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‎.github/workflows/ci.yml‎

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name: CI
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on:
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push:
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branches: [ main, master ]
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pull_request:
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branches: [ main, master ]
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jobs:
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build:
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runs-on: ubuntu-latest
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steps:
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- uses: actions/checkout@v4
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- name: Install build tools and gtest
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run: |
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sudo apt-get update
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sudo apt-get install -y build-essential cmake libgtest-dev
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# Build and install gtest binaries (Ubuntu provides sources only)
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pushd /usr/src/gtest || exit 0
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cmake . && make || true
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sudo cp libgtest*.a /usr/lib/ || true
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popd || true
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- name: Build
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run: make
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- name: Run C tests
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run: |
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if [ -x tests/test_packet ]; then
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./tests/test_packet
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else
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echo "tests/test_packet missing"; exit 1
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fi
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- name: Build and run C tests
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run: |
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make ctest
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if [ -x tests/ctest ]; then
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./tests/ctest
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elif [ -x tests/ctest ] || [ -x tests/ctest ]; then
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./tests/ctest
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elif [ -x tests/ctest ]; then
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./tests/ctest
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else
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# older make target produces tests/ctest or tests/ctest
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if [ -x tests/ctest ]; then ./tests/ctest; else echo "ctest binary missing"; exit 1; fi
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fi

‎Makefile‎

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CC ?= cc
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CFLAGS ?= -O2 -Iinclude -Wall -Wextra -std=c99
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CC ?= cc
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CXX ?= g++
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CFLAGS ?= -O2 -Iinclude -Wall -Wextra -std=c99
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CXXFLAGS ?= -O2 -Iinclude -Wall -Wextra -std=gnu++11
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AR ?= ar
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PREFIX ?= /usr/local
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LIBNAME = libspacepacket.a
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all: lib example test ctest
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lib: src/space_packet.c
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$(CC) $(CFLAGS) -c src/space_packet.c -o src/space_packet.o
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$(AR) rcs $(LIBNAME) src/space_packet.o
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example: lib examples/main.c
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$(CC) $(CFLAGS) -Iinclude -L. examples/main.c -L. -lspacepacket -o examples/spacepacket_example
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ctest: lib tests/unit_tests.c
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$(CC) $(CFLAGS) -Iinclude tests/unit_tests.c -L. -lspacepacket -o tests/ctest
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clean:
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rm -f src/*.o $(LIBNAME) examples/spacepacket_example tests/test_packet tests/gtest_tests
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install: lib
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mkdir -p $(PREFIX)/lib $(PREFIX)/include
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cp $(LIBNAME) $(PREFIX)/lib/
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cp include/space_packet.h $(PREFIX)/include/
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.PHONY: all lib example test gtest clean install

‎README.md‎

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# EmbeddedSpacePacket
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Minimum SpacePacket implementation in C for embedded applications
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Contents
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- tiny header and implementation in `include/` and `src/`
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- example in `examples/`
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- simple host test in `tests/`
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- `Makefile` to build library, example and test
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Build & run (host):
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1. Build everything:
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make
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2. Run example:
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./examples/spacepacket_example
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3. Run tests:
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./tests/test_packet
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Notes
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- This is a minimal, small-footprint implementation designed for embedded use.
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- The primary header implemented is CCSDS-like (6 bytes). The packet length field
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in the header stores `payload_len - 1` when serializing and the parser reconstructs
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`payload_len = header_length + 1`.
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‎examples/main.c‎

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#include <stdio.h>
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#include <stdint.h>
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#include <string.h>
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#include "../include/space_packet.h"
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int main(void) {
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const uint8_t payload[] = { 'H','e','l','l','o',' ', 'S','P' };
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sp_packet_t pkt = {0};
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pkt.ph.apid = 0x100;
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pkt.ph.seq_count = 1;
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/* Example with a minimal secondary header containing flags and zero extra bytes.
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* flags byte LSB=1 requests CRC; byte1=0 indicates zero remaining sec header bytes.
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*/
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const uint8_t sec_hdr[] = { 0x1, 0x0 };
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pkt.ph.sec_hdr_flag = 1;
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pkt.sec_hdr = sec_hdr;
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pkt.sec_hdr_len = sizeof(sec_hdr);
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pkt.payload = payload;
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pkt.payload_len = sizeof(payload);
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uint8_t buf[256];
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size_t n = sp_packet_serialize(&pkt, buf, sizeof(buf));
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if (n == 0) {
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printf("serialize failed\n");
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return 1;
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}
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printf("Serialized %zu bytes:\n", n);
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for (size_t i = 0; i < n; ++i) printf("%02X ", buf[i]);
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printf("\n");
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sp_packet_t parsed;
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if (!sp_packet_parse(&parsed, buf, n)) {
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printf("parse failed\n");
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return 2;
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}
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printf("Parsed APID=0x%03X seq=%u payload_len=%u\n",
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parsed.ph.apid, parsed.ph.seq_count, parsed.payload_len);
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printf("Payload as ASCII: ");
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fwrite(parsed.payload, 1, parsed.payload_len, stdout);
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printf("\n");
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return 0;
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}

