chenBright opened a new pull request, #3341:
URL: https://github.com/apache/brpc/pull/3341
### What problem does this PR solve?
Issue Number: resolve
Problem Summary:
`IOBuf` integrates with protobuf via `IOBufAsZeroCopy{Input,Output}Stream`,
but
there is no direct bridge to the `std::iostream` hierarchy. As a result, any
library that consumes/produces `std::istream&` / `std::ostream&` — most
notably
`nlohmann::json` — cannot read from or write to an `IOBuf` without an
intermediate `std::string`:
```cpp
auto j = nlohmann::json::parse(req->request_attachment().to_string());
```
This is an obstacle to adopting nlohmann::json in bRPC.
### What is changed and the side effects?
Changed:
Introduce four classes in `src/butil/iobuf.{h,cpp}` that bridge IOBuf and
the standard iostream hierarchy:
- `IOBufAsInputStreamBuf` — read-only `std::streambuf` over an IOBuf,
walking the backing blocks via the public `backing_block()` API. Overrides
`underflow`, `xsgetn`(bulk memcpy across block boundaries to avoid the
default per-byte sbumpc loop), and `showmanyc` (saturating sum of
remaining block sizes).
- `IOBufInputStream` — `std::istream` view that wires the streambuf above.
- `IOBufAsOutputStreamBuf` — append-only `std::streambuf` that delegates to
the existing `IOBufAsZeroCopyOutputStream` for block allocation and the
three-branch `BackUp` (including the shared-block degradation that protects
IOBufs sharing blocks from being corrupted by an in-flight write).
Overrides
`overflow`, `xsputn` (block-sized memcpy instead of per-byte sputc),
and `sync` (forwards to shrink()).
- `IOBufOutputStream` — `std::ostream` view that wires the streambuf above;
accepts an optional block_size to allocate dedicated blocks instead of
drawing from the per-thread TLS pool.
Usage with nlohmann::json:
```c++
// Parse: zero string copy
butil::IOBufInputStream in(request_body);
auto j = nlohmann::json::parse(in);
// Serialize: bytes flow straight into IOBuf blocks
butil::IOBufOutputStream os(response_body);
os << j;
```
Side effects:
- Performance effects:
- Breaking backward compatibility:
---
### Check List:
- Please make sure your changes are compilable.
- When providing us with a new feature, it is best to add related tests.
- Please follow [Contributor Covenant Code of
Conduct](https://github.com/apache/brpc/blob/master/CODE_OF_CONDUCT.md).
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