vcr: include some text chunks in the png destHEADmaster

If the caller has some textual information to embed in the PNG
metadata, it should be able to embed it.

This adds three:

timestamp: always populated with the current time
name: always populated with --name arg, or empty
payload: made available for customized usage

payload is aimed at strobe users who have some context associated
with the strobe request they'd like to embed in an easily
machine-readable location attached to the png file.

3 files changed, 41 insertions, 9 deletions

diff --git a/src/vcr.c b/src/vcr.c
index a159379..76158f6 100644
--- a/src/vcr.c
+++ b/src/vcr.c
@@ -58,6 +58,7 @@
 #include <stdarg.h>
 #include <stdint.h>
 #include <stdlib.h>
+#include <time.h>
 
 #ifdef USE_XLIB
 #include <X11/Xlib.h>
@@ -204,6 +205,7 @@ typedef struct vcr_dest_t {
 			png_infop	info_ctx;
 			png_structp	png_ctx;
 			FILE		*output;
+			png_text	text[3];
 		} png;
 #endif /* USE_PNG */
 	};
@@ -617,7 +619,7 @@ vcr_dest_t * vcr_dest_xpicture_new(vcr_backend_t *vbe, Picture picture)
 
 
 #ifdef USE_PNG
-vcr_dest_t * vcr_dest_png_new(vcr_backend_t *vbe, FILE *output)
+vcr_dest_t * vcr_dest_png_new(vcr_backend_t *vbe, FILE *output, const char *name, const char *payload)
 {
 	vcr_dest_t	*dest;
 
@@ -651,6 +653,36 @@ vcr_dest_t * vcr_dest_png_new(vcr_backend_t *vbe, FILE *output)
 		return NULL;
 	}
 
+	{
+		time_t		now = time(NULL);
+		struct tm	*t = localtime(&now);
+		char		t_str[32];
+
+		strftime(t_str, sizeof(t_str), "%F %T %Z", t);
+
+		/* we always stick three text fields into the PNGs, the caller is expected to always
+		 * provide a `date` style string for timestamp, the chart name for name, and the
+		 * payload is flexible.  For strobes it's expected the payload may contain some
+		 * context about the cause for strobing.
+		 */
+		dest->png.text[0].compression = -1; /* none */
+		dest->png.text[0].key = "timestamp";
+		dest->png.text[0].text = t_str;
+		dest->png.text[0].text_length = strlen(t_str);
+
+		dest->png.text[1].compression = -1; /* none */
+		dest->png.text[1].key = "name";
+		dest->png.text[1].text = (char *)name;
+		dest->png.text[1].text_length = name ? strlen(name) : 0;
+
+		dest->png.text[2].compression = -1; /* none */
+		dest->png.text[2].key = "payload";
+		dest->png.text[2].text = (char *)payload;
+		dest->png.text[2].text_length = payload ? strlen(payload) : 0;
+
+		png_set_text(dest->png.png_ctx, dest->png.info_ctx, dest->png.text, 3);
+	}
+
 	png_init_io(dest->png.png_ctx, output);
 
 	return dest;
diff --git a/src/vcr.h b/src/vcr.h
index a9ec6c2..343a26d 100644
--- a/src/vcr.h
+++ b/src/vcr.h
@@ -71,7 +71,7 @@ unsigned vcr_dest_xwindow_get_id(vcr_dest_t *dest);
 vcr_dest_t * vcr_dest_xpicture_new(vcr_backend_t *vbe, Picture picture);
 #endif /* USE_XLIB */
 #ifdef USE_PNG
-vcr_dest_t * vcr_dest_png_new(vcr_backend_t *vbe, FILE *output);
+vcr_dest_t * vcr_dest_png_new(vcr_backend_t *vbe, FILE *output, const char *name, const char *payload);
 #endif /* USE_PNG */
 vcr_dest_t * vcr_dest_free(vcr_dest_t *dest);
 
diff --git a/src/vmon.c b/src/vmon.c
index 8e11dca..b42b5df 100644
--- a/src/vmon.c
+++ b/src/vmon.c
@@ -808,7 +808,7 @@ static void vmon_resize(vmon_t *vmon, int width, int height)
 
 
 /* this is like vmon_snapshot() except in-place at a fixed name; truncates what's there, no atomicity */
-static int vmon_strobe(vmon_t *vmon)
+static int vmon_strobe(vmon_t *vmon, const char *payload)
 {
 #ifdef USE_PNG
 	FILE	*output;
@@ -823,7 +823,7 @@ static int vmon_strobe(vmon_t *vmon)
 	{
 		vcr_dest_t	*png_dest;
 
-		png_dest = vcr_dest_png_new(vmon->vcr_backend, output);
+		png_dest = vcr_dest_png_new(vmon->vcr_backend, output, vmon->name, payload);
 		if (!png_dest) {
 			(void) unlink(vmon->strobe_file);
 			(void) fclose(output);
@@ -849,7 +849,7 @@ static int vmon_strobe(vmon_t *vmon)
 }
 
 
-static int vmon_snapshot(vmon_t *vmon)
+static int vmon_snapshot(vmon_t *vmon, const char *payload)
 {
 #ifdef USE_PNG
 	time_t		now, *t_ptr = &now;
@@ -905,7 +905,7 @@ static int vmon_snapshot(vmon_t *vmon)
 	{
 		vcr_dest_t	*png_dest;
 
-		png_dest = vcr_dest_png_new(vmon->vcr_backend, output);
+		png_dest = vcr_dest_png_new(vmon->vcr_backend, output, vmon->name, payload);
 		if (!png_dest) {
 			(void) unlink(tmp_path);
 			(void) fclose(output);
@@ -1037,7 +1037,7 @@ int main(int argc, const char * const *argv)
 					continue;
 
 				if (WIFEXITED(status) || WIFSIGNALED(status)) {
-					if (vmon->snapshot && (r = vmon_snapshot(vmon)) < 0)
+					if (vmon->snapshot && (r = vmon_snapshot(vmon, NULL)) < 0)
 						VWM_ERROR("error saving snapshot: %s", strerror(-r));
 
 					ret = WEXITSTATUS(status);
@@ -1056,7 +1056,7 @@ int main(int argc, const char * const *argv)
 		if (got_sigusr2) {
 			int	r;
 
-			if ((r = vmon_strobe(vmon)) < 0)
+			if ((r = vmon_strobe(vmon, NULL)) < 0)
 				VWM_ERROR("error saving strobe file: %s", strerror(-r));
 
 			got_sigusr2 = 0;
@@ -1065,7 +1065,7 @@ int main(int argc, const char * const *argv)
 		if (got_sigusr1 || (vmon->snapshots_interval && !vmon->n_snapshots)) {
 			int	r;
 
-			if ((r = vmon_snapshot(vmon)) < 0)
+			if ((r = vmon_snapshot(vmon, NULL)) < 0)
 				VWM_ERROR("error saving snapshot: %s", strerror(-r));
 
 			got_sigusr1 = 0;