From 3b0acaf5356c581253d48c60bf728565993ee067 Mon Sep 17 00:00:00 2001
From: parihaaraka <lukyanov@kickico.com>
Date: Wed, 1 Dec 2021 14:19:03 +0300
Subject: [PATCH 1/6] [u]int64_t parameters; decimal->number cast removed in
 favor of original textual representation

---
 pg/driver.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/pg/driver.c b/pg/driver.c
index 0bc9620..126d5ea 100644
--- a/pg/driver.c
+++ b/pg/driver.c
@@ -108,8 +108,7 @@ parse_pg_value(struct lua_State *L, PGresult *res, int row, int col)
 
 	switch (PQftype(res, col)) {
 		case INT2OID:
-		case INT4OID:
-		case NUMERICOID: {
+		case INT4OID: {
 			lua_pushlstring(L, val, len);
 			double v = lua_tonumber(L, -1);
 			lua_pop(L, 1);
@@ -127,6 +126,7 @@ parse_pg_value(struct lua_State *L, PGresult *res, int row, int col)
 			else
 				lua_pushboolean(L, 0);
 			break;
+		//case NUMERICOID: // leave it as is (otherwise cast to decimal)
 		default:
 			lua_pushlstring(L, val, len);
 	}
@@ -293,6 +293,27 @@ lua_parse_param(struct lua_State *L,
 		return;
 	}
 
+	if (luaL_iscdata(L, idx)) {
+		uint32_t ctypeid = 0;
+		void *cdata = luaL_checkcdata(L, idx, &ctypeid);
+		static char buf[24];
+		int len = 0;
+		if (ctypeid == luaL_ctypeid(L, "int64_t")) {
+			len = snprintf(buf, sizeof(buf), "%ld", *(int64_t*)cdata);
+			*type = INT8OID;
+		}
+		else if (ctypeid == luaL_ctypeid(L, "uint64_t")) {
+			len = snprintf(buf, sizeof(buf), "%lu", *(uint64_t*)cdata);
+			*type = NUMERICOID;
+		}
+
+		if (len > 0) {
+			*value = buf;
+			*length = len;
+			return;
+		}
+	}
+
 	// We will pass all other types as strings
 	size_t len;
 	*value = lua_tolstring(L, idx, &len);

From 6b93cc8f5a8c22bacc5229c6474ab88317aada2f Mon Sep 17 00:00:00 2001
From: parihaaraka <parihaaraka@gmail.com>
Date: Wed, 30 Mar 2022 16:31:58 +0300
Subject: [PATCH 2/6] new `connection.dec_cast` option ('s' - string, 'n' -
 number, default is 'n')

---
 pg/driver.c | 37 +++++++++++++++++++++++++++----------
 pg/init.lua |  3 ++-
 2 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/pg/driver.c b/pg/driver.c
index 126d5ea..9715852 100644
--- a/pg/driver.c
+++ b/pg/driver.c
@@ -97,7 +97,7 @@ lua_push_error(struct lua_State *L)
  * Parse pg values to lua
  */
 static int
-parse_pg_value(struct lua_State *L, PGresult *res, int row, int col)
+parse_pg_value(struct lua_State *L, char dec_cast, PGresult *res, int row, int col)
 {
 	if (PQgetisnull(res, row, col))
 		return false;
@@ -107,6 +107,14 @@ parse_pg_value(struct lua_State *L, PGresult *res, int row, int col)
 	int len = PQgetlength(res, row, col);
 
