Added a function to retrieve columns of a prepared statement

c_src/sqlite3_drv.c

@@ -147,6 +147,9 @@ static int control(
   case CMD_PREPARED_FINALIZE:
     prepared_finalize(driver_data, buf, len);
     break;
+  case CMD_PREPARED_COLUMNS:
+    prepared_columns(driver_data, buf, len);
+    break;
   default:
     unknown(driver_data, buf, len);
   }
@@ -396,14 +399,13 @@ static int bind_parameters(
 }
 
 static void get_columns(
-    sqlite3_drv_t *drv, sqlite3_stmt *statement, int column_count,
+    sqlite3_drv_t *drv, sqlite3_stmt *statement, int column_count, int base,
     int *p_term_count, int *p_term_allocated, ErlDrvTermData **p_dataset) {
   int i;
 
-  int base = *p_term_count;
+  *p_term_count += column_count * 3 + 3;
-  *p_term_count += column_count * 3 + 1 + 2 + 2;
   if (*p_term_count > *p_term_allocated) {
-    *p_term_allocated = max(*p_term_count, *p_term_allocated*2);
+    *p_term_allocated = max(*p_term_count, (*p_term_allocated)*2);
     *p_dataset = driver_realloc(*p_dataset, sizeof(ErlDrvTermData) * *p_term_allocated);
   }
   for (i = 0; i < column_count; i++) {
@@ -413,13 +415,13 @@ static void get_columns(
     fflush(drv->log);
 #endif
 
-    (*p_dataset)[base + 2 + (i * 3)] = ERL_DRV_STRING;
+    (*p_dataset)[base + (i * 3)] = ERL_DRV_STRING;
-    (*p_dataset)[base + 2 + (i * 3) + 1] = (ErlDrvTermData) column_name;
+    (*p_dataset)[base + (i * 3) + 1] = (ErlDrvTermData) column_name;
-    (*p_dataset)[base + 2 + (i * 3) + 2] = strlen(column_name);
+    (*p_dataset)[base + (i * 3) + 2] = strlen(column_name);
   }
-  (*p_dataset)[base + 2 + column_count * 3 + 0] = ERL_DRV_NIL;
+  (*p_dataset)[base + column_count * 3 + 0] = ERL_DRV_NIL;
-  (*p_dataset)[base + 2 + column_count * 3 + 1] = ERL_DRV_LIST;
+  (*p_dataset)[base + column_count * 3 + 1] = ERL_DRV_LIST;
-  (*p_dataset)[base + 2 + column_count * 3 + 2] = column_count + 1;
+  (*p_dataset)[base + column_count * 3 + 2] = column_count + 1;
 }
 
 static int sql_bind_and_exec(sqlite3_drv_t *drv, char *buffer, int buffer_size) {
@@ -519,14 +521,19 @@ static void sql_exec_async(void *_async_command) {
     }
     dataset[term_count - 2] = ERL_DRV_ATOM;
     dataset[term_count - 1] = drv->atom_columns;
-    int base = term_count;
+    int base_term_count = term_count;
     get_columns(
-        drv, statement, column_count, &term_count, &term_allocated, &dataset);
+        drv, statement, column_count, base_term_count, &term_count, &term_allocated, &dataset);
-    dataset[base + column_count * 3 + 3] = ERL_DRV_TUPLE;
+    term_count += 4;
-    dataset[base + column_count * 3 + 4] = 2;
+    if (term_count > term_allocated) {
+      term_allocated = max(term_count, term_allocated*2);
+      dataset = driver_realloc(dataset, sizeof(ErlDrvTermData) * term_allocated);
+    }
+    dataset[base_term_count + column_count * 3 + 3] = ERL_DRV_TUPLE;
+    dataset[base_term_count + column_count * 3 + 4] = 2;
 
-    dataset[base + column_count * 3 + 5] = ERL_DRV_ATOM;
+    dataset[base_term_count + column_count * 3 + 5] = ERL_DRV_ATOM;
-    dataset[base + column_count * 3 + 6] = drv->atom_rows;
+    dataset[base_term_count + column_count * 3 + 6] = drv->atom_rows;
   }
 
 #ifdef DEBUG
@@ -954,9 +961,8 @@ static int prepared_bind(sqlite3_drv_t *drv, char *buffer, int buffer_size) {
 }
 
 static int prepared_columns(sqlite3_drv_t *drv, char *buffer, int buffer_size) {
-  int result;
   long long_prepared_index;
-  int index = 0, type, size;
+  int index = 0, term_count = 0, term_allocated = 0;
 
