Peter M. Groen / libmodbus

Commit 1d4241dff55c5bbaabef9518aed54b883edb492f

Authored by Stéphane Raimbault
1 parent 97ccd92c

Detect abnormal use of compute_header_length and fix comment

Inline Side-by-side
Showing 1 changed file with 21 additions and 16 deletions
src/modbus.c
  View file @1d4241d
... ... @@ -268,8 +268,7 @@ static unsigned int compute_response_length(modbus_t *ctx, uint8_t *req)
268 268 case FC_READ_HOLDING_REGISTERS:
269 269 case FC_READ_INPUT_REGISTERS:
270 270 /* Header + 2 * nb values */
271   - length = 2 + 2 * (req[offset + 3] << 8 |
272   - req[offset + 4]);
  271 + length = 2 + 2 * (req[offset + 3] << 8 | req[offset + 4]);
273 272 break;
274 273 case FC_READ_EXCEPTION_STATUS:
275 274 length = 3;
... ... @@ -497,26 +496,32 @@ typedef enum {
497 496 MSG_CONFIRMATION
498 497 } msg_type_t;
499 498  
500   -/* Computes the header length (to reach the the function code) */
  499 +/* Computes the header length (to reach the real data) */
501 500 static uint8_t compute_header_length(int function, msg_type_t msg_type)
502 501 {
503 502 int length;
504 503  
505   - if (function <= FC_WRITE_SINGLE_COIL ||
506   - function == FC_WRITE_SINGLE_REGISTER) {
507   - length = 4;
508   - } else if (function == FC_WRITE_MULTIPLE_COILS ||
509   - function == FC_WRITE_MULTIPLE_REGISTERS) {
510   - length = 5;
511   - } else if (function == FC_REPORT_SLAVE_ID) {
512   - if (msg_type == MSG_INDICATION)
  504 + if (msg_type == MSG_INDICATION) {
  505 + if (function == FC_REPORT_SLAVE_ID) {
513 506 length = 0;
514   - else
  507 + } else {
  508 + /* Should never happen, the other header lengths are precomputed */
  509 + abort();
  510 + }
  511 + } else /* MSG_CONFIRMATION */ {
  512 + if (function <= FC_WRITE_SINGLE_COIL ||
  513 + function == FC_WRITE_SINGLE_REGISTER) {
  514 + length = 4;
  515 + } else if (function == FC_WRITE_MULTIPLE_COILS ||
  516 + function == FC_WRITE_MULTIPLE_REGISTERS) {
  517 + length = 5;
  518 + } else if (function == FC_REPORT_SLAVE_ID) {
515 519 length = 1;
516   - } else if (function == FC_READ_AND_WRITE_REGISTERS) {
517   - length = 9;
518   - } else {
519   - length = 0;
  520 + } else if (function == FC_READ_AND_WRITE_REGISTERS) {
  521 + length = 9;
  522 + } else {
  523 + length = 0;
  524 + }
520 525 }
521 526 return length;
522 527 }
... ...