From f0b6788817ff9910bc3fb996591ef48ecc546fea Mon Sep 17 00:00:00 2001
From: Stéphane Raimbault <stephane.raimbault@gmail.com>
Date: Wed, 22 Sep 2010 18:28:27 +0200
Subject: [PATCH] Check the received function code on the client side

---
 src/modbus.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/modbus.c b/src/modbus.c
index 48de3fb..b69ac81 100644
--- a/src/modbus.c
+++ b/src/modbus.c
@@ -464,10 +464,21 @@ static int receive_msg_req(modbus_t *ctx, uint8_t *req, uint8_t *rsp)
         /* GOOD RESPONSE */
         int req_nb_value;
         int rsp_nb_value;
+        int function = rsp[offset];
+
+        if (function != req[offset]) {
+            if (ctx->debug) {
+                fprintf(stderr,
+                        "Received function not corresponding to the request (%d != %d)\n",
+                        function, req[offset]);
+            }
+            errno = EMBBADDATA;
+            return -1;
+        }
 
         /* The number of values is returned if it's corresponding
          * to the request */
-        switch (rsp[offset]) {
+        switch (function) {
         case _FC_READ_COILS:
         case _FC_READ_DISCRETE_INPUTS:
             /* Read functions, 8 values in a byte (nb
--
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