Fix excessive memory usage

[x-wesley]

When the website has too much text content, the response will take up too much memory.

Use sync.Pool to reduce memory applications.

Thanks.

[WGH-]

Does it really help that much, given that the []byte body, headers, and even net/http.Response objects are still allocated?

[x-wesley]

Does it really help that much, given that the []byte body, headers, and even net/http.Response objects are still allocated?

Yeah, when there are a lot of URLs in a website and a lot of content on the webpage, a lot of memory space will be requested in a short time.

[asciimoo]

@x-wesley do you have measurements about how much improvement this change causes?

[x-wesley]

@x-wesley do you have measurements about how much improvement this change causes?

yeah
In May, we have a scheduled task. We will receive a high memory usage alarm (>80%) every time the task is executed.
The problem is located through pprof, and the peak memory usage after modification is about 50%-60%.