in_winevtlog: Launch w/o valid subscription when using ignore_missing_channels parameter

When using small amount of log volume but sometimes absent channels,
users are forcibly ought to specify with the defenetely existing
channels together.
This causes glitches of log flow controls.
So, we decided to permit absence of valid channel subscriptions when
using ignore_missing_channels parameter.
This permits to use sometimes absent but low log volume and needed to
consume A-to-Z EventLog channels.

Signed-off-by: Hiroshi Hatake <[email protected]>

Author: cosmo0920

plugins/in_winevtlog/in_winevtlog.c

@@ -237,10 +237,15 @@ static int in_winevtlog_init(struct flb_input_instance *in,
 
     ctx->active_channel = winevtlog_open_all(tmp, ctx);
     if (!ctx->active_channel) {
-        flb_plg_error(ctx->ins, "failed to open channels");
-        flb_log_event_encoder_destroy(ctx->log_encoder);
-        flb_free(ctx);
-        return -1;
+        if (ctx->ignore_missing_channels) {
+            flb_plg_debug(ctx->ins, "failed to open and no subscribed channels");
+        }
+        else {
+            flb_plg_error(ctx->ins, "failed to open and no subscribed channels. Subscribe at least one");
+            flb_log_event_encoder_destroy(ctx->log_encoder);
+            flb_free(ctx);
+            return -1;
+        }
     }
 
     /* Initialize SQLite DB (optional) */