support frame building

Author: Michal-Pogorzelec

examples/main.c

@@ -5,22 +5,20 @@
 
 int main(void) {
   const uint8_t payload[] = {'H', 'e', 'l', 'l', 'o', ' ', 'S', 'P'};
-  sp_packet_t pkt = {0};
-  pkt.ph.apid = 0x100;
-  pkt.ph.seq_count = 1;
+  sp_packet_t pkt;
+  sp_packet_init(&pkt);
+  sp_set_primary_header(&pkt, 0 /*version*/, 0 /*type*/, 1 /*sec hdr*/, 0x100, 0 /*seq flags*/, 1);
   /* Example with a minimal secondary header containing flags and zero extra
    * bytes. flags byte LSB=1 requests CRC; byte1=0 indicates zero remaining sec
    * header bytes.
    */
   const uint8_t sec_hdr[] = {0x1, 0x0};
-  pkt.ph.sec_hdr_flag = 1;
-  pkt.sec_hdr = sec_hdr;
-  pkt.sec_hdr_len = sizeof(sec_hdr);
+  sp_set_secondary_header(&pkt, sec_hdr, sizeof(sec_hdr));
   pkt.payload = payload;
   pkt.payload_len = sizeof(payload);
 
   uint8_t buf[256];
-  size_t n = sp_packet_serialize(&pkt, buf, sizeof(buf));
+  size_t n = sp_packet_build_frame(&pkt, buf, sizeof(buf));
   if (n == 0) {
     printf("serialize failed\n");
     return 1;

include/space_packet.h

@@ -71,4 +71,27 @@ int sp_packet_parse(sp_packet_t *out, uint8_t *buf, size_t buf_len);
  * 16-bit CRC. */
 uint16_t sp_crc16_ccitt(const uint8_t *data, size_t len);
 
+/* High-level helpers to build packets programmatically */
+/* Initialize packet structure to safe defaults (zeroed header and no payload). */
+void sp_packet_init(sp_packet_t *pkt);
+
+/* Configure primary header fields. Values will be masked to valid bit widths. */
+void sp_set_primary_header(sp_packet_t *pkt,
+                          uint8_t version,
+                          uint8_t type,
+                          uint8_t sec_hdr_flag,
+                          uint16_t apid,
+                          uint8_t seq_flags,
+                          uint16_t seq_count);
+
+/* Set secondary header pointer and length (application-owned memory). */
+void sp_set_secondary_header(sp_packet_t *pkt, const uint8_t *sec_hdr, uint16_t sec_hdr_len);
+
+/* Set payload pointer and length (application-owned memory). */
+void sp_set_payload(sp_packet_t *pkt, const uint8_t *payload, uint16_t payload_len);
+
+/* Build full packet frame into `buf` (header+data[+crc]). Returns bytes written or
+ * 0 on error. */
+size_t sp_packet_build_frame(const sp_packet_t *pkt, uint8_t *buf, size_t buf_len);
+
 #endif /* SPACE_PACKET_H */

src/space_packet.c

@@ -179,3 +179,42 @@ uint16_t sp_crc16_ccitt(const uint8_t *data, size_t len) {
   }
   return crc & 0xFFFF;
 }
+
+/* High-level helpers implementation */
+void sp_packet_init(sp_packet_t *pkt) {
+  if (!pkt) return;
+  memset(pkt, 0, sizeof(*pkt));
+}
+
+void sp_set_primary_header(sp_packet_t *pkt,
+               uint8_t version,
+               uint8_t type,
+               uint8_t sec_hdr_flag,
+               uint16_t apid,
+               uint8_t seq_flags,
+               uint16_t seq_count) {
+  if (!pkt) return;
+  pkt->ph.version = version & 0x7;
+  pkt->ph.type = type & 0x1;
+  pkt->ph.sec_hdr_flag = sec_hdr_flag ? 1 : 0;
+  pkt->ph.apid = apid & 0x07FF;
+  pkt->ph.seq_flags = seq_flags & 0x3;
+  pkt->ph.seq_count = seq_count & 0x3FFF;
+}
+
+void sp_set_secondary_header(sp_packet_t *pkt, const uint8_t *sec_hdr, uint16_t sec_hdr_len) {
+  if (!pkt) return;
+  pkt->sec_hdr = sec_hdr;
+  pkt->sec_hdr_len = sec_hdr_len;
+  pkt->ph.sec_hdr_flag = (sec_hdr && sec_hdr_len) ? 1 : 0;
+}
+
+void sp_set_payload(sp_packet_t *pkt, const uint8_t *payload, uint16_t payload_len) {
+  if (!pkt) return;
+  pkt->payload = payload;
+  pkt->payload_len = payload_len;
+}
+
+size_t sp_packet_build_frame(const sp_packet_t *pkt, uint8_t *buf, size_t buf_len) {
+  return sp_packet_serialize(pkt, buf, buf_len);
+}