 #ifdef DEBUG
   fprintf(drv->log, "Finalizing prepared statement: %.*s\n", buffer_size, buffer);
@@ -973,13 +979,25 @@ static int prepared_columns(sqlite3_drv_t *drv, char *buffer, int buffer_size) {
   }
 
   sqlite3_stmt *statement = drv->prepared_stmts[prepared_index];
-//  result =
+  ErlDrvTermData *dataset = NULL;
-//      bind_parameters(drv, buffer, buffer_size, &index, statement, &type, &size);
+
-//  if (result == SQLITE_OK) {
+  term_count += 2;
-//    return output_ok(drv);
+  if (term_count > term_allocated) {
-//  } else {
+    term_allocated = max(term_count, term_allocated*2);
-//    return result; // error has already been output
+    dataset = driver_realloc(dataset, sizeof(ErlDrvTermData) * term_allocated);
-//  }
+  }
+  dataset[term_count - 2] = ERL_DRV_PORT;
+  dataset[term_count - 1] = driver_mk_port(drv->port);
+
+  int column_count = sqlite3_column_count(statement);
+
+  get_columns(
+      drv, statement, column_count, 2, &term_count, &term_allocated, &dataset);
+  term_count += 2;
+  dataset[term_count - 2] = ERL_DRV_TUPLE;
+  dataset[term_count - 1] = 2;
+
+  return driver_output_term(drv->port, dataset, term_count);
 }
 
 static int prepared_step(sqlite3_drv_t *drv, char *buffer, int buffer_size) {

c_src/sqlite3_drv.h

@@ -26,6 +26,7 @@
 #define CMD_PREPARED_RESET 8
 #define CMD_PREPARED_CLEAR_BINDINGS 9
 #define CMD_PREPARED_FINALIZE 10
+#define CMD_PREPARED_COLUMNS 11
 
 // Number of bytes for each key
 // (160 bits for SHA1 hash)
@@ -82,6 +83,7 @@ static int prepared_step(sqlite3_drv_t *drv, char *buf, int len);
 static int prepared_reset(sqlite3_drv_t *drv, char *buf, int len);
 static int prepared_clear_bindings(sqlite3_drv_t *drv, char *buf, int len);
 static int prepared_finalize(sqlite3_drv_t *drv, char *buf, int len);
+static int prepared_columns(sqlite3_drv_t *drv, char *buf, int len);
 static void sql_exec_async(void *async_command);
 static void sql_free_async(void *async_command);
 static void ready_async(ErlDrvData drv_data, ErlDrvThreadData thread_data);

src/sqlite3.erl

@@ -16,7 +16,8 @@
 -export([start_link/1, start_link/2]).
 -export([stop/0, close/1]).
 -export([sql_exec/1, sql_exec/2, sql_exec/3]).
--export([prepare/2, bind/3, next/2, reset/2, clear_bindings/2, finalize/2]).
+-export([prepare/2, bind/3, next/2, reset/2, clear_bindings/2, finalize/2,
+         columns/2]).
 -export([create_table/2, create_table/3, create_table/4]).
 -export([list_tables/0, list_tables/1, table_info/1, table_info/2]).
 -export([write/2, write/3, write_many/2, write_many/3]).
@@ -192,6 +193,10 @@ clear_bindings(Db, Ref) ->
 finalize(Db, Ref) ->
     gen_server:call(Db, {finalize, Ref}).
 
+-spec columns(atom(), reference()) -> sql_non_query_result().
+columns(Db, Ref) ->
+    gen_server:call(Db, {columns, Ref}).
+
 %%--------------------------------------------------------------------
 %% @spec create_table(Tbl :: atom(), TblInfo :: [{atom(), atom()}]) -> sql_non_query_result()
 %% @doc
@@ -785,6 +790,7 @@ get_priv_dir() ->
 -define(PREPARED_RESET, 8).
 -define(PREPARED_CLEAR_BINDINGS, 9).
 -define(PREPARED_FINALIZE, 10).
+-define(PREPARED_COLUMNS, 11).
 
 create_port_cmd(DbFile) ->
     atom_to_list(?DRIVER_NAME) ++ " " ++ DbFile.
@@ -824,7 +830,8 @@ exec(Port, {Cmd, Index}) when is_integer(Index) ->
                   next -> ?PREPARED_STEP;
                   reset -> ?PREPARED_RESET;
                   clear_bindings -> ?PREPARED_CLEAR_BINDINGS;
-                  finalize -> ?PREPARED_FINALIZE
+                  finalize -> ?PREPARED_FINALIZE;
+                  columns -> ?PREPARED_COLUMNS
               end,
     Bin = term_to_binary(Index),
     port_control(Port, CmdCode, Bin),

test/sqlite3_test.erl

@@ -202,6 +202,7 @@ large_number() ->
     ?assertNot([{N1 + 1, N2 - 1}] == rows(sqlite3:sql_exec(ct, Query2, [N1 + 1, N2 - 1]))).
 
 prepared_test() ->
+    Columns = ["id", "name", "age", "wage"],
     Abby = {1, <<"abby">>, 20, 2000},
     Marge = {2, <<"marge">>, 30, 2000},
     TableInfo = [{id, integer, [primary_key]}, {name, text, [not_null, unique]}, {age, integer}, {wage, integer}],
@@ -210,6 +211,7 @@ prepared_test() ->
     sqlite3:write(prepared, user, [{name, "abby"}, {age, 20}, {wage, 2000}]),
     sqlite3:write(prepared, user, [{name, "marge"}, {age, 30}, {wage, 2000}]),
     {ok, Ref} = sqlite3:prepare(prepared, "SELECT * FROM user"),
+    ?assertEqual(Columns, sqlite3:columns(prepared, Ref)),
     ?assertEqual(Abby, sqlite3:next(prepared, Ref)),
     ?assertEqual(ok, sqlite3:reset(prepared, Ref)),
     ?assertEqual(Abby, sqlite3:next(prepared, Ref)),