Category Archives: Programming

Debugging Laravel in Eclipse PDT

I don't use PHP enough to justify buying a PHPStorm license so I am using Eclipse PDT instead. I am a bit rusty with Eclipse and PHP so I couldn't really find anything on Google about debugging Laravel projects in Eclipse. Finally figured it out, here is how.

Examples are done on Eclipse IDE Version: 2019-12 (4.14.0).

First, configure XDebug with Eclipse. On Fedora you can install it via

Check that XDebug remote is enabled with phpinfo() test site, if not add the following line to your php.ini:

Now in Eclipse, we first add a server. In Window->Preferences->PHP->Servers add a new server like this:

Document root is our Laravel public folder and base URL is the default host and port of

Now check your Debug settings in PHP->Debug, select the newly created server and check that XDebug is set as the debugger:

If XDebug is not present here, configure it under PHP->Debug->Debuggers first.

Finally, under General->Web Browser, we select an external web browser to launch our website instead of integrated Eclipse Browser.

We are done with Preferences so close it. Next to the Debug button in main Eclipse toolbar, click on the arrow for the dropdown and select Debug configurations…

Create a new PHP Web Application config like this.

We point the file to public index and map it to root URL (default by artisan serve). Under Debugger tab check that XDebug is selected.

Now go to the terminal and serve your laravel app as you would with

Finally, run the "web" Debug configuration from Eclipse. Eclipse should go into the Debug mode and open up your site in your selected browser. You can now place your breakpoints in controllers or wherever and things just work like you would expect.

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Apache http to https redirect – use 307

Who knew that a simple thing like HTTP redirects would be so complicated? It turns out clients will just change POST to GET on 301 (Postman, curl, everyone?), same with 302 which really behaves like 303 and that is also an old implementation "bug". Yeah, seriously.

If you have a REST API with POST (or other non-GET) request endpoints (who doesn't?) this behaviour will completely destroy everything.  Many guides (top google results) out there for configuring Apache redirect do not mention this problem. The code of choice would be 308 Permanent Redirect but that is fairly new so I would not risk it, older clients don't know it exists. The only thing left is 307 which does not allow changing methods on redirect – exactly how it should be.

Solution:

 

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Setting env variables with hyphen and running a program

Docker compose allows you very unrestrictive naming of your environment variables. It allows you to use hyphen and other "special" characters in variables names. When you need to use these variables in regular shell you are out of luck, bash and many other shells do not allow hyphens in variable names. But this is merely a shell restriction, so how to do it?

With env

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Obscure IntelliJ IDEA "bug" with maven jdk profile activation "not working"

Since Java 9 it is popular to activate additional dependencies which were removed from the core JDK through maven profile.

Using Java 11 , jaxb-api would correctly show in maven dependency tree and Docker packaged application would work correctly with the dependency jar in the classpath.

However, when running the app from IntelliJ it would fall apart with

Opening module dependencies in IDE would show that jaxb-api is not on the list of dependencies. IntelliJ is therefore not activating the maven profile correctly even though:

  • maven compiler release is set to 11
  • project and Module SDK is set to Java 11
  • app is run with Java 11

Why is that? There is this snippet in IntelliJ Maven Profiles documentation:

If you use a profile activation with the JDK condition (JDK tags in the POM: <jdk></jdk>), IntelliJ IDEA will use the JDK version of the Maven importer instead of the project's JDK version when syncing the project and resolving dependencies. Also, if you use https certificates, you need to include them manually for the Maven importer as well as for the Maven runner.

Why IntelliJ developers decided to tie the maven profile activation to importer I do not know. It would make much more sense to tie it to Project/Module SDK. If app is being developed with Java 11 target one would expect to activate that profile at build and runtime, not at import time.

With more digging around I managed to find an issue complaining about this problem. Unfortunately the issue is 4 years old now with no apparent activity. Preferrably the default should be changed, if not at least give us an option to choose the source of profile activation in preferences.