 	switch (PQftype(res, col)) {
+		case NUMERICOID: {
+			if (dec_cast == 's')
+			{
+				lua_pushlstring(L, val, len);
+				break;
+			}
+			// else fallthrough
+		}
 		case INT2OID:
 		case INT4OID: {
 			lua_pushlstring(L, val, len);
@@ -126,7 +134,6 @@ parse_pg_value(struct lua_State *L, PGresult *res, int row, int col)
 			else
 				lua_pushboolean(L, 0);
 			break;
-		//case NUMERICOID: // leave it as is (otherwise cast to decimal)
 		default:
 			lua_pushlstring(L, val, len);
 	}
@@ -141,6 +148,7 @@ static int
 safe_pg_parsetuples(struct lua_State *L)
 {
 	PGresult *res = (PGresult *)lua_topointer(L, 1);
+	const char dec_cast = (char)lua_tointeger(L, 2);
 	int row, rows = PQntuples(res);
 	int col, cols = PQnfields(res);
 	lua_newtable(L);
@@ -148,7 +156,7 @@ safe_pg_parsetuples(struct lua_State *L)
 		lua_pushnumber(L, row + 1);
 		lua_newtable(L);
 		for (col = 0; col < cols; ++col)
-			parse_pg_value(L, res, row, col);
+			parse_pg_value(L, dec_cast, res, row, col);
 		lua_settable(L, -3);
 	}
 	return 1;
@@ -205,7 +213,7 @@ pg_wait_for_result(PGconn *conn)
  * Appends result fom postgres to lua table
  */
 static int
-pg_resultget(struct lua_State *L, PGconn *conn, int *res_no, int status_ok)
+pg_resultget(struct lua_State *L, const char dec_cast, PGconn *conn, int *res_no, int status_ok)
 {
 	int wait_res = pg_wait_for_result(conn);
 	if (wait_res != 1)
@@ -235,7 +243,8 @@ pg_resultget(struct lua_State *L, PGconn *conn, int *res_no, int status_ok)
 			lua_pushinteger(L, (*res_no)++);
 			lua_pushcfunction(L, safe_pg_parsetuples);
 			lua_pushlightuserdata(L, pg_res);
-			fail = lua_pcall(L, 1, 1, 0);
+			lua_pushinteger(L, dec_cast);
+			fail = lua_pcall(L, 2, 1, 0);
 			if (!fail)
 				lua_settable(L, -3);
 		case PGRES_COMMAND_OK:
@@ -328,12 +337,20 @@ static int
 lua_pg_execute(struct lua_State *L)
 {
 	PGconn *conn = lua_check_pgconn(L, 1);
-	if (!lua_isstring(L, 2)) {
+
+	char dec_cast = 'n';
+	if (lua_isstring(L, 2)) {
+		const char *tmp = lua_tostring(L, 2);
+		if (*tmp == 'n' || *tmp == 's') // TODO 'd' - decimal
+			dec_cast = *tmp;
+	}
+
+	if (!lua_isstring(L, 3)) {
 		safe_pushstring(L, "Second param should be a sql command");
 		return lua_push_error(L);
 	}
-	const char *sql = lua_tostring(L, 2);
-	int paramCount = lua_gettop(L) - 2;
+	const char *sql = lua_tostring(L, 3);
+	int paramCount = lua_gettop(L) - 3;
 
 	const char **paramValues = NULL;
 	int  *paramLengths = NULL;
@@ -354,7 +371,7 @@ lua_pg_execute(struct lua_State *L)
 
 		int idx;
 		for (idx = 0; idx < paramCount; ++idx) {
-			lua_parse_param(L, idx + 3, paramValues + idx,
+			lua_parse_param(L, idx + 4, paramValues + idx,
 				paramLengths + idx, paramTypes + idx);
 		}
 		res = PQsendQueryParams(conn, sql, paramCount, paramTypes,
@@ -373,7 +390,7 @@ lua_pg_execute(struct lua_State *L)
 
 	int res_no = 1;
 	int status_ok = 1;
-	while ((status_ok = pg_resultget(L, conn, &res_no, status_ok)));
+	while ((status_ok = pg_resultget(L, dec_cast, conn, &res_no, status_ok)));
 
 	return 2;
 }
diff --git a/pg/init.lua b/pg/init.lua
index b1000d6..d95e84b 100644
--- a/pg/init.lua
+++ b/pg/init.lua
@@ -15,6 +15,7 @@ local function conn_create(pg_conn)
         usable = true,
         conn = pg_conn,
         queue = queue,
+        dec_cast = 'n' -- 'n' - number, 's' - string
     }, conn_mt)
 
     return conn
@@ -60,7 +61,7 @@ conn_mt = {
                 self.queue:put(false)
                 return get_error(self.raise.pool, 'Connection is broken')
             end
-            local status, datas = self.conn:execute(sql, ...)
+            local status, datas = self.conn:execute(self.dec_cast, sql, ...)
             if status ~= 0 then
                 self.queue:put(status > 0)
                 return error(datas)

