Unresolved requirement: Import-Package: org.slf4j when starting bundle in Kura Emulator

Question

Hi everyone,

Using the Kura Linux emulator, I am running the Hello World example from the Kura Documentation http://eclipse.github.io/kura/dev/deploying-bundles.html#remote-target-device

I managed to run the OSGi plugin in local emulation mode, here's the output from the Kura Emulator Linux/java log.

21:14:18,036 [Component Resolve Thread] INFO  HelloOsgi:15  - Bundle org.eclipse.kura.example.hello_osgi has started!

However when I try to start/stop the bundle from the console, I only manage to implement the install step. Here are some relevant outputs from the Host OSGi console after installation.

osgi> install file:/home/tihomir/workspace/kura/plugins/org.eclipse.kura.example.hello_osgi_1.0.0.201712111129.jar
Bundle id is 1020
LastModified         1513020115678
Headers               Bundle-ManifestVersion = 2
 Bundle-Name = Hello World Example with Logger
 Bundle-RequiredExecutionEnvironment = JavaSE-1.8
 Bundle-SymbolicName = org.eclipse.kura.example.hello_osgi
 Bundle-Version = 1.0.0.201712111129
 Import-Package = org.eclipse.osgi.framework.console;version="1.0.0",
org.osgi.framework;version="1.3.0",
org.osgi.service.component;version="1.2.2",
org.osgi.service.component.annotations;version="1.2.0";resolution:=optional,
org.osgi.util.tracker;version="1.3.1",org.4j;version="1.7.21"
 Manifest-Version = 1.0
 Service-Component = OSGI-INF/*.xml
Location             file:/home/tihomir/workspace/kura/plugins/org.eclipse.kura.example.hello_osgi_1.0.0.201712111129.jar
State                2
Bundle                1020|Installed  |    1|org.eclipse.kura.example.hello_osgi (1.0.0.201712111129)
Version              1.0.0.201712111129
RegisteredServices   null
ServicesInUse        null
Module               osgi.identity; osgi.identity="org.eclipse.kura.example.hello_osgi"; type="osgi.bundle"; version:Version="1.0.0.201712111129" [id=1020]
SymbolicName         org.eclipse.kura.example.hello_osgi
BundleContext        null
BundleId             1020


osgi> ss
"Framework is launched."
id  State       Bundle
0   ACTIVE      org.eclipse.osgi_3.12.50.v20170928-1321
                Fragments=1
997 RESOLVED    org.slf4j.api_1.7.2.v20121108-1250
                Fragments=5, 998
998 RESOLVED    org.slf4j.impl.log4j12_1.7.2.v20131105-2200
                Master=997
1020    INSTALLED   org.eclipse.kura.example.hello_osgi_1.0.0.201712111129

But now, when I try to activate the bundle, despite the output above showing org.slf4j is resolved, I get the following exception

osgi> start 1020
gogo: BundleException: Could not resolve module: org.eclipse.kura.example.hello_osgi [1020]
  Unresolved requirement: Import-Package: org.slf4j; version="1.7.21"

I am running the emulator on Debian 9. Here's also the plugin manifest

Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Hello World Example with Logger
Bundle-SymbolicName: org.eclipse.kura.example.hello_osgi
Bundle-Version: 1.0.0.qualifier
Bundle-RequiredExecutionEnvironment: JavaSE-1.8
Service-Component: OSGI-INF/*.xml
Import-Package: org.eclipse.osgi.framework.console;version="1.0.0",
 org.osgi.framework;version="1.3.0",
 org.osgi.service.component;version="1.2.2",
 org.osgi.service.component.annotations;version="1.2.0";resolution:=optional,
 org.osgi.util.tracker;version="1.3.1",
 org.slf4j;version="1.7.21"

Already tried a few checks/fixes that I found here and on the Eclipse forum, but nothing worked, so any fresh suggestions are welcome.

Answer 1

Edit the POM of your project and downgrade SLF4j, since Kura seems to offer SLF4j v 1.7.2 whilst your bundle requires at least v 1.7.21

---

As per @NeilBartlett's comment starting the SLF4j bundles is not required for your bundle's dependency to resolve. I leave here this part of the answer as reminder in the case that you don't see any log line coming from your bundle.

SLF4j bundles are not started (ss shows them in RESOLVED state). Try with start 997 998 to start them.

Answer 2

Your Import-Package ranges look wrong in general. For example you have this:

Import-Package: org.slf4j;version="1.7.21"

First: specifying the micro segment (i.e. the last segment, 21) is unnecessary. The micro version indicates bug fixes, performance improvements, documentation changes etc. None of which have any semantic impact on you as a consumer. Therefore you should just import from version 1.7 because any micro version below that will be compatible with your code.

Second: you have no upper bound on your import range! This means you will import from version 1.7.21 or any higher version, up to infinity. So while you are extremely anal about the bottom end of your range, you are fantastically carefree about the upper end! You should limit the range as follows:

Import-Package: org.slf4j; version="[1.7,2.0)"

This allows your bundle to import version 1.7 up to but NOT including version 2.0 of Slf4j (if that ever exists). This is correct because version 2 would indicate a breaking change in the Slf4j APIs.

Same advice for all your other imports:

Import-Package: org.osgi.framework;version="[1.3, 2.0)",
  org.osgi.service.component;version="[1.2, 2.0)",
  ... etc

If you use bnd or one of its derivative tools to generate your manifest, you won't have to think about any of this and it will all just be correct.

Answer 3

Thanks @NeilBartlett @AlessandroDaRugna

It turned out that the example was working as expected after all. It was a matter of figuring out which console was meant in the documentation, since in Eclipse IDE you can choose between two options. The Kura Emulator Linux/java console, the one the instructions apparently had in mind, is not very user friendly and takes some time getting used to. The other console, the Host OSGi, I couldn't really it figure out, but it seems to be decoupled from the emulator, maybe a general purpose interface of a kind.

Again, thank you for the support.