v.info: add json output for columns

vector/v.info/local_proto.h

@@ -19,7 +19,8 @@ void parse_args(int, char **, char **, char **, int *, int *, int *,
 void format_double(double, char *);
 void print_region(struct Map_info *, enum OutputFormat, JSON_Object *);
 void print_topo(struct Map_info *, enum OutputFormat, JSON_Object *);
-void print_columns(struct Map_info *, const char *, const char *);
+void print_columns(struct Map_info *, const char *, const char *,
+                   enum OutputFormat);
 void print_info(struct Map_info *);
 void print_shell(struct Map_info *, const char *, enum OutputFormat,
                  JSON_Object *);

vector/v.info/main.c

@@ -85,7 +85,7 @@ int main(int argc, char *argv[])
             }
         }
         else if (col_flag) {
-            print_columns(&Map, input_opt, field_opt);
+            print_columns(&Map, input_opt, field_opt, format);
         }
         Vect_close(&Map);
 

vector/v.info/print.c

@@ -176,7 +176,7 @@ void print_topo(struct Map_info *Map, enum OutputFormat format,
 }
 
 void print_columns(struct Map_info *Map, const char *input_opt,
-                   const char *field_opt)
+                   const char *field_opt, enum OutputFormat format)
 {
     int num_dblinks, col, ncols;
 
@@ -189,6 +189,7 @@ void print_columns(struct Map_info *Map, const char *input_opt,
     num_dblinks = Vect_get_num_dblinks(Map);
 
     if (num_dblinks <= 0) {
+        Vect_close(Map);
         G_fatal_error(
             _("Database connection for map <%s> is not defined in DB file"),
             input_opt);
@@ -198,32 +199,97 @@ void print_columns(struct Map_info *Map, const char *input_opt,
                 "layer <%s>:"),
               field_opt);
 
-    if ((fi = Vect_get_field2(Map, field_opt)) == NULL)
+    if ((fi = Vect_get_field2(Map, field_opt)) == NULL) {
+        Vect_close(Map);
         G_fatal_error(
             _("Database connection not defined for layer <%s> of <%s>"),
             field_opt, input_opt);
+    }
     driver = db_start_driver(fi->driver);
-    if (driver == NULL)
+    if (driver == NULL) {
+        Vect_close(Map);
         G_fatal_error(_("Unable to open driver <%s>"), fi->driver);
+    }
     db_init_handle(&handle);
     db_set_handle(&handle, fi->database, NULL);
-    if (db_open_database(driver, &handle) != DB_OK)
+    if (db_open_database(driver, &handle) != DB_OK) {
+        db_shutdown_driver(driver);
+        Vect_close(Map);
         G_fatal_error(_("Unable to open database <%s> by driver <%s>"),
                       fi->database, fi->driver);
+    }
     db_init_string(&table_name);
     db_set_string(&table_name, fi->table);
-    if (db_describe_table(driver, &table_name, &table) != DB_OK)
+    if (db_describe_table(driver, &table_name, &table) != DB_OK) {
+        db_close_database_shutdown_driver(driver);
+        Vect_close(Map);
         G_fatal_error(_("Unable to describe table <%s>"), fi->table);
+    }
+
+    JSON_Value *root_value = NULL, *columns_value = NULL, *column_value = NULL;
+    JSON_Object *root_object = NULL, *column_object = NULL;
+    JSON_Array *columns_array = NULL;
+
+    if (format == JSON) {
+        root_value = json_value_init_object();
+        root_object = json_object(root_value);
+        columns_value = json_value_init_array();
+        columns_array = json_array(columns_value);
+        json_object_set_value(root_object, "columns", columns_value);
+    }
 
     ncols = db_get_table_number_of_columns(table);
-    for (col = 0; col < ncols; col++)
-        fprintf(stdout, "%s|%s\n",
-                db_sqltype_name(
-                    db_get_column_sqltype(db_get_table_column(table, col))),
+    for (col = 0; col < ncols; col++) {
+        switch (format) {
+        case SHELL:
+            break;
+
+        case JSON:
+            column_value = json_value_init_object();
+            column_object = json_object(column_value);
+
+            json_object_set_string(
+                column_object, "name",
                 db_get_column_name(db_get_table_column(table, col)));
 
-    db_close_database(driver);
-    db_shutdown_driver(driver);
+            int sql_type =
+                db_get_column_sqltype(db_get_table_column(table, col));
+            json_object_set_string(column_object, "sql_type",
+                                   db_sqltype_name(sql_type));
+
+            int c_type = db_sqltype_to_Ctype(sql_type);
+            json_object_set_boolean(
+                column_object, "is_number",
+                (c_type == DB_C_TYPE_INT || c_type == DB_C_TYPE_DOUBLE));
+
+            json_array_append_value(columns_array, column_value);
+            break;
+
+        case PLAIN:
+            fprintf(stdout, "%s|%s\n",
+                    db_sqltype_name(
+                        db_get_column_sqltype(db_get_table_column(table, col))),
+                    db_get_column_name(db_get_table_column(table, col)));
+            break;
+        }
+    }
+
+    if (format == JSON) {
+        char *serialized_string = NULL;
+        serialized_string = json_serialize_to_string_pretty(root_value);
+        if (serialized_string == NULL) {
+            json_value_free(root_value);
+            db_close_database_shutdown_driver(driver);
+            Vect_close(Map);
+            G_fatal_error(_("Failed to initialize pretty JSON string."));
+        }
+        puts(serialized_string);
+        json_free_serialized_string(serialized_string);
+        json_value_free(root_value);
+    }
+
+    Vect_destroy_field_info(fi);
+    db_close_database_shutdown_driver(driver);
 }
 
 void print_shell(struct Map_info *Map, const char *field_opt,

vector/v.info/testsuite/test_vinfo.py

@@ -250,6 +250,27 @@ def test_json(self):
             result.pop(field)
         self.assertDictEqual(expected, result)
 
+    def test_json_column(self):
+        module = SimpleModule(
+            "v.info", map=self.test_vinfo_with_db_3d, format="json", flags="c"
+        )
+        self.runModule(module)
+
+        expected_json = {
+            "columns": [
+                {"is_number": True, "name": "cat", "sql_type": "INTEGER"},
+                {
+                    "is_number": True,
+                    "name": "elevation",
+                    "sql_type": "DOUBLE PRECISION",
+                },
+            ]
+        }
+
+        result = json.loads(module.outputs.stdout)
+
+        self.assertDictEqual(expected_json, result)
+
     def test_database_table(self):
         """Test the database table column and type of the two vector maps with attribute data"""
         self.assertModuleKeyValue(