On 11/19/18 8:27 PM, n.pettik wrote:

EXPLAIN envokes SEGMENTATION FAULT when being executed through

Typo: invokes.

net.box. It happens due to column type of the result of this
function being NULL.

I’ve checked and not only EXPLAIN results, but also EXPLAIN QUERY PLAN,
several pragmas (for instance, pragma table_info()) etc. So, initially problem
was not only in EXPLAIN statement. Please exposed commit message and
add tests on other cases.

Also, why did you decide to avoid sending type at all, instead of sending
UNKNOWN for example?

Diff between versions:

diff --git a/src/box/execute.c b/src/box/execute.c
index 5b747cf..cd809f8 100644
--- a/src/box/execute.c
+++ b/src/box/execute.c
@@ -529,6 +529,9 @@ sql_get_description(struct sqlite3_stmt *stmt, struct obuf *out,
         return -1;
 
     for (int i = 0; i < column_count; ++i) {
+        size_t size = mp_sizeof_map(2) +
+                  mp_sizeof_uint(IPROTO_FIELD_NAME) +
+                  mp_sizeof_uint(IPROTO_FIELD_TYPE);
         const char *name = sqlite3_column_name(stmt, i);
         const char *type = sqlite3_column_datatype(stmt, i);
         /*
@@ -537,27 +540,20 @@ sql_get_description(struct sqlite3_stmt *stmt, struct obuf *out,
          * column_name simply returns them.
          */
         assert(name != NULL);
-        size_t size = mp_sizeof_uint(IPROTO_FIELD_NAME) +
-                  mp_sizeof_str(strlen(name));
-        if (type != NULL) {
-            size += mp_sizeof_map(2) +
-                mp_sizeof_uint(IPROTO_FIELD_TYPE) +
-                mp_sizeof_str(strlen(type));
-        } else {
-            size += mp_sizeof_map(1);
-        }
+        if (type == NULL)
+            type = "UNKNOWN";
+        size += mp_sizeof_str(strlen(name));
+        size += mp_sizeof_str(strlen(type));
         char *pos = (char *) obuf_alloc(out, size);
         if (pos == NULL) {
             diag_set(OutOfMemory, size, "obuf_alloc", "pos");
             return -1;
         }
-        pos = mp_encode_map(pos, 1 + (type != NULL));
+        pos = mp_encode_map(pos, 2);
         pos = mp_encode_uint(pos, IPROTO_FIELD_NAME);
         pos = mp_encode_str(pos, name, strlen(name));
-        if (type != NULL) {
-            pos = mp_encode_uint(pos, IPROTO_FIELD_TYPE);
-            pos = mp_encode_str(pos, type, strlen(type));
-        }
+        pos = mp_encode_uint(pos, IPROTO_FIELD_TYPE);
+        pos = mp_encode_str(pos, type, strlen(type));
     }
     return 0;
 }
diff --git a/src/box/lua/net_box.c b/src/box/lua/net_box.c
index 342c6a7..c7063d9 100644
--- a/src/box/lua/net_box.c
+++ b/src/box/lua/net_box.c
@@ -644,7 +644,8 @@ netbox_decode_metadata(struct lua_State *L, const char **data)
     lua_createtable(L, count, 0);
     for (uint32_t i = 0; i < count; ++i) {
         uint32_t map_size = mp_decode_map(data);
-        assert(map_size == 1 || map_size == 2);
+        assert(map_size == 2);
+        (void) map_size;
         uint32_t key = mp_decode_uint(data);
         assert(key == IPROTO_FIELD_NAME);
         (void) key;
@@ -653,13 +654,11 @@ netbox_decode_metadata(struct lua_State *L, const char **data)
         const char *str = mp_decode_str(data, &len);
         lua_pushlstring(L, str, len);
         lua_setfield(L, -2, "name");
-        if (map_size == 2) {
-            key = mp_decode_uint(data);
-            assert(key == IPROTO_FIELD_TYPE);
-            const char *type = mp_decode_str(data, &len);
-            lua_pushlstring(L, type, len);
-            lua_setfield(L, -2, "type");
-        }
+        key = mp_decode_uint(data);
+        assert(key == IPROTO_FIELD_TYPE);
+        const char *type = mp_decode_str(data, &len);
+        lua_pushlstring(L, type, len);
+        lua_setfield(L, -2, "type");
         lua_rawseti(L, -2, i + 1);
     }
 }
diff --git a/test/sql/iproto.result b/test/sql/iproto.result
index 31e5d2e..f229427 100644
--- a/test/sql/iproto.result
+++ b/test/sql/iproto.result
@@ -774,9 +774,9 @@ cn:close()
 ---
 ...
 --
--- EXPLAIN could lead to segfault because it does not send column
--- data type, but looks like DQL. Netbox had been trying to decode
--- type for any DQL.
+-- Some commands, e.g. EXPLAIN, could lead to segfault because it
+-- does not send column data type, but looks like DQL. Netbox had
+-- been trying to decode type for any DQL.
 --
 cn = remote.connect(box.cfg.listen)
 ---
@@ -785,6 +785,32 @@ cn = remote.connect(box.cfg.listen)
 _ = cn:execute("EXPLAIN SELECT 1;")
 ---
 ...
+-- Segmentation fault when PRAGMA TABLE_INFO() executed using
+-- net.box.
+box.sql.execute('CREATE TABLE test (id INT PRIMARY KEY)')
+---
+...
+cn:execute("PRAGMA TABLE_INFO(test);")
+---
+- metadata:
+  - name: cid
+    type: UNKNOWN
+  - name: name
+    type: UNKNOWN
+  - name: type
+    type: UNKNOWN
+  - name: notnull
+    type: UNKNOWN
+  - name: dflt_value
+    type: UNKNOWN
+  - name: pk
+    type: UNKNOWN
+  rows:
+  - [0, 'ID', 'integer', 1, null, 1]
+...
+box.sql.execute('DROP TABLE test')
+---
+...
 cn:close()
 ---
 ...
diff --git a/test/sql/iproto.test.lua b/test/sql/iproto.test.lua
index a0f0f15..9bcc7ef 100644
--- a/test/sql/iproto.test.lua
+++ b/test/sql/iproto.test.lua
@@ -248,15 +248,21 @@ cn:execute('drop table test')
 cn:close()
 
 --
--- EXPLAIN could lead to segfault because it does not send column
--- data type, but looks like DQL. Netbox had been trying to decode
--- type for any DQL.
+-- Some commands, e.g. EXPLAIN, could lead to segfault because it
+-- does not send column data type, but looks like DQL. Netbox had
+-- been trying to decode type for any DQL.
 --
 cn = remote.connect(box.cfg.listen)
 
 -- Segmentation fault when EXPLAIN executed using net.box.
 _ = cn:execute("EXPLAIN SELECT 1;")
 
+-- Segmentation fault when PRAGMA TABLE_INFO() executed using
+-- net.box.
+box.sql.execute('CREATE TABLE test (id INT PRIMARY KEY)')
+cn:execute("PRAGMA TABLE_INFO(test);")
+box.sql.execute('DROP TABLE test')
+
 cn:close()
 
 box.schema.user.revoke('guest', 'read,write,execute', 'universe')

New version: