Add macros to eliminate magic constants from Compost transport implementations in C

Author: blazraST

compost_rpc/lib/c/header_template.py

@@ -22,6 +22,21 @@
 #define COMPOST_EFLAGS   -91 ///< Reserved flags set
 #define COMPOST_ETXN     -92 ///< Unexcepted transaction value
 
+/// Length of the message header in bytes
+#define COMPOST_HEADER_LEN 4
+
+/**
+ * @brief Calculates the length of the entire message in bytes from the first byte of the header
+ * @param msg Pointer to the message
+ */
+#define COMPOST_MSG_LEN(msg) (4 + (4 * (((uint8_t *)msg)[0])))
+
+/**
+ * @brief Calculates the length of the payload in bytes from the first byte of the header
+ * @param msg Pointer to the message
+ */
+#define COMPOST_PAYLOAD_LEN(msg) (4 * (((uint8_t *)msg)[0]))
+
 struct CompostMsg {
     uint16_t len;
     uint16_t rpc_id;

examples/pc_to_pc/main.c

@@ -87,20 +87,20 @@ int main(int argc, char *argv[])
         for (;;) {
 
             // Read the header (first 4 bytes)
-            if (read_bytes(connection, rx_buf, HEADER_SIZE) < 1)
+            if (read_bytes(connection, rx_buf, COMPOST_HEADER_LEN) < 1)
                 break;
 
             // Calculate the size of the payload
             // (first byte of the header indicates the number of 32-bit words of the payload)
-            size_t rx_payload_size = 4 * rx_buf[0];
+            size_t rx_payload_size = COMPOST_PAYLOAD_LEN(rx_buf);
 
             // Read the payload
-            if (read_bytes(connection, rx_buf + HEADER_SIZE, rx_payload_size) < 1)
+            if (read_bytes(connection, rx_buf + COMPOST_HEADER_LEN, rx_payload_size) < 1)
                 break;
 
             // Process the request and prepare the response
             int16_t tx_msg_size =
-                compost_msg_process(tx_buf, sizeof(tx_buf), rx_buf, HEADER_SIZE + rx_payload_size);
+                compost_msg_process(tx_buf, sizeof(tx_buf), rx_buf, COMPOST_MSG_LEN(rx_buf));
 
             // If the message size is negative, it indicates an error
             if (tx_msg_size > 0) {

test/mock/main.c

@@ -92,17 +92,18 @@ int main(int argc, char *argv[])
     compost_set_assert_func(compost_assert);
 
     for (;;) {
-        if (fread(rx_buf, 1, 4, stdin) != 4) {
+        if (fread(rx_buf, 1, COMPOST_HEADER_LEN, stdin) != 4) {
             break;
         }
-        uint16_t data_len8 = rx_buf[0] * 4;
-        if (data_len8 > 0) {
-            if (fread(rx_buf + 4, 1, data_len8, stdin) != data_len8) {
+        size_t payload_len = COMPOST_PAYLOAD_LEN(rx_buf);
+        if (payload_len > 0) {
+            if (fread(rx_buf + COMPOST_HEADER_LEN, 1, payload_len, stdin) != payload_len) {
                 break;
             }
         }
-        log_msg("  mock <- ", rx_buf, 4 + data_len8);
-        int16_t tx_len = compost_msg_process(tx_buf, sizeof(tx_buf), rx_buf, 4 + data_len8);
+        size_t msg_len = COMPOST_MSG_LEN(rx_buf);
+        log_msg("  mock <- ", rx_buf, msg_len);
+        int16_t tx_len = compost_msg_process(tx_buf, sizeof(tx_buf), rx_buf, msg_len);
         log_msg("  mock -> ", tx_buf, tx_len);
 
         if (tx_len) {