Issue when trying to extract in unix root directory (/): AbstractExtractFileTask

[christian3042]

Hi,
I was running the zip4j library in a docker container. When I tried to extract something in the root directory, I received the following error:
net.lingala.zip4j.exception.ZipException: illegal file name that breaks out of the target directory: backup_keys.csv
at net.lingala.zip4j.tasks.AbstractExtractFileTask.assertCanonicalPathsAreSame(AbstractExtractFileTask.java:84) ~[zip4j-2.11.1.jar!/:na]
at net.lingala.zip4j.tasks.AbstractExtractFileTask.extractFile(AbstractExtractFileTask.java:52) ~[zip4j-2.11.1.jar!/:na]
at net.lingala.zip4j.tasks.ExtractAllFilesTask.executeTask(ExtractAllFilesTask.java:41) ~[zip4j-2.11.1.jar!/:na]
at net.lingala.zip4j.tasks.ExtractAllFilesTask.executeTask(ExtractAllFilesTask.java:17) ~[zip4j-2.11.1.jar!/:na]
at net.lingala.zip4j.tasks.AsyncZipTask.performTaskWithErrorHandling(AsyncZipTask.java:51) ~[zip4j-2.11.1.jar!/:na]
at net.lingala.zip4j.tasks.AsyncZipTask.execute(AsyncZipTask.java:45) ~[zip4j-2.11.1.jar!/:na]
at net.lingala.zip4j.ZipFile.extractAll(ZipFile.java:470) ~[zip4j-2.11.1.jar!/:na]
at net.lingala.zip4j.ZipFile.extractAll(ZipFile.java:441) ~[zip4j-2.11.1.jar!/:na]

I think I found the issue in the following file: https://github.com/srikanth-lingala/zip4j/blob/master/src/main/java/net/lingala/zip4j/tasks/AbstractExtractFileTask.java

and the following line:
String outputCanonicalPath = (new File(outputPath).getCanonicalPath()) + File.separator;

So when I'm in the root directory / it appends another /, which results in // and then the startsWith check fails. As a workaround I think I could create a subdirectory. Even though it might be strange to extract into the subdirectory, it should be technically possible in my opinion. When I was running the Spring Boot application locally, I did not face any issues. This was due to the relative path "." was not resolved to the root directory, but to the directory, where the application was running. Please let me know if this can be fixed.

[srikanth-lingala]

I modified the code to append file separator only if it doesn't already contain one. I will include this fix in the next release.

[srikanth-lingala]

Fix included in v2.11.2 released today