Incorrect documentation for `max_request_body_size`

[ntkme]

Describe the bug

https://github.com/open-telemetry/opentelemetry-collector/blob/main/receiver/otlpreceiver/config.md#confighttp-httpserversettings

The linked document says:

MaxRequestBodySize configures the maximum allowed body size in bytes for a single request. The default 0 means there's no restriction

However, in actual code if max_request_body_size is set to 0, the actual effective value is 20MiB, instead of no restriction:

opentelemetry-collector/config/confighttp/confighttp.go

Line 35 in e99074d

const defaultMaxRequestBodySize = 20 * 1024 * 1024 // 20MiB

opentelemetry-collector/config/confighttp/confighttp.go

Lines 414 to 416 in e99074d

	if hss.MaxRequestBodySize <= 0 {
	hss.MaxRequestBodySize = defaultMaxRequestBodySize
	}

Steps to reproduce

Send a larger than 20MiB payload to otlp receiver via otlp/http.

What did you expect to see?

Large payload is accepted

What did you see instead?

HTTP Status Code 400, Message=http: request body too large

What version did you use?

0.107.0

What config did you use?

Default otlp receiver config from otel collector helm chart 0.102.1

[crobert-1]

Setting a non-zero default value for the maximum request body size was required to fix CVE-2024-36129. It looks like we need to update the documentation to match the updated behavior.

If you require larger request sizes you're welcome to update the value to something larger than you'd ever need to send. 👍