[Performance Bug] HeaderHelper.getSafeFromHeader uses ThreadContext.getHeaders() causing major performance overhead

[parasjain1]

What is the bug?
Within HeaderHelper.deserializeSafeFromHeader we make a call to HeaderHelper.getSafeFromHeader which “safely” retrieves a header value from ThreadContext. For retrieving a header value for given header name ThreadContext.getHeaders() is being called which creates a new map for all existing headers and returns the same. This creation of new map every time getSafeFromHeader is called causes a major overhead, especially for search use cases.

What is the expected behavior?
Retrieve the header value from ThreadContext without creating a new map

Additional Context & Proposed Solution
Instead of using ThreadContext.getHeaders() we could use ThreadContext.getHeader(key).

One caveat is that ThreadContext.getHeader(key) will return the current header value if present, else the default value. If default value is not present, it’ll return a null value.

While in HeaderHelper.getSafeFromHeader we expect to retrieve the current header value OR null (not the default value).

I'm proposing the following changes to fix this -

Within OpenSearch -

• Add a method ThreadContext.getHeaderOrDefault(key, defaultVal) which will return the current header value if present, defaultVal otherwise.
• Optionally, can also add a ThreadContext.isHeaderPresent(key) method which returns true if header is present, false otherwise.

Within Security Plugin -

• Replace call to ThreadContext.getHeaders() with ThreadContext.getHeaderOrDefault(headerName, null) to avoid unnecessarily creating an additional map

What is your host/environment?

• OS1.3
• Security Plugin

[parasjain1]

ThreadContext.getHeaders() too returns defaultHeaders when headers are absent in the current requestHeaders. Hence, we can just safely replace ThreadContext.getHeaders() with ThreadContext.getHeader() without any other change needed in ThreadContext.

Following from above, the only change needed is -

Within Security Plugin -

• Replace call to ThreadContext.getHeaders() with ThreadContext.getHeaderOrDefault(headerName, null) to avoid unnecessarily creating an additional map