Processing conversation with priority order

March 28th, 2006

One of the most frequent questions about Service Broker is whether it supports any sort of priority for messages. But having priority within a conversation would conflict directly with the exactly-once-in-order guarantee of a conversation. In a good SOA design the two services involved in a conversation are supposed to be independent: separate developers, separate orgs, separate admins etc. If one service can set the priority of an individual message w/o the consent of the other, this action could wreck havoc on how the messages are processed, since the other service may expect the messages in order. A different story though is to have priority for individual conversations. Conversations are supposed to be independent and atomic; the processing order should not matter so having the possibility of setting a priority for a conversation makes sense. Roger has recently addressed the same problem and he already has a couple of posts on the topic: http://blogs.msdn.com/rogerwolterblog/archive/2006/03/11/549730.aspx and http://blogs.msdn.com/rogerwolterblog/archive/2006/03/17/554134.aspx

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Call a procedure in another database from an activated procedure

March 7th, 2006

In my previous post http://rusanu.com/2006/03/01/signing-an-activated-procedure/ I’ve showed how to use code signing to enable a server level privilege (view server state) when running an activated stored procedure. I’ll show now how to solve a very similar issue: call a stored procedure from another database. Why this is a problem is explained in this post: http://rusanu.com/2006/01/12/why-does-feature-not-work-under-activation/

So let’s say the ‘SessionsService’ from my previous post needs some new functionality: it has to audit the requests it’s receive. An audit infrastructure already exists in the [AuditInfrastructure] database, all is needed is to call the stored procedure [audit_record_request] in that database and the request will be audited. First create this ‘audit infrastructure’, which for our example will be very simple:

create database [AuditInfrastructure]
go

use [AuditInfrastructure]
go

-- An audit table, simply stores the time of the request
--
create table audit_table (request_time datetime);
go

-- this is the audit procedure
--
create procedure audit_record_request
as
begin
      set nocount on
      insert into audit_table (request_time) values (getdate());
end

So now all we have to do is to change the SessionService procedure to call this audit procedure:

USE [DemoActivationSigning];
GO

ALTER PROCEDURE [SessionsServiceProcedure]
AS 
BEGIN
      SET NOCOUNT ON;
      DECLARE @dh UNIQUEIDENTIFIER;
      DECLARE @mt SYSNAME;

      BEGIN TRANSACTION;
      WAITFOR (RECEIVE TOP (1) @dh = conversation_handle,
            @mt = message_type_name
            FROM [SessionsQueue]), TIMEOUT 1000;
      WHILE (@dh IS NOT NULL)
      BEGIN
            If the message is a request message,
            send back a response with the list of sessions
            IF (@mt = N‘RequestSessions’)
            BEGIN
                  Get the list of current sessions
                  and send it back as a response
                  –
                  DECLARE @response XML;
                  SELECT @response = (
                        SELECT * FROM sys.dm_exec_sessions
                              FOR XML PATH (session), TYPE);
                  SEND ON CONVERSATION @dh
                        MESSAGE TYPE [Sessions]
                        (@response);
                  --  This is the extra call to the audit procedure                        
                  EXECUTE [AuditInfrastructure]..[audit_record_request]; 
            END
            End the conversation and commit
            END CONVERSATION @dh;
            COMMIT;

            Try to loop once more if there are message
            SELECT @dh = NULL;
            BEGIN TRANSACTION;
            WAITFOR (RECEIVE TOP (1) @dh = conversation_handle,
                  @mt = message_type_name
                  FROM [SessionsQueue]), TIMEOUT 1000;
      END
      COMMIT;
END
GO

So now we send a request to the ‘SessionsService’

 

DECLARE @dh UNIQUEIDENTIFIER;

BEGIN DIALOG CONVERSATION @dh

      FROM SERVICE [Requests]

      TO SERVICE ‘SessionsService’

      ON CONTRACT [SessionsContract]

      WITH ENCRYPTION = OFF;

SEND ON CONVERSATION @dh

      MESSAGE TYPE [RequestSessions];

 

 

We expect a response back, but nothing happens. The ‘SessionsService’ has gone silent. If we look into the Event Viewer, will find some troublesome entries:

 

Event Type: Information
Event Source: MSSQLSERVER
Event Category: (2)
Event ID: 9724
Date:  3/7/2006
Time:  10:36:25 AM
User:  REDMOND\remusr
Computer: REMUSR10
Description:
The activated proc [dbo].[SessionsServiceProcedure] running on queue DemoActivationSigning.dbo.SessionsQueue output the following:  ‘The server principal “REDMOND\remusr” is not able to access the database “AuditInfrastructure” under the current security context.’

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.
Data:
0000: fc 25 00 00 0a 00 00 00   ü%……
0008: 09 00 00 00 52 00 45 00   ….R.E.
0010: 4d 00 55 00 53 00 52 00   M.U.S.R.
0018: 31 00 30 00 00 00 14 00   1.0…..
0020: 00 00 41 00 75 00 64 00   ..A.u.d.
0028: 69 00 74 00 49 00 6e 00   i.t.I.n.
0030: 66 00 72 00 61 00 73 00   f.r.a.s.
0038: 74 00 72 00 75 00 63 00   t.r.u.c.
0040: 74 00 75 00 72 00 65 00   t.u.r.e.
0048: 00 00
                     ..

