Added optional lsn data to json output

.gitignore

@@ -0,0 +1,2 @@
+*.o
+*.so

wal2json.c

@@ -26,6 +26,7 @@
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
+#include "utils/pg_lsn.h"
 #include "utils/rel.h"
 #include "utils/relcache.h"
 #include "utils/syscache.h"
@@ -40,6 +41,7 @@ typedef struct
 {
 	MemoryContext context;
 	bool		include_xids;		/* include transaction ids */
+	bool		include_lsn;		/* include lsn for safer syncing */
 	bool		include_timestamp;	/* include transaction timestamp */
 	bool		include_schemas;	/* qualify tables */
 	bool		include_types;		/* include data types */
@@ -91,6 +93,7 @@ pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt, bool is
 										ALLOCSET_DEFAULT_INITSIZE,
 										ALLOCSET_DEFAULT_MAXSIZE);
 	data->include_xids = true;
+	data->include_lsn = true;
 	data->include_timestamp = false;
 	data->include_schemas = true;
 	data->include_types = true;
@@ -160,6 +163,20 @@ pg_decode_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt, bool is
 						 errmsg("could not parse value \"%s\" for parameter \"%s\"",
 							 strVal(elem->arg), elem->defname)));
 		}
+		else if (strcmp(elem->defname, "include-lsn") == 0)
+		{
+			/* If option does not provide a value, it means its value is true */
+			if (elem->arg == NULL)
+			{
+				elog(LOG, "include-lsn argument is null");
+				data->include_xids = true;
+			}
+			else if (!parse_bool(strVal(elem->arg), &data->include_lsn))
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("could not parse value \"%s\" for parameter \"%s\"",
+							 strVal(elem->arg), elem->defname)));
+		}
 		else
 		{
 			elog(WARNING, "option %s = %s is unknown",
@@ -194,6 +211,16 @@ pg_decode_begin_txn(LogicalDecodingContext *ctx, ReorderBufferTXN *txn)
 	if (data->include_xids)
 		appendStringInfo(ctx->out, "\t\"xid\": %u,\n", txn->xid);
 
+	if (data->include_lsn) {
+		// uint32 id, off;
+		// id = (uint32) (ctx->write_location >> 32);
+		// off = (uint32) ctx->write_location;
+		// appendStringInfo(ctx->out, "\t\"lsn\": %X/%X,\n", id, off);
+		char *lsn_str = DatumGetCString(DirectFunctionCall1(pg_lsn_out, ctx->write_location));
+		appendStringInfo(ctx->out, "\t\"lsn\": \"%s\",\n", lsn_str);
+		pfree(lsn_str);
+	}
+
 	if (data->include_timestamp)
 		appendStringInfo(ctx->out, "\t\"timestamp\": \"%s\",\n", timestamptz_to_str(txn->commit_time));