From 6b7de5657748e4757e1a926df95d7bcfc9339e51 Mon Sep 17 00:00:00 2001
From: parihaaraka <parihaaraka@gmail.com>
Date: Thu, 31 Mar 2022 13:31:56 +0300
Subject: [PATCH 3/6] optional pg decimal to tnt decimal cast

---
 pg/driver.c | 56 +++++++++++++++++++++++++++++++++++++++--------------
 pg/init.lua | 12 ++++++++++--
 2 files changed, 51 insertions(+), 17 deletions(-)

diff --git a/pg/driver.c b/pg/driver.c
index 9715852..8ad8376 100644
--- a/pg/driver.c
+++ b/pg/driver.c
@@ -49,6 +49,12 @@
 #undef PACKAGE_VERSION
 #include <module.h>
 
+struct dec_opt {
+	char cast;
+	int dnew_index;
+};
+typedef struct dec_opt dec_opt_t;
+
 /**
  * Infinity timeout from tarantool_ev.c. I mean, this should be in
  * a module.h file.
@@ -97,7 +103,7 @@ lua_push_error(struct lua_State *L)
  * Parse pg values to lua
  */
 static int
-parse_pg_value(struct lua_State *L, char dec_cast, PGresult *res, int row, int col)
+parse_pg_value(struct lua_State *L, dec_opt_t *dopt, PGresult *res, int row, int col)
 {
 	if (PQgetisnull(res, row, col))
 		return false;
@@ -108,9 +114,18 @@ parse_pg_value(struct lua_State *L, char dec_cast, PGresult *res, int row, int c
 
 	switch (PQftype(res, col)) {
 		case NUMERICOID: {
-			if (dec_cast == 's')
-			{
+			if (dopt->cast == 's') {
+				lua_pushlstring(L, val, len);
+				break;
+			}
+			else if (dopt->cast == 'd' && dopt->dnew_index != -1) {
+				lua_rawgeti(L, LUA_REGISTRYINDEX, dopt->dnew_index);
 				lua_pushlstring(L, val, len);
+				int fail = lua_pcall(L, 1, 1, 0);
+				if (fail) {
+					lua_pop(L, 2);
+					return false;
+				}
 				break;
 			}
 			// else fallthrough
@@ -148,7 +163,7 @@ static int
 safe_pg_parsetuples(struct lua_State *L)
 {
 	PGresult *res = (PGresult *)lua_topointer(L, 1);
-	const char dec_cast = (char)lua_tointeger(L, 2);
+	dec_opt_t *dopt = (dec_opt_t *)lua_topointer(L, 2);
 	int row, rows = PQntuples(res);
 	int col, cols = PQnfields(res);
 	lua_newtable(L);
@@ -156,7 +171,7 @@ safe_pg_parsetuples(struct lua_State *L)
 		lua_pushnumber(L, row + 1);
 		lua_newtable(L);
 		for (col = 0; col < cols; ++col)
-			parse_pg_value(L, dec_cast, res, row, col);
+			parse_pg_value(L, dopt, res, row, col);
 		lua_settable(L, -3);
 	}
 	return 1;
@@ -213,7 +228,7 @@ pg_wait_for_result(PGconn *conn)
  * Appends result fom postgres to lua table
  */
 static int
-pg_resultget(struct lua_State *L, const char dec_cast, PGconn *conn, int *res_no, int status_ok)
+pg_resultget(struct lua_State *L, dec_opt_t *dopt, PGconn *conn, int *res_no, int status_ok)
 {
 	int wait_res = pg_wait_for_result(conn);
 	if (wait_res != 1)
@@ -243,7 +258,7 @@ pg_resultget(struct lua_State *L, const char dec_cast, PGconn *conn, int *res_no
 			lua_pushinteger(L, (*res_no)++);
 			lua_pushcfunction(L, safe_pg_parsetuples);
 			lua_pushlightuserdata(L, pg_res);
-			lua_pushinteger(L, dec_cast);
+			lua_pushlightuserdata(L, dopt);
 			fail = lua_pcall(L, 2, 1, 0);
 			if (!fail)
 				lua_settable(L, -3);
@@ -338,19 +353,25 @@ lua_pg_execute(struct lua_State *L)
 {
 	PGconn *conn = lua_check_pgconn(L, 1);
 
