junrao commented on code in PR #23665:
URL: https://github.com/apache/kafka/pull/23665#discussion_r4285550195
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clients/src/main/java/org/apache/kafka/common/requests/RequestContext.java:
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@@ -109,11 +110,31 @@ public RequestContext(RequestHeader header,
this.principalSerde = principalSerde;
}
+ /**
+ * Parses the request body from the given buffer, which must be positioned
at the start of the request body.
+ * If the header indicates the request version is unsupported, the request
body is not parsed. An unsupported
+ * {@link ApiVersionsRequest} is treated as a v0 request. For other
requests, an UnsupportedVersionException is thrown.
+ * <p>
+ * This allows the broker to handle {@link ApiVersionsRequest} from newer
clients, which uses a request version
+ * unknown to the broker. The broker responds with a v0 {@link
ApiVersionsResponse} in that case, and the client
+ * falls back to parsing the response as v0 if it cannot parse it as the
expected version.
Review Comment:
How about the following?
Parses the request body from the given buffer, which must be positioned at
the start of the request body.
If the header indicates the request version is unsupported, the request
body is not parsed. For all unsupported requests other than {@link
ApiVersionsRequest} , an UnsupportedVersionException is thrown. An unsupported
{@link ApiVersionsRequest} could come from new clients and is treated specially
as a v0 request. The broker responds with a v0 {@link ApiVersionsResponse}
including the supported versions of {@link ApiVersionsRequest}. If the client
can't parse the response with the version in the original request it sent, it
falls back to parsing the response as v0. This allows the new client to
discover the version of {@link ApiVersionsRequest} supported by the broker.
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