‎include/space_packet.h‎

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/* Minimal SpacePacket header for embedded applications
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* Provides a tiny API to create, serialize and parse CCSDS-like packets.
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*/
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#ifndef SPACE_PACKET_H
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#define SPACE_PACKET_H
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#include <stdint.h>
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#include <stddef.h>
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/* Primary header is 6 bytes (CCSDS-like):
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* - bytes 0-1: version(3), type(1), sec_hdr(1), apid(11)
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* - bytes 2-3: seq_flags(2), seq_count(14)
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* - bytes 4-5: packet_length (payload length - 1)
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*/
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typedef struct {
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/* Primary header represented as bitfields (CCSDS-like) */
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#if defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
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unsigned version:3;
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unsigned type:1;
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unsigned sec_hdr_flag:1; /* whether secondary header present */
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unsigned apid:11;
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#else
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unsigned apid:11;
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unsigned sec_hdr_flag:1;
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unsigned type:1;
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unsigned version:3;
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#endif
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/* sequence control */
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#if defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
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unsigned seq_flags:2;
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unsigned seq_count:14;
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#else
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unsigned seq_count:14;
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unsigned seq_flags:2;
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#endif
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uint16_t packet_length;
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} sp_primary_header_t;
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typedef struct {
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sp_primary_header_t ph; /* primary header (bitwise representation) */
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const uint8_t *sec_hdr; /* secondary header pointer (if ph.bits.sec_hdr_flag), as provided */
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uint16_t sec_hdr_len; /* total secondary header length in bytes (>=2 when present)
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* Layout: byte0 = flags, byte1 = remaining_sec_len (n), followed by n bytes
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*/
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const uint8_t *payload; /* points into a buffer when parsed */
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uint16_t payload_len;
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/* If the secondary header flags (byte0) LSB is 1, a 16-bit CRC (big-endian)
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* is appended after payload. The CRC covers the secondary header and payload.
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*/
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} sp_packet_t;
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/* Return required buffer size to serialize this packet (header + payload) */
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size_t sp_packet_serialize_size(const sp_packet_t *pkt);
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/* Serialize packet into `buf` of length `buf_len`. Returns bytes written or 0 on error. */
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size_t sp_packet_serialize(const sp_packet_t *pkt, uint8_t *buf, size_t buf_len);
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/* Parse buffer into packet fields. Note: this does not allocate payload memory; it sets
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* `out->payload` to point into `buf`. Returns 1 on success, 0 on failure.
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*/
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int sp_packet_parse(sp_packet_t *out, uint8_t *buf, size_t buf_len);
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/* Utility: compute CRC-16-CCITT (polynomial 0x1021, init 0xFFFF). Returns 16-bit CRC. */
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uint16_t sp_crc16_ccitt(const uint8_t *data, size_t len);
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#endif /* SPACE_PACKET_H */