-	char dec_cast = 'n';
+	dec_opt_t dopt = {'n', -1};
 	if (lua_isstring(L, 2)) {
 		const char *tmp = lua_tostring(L, 2);
-		if (*tmp == 'n' || *tmp == 's') // TODO 'd' - decimal
-			dec_cast = *tmp;
+		if (*tmp == 'n' || *tmp == 's' || *tmp == 'd')
+			dopt.cast = *tmp;
 	}
 
-	if (!lua_isstring(L, 3)) {
+	if (!lua_isstring(L, 4)) {
 		safe_pushstring(L, "Second param should be a sql command");
 		return lua_push_error(L);
 	}
-	const char *sql = lua_tostring(L, 3);
-	int paramCount = lua_gettop(L) - 3;
+
+	if (lua_isfunction(L, 3)) {
+		lua_pushvalue(L, 3);
+		dopt.dnew_index = luaL_ref(L, LUA_REGISTRYINDEX);
+	}
+
+	const char *sql = lua_tostring(L, 4);
+	int paramCount = lua_gettop(L) - 4;
 
 	const char **paramValues = NULL;
 	int  *paramLengths = NULL;
@@ -371,7 +392,7 @@ lua_pg_execute(struct lua_State *L)
 
 		int idx;
 		for (idx = 0; idx < paramCount; ++idx) {
-			lua_parse_param(L, idx + 4, paramValues + idx,
+			lua_parse_param(L, idx + 5, paramValues + idx,
 				paramLengths + idx, paramTypes + idx);
 		}
 		res = PQsendQueryParams(conn, sql, paramCount, paramTypes,
@@ -383,6 +404,8 @@ lua_pg_execute(struct lua_State *L)
 	if (res == -1) {
 		lua_pushinteger(L, PQstatus(conn) == CONNECTION_BAD ? -1: 0);
 		lua_pushstring(L, PQerrorMessage(conn));
+		if (dopt.dnew_index != -1)
+			luaL_unref(L, LUA_REGISTRYINDEX, dopt.dnew_index);
 		return 2;
 	}
 	lua_pushinteger(L, 0);
@@ -390,7 +413,10 @@ lua_pg_execute(struct lua_State *L)
 
 	int res_no = 1;
 	int status_ok = 1;
-	while ((status_ok = pg_resultget(L, dec_cast, conn, &res_no, status_ok)));
+	while ((status_ok = pg_resultget(L, &dopt, conn, &res_no, status_ok)));
+
+	if (dopt.dnew_index != -1)
+		luaL_unref(L, LUA_REGISTRYINDEX, dopt.dnew_index);
 
 	return 2;
 }
diff --git a/pg/init.lua b/pg/init.lua
index d95e84b..686f426 100644
--- a/pg/init.lua
+++ b/pg/init.lua
@@ -4,6 +4,14 @@ local fiber = require('fiber')
 local driver = require('pg.driver')
 local ffi = require('ffi')
 
+local dnew
+do
+    local ok, dec = pcall(require, "decimal")
+    if ok then
+        dnew = dec.new
+    end
+end
+
 local pool_mt
 local conn_mt
 
@@ -15,7 +23,7 @@ local function conn_create(pg_conn)
         usable = true,
         conn = pg_conn,
         queue = queue,
-        dec_cast = 'n' -- 'n' - number, 's' - string
+        dec_cast = 'n' -- 'n' - number, 's' - string, 'd' - decimal
     }, conn_mt)
 
     return conn
@@ -61,7 +69,7 @@ conn_mt = {
                 self.queue:put(false)
                 return get_error(self.raise.pool, 'Connection is broken')
             end
-            local status, datas = self.conn:execute(self.dec_cast, sql, ...)
+            local status, datas = self.conn:execute(self.dec_cast, dnew, sql, ...)
             if status ~= 0 then
                 self.queue:put(status > 0)
                 return error(datas)

From 9ed329115bf66d4d48771b109eefc072ccf20f96 Mon Sep 17 00:00:00 2001
From: parihaaraka <parihaaraka@gmail.com>
Date: Thu, 31 Mar 2022 21:52:06 +0300
Subject: [PATCH 4/6] multiple [u]int64_t parameters usage fix

