Expose the workarounds struct as part of public API

examples/sml_server.c

@@ -41,6 +41,7 @@
 // globals
 int sflag = false; // flag to process only a single OBIS data stream
 int vflag = false; // verbose flag
+sml_workarounds workarounds = 0;
 
 
 int serial_port_open(const char* device) {
@@ -88,7 +89,7 @@ void transport_receiver(unsigned char *buffer, size_t buffer_len) {
 	int i;
 	// the buffer contains the whole message, with transport escape sequences.
 	// these escape sequences are stripped here.
-	sml_file *file = sml_file_parse(buffer + 8, buffer_len - 16);
+	sml_file *file = sml_file_parse(buffer + 8, buffer_len - 16, workarounds);
 	// the sml file is parsed now
 
 	// this prints some information about the file
@@ -161,13 +162,17 @@ int main(int argc, char *argv[]) {
 	while ((c = getopt(argc, argv, "+hsv")) != -1) {
 		switch (c) {
 		case 'h':
-			printf("usage: %s [-h] [-s] [-v] device\n", argv[0]);
+			printf("usage: %s [-d] [-h] [-s] [-v] device\n", argv[0]);
 			printf("device - serial device of connected power meter e.g. /dev/cu.usbserial, or - for stdin\n");
+			printf("-d - Enable negative values workaround for certain DZG meters\n");
 			printf("-h - help\n");
 			printf("-s - process only one OBIS data stream (single)\n");
 			printf("-v - verbose\n");
 			exit(0); // exit here
 			break;
+		case 'd':
+			workarounds |= SML_WORKAROUND_DZG_NEGATIVE;
+			break;
 		case 's':
 			sflag = true;
 			break;

sml/include/sml/sml_file.h

@@ -36,7 +36,8 @@ typedef struct {
 
 sml_file *sml_file_init();
 // parses a SML file.
-sml_file *sml_file_parse(unsigned char *buffer, size_t buffer_len);
+sml_file *sml_file_parse(unsigned char *buffer, size_t buffer_len,
+						 const sml_workarounds workarounds);
 void sml_file_add_message(sml_file *file, sml_message *message);
 void sml_file_write(sml_file *file);
 void sml_file_free(sml_file *file);

sml/include/sml/sml_shared.h

@@ -56,6 +56,43 @@ typedef int64_t i64;
 #define SML_TYPE_NUMBER_32 sizeof(u32)
 #define SML_TYPE_NUMBER_64 sizeof(u64)
 
+// A bitmap to configure workarounds.
+typedef int16_t sml_workarounds;
+
+/*
+ * Workaround for certain DZG meters that encode the consumption wrongly.
+ * Affected:
+ * - Model TODO with serial numbers starting with 6 (in decimal)
+ *
+ * We only get the serial number, not the meter model via SML. Since model
+ * DWSB.2TH (serial starting with 4) does not exhibit this bug, we can't
+ * apply the workaround automatically.
+ *
+ * The value uses a scaler of -2, so e.g. 328.05 should be
+ * encoded as an unsigned int with 2 bytes (called Unsigned16 in the standard):
+ *   63 80 25 (0x8025 == 32805 corresponds to 328.05W)
+ * or as an unsigned int with 3 bytes (not named in the standard):
+ *   64 00 80 25
+ * or as a signed int with 3 bytes (not named in the standard):
+ *   54 00 80 25
+ * but they encode it as a signed int with 2 bytes (called Integer16 in the standard):
+ *   53 80 25
+ * which reads as -32731 corresponding to -327.31W.
+ *
+ * Luckily, it doesn't attempt to do any compression on
+ * negative values, they're always encoded as, e.g.
+ *   55 ff fe 13 93 (== -126061 -> -1260.61W)
+ *
+ * Since we cannot have positive values >= 0x80000000
+ * (that would be 21474836.48 W, yes, >21MW), we can
+ * assume that for 1, 2, 3 bytes, if they look signed,
+ * they really were intended to be unsigned.
+ *
+ * Note that this will NOT work if a meter outputs negative
+ * values compressed as well - but mine doesn't.
+ */
+#define SML_WORKAROUND_DZG_NEGATIVE 0x0001
+
 // This sml_buffer is used in two different use-cases.
 //
 // Parsing: the raw data is in the buffer field,
@@ -74,6 +111,7 @@ typedef struct {
 	size_t cursor;
 	int error;
 	char *error_msg;
+	sml_workarounds workarounds;
 } sml_buffer;
 