 

 

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Receive only the data your client needs – full dynamic JSON filtering with Jackson

A lot of times JSON returned by your REST API grows to incredibly big structures and data sizes due to business logic complexity that is added over time. Then there are API methods returning a list of objects which can be huge in size. If you serve multiple clients, each one can have different demands on what is and is not needed from that data so backend can't decide on it's own what to prune and what to keep. Ideally, backend would always return full JSON by default but allow clients to specify exactly what they want and have backend adjust the response accordingly.  We can achieve this using the power of Jackson library.

Goal:
– allow REST API clients to decide on their own which parts of JSON to receive (full JSON filtering)

Resources for this tutorial:
– Microprofile or JakartaEE platform (JAX-RS)
– Jackson library
– Java classes (lib) representing your API responses which are serialized to JSON
– some custom code to bring things together

The lib module

First lets define a few classes which represent our JSON responses.

Our lib serialized to JSON would look something like this:

Let's say one of our clients only needs the engine horse power and brand information. We want to be able to specify a query parameter like filter=car:engine,brand;engine:hp and receive the following:

Step in Jackson

Jackson provides an annotation for such tasks called @JsonFilter. This annotation expects a filter name as a parameter and a named filter must be applied to serialization mapper, for example:

As you can see, all we need is already there but is a rather static affair. We need to take this and make it fully dynamic and client driven.

The reason filter needs a name is because each one is bound to a class and attribute filtering is done on that class. What we need to do is transform car:engine,brand into a carFilter and SimpleBeanPropertyFilter.filterOutAllExcept("engine", "brand").

For starters, lets add the filters to our classes:

There is one thing about this that bothers me.. the filter name is a static String so it is refactor unfriendly if class name changes some day. Couldn't we just name the filters by taking a look at the name of the underlying class? Yes we can, by extending Jackson introspection:

With this, any class annotated with @JsonFilter("") will automatically get a filter called classNameFilter. We no longer need to specify filter names and keep them in sync with class names.

Our lib now looks like:

Next step is to transform and apply the query parameters into our filter structure.

First, register a Jackson provider for JAX-RS server:

We register our own introspector and disable failures on unknown filters (in case client filters by something nonexisting).

Provider must be registered in your rest Application.

Finally, we implement our own MessageBodyWriter to override the default serialization and apply the filters dynamically.

getFilterLogic method assembles the query parameter structure into a map of <String className, Set<String> fields> which is then applied as a Jackson filter.

Finally, we need to register our JsonFilterProvider in our Application as we did with JacksonProvider.

One small deficiency with this solution is that once you specify a class with fields to filter, it will be filtered wherever in the nested JSON structure it appears, you can't just filter a specific class at a specific level. Realistically, I think this is a rather minor problem compared to the benefits and the simplicity of the implementation.

Finally a question on documentation. How do you tell the client developer about all the possible filter object names and their attributes? If you use OpenAPI you are 95% there. Simply document that you can filter by model name followed by attribute name. Client developer can easily figure out the names from your OpenAPI specification. The only remaining problem is when you don't want to allow filtering on all classes. In this case my approach would be to document a filterable class in OpenAPI description:

This manual approach of documenting goes against the rest of the paradigm so a real purist would write an OpenAPI extension that would introspect all @JsonFilter annotations and modify the descriptions automatically. But let's leave that for a future blog post.

 

A similar, more advanced and out-of-the-box solution is squiggly, which also uses Jackson under the hood.

 

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HTPP Accept-Language request header to ResourceBundle

HTTP Accept-Language header is specified by the client to inform the backend what the preferred language for the response is. In Java, the go-to utility for handling localization is ResourceBundle.

What is missing is a standard way to properly convert the input header to the correct ResourceBundle. Specifically,

is insufficient. HttpServletRequest::getLocale() method returns the top preferred locale but if no such ResourceBundle exists, it will fall back to default locale instead of going down the priority list. For example, this header:

Accept-Language: de-DE;q=1.0,fr-FR;q=0.9,en-GB;q=0.8

when backend is missing de-DE translations will return the system default (e.g. en-GB) instead of fr-FR which is the second by priority.

