Creating empty file with writer in webdav for owncloud fails

[prabirshrestha]

Repro steps:

• Create an empty file locally in your machine - emptyfile.txt
• Go to https://demo.owncloud.com and login with demo as username and password.
• Upload the empty file and see it created.

Now do the same but with opendal webdav backend and verify in demo.owncloud.com website. The emptyfile doesn't exist as it seems to fail creating empty file. update let data = b" "; to contain empty space and it works.

let mut builder = opendal::services::Webdav::default();

builder
    .endpoint("https://demo.owncloud.com/remote.php/dav/files/demo/")
    .username("demo")
    .password("demo")
    .root("/");

let data = b"";
let stream = tokio_util::io::ReaderStream::new(&data[..]);
let mut reader = tokio_util::io::StreamReader::new(stream);

let op = Operator::new(builder).unwrap().finish();
let mut writer = op
    .writer_with("/emptyfile.txt")
    .content_length(data.len() as u64)
    .await
    .unwrap();
tokio::io::copy(&mut reader, &mut writer).await.unwrap();
writer.close().await.unwrap();

dependencies:

[dependencies]
opendal = "0.39.0"
tokio = { version = "1.32.0", features = ["macros", "rt-multi-thread"] }
tokio-util = { version = "0.7.8", features = ["io"] }

[Xuanwo]

Thanks for the report!

The root cause here is tokio::io::copy(&mut reader, &mut writer).await.unwrap(); won't call write, so no real PUT request has been sent.

I have tested the following code with success:

let mut writer = op
    .writer_with("/emptyfile.txt")
    .content_length(data.len() as u64)
    .await
    .unwrap();
writer.write("").await.unwrap();
writer.close().await.unwrap();

---

I believe this use case will be fixed after our buffer refactor: we should flush to storage even when our buffer is empty.

[prabirshrestha]

Sounds good. Will apply the fix for now.

[prabirshrestha]

Seems like writer.write("").await? no longer works.

Works in opendal = "0.39.0", silently works but no file is created in opendal = { git = "https://github.com/apache/incubator-opendal.git", rev = "1bb63ab" }

[Xuanwo]

Work in opendal = "0.39.0", silently works but no file is created in opendal = { git = "https://github.com/apache/incubator-opendal.git", rev = "1bb63ab" }

Thanks for the feedback. I will add a new test case to cover this.

[damooo]

Creating empty file fails in s3 too. And most of the backends.

TheWriter doesn't call the backend at all if size is zero.

https://github.com/apache/incubator-opendal/blob/30f14926177b54713f014cc3a5bec3e382a40826/core/src/types/writer.rs#L93-L99