Add file-based backend

[nbenn]

Ad #52

• keyrings are implemented as .yml files (multiple keyrings are supported)
• each keyring has some metadata, including a version number keyring_version, a nonce nonce stored as hex string and a random string integrity_check used to make sure that all keys in this keyring are encrypted using the same nonce/key
• items have 3 fields: service_name, user_name and secret (stored as hex string)
• example keyring file:

  keyring_info:
    keyring_version: 1.0.0
    nonce: 24bda08d1095d9af9b4eac0c77c974978c168a7173750fb7
    integrity_check: 200d284e29bc5efa342b39d461ad2c2f1d1c53af245c312d7fb8007ad480e27f883008c2bae9
  items:
  - service_name: R-keyring-test-service-MWHakEpCrNwvMiq
    user_name: SewQIZZhiY
    secret: acf6c460375f0d39c3eaa4f438ecb9183f084cf62474287b51913071c380df66

• in order to hold on to session info, the keyrings env is used, which contains an env per unlocked keyring; this is the best I could come up with that is compatible with how the api functions work

• each of the keyring envs can store

  • the unlock key (key)
  • the keyring nonce (nonce)
  • the integrity check string (check)
  • the items list (items)

  all except the unlock key is not strictly necessary as this information can at any time be read from the keyring file; however as retrieving any piece of info from the file requires reading and parsing of the whole file, the important stuff is cached

• secrets are only decrypted when requested using get()

[codecov-io]

Codecov Report

Merging #54 into master will increase coverage by 17.53%. The diff coverage is 87.18%.

@@             Coverage Diff             @@
##           master      #54       +/-   ##
===========================================
+ Coverage    36.5%   54.03%   +17.53%     
===========================================
  Files          13       14        +1     
  Lines        1249     1312       +63     
===========================================
+ Hits          456      709      +253     
+ Misses        793      603      -190

Impacted Files	Coverage Δ
R/default_backend.R	87.5% <ø> (-2.25%)	:arrow_down:
R/assertions.R	100% <100%> (ø)	:arrow_up:
R/backend-file.R	87.02% <87.02%> (ø)
R/backend-secret-service.R	0% <0%> (-6.61%)	:arrow_down:
R/backend-class.R	5.33% <0%> (-5.06%)	:arrow_down:
src/keyring_secret_service.c	0% <0%> (-5.03%)	:arrow_down:
R/backend-macos.R	73.94% <0%> (-1.06%)	:arrow_down:
R/backend-wincred.R	1.88% <0%> (+0.11%)	:arrow_up:
... and 1 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update bdaaab7...2819a85. Read the comment docs.

[nbenn]

Sorry for the delay in finishing up the requested changes. I think I now incorporated everything you asked for. Let me know if you have any additional stuff you want me to modify, or also if you want me to explain something in more detail.

[gaborcsardi]

Thanks! I'll look at it ASAP.

[gaborcsardi]

Great stuff, thank you!

[gaborcsardi]

OK, after a better look, I think it is not optimal that unlocking a keyring in one R session makes it impossible to use it in another session. This might have been a misunderstanding between us. I'll fix this.