Properly acknowledge results when not consuming results

Author: andyundso

CHANGELOG.md

@@ -4,6 +4,7 @@
 * Drop support for SQL Server < 2017
 * Drop support for FreeTDS < 1.0
 * Raise error if FreeTDS is unable to sent command buffer to the server
+* Cancel previous query results automatically when invoking a new query
 
 ## 2.1.7
 * Add Ruby 3.3 to the cross compile list

README.md

@@ -150,7 +150,7 @@ result = client.execute("SELECT * FROM [datatypes]")
 
 ## TinyTds::Result Usage
 
-A result object is returned by the client's execute command. It is important that you either return the data from the query, most likely with the #each method, or that you cancel the results before asking the client to execute another SQL batch. Failing to do so will yield an error.
+A result object is returned by the client's execute command. It is important that you either return the data from the query, most likely with the #each method. You can manually cancel the results early using `#cancel`, otherwise tiny_tds will also automatically do so when running a new query with `#execute`.
 
 Calling #each on the result will lazily load each row from the database.
 
@@ -171,7 +171,6 @@ result.do
 
 result = client.execute("SELECT [id] FROM [datatypes]")
 result.fields # => ["id"]
-result.cancel
 result = client.execute("SELECT [id] FROM [datatypes]")
 result.each(:symbolize_keys => true)
 result.fields # => [:id]

ext/tiny_tds/client.c

@@ -15,12 +15,6 @@ VALUE opt_escape_regex, opt_escape_dblquote;
   tinytds_client_wrapper *cwrap; \
   Data_Get_Struct(self, tinytds_client_wrapper, cwrap)
 
-#define REQUIRE_OPEN_CLIENT(cwrap) \
-  if (cwrap->closed || cwrap->userdata->closed) { \
-    rb_raise(cTinyTdsError, "closed connection"); \
-    return Qnil; \
-  }
-
 
 // Lib Backend (Helpers)
 
@@ -295,8 +289,32 @@ static VALUE rb_tinytds_execute(VALUE self, VALUE sql) {
   VALUE result;
 
   GET_CLIENT_WRAPPER(self);
+  
+  if (cwrap->closed || cwrap->userdata->closed) {
+    rb_raise(cTinyTdsError, "closed connection");
+    return Qnil;
+  }
+
+  if (rb_tinytds_dead(self) == Qtrue) {
+    rb_raise(cTinyTdsError, "client is dead, please create a new instance");
+    return Qnil;
+  }
+
+  // user is coming back from an each loop, make sure we cancel the pending results
+  if (cwrap->userdata->dbsql_sent) {
+    // if we do not run dbsqlok, FreeTDS will throw an error
+    // Attempt to initiate a new Adaptive Server operation with results pending
+    // note that both of these operations are blocking as we do not have access to these
+    // "NOGVL" methods from result.c
+    if (cwrap->userdata->dbsqlok_sent == 0) {
+      dbsqlok(cwrap->client);
+    }
+
+    dbcancel(cwrap->client);
+  }
+
   rb_tinytds_client_reset_userdata(cwrap->userdata);
-  REQUIRE_OPEN_CLIENT(cwrap);
+
   dbcmd(cwrap->client, StringValueCStr(sql));
   if (dbsqlsend(cwrap->client) == FAIL) {
     rb_raise(cTinyTdsError, "failed dbsqlsend() function");

test/client_test.rb

@@ -269,4 +269,45 @@ class ClientTest < TinyTds::TestCase
       ).must_equal 'user'
     end
   end
+
+  describe "#execute" do
+    it "cancels pending select query" do
+      client = new_connection
+      client.execute("SELECT 1 as [one]")
+
+      assert client.sqlsent?
+      assert !client.canceled?
+
+      result = client.execute("SELECT 1 as [one]")
+      assert_equal [{"one"=>1}], result.to_a
+      assert_client_works(client)
+    end
+
+    it "cancels pending wait query" do
+      client = new_connection
+      client.execute("WaitFor Delay '00:00:05'")
+
+      assert client.sqlsent?
+      assert !client.canceled?
+
+      result = client.execute("SELECT 1 as [one]")
+      assert_equal [{"one"=>1}], result.to_a
+      assert_client_works(client)
+    end
+
+    # this requires to not send another `dbsqlok` compared to the previous to test cases
+    it "cancel partially retrieved results" do
+      client = new_connection
+      result = client.execute("SELECT 1 as [one]; SELECT 2 as [two]; SELECT 3 as [three]")
+      result.each { |r| break if r.key?("two") }
+
+      assert_equal 1, result.count
+      assert client.sqlsent?
+      assert !client.canceled?
+
+      result = client.execute("SELECT 1 as [one]")
+      assert_equal [{"one"=>1}], result.to_a
+      assert_client_works(client)
+    end
+  end
 end