feat: implemented ftp backend

[ArberSephirotheca]

I hereby agree to the terms of the CLA available at: https://databend.rs/dev/policies/cla/

Summary

Summary about this PR
I've implemented ftp backend.
I tested it locally with vsftpd and it works fine. I didn't make too much tests on tls mode, but it should be working as supftp almost handle everything for us.

It also pass all the behavior tests:

czy@czy-Inspiron-5680:~/opendal$ cargo test ftp
   Compiling opendal v0.13.1 (/home/czy/opendal)
    Finished test [unoptimized + debuginfo] target(s) in 9.02s
     Running unittests src/lib.rs (target/debug/deps/opendal-5b46cd0e7a5789ec)

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 29 filtered out; finished in 0.00s

     Running tests/behavior/main.rs (target/debug/deps/behavior-516c49dc2e664db6)

running 42 tests
test behavior::services_ftp::test_create_dir ... ok
test behavior::services_ftp::test_create_file_existing ... ok
test behavior::services_ftp::test_create_file_with_special_chars ... ok
test behavior::services_ftp::test_delete_empty_dir ... ok
test behavior::services_ftp::test_create_file ... ok
test behavior::services_ftp::test_list_dir_with_file_path ... ok
test behavior::services_ftp::test_delete ... ok
test behavior::services_ftp::test_list_dir ... ok
test behavior::services_ftp::test_delete_not_existing ... ok
test behavior::services_ftp::test_check ... ok
test behavior::services_ftp::test_create_dir_exising ... ok
test behavior::services_ftp::test_delete_with_special_chars ... ok
test behavior::services_ftp::test_list_nested_dir ... ok
test behavior::services_ftp::test_list_empty_dir ... ok
test behavior::services_ftp::test_list_sub_dir ... ok
test behavior::services_ftp::test_object_id ... ok
test behavior::services_ftp::test_object_name ... ok
test behavior::services_ftp::test_multipart_abort ... ok
test behavior::services_ftp::test_multipart_complete ... ok
test behavior::services_ftp::test_object_path ... ok
test behavior::services_ftp::test_presign_read ... ok
test behavior::services_ftp::test_presign_write ... ok
test behavior::services_ftp::test_presign_write_multipart ... ok
test behavior::services_ftp::test_metadata ... ok
test behavior::services_ftp::test_read_full ... ok
test behavior::services_ftp::test_read_not_exist ... ok
test behavior::services_ftp::test_read_range ... ok
test behavior::services_ftp::test_read_with_dir_path ... ok
test behavior::services_ftp::test_stat_dir ... ok
test behavior::services_ftp::test_stat_not_cleaned_path ... ok
test behavior::services_ftp::test_read_with_special_chars ... ok
test behavior::services_ftp::test_remove_all ... ok
test behavior::services_ftp::test_stat_not_exist ... ok
test behavior::services_ftp::test_stat_root ... ok
test behavior::services_ftp::test_stat_with_special_chars ... ok
test behavior::services_ftp::test_walk_bottom_up ... ok
test behavior::services_ftp::test_write ... ok
test behavior::services_ftp::test_write_with_special_chars ... ok
test behavior::services_ftp::test_write_with_dir_path ... ok
test behavior::services_ftp::test_stat ... ok
test behavior::services_ftp::test_walk_top_down ... ok
test behavior::services_ftp::test_walk_top_down_within_empty_dir ... ok

test result: ok. 42 passed; 0 failed; 0 ignored; 0 measured; 252 filtered out; finished in 0.01s

I created a example file in examples/ if you want to try.
The error handling looks kind cluttered tho, and Im trying to improve it.

[Xuanwo]

So nice!

[ClSlaid]

Bravo!

[ClSlaid]

Clippy and Rustfmt are your friends. Before commit, you can run cargo clippy for checks and advices, and run cargo fmt to reformat you code.

[ArberSephirotheca]

@ClSlaid Thanks for the review. I am moving house right now so I may not update too frequent, but I hope I can get all these thing fixed within a week.

[Xuanwo]

This PR is really great and almost done. I left some reviews on this PR. Please take a look when you are free.

I am moving house right now so I may not update too frequent

And congrats on your new move. Hoping your new house is nice and comfortable.

[ArberSephirotheca]

@Xuanwo I think I got everything fixed. If you find anything needed to be changed, Please point out.

CI/check indicates a vulnerability due to outdated time crate:

Crate:     time
error: 1 vulnerability found!
Version:   0.1.44
Title:     Potential segfault in the time crate
Date:      2020-11-18
ID:        RUSTSEC-2020-0071
URL:       https://rustsec.org/advisories/RUSTSEC-2020-0071
Solution:  Upgrade to >=0.2.23
Dependency tree:
time 0.1.44
└── chrono 0.4.22
    └── suppaftp 4.4.0
        └── opendal 0.14.1

However, according to this, the chrono team are mostly likely not going to update this dependency as the vulnerability does not affect them, and they will remove this dependency in the future.
Also for Service Test HDFS, my change doesn't touch this part, I don't know why it fails(and it success in my previous commit...).

[Xuanwo]

However, according to this, the chrono team are mostly likely not going to update this dependency as the vulnerability does not affect them, and they will remove this dependency in the future.

Please add an audit.toml like databend dose: https://github.com/datafuselabs/databend/blob/main/.cargo/audit.toml#L9

Also for Service Test HDFS, my change doesn't touch this part, I don't know why it fails(and it success in my previous commit...).

It's a known issue that the HDFS test is flaky: #465

Please just ignore it.

[Xuanwo]

I have to admit that we (reviewers) made a mistake.

Reusing the same connection makes everything complex:

• We can't use async API because we can't init the stream during build
  • Thus, we can't use put_with_stream because the requirement for the reader is different.
• We can't return the reader/dirstream to users because they referred to FtpStream.
  • Thus, we have to read them in memory slower than multiple connections.

I plan to merge this PR and leave this improvement as new issue.

• Use multiple connections instead of reusing the same one.
• In the future, we can implement a connection pool for FTP connections.

[Xuanwo]

Great work!