higress 转发HTTP请求/响应时，如何保持Header大小写 about higress

[CH3CHO]

HTTP header 按规范是不区分大小写的。什么场景下需要强制约定大小写呢？

[johnlanni]

http header不区分大小写时符合RFC规范的，所以envoy默认转换成小写了，跟HTTP2保持一致。

如果要绕过此问题，可以开启istio api支持，然后下发这个envoyfilter：

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: header-preserve-case
  namespace: higress-system
spec:
  configPatches:
  - applyTo: NETWORK_FILTER
    match:
      context: GATEWAY
      listener:
        filterChain:
          filter:
            name: envoy.filters.network.http_connection_manager
    patch:
      operation: MERGE
      value:
        name: envoy.filters.network.http_connection_manager
        typed_config:
          '@type': type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
          http_protocol_options:
            header_key_format:
              stateful_formatter:
                name: preserve_case
                typed_config:
                  '@type': type.googleapis.com/envoy.extensions.http.header_formatters.preserve_case.v3.PreserveCaseFormatterConfig
  - applyTo: CLUSTER
    match:
      context: GATEWAY
    patch:
      operation: MERGE
      value:
        typed_extension_protocol_options:
          envoy.extensions.upstreams.http.v3.HttpProtocolOptions:
            '@type': type.googleapis.com/envoy.extensions.upstreams.http.v3.HttpProtocolOptions
            explicit_http_config:
              http_protocol_options:
                header_key_format:
                  stateful_formatter:
                    name: preserve_case
                    typed_config:
                      '@type': type.googleapis.com/envoy.extensions.http.header_formatters.preserve_case.v3.PreserveCaseFormatterConfig