Fix: Custom filesystem exception for invalid ciphertext nodes

[infeo]

This PR changes an error behavior of the filesystem.

On the encrypted/ciphertext side, Cryptofs can represent decrypted/cleartext filenodes either as single files or directories. In the latter case the directory must contain any identification files in order to be recognized. (dir.c9r, symlink.c9r, etc)

In the current version, if such a file was not present, a NoSuchFileException is thrown. But this exception does not represent the actual state of the filesystem node: Instead of not being present, it is broken. And with the wrong exception library consumer might be tempted to use the "free" path, albeit it is not, only running into the next exception.

I replaced the wrong exception with a new, custom FileSystemException: InvalidFileNodeException. The consumer does not know about it and recieves ultimately a generic IOException, indicating there is something wrong with the filesystem node.

[coderabbitai]

Walkthrough

This pull request involves updates to exception handling in the CryptoPathMapper module. The getCiphertextFileType method's documentation has been revised to clarify the conditions under which exceptions are thrown, specifically changing the description of NoSuchFileException and introducing a new exception, InvalidFileNodeException, for cases where a ciphertext directory lacks an identification file. Additionally, a new class, InvalidFileNodeException, has been added to the org.cryptomator.cryptofs package, extending FileSystemException. The related unit test, testNoKnownFileExists, has been modified to expect the new exception type instead of the previous one, reflecting the changes in the error handling logic.

Possibly related PRs

• Feature: More events and event refinement  #284: Introduces modifications in the same method (getCiphertextFileType) by switching exception types and handling broken file nodes, directly aligning with the exception handling changes in this PR.

Suggested labels

enhancement

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Reviewing files that changed from the base of the PR and between 0bdad47 and 4dd38ab.

📒 Files selected for processing (2)

• src/main/java/org/cryptomator/cryptofs/CryptoPathMapper.java (2 hunks)
• src/main/java/org/cryptomator/cryptofs/CryptoPathMapper.java (1 hunks)

🚧 Files skipped from review as they are similar to previous changes (2)

• src/main/java/org/cryptomator/cryptofs/CryptoPathMapper.java
• src/main/java/org/cryptomator/cryptofs/CryptoPathMapper.java

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