Clients don't usually request languages unknown to backend but it is possible in theory and languages can be automatically added by the client platform (iOS does this) without the client knowing.

We need to iterate the locale chain and find the highest match that exists as a bundle.

Below is a sample in JAX-RS environment.

 

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That moment when you need to look up definition of C++ for loop

I was getting a segfault on an old piece of code which I maintain. The culprit was pinpointed to this:


I went through this piece if code at least 10 times without noticing the problem. The snippet is simple enough.. when match is found, set found to true and that breaks the loop since loop condition now evaluates to false. The iterator remains at the position of matched element.

WRONG.

What we are actually getting is iterator+1.

What we don't see directly from the code is that increment happens before the condition is evaluated for the next loop, giving us iterator+1 which causes a segfault if match is found on last element.

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Keycloak OAuth endpoints for Postman/HTTP Clients

When testing REST services secured by Keycloak you need to retrieve access tokens via Postman or similar REST client. If you want to implement your own client that has to authenticate with a token you also need to know the Keycloak OpenID endpoints in order to retrieve the access token, refresh it or to end the session (logout).

Retreiving the tokens for a public client using username and password

Public client is typically used for web applications and other client side apps.

Method: POST
URL: https://keycloak.example.com/auth/realms/myrealm/protocol/openid-connect/token
Body type: x-www-form-urlencoded
Form fields:
client_id <my-client-name>
grant_type password
username <username>
password <password>

Retreiving the tokens for a confidential client using client secret

Confidential client is typically used for secure apps on the back-end.

Method: POST
URL: https://keycloak.example.com/auth/realms/myrealm/protocol/openid-connect/token
Body type: x-www-form-urlencoded
Form fields:
client_id <my-confidential-client-name>
grant_type client_credentials
client_secret <my-client-secret>

Retreive an access token with a refresh token

The first two methods will yield you an access token which you use in the Authorization HTTP header and a refresh token which you save for later. Refresh tokens have much longer expire time as access tokens. The idea is that when the access token expires you use the refresh token to get a new access token. This request also gives you a new refresh token so you can keep the session alive until maximum refresh token expire time is reached. Refresh token expire time equals the session expire time.

Method: POST
URL: https://keycloak.example.com/auth/realms/myrealm/protocol/openid-connect/token
Body type: x-www-form-urlencoded
Form fields:
client_id <my-client-name>
grant_type refresh_token
refresh_token <my-refresh-token>

Logout the session

To logout and invalidate the session, call a /logout endpoint with your refresh token. The validity of the refresh token is essentially the validity of your entire session.

Method: POST
URL: https://keycloak.example.com/auth/realms/myrealm/protocol/openid-connect/logout
Body type: x-www-form-urlencoded
Form fields:
client_id <my-client-name>
refresh_token <my-refresh-token>

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OJDBC7 in a Docker container? Prepare for trouble

Scenario: A JDK8 Docker container using OJDBC7 to connect to the database. Sounds simple enough, what could go wrong?

Simptoms: Connecting to the database randomly takes several minutes, fails with a weird SqlRecoverableException: no more data to read from socket or just works fine as if there is no problem.

The same Docker image also works fine on some machine but fails consistently on other.

The reason is this. Docker is not good at /dev/random. Probably even more so if you run it in a VM, since it's double isolated from actual entropy sources (my non scientific observation). For whatever reason, OJDBC defaults to /dev/random and this causes a block when connecting to the database due to high probability of /dev/random depletion.

Simple solution is to just mount /dev/urandom to /dev/random inside the Docker, in docker run command:

So.. if you ever want to use OJDBC inside Docker, remember this flag. It will save lives or at least spare you hours of useless debugging.

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