Binary protocol example binprot.c

binprot.c

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+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+/*
+ * Example binary protocol for passing small, statically sized messages.
+ *
+ * These messages are efficient and easily serializable. Since there is no variable length payload in the message, no
+ * parsing is required, and a simple cast into whatever reciever buffer you're using, or a memcpy into a preallocated
+ * CommandMessage, is enough. Keep in mind; the largest member of the data union determines the size of the struct.
+ */
+
+// clang-format off
+typedef enum {
+    CMD_SET_LEVEL = 1,
+    CMD_SET_LIGHTS = 2,
+    CMD_SET_DISTANCE_FACTOR = 3
+} CommandType;
+
+typedef struct __attribute__((__packed__)) {
+    uint8_t type;
+    union {
+        struct { uint8_t level; } set_level;
+        struct { uint8_t on; } set_lights; // 1 = on, 0 = off
+        struct { float factor; } set_distance;
+    } data;
+    /* NOTE: Consider adding crc checksum here, or in a wrapper struct */
+} CommandMessage;
+// clang-format on
+
+void print_command(CommandMessage *m) {
+    switch (m->type) {
+    case CMD_SET_LEVEL:
+        printf("Type: SetLevel\nPayload: %d\n", m->data.set_level.level);
+        break;
+    case CMD_SET_LIGHTS:
+        printf("Type: SetLights\nPayload: %d\n", m->data.set_lights.on);
+        break;
+    case CMD_SET_DISTANCE_FACTOR:
+        printf("Type: SetDistanceFactor\nPayload: %.2f\n", m->data.set_distance.factor);
+        break;
+    }
+}
+
+char buf[sizeof(CommandMessage)];
+
+int main(void) {
+    CommandMessage m = {CMD_SET_LIGHTS, .data.set_lights.on = 1};
+    memcpy(buf, &m, sizeof(CommandMessage));
+
+    /* Here we can send buf through a socket, to uart, wherever */
+
+    CommandMessage r = {0};
+    memcpy(&r, &buf, sizeof(CommandMessage));
+
+    /* We can then dispatch based on the message type */
+    print_command(&r);
+
+    m.type = CMD_SET_LEVEL;
+    m.data.set_level.level = 10;
+    print_command(&m);
+
+    m.type = CMD_SET_DISTANCE_FACTOR;
+    m.data.set_distance.factor = 1337.42;
+    print_command(&m);
+
+    return 0;
+}