 

 

Note: In case you wonder ‘so what happened to my request?.The activated stored procedure has thrown an error and it rolled back. Because Service Broker is a fully transactional, the dequeued request was rolled back and is again available for dequeue. The activation will kick in again, causing the same error and again the request to be rolled back. Then again activation will kick in and so on and so forth. Eventually (after 5 consecutive rollbacks) the Service Broker Poisson Message support will detect this situation and will disable the queue.

 

The problem is, as expected, the database impersonation context, as explained here. Same as in the case of server level privileges, the easiest fix is to mark the database trustworthy:

 

ALTER DATABASE [DemoActivationSigning] SET TRUSTWORTHY ON

 

If we cannot afford this due to security risks (marking the database trustworthy elevates the database dbo to a de-facto sysadmin), we must reside to code signing. The steps are these:

-         alter the procedure to have an EXECUTE AS clause (otherwise the code signing infrastructure does not work)

-         create a certificate with a private key in the [DemoActivationSigning] database

-         sign the procedure

-         drop the private key of the certificate

-         copy the certificate into the [AuditInfrastructure] database (backup the certificate to a file and the create from that file)

-         derive a user from the certificate in the [AuditInfrastructure]database

-         grant the desired privileges to this user

 

Here is the code for these steps:

 

USE [DemoActivationSigning];

GO

 

– Create aprocedure that implements

– the [SessionsService] service

ALTER PROCEDURE [SessionsServiceProcedure]

      WITH EXECUTE AS OWNER

AS

BEGIN

      SET NOCOUNT ON;

      DECLARE @dh UNIQUEIDENTIFIER;

      DECLARE @mt SYSNAME;

 

      BEGIN TRANSACTION;

      WAITFOR (RECEIVE TOP (1) @dh = conversation_handle,

            @mt = message_type_name

            FROM [SessionsQueue]), TIMEOUT 1000;

      WHILE (@dh IS NOT NULL)

      BEGIN

            – If the message is a request message,

            – send back a response with the list of sessions

           

            IF (@mt = N‘RequestSessions’)

            BEGIN

                  – Get the list of current sessions

                  – and send it back as a response

                 

                  DECLARE @response XML;

                  SELECT @response = (

                        SELECT * FROM sys.dm_exec_sessions

                              FOR XML PATH (‘session’), TYPE);

                  SEND ON CONVERSATION @dh

                        MESSAGE TYPE [Sessions]

                        (@response);

                  EXECUTE [AuditInfrastructure]..[audit_record_request];

            END

            – End the conversation and commit

            END CONVERSATION @dh;

            COMMIT;

     

            – Try to loop once more if there are message

           

            SELECT @dh = NULL;

            BEGIN TRANSACTION;

            WAITFOR (RECEIVE TOP (1) @dh = conversation_handle,

                  @mt = message_type_name

                  FROM [SessionsQueue]), TIMEOUT 1000;

      END

      COMMIT;

END

GO

 

– Create a certificate with a private key

– to sign the procedure with. The password

– used is not important, we’ll drop the

– private key

CREATE CERTIFICATE [SessionsServiceProcedureAudit]

      ENCRYPTION BY PASSWORD = ‘Password#1234′

      WITH SUBJECT = ‘SessionsServiceProcedure Signing  for audit certificate’;

GO

 

– Sign the procedure with the certificate’s private key

ADD SIGNATURE TO OBJECT::[SessionsServiceProcedure]

      BY CERTIFICATE [SessionsServiceProcedureAudit]

            WITH PASSWORD = ‘Password#1234′;

GO

 

– Drop the private key. This way it cannot be

– used again to sign other procedures.

ALTER CERTIFICATE [SessionsServiceProcedureAudit]

      REMOVE PRIVATE KEY;

GO

 

– Copy the certificate in [master]

– We must backup to a file and create

– the certificate in [master] from this file

BACKUP CERTIFICATE [SessionsServiceProcedureAudit]

      TO FILE = ‘C:\SessionsServiceProcedureAudit.CER’;

GO

 

USE [AuditInfrastructure]

GO

 

CREATE CERTIFICATE [SessionsServiceProcedureAudit]

      FROM FILE = ‘C:\SessionsServiceProcedureAudit.CER’;

GO

 

CREATE USER [SessionsServiceProcedureAudit] FROM CERTIFICATE [SessionsServiceProcedureAudit];

G0

 

– ‘AUTHENTICATE’ permission is required for all other permissions to take effect

GRANT AUTHENTICATE TO [SessionsServiceProcedureAudit];

GRANT EXECUTE ON [audit_record_request] TO [SessionsServiceProcedureAudit];

GO

 

– Enable back the disabled ‘SessionsService’ queue

ALTER QUEUE [SessionsQueue] WITH STATUS = ON;

GO

 

– Check that the response is now sent back

WAITFOR (RECEIVE CAST(message_body AS XML) FROM [RequestsQueue]);

 

Notice that I did not sent another request. The existing request was still there, waiting for the procedure to be fixed so it can be processed correctly.

Signing an activated procedure

March 1st, 2006

In my previous entry http://rusanu.com/2006/01/12/why-does-feature-not-work-under-activation/ I mentioned that one way to enable an activated procedure to be trusted at the server level is to sign the stored procedure with a certificate and grant appropriate permissions to the signing certificate. In this entry I want to show the details how to do this.

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