disagg: The S3 LIST always return nothing after bumping the aws-sdk-cpp

[JaySon-Huang]

Bug Report

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1. Minimal reproduce step (Required)

2. What did you expect to see? (Required)

3. What did you see instead (Required)

The LIST result from S3 always return empty result.

We must pick this commit to make the aws-sdk-cpp work with Poco client: JaySon-Huang/aws-sdk-cpp@75b6642

4. What is your TiFlash version? (Required)

Introduced by #8247

[JaySon-Huang]

The root cause of it is we use PocoHTTPClient in TiFlash. The class uses HTTPFixedLengthStreamBuf, a subclass of the Poco::BasicBufferedStreamBuf, as the underlying buffer of HTTP response inputstream.

And the Poco::BasicBufferedStreamBuf is a lazy fetching response buffer. So the result of tellp() is not reliable. Only peek() will run into Poco::BasicBufferedStreamBuf::underflow() and get the correct result into buffer.

https://github.com/pingcap/poco/blob/170872b2a15ea042d99f8168a01aec896eef0840/Foundation/include/Poco/BufferedStreamBuf.h#L91-L110