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#include ...
#include "proxy_wasm_intrinsics.h"
#include "http_parser.h" //from https://github.com/nodejs/http-parser 

/**
在每个 Filter 配置对应一个对象实例
**/
class ExampleRootContext : public RootContext
{
public:
  explicit ExampleRootContext(uint32_t id, std::string_view root_id) : RootContext(id, root_id) {}

    
  //Fitler 启动事件
  bool onStart(size_t) override
  {
    LOG_DEBUG("ready to process streams");
    return true;
  }
};

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/**
在每个 downstream 连接对应一个对象实例
**/
class MainContext : public Context
{
public:
  http_parser_settings settings_;
  http_parser parser_;
  ...

  //构造函数，在每个新 downstream 连接可用时调用。如 TLS 握手后，或 Plain text 时的 TCP 连接后。注意， HTTP 1.1 是支持长连接的，即这个 object 需要支持多个 Request。
  explicit MainContext(uint32_t id, RootContext *root) : Context(id, root)
  {
    logInfo(std::string("new MainContext"));

    // http_parser_settings_init(&settings_);
    http_parser_init(&parser_, HTTP_REQUEST);
    parser_.data = this;
    //注册 HTTP Parser 的回调事件
    settings_ = {
        //on_message_begin:
        [](http_parser *parser) -> int
        {
          MainContext *hpContext = static_cast<MainContext *>(parser->data);
          return hpContext->on_message_begin();        
        },
        //on_header_field
        [](http_parser *parser, const char *at, size_t length) -> int
        {
          MainContext *hpContext = static_cast<MainContext *>(parser->data);
          return hpContext->on_header_field(at, length);
        },
        //on_header_value
        [](http_parser *parser, const char *at, size_t length) -> int
        {
          MainContext *hpContext = static_cast<MainContext *>(parser->data);
          return hpContext->on_header_value(at, length);
        },
        //on_headers_complete
        [](http_parser *parser) -> int
        {
          MainContext *hpContext = static_cast<MainContext *>(parser->data);
          return hpContext->on_headers_complete();
        },        
        ...
    }
  }
   
  //收到新 Buffer 事件，注意，一个 HTTP 请求由于网络原因，可以打散为多个 Buffer，回调多次。
  FilterStatus onDownstreamData(size_t length, bool end_of_stream) override
  {
    logInfo(std::string("onDownstreamData START"));      
    ...
        
    WasmDataPtr wasmDataPtr = getBufferBytes(WasmBufferType::NetworkDownstreamData, 0, length);

    {
      std::ostringstream out;
      out << "onDownstreamData length:" << length << ",end_of_stream:" << end_of_stream;
      logInfo(out.str());
      logInfo(std::string("onDownstreamData Buf:\n") + wasmDataPtr->toString());
    }

    //这里会执行各种 HTTP 解释，调用相关的 HTTP 解释回调函数。我们实现了这些函数，记录下问题 Header 的位置。并修正。
    size_t parsedBytes = http_parser_execute(&parser_, &settings_, wasmDataPtr->data(), length); // callbacks
	...      
        
    // because Envoy drain `length` size of buf require start=0 :
    // see proxy-wasm-cpp-sdk proxy_wasm_api.h setBuffer()
    // see proxy-wasm-cpp-host src/exports.cc set_buffer_bytes()
    // see Envoy source/extensions/common/wasm/context.cc Buffer::copyFrom()
    size_t start = 0;
        
    // WasmResult setBuffer(WasmBufferType type, size_t start, size_t length, std::string_view data,
    //                           size_t *new_size = nullptr)
    // Ref. https://github.com/proxy-wasm/spec/tree/master/abi-versions/vNEXT#proxy_set_buffer
    // Set content of the buffer buffer_type to the bytes (buffer_data, buffer_size), replacing size bytes, starting at offset in the existing buffer.
    // setBuffer(WasmBufferType::NetworkDownstreamData, start, length, data);
    setBuffer(WasmBufferType::NetworkDownstreamData, start, length, outputBuffer);
  }
    
  /**
   * on HTTP Stream(Connection) closed
   */
  void onDone() override { logInfo("onDone " + std::to_string(id())); }

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static RegisterContextFactory register_ExampleContext(CONTEXT_FACTORY(MainContext),
                                                      ROOT_FACTORY(ExampleRootContext),
                                                      "myparser_id");

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kubectl apply -f - <<"EOF"

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: myparser-envoy-wasm-net-filter
spec:
  workloadSelector:
    labels:
      istio: ingressgateway
      app: istio-ingressgateway
  configPatches:
  - applyTo: NETWORK_FILTER
    match:
      context: GATEWAY
      listener:
        portNumber: 8443
        filterChain:
          filter:
            name: "envoy.filters.network.http_connection_manager"
    patch:
      operation: INSERT_BEFORE
      value:
        name: envoy.filters.network.wasm
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.filters.network.wasm.v3.Wasm
          config:
            name: "myparser"
            root_id: "myparser_id"
            vm_config:
              runtime: "envoy.wasm.runtime.v8"
              code:
                local:
                  filename: "/etc/istio/myparser-envoy-wasm-net-filter/myparser.wasm"
              allow_precompiled: true 

EOF