Allow multiple web applications under IIS to use the same SQL server session state database without modifying the database stored procedures.
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/* | |
* This code is a workaround for the fact that session state in ASP.NET SqlServer mode is isolated by application. The AppDomain's appId is used to | |
* segregate applications, and there is no official way exposed to modify this behaviour. | |
* | |
* Some workarounds tackle the problem by modifying the ASP.NET state database. This workaround approaches the problem from the application code | |
* and will be appropriate for those who do not want to alter the database. We are using it during a migration process from old to new technology stacks, | |
* where we want the transition between the two sites to be seamless. | |
* | |
* As always, when relying on implementation details, the reflection based approach used here may break in future / past versions of the .NET framework. | |
* Test thoroughly. | |
* | |
* Usage: add this to your Global.asax: | |
* protected void Application_BeginRequest() | |
* { | |
* SessionStateCrossApplicationHacker.SetSessionStateApplicationName("an application"); | |
* } | |
*/ | |
using System; | |
using System.Data.SqlClient; | |
using System.Globalization; | |
using System.Reflection; | |
using System.Web.SessionState; | |
public static class SessionStateCrossApplicationHacker | |
{ | |
static string _appName; | |
static readonly object _appNameLock = new object(); | |
public static void SetSessionStateApplicationName(string appName) | |
{ | |
if (_appName != appName) | |
{ | |
lock (_appNameLock) | |
{ | |
if (_appName != appName) | |
{ | |
SetSessionStateApplicationNameOnceOnly(appName); | |
_appName = appName; | |
} | |
} | |
} | |
} | |
static void SetSessionStateApplicationNameOnceOnly(string appName) | |
{ | |
//get the static instance of SqlSessionStateStore.SqlPartitionInfo from System.Web.SessionState.SqlSessionStateStore.s_singlePartitionInfo | |
var sqlSessionStateStoreType = typeof (SessionStateMode).Assembly.GetType("System.Web.SessionState.SqlSessionStateStore"); | |
var sqlSessionStatePartitionInfoInstance = GetStaticFieldValue(sqlSessionStateStoreType, "s_singlePartitionInfo"); | |
if (sqlSessionStatePartitionInfoInstance == null) | |
throw new InvalidOperationException("You'll need to call this method later in the pipeline - the session state mechanism (SessionStateModule, which is an IHttpModule) has not been initialised yet. Try calling this method in Global.asax's Application_BeginRequest. Also make sure that you do not specify a partitionResolverType in your web.config."); | |
//ensure that the session has not been used prior to this with an incorrect app ID | |
var isStaticSqlPartitionInfoInitialised = GetFieldValue<bool>(sqlSessionStatePartitionInfoInstance, "_sqlInfoInited"); | |
if (isStaticSqlPartitionInfoInitialised) | |
throw new InvalidOperationException("You'll need to call this method earlier in the pipeline - before any sessions have been loaded."); | |
//force initialisation of the static SqlSessionStateStore.SqlPartitionInfo instance - otherwise this will happen later and overwrite our change | |
var connectionString = GetFieldValue<string>(sqlSessionStatePartitionInfoInstance, "_sqlConnectionString"); | |
using (var connection = new SqlConnection(connectionString)) | |
{ | |
connection.Open(); | |
CallInstanceMethod(sqlSessionStatePartitionInfoInstance, "InitSqlInfo", connection); | |
} | |
//calculate and set the application hash code | |
string applicationNameHashCode = GetHashCode(appName).ToString("x8", CultureInfo.InvariantCulture); | |
GetField(sqlSessionStatePartitionInfoInstance, "_appSuffix").SetValue(sqlSessionStatePartitionInfoInstance, applicationNameHashCode); | |
} | |
static int GetHashCode(string appName) | |
{ | |
string s = appName.ToLower(); | |
int hash = 5381; | |
int len = s.Length; | |
for (int i = 0; i < len; i++) | |
{ | |
int c = Convert.ToInt32(s[i]); | |
hash = ((hash << 5) + hash) ^ c; | |
} | |
return hash; | |
} | |
static void CallInstanceMethod(object instance, string methodName, params object[] parameters) | |
{ | |
var methodInfo = instance.GetType().GetMethod(methodName, BindingFlags.NonPublic | BindingFlags.Instance); | |
methodInfo.Invoke(instance, parameters); | |
} | |
static object GetStaticFieldValue(Type typeWithStaticField, string staticFieldName) | |
{ | |
return typeWithStaticField.GetField(staticFieldName, BindingFlags.NonPublic | BindingFlags.Static).GetValue(null); | |
} | |
static FieldInfo GetField(object instance, string name) | |
{ | |
return instance.GetType().GetField(name, BindingFlags.NonPublic | BindingFlags.Instance); | |
} | |
static T GetFieldValue<T>(object instance, string name) | |
{ | |
return (T)GetField(instance, name).GetValue(instance); | |
} | |
} |
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