JSON converter: fix invalid hexa string if an IPFIX field has zero size and FDS_CD2J_OCTETS_NOINT is enabled

Previous (invalid) output: "0x", new output: null

Author: Lukas955

src/converters/json.c

@@ -227,11 +227,17 @@ to_uint(struct context *buffer, const struct fds_drec_field *field)
 static int
 to_octet(struct context *buffer, const struct fds_drec_field *field)
 {
-    if (field->size <= 8 && (buffer->flags & FDS_CD2J_OCTETS_NOINT) == 0) {
+    if (field->size == 0) {
+        // Empty field cannot be converted -> null
+        return FDS_ERR_ARG;
+    }
+
+    if ((buffer->flags & FDS_CD2J_OCTETS_NOINT) == 0 && field->size <= 8) {
         // Print as unsigned integer
         return to_uint(buffer, field);
     }
 
+    // Print as hexadecimal number
     const size_t mem_req = (2 * field->size) + 5U; // "0x" + 2 chars per byte + 2x "\"" + "\0"
 
     int ret_code = buffer_reserve(buffer, buffer_used(buffer) + mem_req);

tests/unit_tests/converters/json.cpp

@@ -1042,7 +1042,7 @@ TEST_F(Drec_invalid, nullInMulti)
     free(buff);
 }
 
-// Test fot string with size 0
+// Test for string with size 0
 TEST_F(Drec_invalid, zeroSizeStr)
 {
     constexpr size_t BSIZE = 2U;
@@ -1063,6 +1063,22 @@ TEST_F(Drec_invalid, zeroSizeStr)
    free(buff);
 }
 
+// Test for octetArray with size 0 and disabled integer conversion
+TEST_F(Drec_invalid, zeroSizeOctetArray)
+{
+    constexpr size_t BSIZE = 2U;
+    char* buff = (char*) malloc(BSIZE);
+    uint32_t flags = FDS_CD2J_ALLOW_REALLOC | FDS_CD2J_OCTETS_NOINT; // do not use int conversion!
+    size_t buff_size = BSIZE;
+
+    int rc = fds_drec2json(&m_drec, flags, m_iemgr.get(), &buff, &buff_size);
+    ASSERT_GT(rc, 0);
+    EXPECT_EQ(size_t(rc), strlen(buff));
+    Config cfg = parse_string(buff, JSON, "drec2json");
+    EXPECT_TRUE(cfg["en0:id32000"].is_null());
+    free(buff);
+}
+
 // Testing return of error code FDS_ERR_BUFFER
 TEST_F(Drec_invalid, errorBuff)
 {