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Posted to commits@opendal.apache.org by "akx (via GitHub)" <gi...@apache.org> on 2026/07/22 13:25:19 UTC
[I] CompleteReader rejects a bounded range that extends past EOF [opendal]
akx opened a new issue, #7938:
URL: https://github.com/apache/opendal/issues/7938
Somewhere between opendal 0.45 and 0.57, the semantics for a short read changed: in 0.57, a bounded range read whose end extends past the end of the object fails with
```
Unexpected (permanent) => reader got too little data { expect: <end-start>, actual: <object_len> }
```
instead of returning the available bytes (a short read).
This is a behavior change from earlier releases, and it breaks the common "over-request a header window without first knowing the object size" pattern.
Standard HTTP Range semantics already clamp this: `Range: bytes=0-16383` against a 1088-byte object returns `206` with `Content-Range: bytes 0-1087/1088`. `CompleteLayer` ignores what was actually served and validates against the requested length instead, so it also fires for the `fs` service where there is no HTTP layer at all.
## Minimal reproduction (`services-fs`)
```rust
use opendal::{services::Fs, Operator};
#[tokio::main]
async fn main() {
let dir = std::env::temp_dir().join("opendal-range-repro");
std::fs::create_dir_all(&dir).unwrap();
let op = Operator::new(Fs::default().root(dir.to_str().unwrap()))
.unwrap()
.finish();
// Object is 100 bytes.
op.write("small", vec![b'x'; 100]).await.unwrap();
// Ask for the first 16 KiB. The object is shorter than that.
let res = op.read_with("small").range(0..16_384).await;
match res {
Ok(buf) => println!("ok: {} bytes", buf.len()), // expected: 100
Err(e) => println!("ERR: {e}"), // actual (0.57): reader got too little data
}
}
```
Output on 0.57 (verified):
```
ERR: Unexpected (permanent) at , context: { expect: 16384, actual: 100 } => reader got too little data
```
## Expected
A range whose end runs past EOF returns the available bytes (here, 100), as it did before and as HTTP Range semantics imply. Reading the first N bytes of an object of unknown length should preferably not require a preceding `stat`, or at least there should be an option to allow for it?
### AI Disclosure
This was partially triaged, and the verifier written, by Claude Opus 4.8.
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Re: [I] CompleteReader rejects a bounded range that extends past EOF [opendal]
Posted by "Xuanwo (via GitHub)" <gi...@apache.org>.
Xuanwo commented on issue #7938:
URL: https://github.com/apache/opendal/issues/7938#issuecomment-5069969413
Proposed https://github.com/apache/opendal/pull/7945 for this, welcome to check this out
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Re: [I] CompleteReader rejects a bounded range that extends past EOF [opendal]
Posted by "dosubot[bot] (via GitHub)" <gi...@apache.org>.
dosubot[bot] commented on issue #7938:
URL: https://github.com/apache/opendal/issues/7938#issuecomment-5050197277
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<!-- Answer -->
Fair point — sorry for the incomplete advice earlier. Let me clarify what actually works and what doesn't:
Using `range(0..)` (unbounded end) **does** bypass the size validation, because `BytesRange::size()` returns `None` for unbounded ranges and `CompleteReader::check()` [skips validation entirely when size is `None`](https://github.com/apache/opendal/blob/27d5677d4526519313cbce00cd28f8fbcc099642/core/src/layers/complete.rs#L260-L263). But of course that doesn't solve the "read up to N bytes" use case — it just reads everything from offset 0 to EOF, which could be arbitrarily large.
The core issue is that there's no way to express "read *up to* N bytes" with the current API. Bounded ranges (`0..N`) enforce an exact-size guarantee [[1]](https://github.com/apache/opendal/blob/27d5677d4526519313cbce00cd28f8fbcc099642/core/src/raw/http_util/bytes_range.rs#L69-L72), and unbounded ranges (`0..`) read everything. There's nothing in between.
Your request is reasonable — the "over-request a header window" pattern is common and shouldn't require a preceding `stat()`. The fix likely needs to happen in `CompleteReader` itself: when a bounded range read returns fewer bytes than requested, it should check whether the short read is because the object is simply smaller than the range (which is fine per HTTP Range semantics) versus a genuine data integrity issue. Alternatively, a new range variant or read option like `.allow_short_read(true)` could opt into the lenient behavior.
