cobs_encode_max (#11)

Makefile

@@ -1,4 +1,5 @@
 SRCS := cobs.c \
+		tests/test_cobs_encode_max.cc \
 		tests/test_cobs_encode.cc \
 		tests/test_cobs_encode_inplace.cc \
 		tests/test_cobs_decode_inplace.cc \

cobs.c

@@ -61,6 +61,10 @@ cobs_ret_t cobs_decode_inplace(void *buf, unsigned len) {
   return COBS_RET_SUCCESS;
 }
 
+unsigned cobs_encode_max(unsigned dec_len) {
+  return 1 + dec_len + ((dec_len + 253) / 254) + (dec_len == 0);
+}
+
 cobs_ret_t cobs_encode(void const *dec,
                        unsigned dec_len,
                        void *out_enc,

cobs.h

@@ -19,6 +19,8 @@ extern "C" {
 cobs_ret_t cobs_encode_inplace(void *buf, unsigned len);
 cobs_ret_t cobs_decode_inplace(void *buf, unsigned len);
 
+unsigned cobs_encode_max(unsigned dec_len);
+
 cobs_ret_t cobs_encode(void const *dec,
                        unsigned dec_len,
                        void *out_enc,

tests/test_cobs_encode.cc

@@ -110,5 +110,18 @@ TEST_CASE("Simple encodings", "[cobs_encode]") {
   }
 }
 
-TEST_CASE("0xFE and 0xFF single code-block cases", "[cobs_encode]") {
+TEST_CASE("0xFF single code-block case", "[cobs_encode]") {
+  byte_vec_t dec(254, 0x01);
+  byte_vec_t enc( cobs_encode_max(static_cast< unsigned >(dec.size())) );
+  unsigned enc_len;
+  REQUIRE( cobs_encode(dec.data(),
+                       static_cast< unsigned >(dec.size()),
+                       enc.data(),
+                       static_cast< unsigned >(enc.size()),
+                       &enc_len) == COBS_RET_SUCCESS );
+
+  byte_vec_t expected(255, 0x01);
+  expected[0] = 0xFF;
+  expected.push_back(0x00);
+  REQUIRE ( enc == expected );
 }

tests/test_cobs_encode_max.cc

@@ -0,0 +1,22 @@
+#include "../cobs.h"
+#include "catch.hpp"
+
+TEST_CASE("cobs_encode_max", "[cobs_encode_max]") {
+  SECTION("0 bytes") { REQUIRE( cobs_encode_max(0) == 2 ); }
+  SECTION("1 byte")  { REQUIRE( cobs_encode_max(1) == 3 ); }
+  SECTION("2 bytes") { REQUIRE( cobs_encode_max(2) == 4 ); }
+
+  SECTION("3 - 254 bytes") {
+    for (auto i = 3u; i <= 254u; ++i) {
+      REQUIRE( cobs_encode_max(i) == i + 2 );
+    }
+  }
+
+  SECTION("255-508 bytes") {
+    for (auto i = 255u; i <= 508u; ++i) { REQUIRE( cobs_encode_max(i) == i + 3 ); }
+  }
+
+  SECTION("Input size plus boilerplate plus ceil(x/254)") {
+    REQUIRE( cobs_encode_max(12345) == 1 + 12345 + ((12345 + 253) / 254) );
+  }
+}