 sml_buffer *sml_buffer_init(size_t length);

sml/src/sml_file.c

@@ -27,11 +27,14 @@
 // EDL meter must provide at least 250 bytes as a receive buffer
 #define SML_FILE_BUFFER_LENGTH 512
 
-sml_file *sml_file_parse(unsigned char *buffer, size_t buffer_len) {
+sml_file *sml_file_parse(unsigned char *buffer, 
+						 size_t buffer_len,
+						 const sml_workarounds workarounds) {
 	sml_file *file = (sml_file *)malloc(sizeof(sml_file));
 	*file = (sml_file){.messages = NULL, .messages_len = 0, .buf = NULL};
 
 	sml_buffer *buf = sml_buffer_init(buffer_len);
+	buf->workarounds = workarounds;
 	memcpy(buf->buffer, buffer, buffer_len);
 	file->buf = buf;
 

sml/src/sml_list.c

@@ -112,16 +112,7 @@ sml_list *sml_list_init() {
 
 void sml_list_add(sml_list *list, sml_list *new_entry) { list->next = new_entry; }
 
-struct workarounds {
-	unsigned int old_dzg_meter : 1;
-};
-
-sml_list *sml_list_entry_parse(sml_buffer *buf, struct workarounds *workarounds) {
-	static const unsigned char dzg_serial_name[] = {1, 0, 96, 1, 0, 255};
-	static const unsigned char dzg_serial_start[] = {0x0a, 0x01, 'D', 'Z', 'G', 0x00};
-	// this is "1 DZG 00 60000000" in the hex encoding, see comment below
-	static const unsigned char dzg_serial_fixed[] =
-		{0x0a, 0x01, 'D', 'Z', 'G', 0x00, 0x03, 0x93, 0x87, 0x00};
+sml_list *sml_list_entry_parse(sml_buffer *buf) {
 	static const unsigned char dzg_power_name[] = {1, 0, 16, 7, 0, 255};
 	u8 value_tl, value_len_more;
 	sml_list *l = NULL;
@@ -171,43 +162,10 @@ sml_list *sml_list_entry_parse(sml_buffer *buf, struct workarounds *workarounds)
 	if (sml_buf_has_errors(buf))
 		goto error;
 
