+                  void** payload);
+
+  typedef struct
+  {
+    pid_t pid;
+    int   port;
+    int   socket;
+
+    const char *name;
+
+  } process;
+
+  /*! \brief  Attempts to start \a program as a child process
+   */
+  process * ipc_exec (const char *program, const char *pkglibdir,
+                      SANE_Status *status);
+
+  /*! \brief  Terminates a child process
+   */
+  process * ipc_kill (process *child);
+
+  typedef struct
+  {
+    SANE_Parameters parms;
+    SANE_Int        res_x;
+    SANE_Int        res_y;
+    SANE_Int        gamma;
+    SANE_Bool       bside;
+    char            fw_name[16 + 1];
+
+  } ipc_dip_parms;
+
+  /*! \brief Performs an image processing action
+   *
+   *  If any of the IPC messaging signals an error, the original image
+   *  data will not be modified at all.  That is, \a ctx and \a buffer
+   *  remain unchanged in such a case.
+   */
+  void ipc_dip_proc (process *child, int flag, const ipc_dip_parms *p,
+                     SANE_Parameters *ctx, void **buffer);
+
+#ifdef __cplusplus
+}       /* extern "C" */
+#endif
+
+#endif  /* !defined (ipc_h) */