I'll defer to @Xuanwo on the right approach here since this is a deliberate design choice in `CompleteReader`.
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Re: [I] CompleteReader rejects a bounded range that extends past EOF [opendal]
Posted by "akx (via GitHub)" <gi...@apache.org>.
akx commented on issue #7938:
URL: https://github.com/apache/opendal/issues/7938#issuecomment-5091692692
That API looks good to me. I left a couple comments on the RFC - I don't know enough about OpenDAL's internals to comment fully on the oio/layer stuff though :)
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Re: [I] CompleteReader rejects a bounded range that extends past EOF [opendal]
Posted by "Xuanwo (via GitHub)" <gi...@apache.org>.
Xuanwo commented on issue #7938:
URL: https://github.com/apache/opendal/issues/7938#issuecomment-5087585073
cc @dentiny & @akx, would you like to take a review on my proposal https://github.com/apache/opendal/pull/7945?
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Re: [I] CompleteReader rejects a bounded range that extends past EOF [opendal]
Posted by "akx (via GitHub)" <gi...@apache.org>.
akx commented on issue #7938:
URL: https://github.com/apache/opendal/issues/7938#issuecomment-5050159687
@dosu Neither workaround helps here :)
@Xuanwo As the author of the PR #4690 (which doesn't have a description or tests...), can you advise?
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Re: [I] CompleteReader rejects a bounded range that extends past EOF [opendal]
Posted by "dosubot[bot] (via GitHub)" <gi...@apache.org>.
dosubot[bot] commented on issue #7938:
URL: https://github.com/apache/opendal/issues/7938#issuecomment-5046478943
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<!-- Answer -->
Hi @akx! I'm [Dosu](https://go.dosu.dev/dosubot) and I'm helping the Apache OpenDAL team.
You've correctly identified the source of this behavior change. The strict validation was introduced in [PR #4690](https://github.com/apache/opendal/pull/4690) (commit `e948ec826`, 2024-06-05), which added a size check to `CompleteReader`. This first shipped in **v0.47**, which is why v0.45 worked but v0.57 does not.
The check lives in [`CompleteReader::check()`](https://github.com/apache/opendal/blob/27d5677d4526519313cbce00cd28f8fbcc099642/core/src/layers/complete.rs#L260-L278) — when a bounded range read finishes, it compares the number of bytes actually read against `args.range().size()` (the requested range length). If they don't match exactly, it returns the "reader got too little data" error. The `CompleteLayer` is [automatically applied to every operator](https://github.com/apache/opendal/blob/27d5677d4526519313cbce00cd28f8fbcc099642/core/src/types/operator/builder.rs#L467) and cannot be disabled or configured.
As you point out, this conflicts with standard HTTP Range semantics where `Range: bytes=0-16383` against a shorter object simply returns a `206` with the available bytes. The current logic ignores the fact that the backend already clamped the response and validates against the originally requested length.
**Workarounds for now:**
- Use `stat()` first to learn the object size, then clamp your range accordingly (the extra round-trip you'd like to avoid).
- Use an unbounded range (e.g., `range(0..)`) which bypasses the size validation since `self.size` will be `None`.
Neither is ideal for the "over-request a header window" pattern you describe. This does seem like a gap worth addressing — the validation is valuable for catching backend bugs, but it shouldn't reject reads that are short solely because the object is smaller than the requested range.
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Re: [I] CompleteReader rejects a bounded range that extends past EOF [opendal]
Posted by "Xuanwo (via GitHub)" <gi...@apache.org>.
Xuanwo commented on issue #7938:
URL: https://github.com/apache/opendal/issues/7938#issuecomment-5069308157
Thank you @akx for raising this up.
In the past, OpenDAL followed the same style as syscalls. That style allowed storage to perform a read like `read(0..1024)` and have only 128 bytes returned. However, we later removed this behavior. We now require users to pass the correct range. This allows us to perform validation and handle concurrent reads correctly. For example, if there is no guarantee that `read(0..4MiB)` must return 4MiB, we cannot plan concurrent reads accordingly.
But I agree that supporting use cases to do limited reading is useful, maybe we can come out a new design for that.
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