‎src/space_packet.c‎

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#include "../include/space_packet.h"
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#include <string.h>
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#include <stdlib.h>
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/* Minimal serializer/parser for a 6-byte primary header + payload.
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* Uses big-endian network byte order for header fields.
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*/
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size_t sp_packet_serialize_size(const sp_packet_t *pkt) {
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if (!pkt) return 0;
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size_t total = 6;
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if (pkt->ph.sec_hdr_flag) total += pkt->sec_hdr_len;
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total += pkt->payload_len;
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/* if secondary header flags request CRC, include 2 bytes
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* (we can't inspect sec_hdr here without checking length) */
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if (pkt->ph.sec_hdr_flag && pkt->sec_hdr_len >= 2) {
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if (pkt->sec_hdr[0] & 0x1) total += 2;
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}
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return total;
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}
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size_t sp_packet_serialize(const sp_packet_t *pkt, uint8_t *buf, size_t buf_len) {
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if (!pkt || !buf) return 0;
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size_t need = sp_packet_serialize_size(pkt);
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if (buf_len < need) return 0;
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uint16_t first = 0;
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uint16_t second = 0;
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uint16_t length_field = 0;
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/* compose first and second words from bitfields */
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first = (uint16_t)(((pkt->ph.version & 0x7) << 13) |
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((pkt->ph.type & 0x1) << 12) |
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((pkt->ph.sec_hdr_flag & 0x1) << 11) |
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(pkt->ph.apid & 0x07FF));
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second = (uint16_t)((((pkt->ph.seq_flags & 0x3) << 14) | (pkt->ph.seq_count & 0x3FFF)));
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/* Compute total length (secondary header + payload [+crc]) */
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uint16_t total_len = 0;
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if (pkt->ph.sec_hdr_flag) total_len += pkt->sec_hdr_len;
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total_len += pkt->payload_len;
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int crc_present = 0;
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if (pkt->ph.sec_hdr_flag && pkt->sec_hdr_len >= 2) {
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crc_present = (pkt->sec_hdr[0] & 0x1) ? 1 : 0;
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}
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if (crc_present) total_len += 2;
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if (total_len == 0) length_field = 0;
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else length_field = (uint16_t)(total_len - 1);
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/* write big-endian */
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buf[0] = (uint8_t)((first >> 8) & 0xFF);
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buf[1] = (uint8_t)(first & 0xFF);
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buf[2] = (uint8_t)((second >> 8) & 0xFF);
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buf[3] = (uint8_t)(second & 0xFF);
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buf[4] = (uint8_t)((length_field >> 8) & 0xFF);
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buf[5] = (uint8_t)(length_field & 0xFF);
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size_t off = 6;
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if (pkt->ph.sec_hdr_flag && pkt->sec_hdr && pkt->sec_hdr_len) {
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memcpy(&buf[off], pkt->sec_hdr, pkt->sec_hdr_len);
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off += pkt->sec_hdr_len;
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}
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if (pkt->payload_len && pkt->payload) {
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memcpy(&buf[off], pkt->payload, pkt->payload_len);
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off += pkt->payload_len;
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}
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if (crc_present) {
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/* compute CRC over secondary header and payload */
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size_t crc_area_len = (pkt->ph.sec_hdr_flag ? pkt->sec_hdr_len : 0) + pkt->payload_len;
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uint16_t crc = sp_crc16_ccitt(&buf[6], crc_area_len);
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buf[off++] = (uint8_t)((crc >> 8) & 0xFF);
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buf[off++] = (uint8_t)(crc & 0xFF);
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}
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return need;
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}
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int sp_packet_parse(sp_packet_t *out, uint8_t *buf, size_t buf_len) {
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if (!out || !buf) return 0;
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if (buf_len < 6) return 0;
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uint16_t first = ((uint16_t)buf[0] << 8) | buf[1];
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uint16_t second = ((uint16_t)buf[2] << 8) | buf[3];
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uint16_t length_field = ((uint16_t)buf[4] << 8) | buf[5];
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out->ph.version = (first >> 13) & 0x7;
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out->ph.type = (first >> 12) & 0x1;
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out->ph.sec_hdr_flag = (first >> 11) & 0x1;
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out->ph.apid = first & 0x07FF;
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out->ph.seq_flags = (second >> 14) & 0x3;
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out->ph.seq_count = second & 0x3FFF;
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out->ph.packet_length = length_field;
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uint16_t total_len = (uint16_t)(length_field + 1);
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size_t off = 6;
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if (out->ph.sec_hdr_flag) {
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/* need at least 2 bytes for secondary header to read its length */
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if (buf_len < off + 2) return 0;
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uint8_t flags = buf[off];
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uint8_t rem_len = buf[off + 1];
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uint16_t sec_len = (uint16_t)(2 + rem_len);
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if (buf_len < off + sec_len) return 0;
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out->sec_hdr = &buf[off];
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out->sec_hdr_len = sec_len;
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off += sec_len;
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int crc_present = (flags & 0x1) ? 1 : 0;
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uint16_t payload_len_calc = 0;
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if (crc_present) {
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if (total_len < sec_len + 2) return 0; /* impossible */
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payload_len_calc = (uint16_t)(total_len - sec_len - 2);
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if (buf_len < off + payload_len_calc + 2) return 0;
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out->payload_len = payload_len_calc;
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out->payload = &buf[off];
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/* verify CRC */
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size_t crc_area_len = sec_len + out->payload_len;
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uint16_t crc_calc = sp_crc16_ccitt(&buf[6], crc_area_len);
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uint16_t crc_recv = ((uint16_t)buf[off + out->payload_len] << 8) | buf[off + out->payload_len + 1];
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if (crc_calc != crc_recv) return 0;
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} else {
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if (total_len < sec_len) return 0;
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payload_len_calc = (uint16_t)(total_len - sec_len);
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if (buf_len < off + payload_len_calc) return 0;
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out->payload_len = payload_len_calc;
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out->payload = &buf[off];
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}
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} else {
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/* no secondary header; CRC not supported */
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out->sec_hdr = NULL;
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out->sec_hdr_len = 0;
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out->payload_len = total_len;
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if (buf_len < off + out->payload_len) return 0;
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out->payload = &buf[off];
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}
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return 1;
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}
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uint16_t sp_crc16_ccitt(const uint8_t *data, size_t len) {
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uint16_t crc = 0xFFFF;
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for (size_t i = 0; i < len; ++i) {
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crc ^= (uint16_t)data[i] << 8;
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for (int k = 0; k < 8; ++k) {
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if (crc & 0x8000) crc = (crc << 1) ^ 0x1021;
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else crc <<= 1;
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}
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}
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return crc & 0xFFFF;
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}

‎tests/ctest‎

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