Added a client context parameter to the modbus_t context, and getter/setter methods.

docs/index.md

@@ -205,6 +205,11 @@ Information about header:
 
 - [modbus_get_header_length](modbus_get_header_length)
 
+Set or get the client data::
+
+- [modbus_set_client_context](modbus_set_client_context)
+- [modbus_get_client_context](modbus_get_client_context)
+
 ## Data handling
 
 Macros for data manipulation:

docs/modbus_get_client_context.md

@@ -0,0 +1,38 @@
+# modbus_get_client_context
+
+
+## Name
+
+`modbus_get_client_context` - returns the client context value from the libmodbus
+context
+
+
+## Synopsis
+
+```c
+const void *modbus_get_client_context(modbus_t *'ctx');
+```
+
+## Description
+
+The `modbus_get_client_context()` function shall return the client context value
+from the `libmodbus` context.
+
+Do not be confused by the overloaded use of “client” and “context” in these
+functions. Here, “client” refers to the code that makes use of `libmodbus`,
+“client context” is the data set and get by the client code, and “libmodbus context”
+is the `modbus_t*` context pointer.
+
+## Return Value
+
+The function shall return the client context or NULL.
+
+
+## Errors
+
+This function does not return an error.
+
+
+## See also
+
+- [`modbus_set_client_context()`](modbus_set_client_context)

docs/modbus_set_client_context.md

@@ -0,0 +1,61 @@
+# modbus_set_client_context
+
+
+## Name
+
+`modbus_set_client_context` - set context information (usually a pointer) for use
+by the client
+
+
+## Synopsis
+
+```c
+int modbus_set_client_context(modbus_t *ctx, void *cctx)
+```
+
+
+## Description
+
+The `modbus_set_client_context()` function can be used to set arbitrary client
+context information. The actual value is not used by libmodbus, but instead
+is available to client callback functions via `modbus_get_client_context()`.
+
+Do not be confused by the overloaded use of “client” and “context” in these
+functions. Here, “client” refers to the code that makes use of libmodbus and
+“client context” is the data used by the client code.
+
+## Return Value
+
+The function shall return 0 if successful. Otherwise it shall return -1 and set
+errno to one of the values defined below.
+
+
+## Errors
+
+- *EINVAL*, The libmodbus context is NULL.
+
+
+## Example
+
+```cpp
+modbus_t *ctx;
+uint16_t tab_reg[10];
+struct ClientContext {
+    int clientData1;
+    int clientData2;
+};
+ClientContext *cctx = new ClientContext();
+
+ctx = modbus_new_rtu("/dev/ttyS0", 115200, 'N', 8, 1);
+modbus_set_slave(ctx, 1);
+modbus_rtu_set_serial_mode(ctx, MODBUS_RTU_RS485);
+modbus_set_client_context(ctx, cctx);
+
+ClientContext *myCCTX = reinterpret_cast<ClientContext*>(modbus_get_client_context(ctx));
+
+modbus_free(ctx);
+```
+
+## See also
+
+[`modbus_get_client_context()`](modbus_get_client_context)

src/modbus-private.h

@@ -101,6 +101,7 @@ struct _modbus {
     struct timeval indication_timeout;
     const modbus_backend_t *backend;
     void *backend_data;
+    const void *client_context;
 };
 
 void _modbus_init_common(modbus_t *ctx);

src/modbus.c

@@ -1826,6 +1826,24 @@ int modbus_set_debug(modbus_t *ctx, int flag)
     return 0;
 }
 
+int modbus_set_client_context(modbus_t *ctx, const void *cctx)
+{
+    if (ctx == NULL) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    ctx->client_context = cctx;
+
+    return 0;
+}
+
+const void *modbus_get_client_context(modbus_t *ctx)
+{
+    return ctx->client_context;
+}
+
+
 /* Allocates 4 arrays to store bits, input bits, registers and inputs
    registers. The pointers are stored in modbus_mapping structure.
 

src/modbus.h

@@ -238,6 +238,9 @@ MODBUS_API int modbus_reply(modbus_t *ctx, const uint8_t *req,
 MODBUS_API int modbus_reply_exception(modbus_t *ctx, const uint8_t *req,
                                       unsigned int exception_code);
 
+MODBUS_API int modbus_set_client_context(modbus_t *ctx, const void *cctx);
+MODBUS_API const void* modbus_get_client_context(modbus_t *ctx);
+
 /**
  * UTILS FUNCTIONS
  **/