From 780b4f4ad8002ce839013f3bc6536caf30125902 Mon Sep 17 00:00:00 2001
From: Memet Bilgin <memet.bilgin@cleandesign.ca>
Date: Sun, 2 May 2021 22:43:32 +1000
Subject: [PATCH] circular buffer implementation

feature tries to co-exist with other options as best it can by
outputing a full log entry once before committing to a line size,
all the while padding the payload size to 25 characters.

So long as all other options are fixed width, this will work fine
for any future options as well.
---
 candump.c | 46 ++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 40 insertions(+), 6 deletions(-)

diff --git a/candump.c b/candump.c
index e26fecb..7949921 100644
--- a/candump.c
+++ b/candump.c
@@ -316,6 +316,8 @@ int main(int argc, char **argv)
 	int timeout_ms = -1; /* default to no timeout */
 	FILE *logfile = NULL;
   int buffer_length = 0; /*  number of entries to store in ring buffer */
+  int buffer_index = 0;
+  int line_length = 0; /*  cached length of entries  */
   unsigned char circular = 0;
 
 
@@ -455,7 +457,7 @@ int main(int argc, char **argv)
   }
 
 	if (silent == SILENT_INI) {
-		if (log) {
+		if (log || circular) {
 			fprintf(stderr, "Disabled standard output while logging.\n");
 			silent = SILENT_ON; /* disable output on stdout */
 		} else
@@ -631,7 +633,7 @@ int main(int argc, char **argv)
 			}
 		}
 
-		if (timestamp || log || logfrmt) {
+		if (timestamp || log || circular || logfrmt) {
 			if (hwtimestamp) {
 				const int timestamping_flags = (SOF_TIMESTAMPING_SOFTWARE |
 								SOF_TIMESTAMPING_RX_SOFTWARE |
@@ -669,7 +671,7 @@ int main(int argc, char **argv)
 		}
 	}
 
-	if (log) {
+	if (log || circular) {
 		time_t currtime;
 		struct tm now;
 		char fname[83]; /* suggested by -Wformat-overflow= */
@@ -692,9 +694,12 @@ int main(int argc, char **argv)
 		if (silent != SILENT_ON)
 			fprintf(stderr, "Warning: Console output active while logging!\n");
 
-		fprintf(stderr, "Enabling Logfile '%s'\n", fname);
+    if(circular)
+        fprintf(stderr, "Enabling Circular Logfile (max %d data points) '%s'\n", buffer_length, fname);
+    else
+        fprintf(stderr, "Enabling Logfile '%s'\n", fname);
 
-		logfile = fopen(fname, "w");
+		logfile = fopen(fname, circular? "w+" : "w");
 		if (!logfile) {
 			perror("logfile");
 			return 1;
@@ -800,6 +805,35 @@ int main(int argc, char **argv)
 					extra_info = " R";
 			}
 
+      if (circular) {
+          char output[1024];
+          char buf[CL_CFSZ]; /* max length */
+          char ts_buf[TIMESTAMPSZ];
+
+          sprint_timestamp(logtimestamp, &tv, &last_tv, ts_buf);
+          /* log CAN frame with absolute timestamp & device */
+          sprint_canframe(buf, &frame, 0, maxdlen);
+
+          /*  force a payload size of exactly 25: this corresponds to
+              8 characters for an extended can-id, 1 character for the hash
+              and 16 character of payload (maximum allowable size)
+           */
+          int len = snprintf(output, 1024, "%s%*s %-25.25s%s\n", ts_buf,
+                             max_devname_len, devname[idx], buf,
+                             extra_info);
+
+          /*  store the formatted size of the finished output string  */
+          if(line_length == 0)
+              line_length = len;
+
+          /*  if the buffer index has grown past the desired count, seek to head of file and reset counter */
+          if(++buffer_index >= buffer_length){
+              rewind(logfile);
+              buffer_index = 0;
+          }
+          fprintf(logfile, output);
+      }
+
 			if (log) {
 				char buf[CL_CFSZ]; /* max length */
 				char ts_buf[TIMESTAMPSZ];
@@ -864,7 +898,7 @@ int main(int argc, char **argv)
 
 	close(fd_epoll);
 
-	if (log)
+	if (log || circular)
 		fclose(logfile);
 
 	return 0;