initctl: escape special characters in JSON output

Strings like command, description, and environment may contain characters
that need escaping for valid JSON, e.g., embedded quotes in command line
arguments like -V "NanoPi R2S".

Add json_escape() helper to handle quotes, backslashes, and control chars.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Author: troglobit

src/initctl.c

@@ -1036,6 +1036,62 @@ static int svc_compare(svc_t *svc, char *arg)
 	return 0;
 }
 
+/*
+ * Escape a string for safe JSON output. Handles quotes, backslashes,
+ * and control characters.  Returns pointer to static buffer.
+ */
+static char *json_escape(const char *str)
+{
+	static char buf[1024];
+	char *ptr = buf;
+	size_t left = sizeof(buf) - 1;
+
+	if (!str)
+		return "";
+
+	while (*str && left > 1) {
+		char c = *str++;
+
+		switch (c) {
+		case '"':
+		case '\\':
+			*ptr++ = '\\';
+			*ptr++ = c;
+			left -= 2;
+			break;
+		case '\n':
+			*ptr++ = '\\';
+			*ptr++ = 'n';
+			left -= 2;
+			break;
+		case '\r':
+			*ptr++ = '\\';
+			*ptr++ = 'r';
+			left -= 2;
+			break;
+		case '\t':
+			*ptr++ = '\\';
+			*ptr++ = 't';
+			left -= 2;
+			break;
+		default:
+			if ((unsigned char)c < 0x20) {
+				/* Other control chars: use \uXXXX */
+				int n = snprintf(ptr, left, "\\u%04x", (unsigned char)c);
+				ptr += n;
+				left -= n;
+			} else {
+				*ptr++ = c;
+				left--;
+			}
+			break;
+		}
+	}
+	*ptr = '\0';
+
+	return buf;
+}
+
 static int json_status_one(FILE *fp, svc_t *svc, char *indent, int prev)
 {
 	long now = jiffies();
@@ -1051,14 +1107,16 @@ static int json_status_one(FILE *fp, svc_t *svc, char *indent, int prev)
 	fprintf(fp,
 		"%s"
 		"%s{\n"
-		"%s  \"identity\": \"%s\",\n"
-		"%s  \"description\": \"%s\",\n"
+		"%s  \"identity\": \"%s\",\n",
+		prev ? ",\n" : indent, prev ? indent : "",
+		indent, svc_ident(svc, NULL, 0));
+	fprintf(fp,
+		"%s  \"description\": \"%s\",\n",
+		indent, json_escape(svc->desc));
+	fprintf(fp,
 		"%s  \"type\": \"%s\",\n"
 		"%s  \"forking\": %s,\n"
 		"%s  \"status\": \"%s\",\n",
-		prev ? ",\n" : indent, prev ? indent : "",
-		indent, svc_ident(svc, NULL, 0),
-		indent, svc->desc,
 		indent, svc_typestr(svc),
 		indent, svc->forking ? "true" : "false",
 		indent, svc_status(svc));
@@ -1080,15 +1138,17 @@ static int json_status_one(FILE *fp, svc_t *svc, char *indent, int prev)
 	}
 
 	fprintf(fp,
-		"%s  \"origin\": \"%s\",\n"
+		"%s  \"origin\": \"%s\",\n",
+		indent, svc->file[0] ? svc->file : "built-in");
+	svc_command(svc, buf, sizeof(buf), 0);
+	fprintf(fp,
 		"%s  \"command\": \"%s\",\n",
-		indent, svc->file[0] ? svc->file : "built-in",
-		indent, svc_command(svc, buf, sizeof(buf), 0));
+		indent, json_escape(buf));
 
 	svc_environ(svc, buf, sizeof(buf), 0);
 	if (buf[0])
 		fprintf(fp,
-			"%s  \"environment\": \"%s\",\n", indent, buf);
+			"%s  \"environment\": \"%s\",\n", indent, json_escape(buf));
 
 	svc_cond(svc, buf, sizeof(buf), 0);
 	if (buf[0])