How to use two different versions of same dll in ASP.Net?

-

 When using 3rd party libraries, sometimes they let out a new version. And sometimes that new version breaks something that used to work in the old version, but also adds features you need. So you found yourself having to use one method from the old version and another from the new version of the same library.

There are two problems here:

  1. It won’t compile. Both libraries have the same namespace, causing ambiguity the compiler can’t handle.

compile-ex

  1. It won’t run. The referenced DLLs are copied to the output dir, but because they have the same name, they will override each other, and will cause the runtime loading of the assembly to have a version mismatch.

runtime-ex

Welcome to DLL hell.


The solution

Let’s take my client’s project as a practical example. The project was using a 3rd party library by Winnovative Software, for handling pdf operations. The new version of the dll broke some specific functionality that had to be supported. The DLL name: wnvhtmltopdf.dll The old version: 14.2 The new version: 14.5

The solution has two parts:

  1. Solve compilation ambiguity with extern alias
  2. Solve runtime loading ambiguity with

Place old DLL in folder

Create a folder for the old DLL, let’s say wnv-old, and put it there. Add a reference to the old DLL.

Solve compilation ambiguity with extern alias

Change the reference aliases:

Every reference we add to the project will have the “global” alias by default. For this duplicate reference we’ll change the alias so we can differentiate the namespaces. In the reference properties in Visual Studio, change the alias field to newVer and oldVer or whatever you want:

runtime-ex

Change the using statements:

Wherever we use the namespace we’ll change the using statements to:

extern alias newVer; // Must be at top of file
using newVer::Winnovative; // Instead of using Winnovative;

And in classes in which you want to use the old version:

extern alias oldVer; 
using oldVer::Winnovative;

This will make the code compile. Now for solving the runtime crash:

Get DLL publicKeyToken

In cmd, use the sn -T command:

sn -T wnvhtmltopdf.dll

Microsoft (R) .NET Framework Strong Name Utility  Version 4.0.30319.0
Copyright (c) Microsoft Corporation.  All rights reserved.

Public key token is b12703d35a33ff98

Modify app.config / web.config

Under <runtime>, add a <codeBase> tag for each version of the DLL. This will resolve the runtime assembly loading conflict.

<dependentAssembly>
  <assemblyIdentity name="wnvhtmltopdf" publicKeyToken="b12703d35a33ff98" culture="neutral" />
  <codeBase version="14.2.0.0" href="DLL\wnv-old\wnvhtmltopdf-old.dll" />
  <codeBase version="14.5.0.0" href="DLL\wnvhtmltopdf.dll" />
</dependentAssembly>

That’s it, now we can use both versions as we please


Comments

Post a Comment

Popular posts from this blog

Email Sending through O365 using OAuth Protocol

-
  Microsoft Office365 EWS servers have been extended to support authorization via the industry-standard OAuth 2.0 protocol. Using OAUTH protocol, user can do authentication by Microsoft Web OAuth instead of inputting user and password directly in application Microsoft / Office 365 OAuth + EWS We can use the OAuth authentication service provided by Azure Active Directory to enable our application to connect with IMAP, POP or SMTP protocols to access Exchange Online in Office 365. To use OAuth with our application we need to register application on Azure Active directory and other steps also we need to do to get the access token back. Below are the steps   To use Microsoft/Office365 OAUTH in your application, you must create an application in  https://portal.azure.com . Sign into the Azure portal using either a work or school account or a personal Microsoft account. If your account gives you access to more than one tenant, select your account in the top ...
Read more

IoT Technology

-
Image
IoT technology The Internet of Things (IoT) is a system of interrelated computing devices, mechanical and digital machines.  IoT is a network of sensors where data is exchanged, using different connectivity protocols, with systems. This set up can be leveraged to create a new business application or to enhance an existing process. The exchange of the data can be bi-directional between sensors and systems Examples of sensors can be temperature sensors, motion sensors, flow meters, heart meter monitors, biometric devices, smoke detectors, & etc Examples of connectivity can be wifi, radio, GPRS, GSM, LAN, WAN, & etc. Examples of systems can be a remote health monitoring applications, SCADA applications, etc Look at next slide about the complete flow of IoT process Examples A doctor in US would like to monitor the heart rate and ECG of a patient in Hyderabad. This is done with the patient having sensors attached to him that collect the ECG data and the hea...
Read more

What is reverse proxy?

-
Image
  What is a reverse proxy? A reverse proxy is a server that sits in front of web servers and forwards client (e.g. web browser) requests to those web servers. Reverse proxies are typically implemented to help increase  security ,  performance , and reliability . In order to better understand how a reverse proxy works and the benefits it can provide, let’s first define what a proxy server is. What’s a proxy server? A forward proxy, often called a proxy, proxy server, or web proxy, is a server that sits in front of a group of client machines. When those computers make requests to sites and services on the Internet, the proxy server intercepts those requests and then communicates with web servers on behalf of those clients, like a middleman. For example, let’s name 3 computers involved in a typical forward proxy communication: A: This is a user’s home computer B: This is a forward proxy server C: This is a website’s origin server (where the website data is stored) In a stand...
Read more