---
 pg/driver.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/pg/driver.c b/pg/driver.c
index 8ad8376..b4f6aa6 100644
--- a/pg/driver.c
+++ b/pg/driver.c
@@ -293,6 +293,13 @@ static void
 lua_parse_param(struct lua_State *L,
 	int idx, const char **value, int *length, Oid *type)
 {
+	static char buf[512]; // buffer for serialized [u]int64_t
+	static char *pos;
+	if (idx == 5) { // lua_parse_param(L, idx + 5, ...
+		*buf = '\0';
+		pos = buf;
+	}
+
 	if (lua_isnil(L, idx)) {
 		*value = NULL;
 		*length = 0;
@@ -320,20 +327,20 @@ lua_parse_param(struct lua_State *L,
 	if (luaL_iscdata(L, idx)) {
 		uint32_t ctypeid = 0;
 		void *cdata = luaL_checkcdata(L, idx, &ctypeid);
-		static char buf[24];
 		int len = 0;
 		if (ctypeid == luaL_ctypeid(L, "int64_t")) {
-			len = snprintf(buf, sizeof(buf), "%ld", *(int64_t*)cdata);
+			len = snprintf(pos, sizeof(buf) - (pos - buf), "%ld", *(int64_t*)cdata);
 			*type = INT8OID;
 		}
 		else if (ctypeid == luaL_ctypeid(L, "uint64_t")) {
-			len = snprintf(buf, sizeof(buf), "%lu", *(uint64_t*)cdata);
+			len = snprintf(pos, sizeof(buf) - (pos - buf), "%lu", *(uint64_t*)cdata);
 			*type = NUMERICOID;
 		}
 
 		if (len > 0) {
-			*value = buf;
+			*value = pos;
 			*length = len;
+			pos += len + 1;
 			return;
 		}
 	}

From 66477ca34f2d04e789be457ede12824683ed29ef Mon Sep 17 00:00:00 2001
From: Sergey Bronnikov <sergeyb@tarantool.org>
Date: Wed, 13 Jul 2022 19:01:20 +0300
Subject: [PATCH 5/6] Set a type for PostreSQL decimal numbers [TO SQUASH]

[REMOVE BEFORE MERGE] Changes proposed in fixup commit: documentation,
regression tests, code style.

Patch adds support of PostgreSQL decimal numbers - it is possible to
choose a Lua/Tarantool type that will be used for casting  values with
NUMERIC type [1]. By default Lua "number" type is used, the same
behaviour was used before changes. Additionally user could choose two
other types: Lua "string" and Tarantool's decimal type [2], [3].

Fixes #26
Fixes #25

1. https://www.postgresql.org/docs/current/datatype-oid.html
2. https://www.tarantool.io/en/doc/latest/reference/reference_lua/decimal/
3. https://www.tarantool.io/en/doc/latest/book/box/data_model/#data-types

Co-authored-by: Sergey Bronnikov <sergeyb@tarantool.org>
---
 README.md        |  2 ++
 pg/driver.c      | 46 +++++++++++++++++++++++++++++++++++-----------
 pg/init.lua      | 14 +++++++-------
 test/pg.test.lua | 36 ++++++++++++++++++++++++++++++++++++
 4 files changed, 80 insertions(+), 18 deletions(-)

diff --git a/README.md b/README.md
index 8a063a6..203bd15 100644
--- a/README.md
+++ b/README.md
@@ -54,6 +54,8 @@ Connect to a database.
  - `db` - a database name
  - `conn_string` (mutual exclusive with host, port, user, pass, db) - PostgreSQL
    [connection string][PQconnstring]
+ - `dec_cast` - an option that switches casting types for `NUMERIC` PostgreSQL
+   type. Possible values: `n` (`number`), `s` (`string`), `d` (`decimal`).
 
