cdba-server: Introduce helper for sending measurements

The current format of the cdb_assist backend status messages was never
intended to be parsed by a non-human, and the format doesn't extend well
to other backends.

Extend the format to be formatted as a json string, with a timestamp,
implemented in a separate status module.

The button status is skipped from the new status message, as it reflect
the output-values as set by cdba itself, rather than any measured state.

The timestamp is offset to the first measurement, to avoid disclosing
the uptime of the machine cdba-server is running on.

Signed-off-by: Bjorn Andersson <[email protected]>

cdb_assist.c

@@ -43,6 +43,7 @@
 
 #include "cdba-server.h"
 #include "device.h"
+#include "status.h"
 
 struct cdb_assist {
 	char serial[9];
@@ -341,20 +342,27 @@ static void cdb_gpio(struct cdb_assist *cdb, int gpio, bool on)
 static void cdb_assist_print_status(struct device *dev)
 {
 	struct cdb_assist *cdb = dev->cdb;
-	char buf[128];
-	int n;
-
-	n = sprintf(buf, "%umV %umA%s%s%s%s%s ref: %umV",
-			 cdb->voltage_set,
-			 cdb->current_actual,
-			 cdb->vbat ? " vbat" : "",
-			 cdb->vbus ? " vbus" : "",
-			 cdb->btn[0] ? " btn1" : "",
-			 cdb->btn[1] ? " btn2" : "",
-			 cdb->btn[2] ? " btn3" : "",
-			 cdb->vref);
-
-	cdba_send_buf(MSG_STATUS_UPDATE, n, buf);
+	struct status_value vbat[] = {
+		{
+			.unit = STATUS_MV,
+			.value = cdb->voltage_set,
+		},
+		{
+			.unit = STATUS_MA,
+			.value = cdb->current_actual,
+		},
+		{}
+	};
+	struct status_value vref[] = {
+		{
+			.unit = STATUS_MV,
+			.value = cdb->vref,
+		},
+		{}
+	};
+
+	status_send_values("vbat", vbat);
+	status_send_values("vref", vref);
 }
 
 static void cdb_set_voltage(struct cdb_assist *cdb, unsigned mV)

meson.build

@@ -71,7 +71,8 @@ server_srcs = ['cdba-server.c',
 	       'local-gpio.c',
 	       'console.c',
 	       'qcomlt_dbg.c',
-	       'ppps.c']
+	       'ppps.c',
+               'status.c']
 
 if gpiod_dep.version().version_compare('>=2.0')
 	server_srcs += ['local-gpio-v2.c']

status.c

@@ -0,0 +1,79 @@
+#include <err.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+#include "cdba-server.h"
+#include "status.h"
+
+static const char *sz_units[] = {
+	[STATUS_MV] = "mv",
+	[STATUS_MA] = "ma",
+	[STATUS_GPIO] = "gpio",
+};
+
+static void status_get_ts(struct timespec *ts)
+{
+	static struct timespec t0;
+	struct timespec t;
+
+	if (!t0.tv_sec && !t0.tv_nsec)
+		clock_gettime(CLOCK_MONOTONIC, &t0);
+
+	clock_gettime(CLOCK_MONOTONIC, &t);
+
+	if (t.tv_nsec < t0.tv_nsec) {
+		ts->tv_sec = t.tv_sec - t0.tv_sec - 1;
+		ts->tv_nsec = 1000000000 + (t.tv_nsec - t0.tv_nsec);
+	} else {
+		ts->tv_sec = t.tv_sec - t0.tv_sec;
+		ts->tv_nsec = t.tv_nsec - t0.tv_nsec;
+	}
+}
+
+void status_send_values(const char *id, struct status_value *values)
+{
+	struct status_value *value;
+	struct timespec ts;
+	char chunk[32];
+	char buf[256];
+	size_t len;
+	size_t n;
+
+	status_get_ts(&ts);
+
+	len = snprintf(buf, sizeof(buf), "{\"ts\":%ld.%03ld, \"%s\":{ ", ts.tv_sec, ts.tv_nsec / 1000000, id);
+
+	for (value = values; value->unit; value++) {
+		if (value != values) {
+			if (len + 3 >= sizeof(buf)) {
+				warnx("status message overflow");
+				return;
+			}
+
+			strcpy(buf + len, ", ");
+			len += 2;
+		}
+
+		n = snprintf(chunk, sizeof(chunk), "\"%s\": %u", sz_units[value->unit], value->value);
+
+		if (len + n + 1>= sizeof(buf)) {
+			warnx("status message overflow");
+			return;
+		}
+
+		strcpy(buf + len, chunk);
+		len += n;
+	}
+
+	if (len + 4 >= sizeof(buf)) {
+		warnx("status message overflow");
+		return;
+	}
+
+	strcpy(buf + len, "}}\n");
+	len += 3;
+
+	cdba_send_buf(MSG_STATUS_UPDATE, len, buf);
+}

status.h

@@ -0,0 +1,20 @@
+#ifndef __STATUS_H__
+#define __STATUS_H__
+
+#include <stdlib.h>
+
+enum status_unit {
+	STATUS_EOF,
+	STATUS_MV,
+	STATUS_MA,
+	STATUS_GPIO,
+};
+
+struct status_value {
+	enum status_unit unit;
+	unsigned int value;
+};
+
+void status_send_values(const char *id, struct status_value *values);
+
+#endif