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Debugging Content Services

As a developer you will need to be able to debug Content Services’ product code, and custom code contained in JARs/AMPs written by you. To do this we usually use so-called Remote debugging. This means that we start up Content Services in debug mode ready to accept remote debugging sessions. We then connect with a debugger such as IntelliJ IDEA or Eclipse using a Remote debugging session.

IntelliJ provides a tutorial on how to do remote debugging with the IDEA IDE using a Hello World example. It is worth having a look at this tutorial before continuing with this article to get an understanding of how to attach a debugger to a remote process. If you are using Eclipse, then there is this article that might be a good read before moving on.

If you are using any of the Alfresco SDKs, then you should be looking at the following sections for information about how to do remote debugging in these environments:

Introduction

Content Services is slightly more complex than the Hello World example above. Let’s see how to debug a ReST API call, such as the login to get a ticket.

Remote debugging can be done either by running Content Services in Docker containers or by running in a local Tomcat environment.

Prerequisites

Download the following projects to your developer machine:

Only the first project is needed here, as it contains the product source code, but it’s recommended to have the other projects available as well. The packaging projects gives valuable information about how the Docker image for the Alfresco Repository is created. The packaging projects also contain information about how to create custom Docker images, which is very useful when custom JARs/AMPs should be applied.

Debug in a Docker environment

To start remote debugging with Content Services running in Docker, then download the following project:

Then change into the /docker-compose directory and create a copy of the file community-docker-compose.yml called debug-community-docker-compose.yml:

% git clone git@github.com:Alfresco/acs-deployment.git
Cloning into 'acs-deployment'...
...
% cd acs-deployment/docker-compose 
docker-compose % cp community-docker-compose.yml debug-community-docker-compose.yml

% ls -l
total 88
-rw-r--r--  1 admin  staff  7979 16 Jun 09:37 6.1.N-docker-compose.yml
-rw-r--r--  1 admin  staff  6846 16 Jun 09:37 6.2.N-docker-compose.yml
-rw-r--r--  1 admin  staff   189 16 Jun 09:37 README.md
-rw-r--r--  1 admin  staff  4931 16 Jun 09:37 community-docker-compose.yml
-rw-r--r--  1 admin  staff  4931 16 Jun 09:38 debug-community-docker-compose.yml
-rw-r--r--  1 admin  staff  7097 16 Jun 09:37 docker-compose.yml

Configure Docker Compose for remote debugging

Edit the debug-community-docker-compose.yml file by adding the following ports and environment settings:

services:
    alfresco:
        image: alfresco/alfresco-content-repository-community:7.1.0-M1
        mem_limit: 1500m
        ports:
            - 8000:8000
        environment:
            CATALINA_OPTS: "
                -agentlib:jdwp=transport=dt_socket,address=*:8000,server=y,suspend=n
                "
            JAVA_TOOL_OPTIONS: "
            ...

The -agentlib:jdwp=transport=dt_socket,address=*:8000,server=y,suspend=n option tells the JVM to start with the port 8000 open, ready to accept remote debugging sessions.

Note that the remote debugging configuration is done via the CATALINA_OPTS variable instead of JAVA_TOOL_OPTIONS or JAVA_OPTS as we need to instruct Tomcat running inside the Docker container, not the JVM directly (this is a big difference from the IntelliJ tutorial).

We need to also open the remote debug port from the container to the host, so that http://localhost:8000 will be propagated to the container and Tomcat. This is done with the ports configuration.

Run Content Services

Now, run Content Services and wait for it to start:

docker-compose -f debug-community-docker-compose.yml up

It’s ready when you see logs as follows:

alfresco_1 | 2021-06-16 09:12:50,699  INFO  [management.subsystems.ChildApplicationContextFactory] [http-nio-8080-exec-9] Starting 'Transformers' subsystem, ID: [Transformers, default]
alfresco_1 | 2021-06-16 09:12:50,884  INFO  [management.subsystems.ChildApplicationContextFactory] [http-nio-8080-exec-9] Startup of 'Transformers' subsystem, ID: [Transformers, default] complete

Debug some source code

To test out the new debug settings, let’s debug the source code that is called when you call the remote API to get a ticket that can be used for authentication.

Open the alfresco-community-repo project in IntelliJ IDEA and look up the src/main/java/org/alfresco/rest/api/impl/AuthenticationsImpl.java file. Set a breakpoint in this file where a ticket is created, as shown:

create-ticket-breakpoint

Set up a Remote debugging session in IDEA (Run -> Debug… -> Edit Configurations… -> + -> Remote JVM Debug):

idea-remote-debug-setup

Click Debug to start the debug session:

remote-debug-session-started

Now, call the Remote API that is used to log in and get a ticket (using the default admin/admin credentials):

% curl --header "Content-Type: application/json" --request POST --data '{"userId":"admin","password":"admin"}' http://localhost:8080/alfresco/api/-default-/public/authentication/versions/1/tickets

This should make the debugger stop on the breakpoint line in IDEA:

idea-remote-debug-breakpoint-stop

We can see the credentials used to log in, and start debugging the code as we are used to.

This way of debugging works equally well for any custom code that you have applied to Content Services.

Debug in a Tomcat environment (no containers)

To start remote debugging with Content Services running directly in Tomcat (i.e. not using containers but running Content Services based on a ZIP installation), then make sure you start Tomcat in debug mode (similar to how we configured the CATALINA_OPTS variable in the container environment).

See this StackOverflow article for more information about how to start Apache Tomcat in debug mode. This article also links to the official Tomcat development page, which is a good read.

Debug some source code

Debugging in a Tomcat environment is the same as in a Docker container environment, see this section above.

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