 *Returns*:
 
diff --git a/pg/driver.c b/pg/driver.c
index b4f6aa6..6ce6c5d 100644
--- a/pg/driver.c
+++ b/pg/driver.c
@@ -49,6 +49,25 @@
 #undef PACKAGE_VERSION
 #include <module.h>
 
+/**
+ * The fallthrough attribute with a null statement serves as a fallthrough
+ * statement. It hints to the compiler that a statement that falls through
+ * to another case label, or user-defined label in a switch statement is
+ * intentional and thus the -Wimplicit-fallthrough warning must not trigger.
+ * The fallthrough attribute may appear at most once in each attribute list,
+ * and may not be mixed with other attributes. It can only be used in a switch
+ * statement (the compiler will issue an error otherwise), after a preceding
+ * statement and before a logically succeeding case label, or user-defined
+ * label.
+ */
+#if defined(__cplusplus) && __has_cpp_attribute(fallthrough)
+#  define FALLTHROUGH [[fallthrough]]
+#elif __has_attribute(fallthrough) || (defined(__GNUC__) && __GNUC__ >= 7)
+#  define FALLTHROUGH __attribute__((fallthrough))
+#else
+#  define FALLTHROUGH
+#endif
+
 struct dec_opt {
 	char cast;
 	int dnew_index;
@@ -103,7 +122,7 @@ lua_push_error(struct lua_State *L)
  * Parse pg values to lua
  */
 static int
-parse_pg_value(struct lua_State *L, dec_opt_t *dopt, PGresult *res, int row, int col)
+parse_pg_value(struct lua_State *L, PGresult *res, int row, int col, dec_opt_t *dopt)
 {
 	if (PQgetisnull(res, row, col))
 		return false;
@@ -128,7 +147,8 @@ parse_pg_value(struct lua_State *L, dec_opt_t *dopt, PGresult *res, int row, int
 				}
 				break;
 			}
-			// else fallthrough
+			/* 'n': fallthrough */
+			FALLTHROUGH;
 		}
 		case INT2OID:
 		case INT4OID: {
@@ -171,7 +191,7 @@ safe_pg_parsetuples(struct lua_State *L)
 		lua_pushnumber(L, row + 1);
 		lua_newtable(L);
 		for (col = 0; col < cols; ++col)
-			parse_pg_value(L, dopt, res, row, col);
+			parse_pg_value(L, res, row, col, dopt);
 		lua_settable(L, -3);
 	}
 	return 1;
@@ -228,7 +248,7 @@ pg_wait_for_result(PGconn *conn)
  * Appends result fom postgres to lua table
  */
 static int
-pg_resultget(struct lua_State *L, dec_opt_t *dopt, PGconn *conn, int *res_no, int status_ok)
+pg_resultget(struct lua_State *L, PGconn *conn, int *res_no, int status_ok, dec_opt_t *dopt)
 {
 	int wait_res = pg_wait_for_result(conn);
 	if (wait_res != 1)
@@ -293,9 +313,11 @@ static void
 lua_parse_param(struct lua_State *L,
 	int idx, const char **value, int *length, Oid *type)
 {
-	static char buf[512]; // buffer for serialized [u]int64_t
-	static char *pos;
-	if (idx == 5) { // lua_parse_param(L, idx + 5, ...
+    /* Serialized [u]int64_t */
+	static char buf[512];
+	static char *pos = NULL;
+    /* lua_parse_param(L, idx + 5, ...) */
+	if (idx == 5) {
 		*buf = '\0';
 		pos = buf;
 	}
@@ -362,9 +384,11 @@ lua_pg_execute(struct lua_State *L)
 
 	dec_opt_t dopt = {'n', -1};
 	if (lua_isstring(L, 2)) {
-		const char *tmp = lua_tostring(L, 2);
-		if (*tmp == 'n' || *tmp == 's' || *tmp == 'd')
-			dopt.cast = *tmp;
+		const char *dec_cast_type = lua_tostring(L, 2);
+		if (*dec_cast_type == 'n' ||
+			*dec_cast_type == 's' ||
+			*dec_cast_type == 'd')
+			dopt.cast = *dec_cast_type;
 	}
 
 	if (!lua_isstring(L, 4)) {
@@ -420,7 +444,7 @@ lua_pg_execute(struct lua_State *L)
 
 	int res_no = 1;
 	int status_ok = 1;
-	while ((status_ok = pg_resultget(L, &dopt, conn, &res_no, status_ok)));
+	while ((status_ok = pg_resultget(L, conn, &res_no, status_ok, &dopt)));
 
 	if (dopt.dnew_index != -1)
 		luaL_unref(L, LUA_REGISTRYINDEX, dopt.dnew_index);
diff --git a/pg/init.lua b/pg/init.lua
index 686f426..91ff0ea 100644
--- a/pg/init.lua
+++ b/pg/init.lua
@@ -4,12 +4,9 @@ local fiber = require('fiber')
 local driver = require('pg.driver')
 local ffi = require('ffi')
 