-	/*
-	 * Work around DZG meters before serial numbers starting with
-	 * 6 (in decimal) - they encode the consumption wrongly:
-	 * The value uses a scaler of -2, so e.g. 328.05 should be
-	 * encoded as an unsigned int with 2 bytes (called Unsigned16 in the standard):
-	 *   63 80 25 (0x8025 == 32805 corresponds to 328.05W)
-	 * or as an unsigned int with 3 bytes (not named in the standard):
-	 *   64 00 80 25
-	 * or as a signed int with 3 bytes (not named in the standard):
-	 *   54 00 80 25
-	 * but they encode it as a signed int with 2 bytes (called Integer16 in the standard):
-	 *   53 80 25
-	 * which reads as -32731 corresponding to -327.31W.
-	 *
-	 * Luckily, it doesn't attempt to do any compression on
-	 * negative values, they're always encoded as, e.g.
-	 *   55 ff fe 13 93 (== -126061 -> -1260.61W)
-	 *
-	 * Since we cannot have positive values >= 0x80000000
-	 * (that would be 21474836.48 W, yes, >21MW), we can
-	 * assume that for 1, 2, 3 bytes, if they look signed,
-	 * they really were intended to be unsigned.
-	 *
-	 * Note that this will NOT work if a meter outputs negative
-	 * values compressed as well - but mine doesn't.
-	 */
-	if (l->obj_name && l->obj_name->len == sizeof(dzg_serial_name) &&
-		memcmp(l->obj_name->str, dzg_serial_name, sizeof(dzg_serial_name)) == 0 && l->value &&
-		l->value->type == SML_TYPE_OCTET_STRING &&
-		l->value->data.bytes->len >= (int)sizeof(dzg_serial_start) &&
-		memcmp(l->value->data.bytes->str, dzg_serial_start, sizeof(dzg_serial_start)) == 0 &&
-		memcmp(l->value->data.bytes->str, dzg_serial_fixed, sizeof(dzg_serial_fixed)) < 0) {
-		workarounds->old_dzg_meter = 1;
-	} else if (workarounds->old_dzg_meter && l->obj_name &&
-			   l->obj_name->len == sizeof(dzg_power_name) &&
-			   memcmp(l->obj_name->str, dzg_power_name, sizeof(dzg_power_name)) == 0 && l->value &&
-			   (value_len_more == 1 || value_len_more == 2 || value_len_more == 3)) {
+	if ((buf->workarounds & SML_WORKAROUND_DZG_NEGATIVE) && l->obj_name &&
+		l->obj_name->len == sizeof(dzg_power_name) &&
+		memcmp(l->obj_name->str, dzg_power_name, sizeof(dzg_power_name)) == 0 && l->value &&
+		(value_len_more == 1 || value_len_more == 2 || value_len_more == 3)) {
 		l->value->type &= ~SML_TYPE_FIELD;
 		l->value->type |= SML_TYPE_UNSIGNED;
 	}
@@ -223,7 +181,6 @@ sml_list *sml_list_entry_parse(sml_buffer *buf, struct workarounds *workarounds)
 }
 
 sml_list *sml_list_parse(sml_buffer *buf) {
-	struct workarounds workarounds = {0};
 	sml_list *ret = NULL, **pos = &ret;
 	int elems;
 
@@ -239,7 +196,7 @@ sml_list *sml_list_parse(sml_buffer *buf) {
 	elems = sml_buf_get_next_length(buf);
 
 	while (elems > 0) {
-		*pos = sml_list_entry_parse(buf, &workarounds);
+		*pos = sml_list_entry_parse(buf);
 		if (sml_buf_has_errors(buf))
 			goto error;
 		pos = &(*pos)->next;

sml/src/sml_shared.c

@@ -118,8 +118,12 @@ void sml_buf_update_bytes_read(sml_buffer *buf, int bytes) { buf->cursor += byte
 
 sml_buffer *sml_buffer_init(size_t length) {
 	sml_buffer *buf = (sml_buffer *)malloc(sizeof(sml_buffer));
-	*buf =
-		(sml_buffer){.buffer = NULL, .buffer_len = 0, .cursor = 0, .error = 0, .error_msg = NULL};
+	*buf = (sml_buffer){.buffer = NULL,
+						.buffer_len = 0,
+						.cursor = 0,
+						.error = 0,
+						.error_msg = NULL,
+						.workarounds = 0};
 	buf->buffer = (unsigned char *)malloc(length);
 	buf->buffer_len = length;
 	memset(buf->buffer, 0, buf->buffer_len);

test/src/sml_file_test.c

@@ -63,8 +63,9 @@ TEST(sml_file, parse_crash_report1) {
 	// sadly not... just 202 TEST_ASSERT_EQUAL(388, sizeof buffer2);
 	memcpy(buffer, buffer2, sizeof buffer2);
 	size_t bytes = 388;
+	sml_workarounds workarounds = 0;
 	// bytes and buffer like from sml_transport_read
-	sml_file *file = sml_file_parse(buffer + 8, bytes - 16);
+	sml_file *file = sml_file_parse(buffer + 8, bytes - 16, workarounds);
 	TEST_ASSERT_NOT_NULL(file);
 	TEST_ASSERT_EQUAL(1, file->messages_len);
 	sml_file_free(file);