Plugin API - Response headers are not transient

From my Elasticsearch plugin, I want to set HTTP response headers. What I do is:


And this works, but when another request comes along, Elasticsearch will still carry "header1" as a response header. In other words, I expected the response headers to be transient, i.e. to be reset for every request.

Or at least, I expected to be able to be able clear/remove/overwrite them, but this is not possible as for current API.

// Throws Method threw 'java.lang.UnsupportedOperationException' exception.

Please advise, am I doing this wrong?

Can you show more of what your plugin is doing? In which thread are you trying to modify the thread context? What plugin apis is your plugin extending?

all this went back to normal when I made sure the response headers were set from a thread in the original ES thread pool. Setting them from a completable future of an async HTTP client request caused problems.

Also, to make it work with 6.7.0 I had to wrap all my code in a:

try (ThreadContext.StoredContext ctx = threadPool.getThreadContext().stashContext()) {
  ... all my code that uses HTTP client and set response headers...

The above was necessary because the deprecation logger set a response header with a null value and threw a NullPointerException.

[2019-03-29T13:10:53,149][WARN ][r.suppressed             ] [d-qW6Ay] path: /_template/metricbeat-6.7.0, params: {name=metricbeat-6.7.0}
java.lang.NullPointerException: value
	at io.netty.util.internal.ObjectUtil.checkNotNull( ~[?:?]
	at io.netty.handler.codec.DefaultHeaders.addObject( ~[?:?]
	at io.netty.handler.codec.http.DefaultHttpHeaders.add( ~[?:?]
	at org.elasticsearch.http.netty4.Netty4HttpChannel.setHeaderField( ~[?:?]
	at org.elasticsearch.http.netty4.Netty4HttpChannel.setHeaderField( ~[?:?]
	at org.elasticsearch.http.netty4.Netty4HttpChannel.addCustomHeaders( ~[?:?]
	at org.elasticsearch.http.netty4.Netty4HttpChannel.sendResponse( ~[?:?]
	at$ResourceHandlingHttpChannel.sendResponse( ~[elasticsearch-6.7.0.jar:6.7.0]
	at ~[elasticsearch-6.7.0.jar:6.7.0]
	at [elasticsearch-6.7.0.jar:6.7.0]
	at$1.onResponse( [elasticsearch-6.7.0.jar:6.7.0]
	at$1.onResponse( [elasticsearch-6.7.0.jar:6.7.0]

Can you share more details about this please?

@jasontedor the issue was described by a user of trying to make the code work with ES 6.7.0

Which was fixed with this commit:

Okay, thanks for clarifying. The way that I read this is that it is not a problem in Elasticsearch server. Please correct me if I have it wrong.

The main issue seems the extra null value in a certain response header which is not set by the plugin.

{Warning=[299 Elasticsearch-6.7.0-8453f77 "[types removal] The parameter include_type_name should be explicitly specified in put template requests to prepare for 7.0. In 7.0 include_type_name will default to 'false', and requests are expected to omit the type name in mapping definitions.",  null]

Apparently the extra null is present only when the plugin is installed. Stashing the thread context removes the header entirely, but it does not look like a solution to the root cause.

Did we forget to implement some interface method?

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