-local dnew
-do
-    local ok, dec = pcall(require, "decimal")
-    if ok then
-        dnew = dec.new
-    end
+local has_decimal, dec = pcall(require, 'decimal')
+if has_decimal then
+    dnew = dec.new
 end
 
 local pool_mt
@@ -23,7 +20,10 @@ local function conn_create(pg_conn)
         usable = true,
         conn = pg_conn,
         queue = queue,
-        dec_cast = 'n' -- 'n' - number, 's' - string, 'd' - decimal
+        dec_cast = 'n' -- Defined in pg/driver.c:
+                       -- 'n' - number,
+                       -- 's' - string,
+                       -- 'd' - decimal.
     }, conn_mt)
 
     return conn
diff --git a/test/pg.test.lua b/test/pg.test.lua
index 144ceea..871f395 100755
--- a/test/pg.test.lua
+++ b/test/pg.test.lua
@@ -129,6 +129,41 @@ function test_pg_int64(t, p)
     p:put(conn)
 end
 
+function test_pg_decimal(t, p)
+    t:plan(8)
+
+    -- Setup
+    conn = p:get()
+    t:isnt(conn, nil, 'connection is established')
+    local num = 4500
+    conn:execute('CREATE TABLE dectest (num NUMERIC(7,2))')
+    conn:execute(('INSERT INTO dectest VALUES(%d)'):format(num))
+
+    local res, r, _
+    -- dec_cast is 'n'
+    t:is(conn.dec_cast, 'n', 'decimal casting type is "n" by default')
+    r, _ = conn:execute('SELECT num FROM dectest')
+    res = r[1][1]['num']
+    t:is(type(res), 'number', 'type is "number"')
+    t:is(res, num, 'decimal number is correct')
+    -- dec_cast is 's'
+    conn.dec_cast = 's'
+    r, _ = conn:execute('SELECT num FROM dectest')
+    res = r[1][1]['num']
+    t:is(type(res), 'string', 'type is "string"')
+    t:is(res, '4500.00', 'decimal number is correct')
+    -- dec_cast is 'd'
+    conn.dec_cast = 'd'
+    r, _ = conn:execute('SELECT num FROM dectest')
+    res = r[1][1]['num']
+    t:is(type(res), 'cdata', 'type is "decimal"')
+    t:is(res, num, 'decimal number is correct')
+
+    -- Teardown
+    conn:execute('DROP TABLE dectest')
+    p:put(conn)
+end
+
 tap.test('connection old api', test_old_api, conn)
 local pool_conn = p:get()
 tap.test('connection old api via pool', test_old_api, pool_conn)
@@ -136,4 +171,5 @@ p:put(pool_conn)
 tap.test('test collection connections', test_gc, p)
 tap.test('connection concurrent', test_conn_concurrent, p)
 tap.test('int64', test_pg_int64, p)
+tap.test('decimal', test_pg_decimal, p)
 p:close()

From b6212637641281d7b43474585051da072464cf0c Mon Sep 17 00:00:00 2001
From: Sergey Bronnikov <sergeyb@tarantool.org>
Date: Mon, 18 Jul 2022 17:24:52 +0300
Subject: [PATCH 6/6] Fix fallthrough compiler warnings

1. https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wimplicit-fallthrough
---
 pg/driver.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/pg/driver.c b/pg/driver.c
index 6ce6c5d..1fba631 100644
--- a/pg/driver.c
+++ b/pg/driver.c
@@ -280,8 +280,11 @@ pg_resultget(struct lua_State *L, PGconn *conn, int *res_no, int status_ok, dec_
 			lua_pushlightuserdata(L, pg_res);
 			lua_pushlightuserdata(L, dopt);
 			fail = lua_pcall(L, 2, 1, 0);
-			if (!fail)
+			if (!fail) {
 				lua_settable(L, -3);
+				break;
+			}
+			break;
 		case PGRES_COMMAND_OK:
 			res = 1;
 			break;