EnvoyFilter WASM (C++) - reading container's environment variables

Question

In an EnvoyFilter WASM (C++) I need to read the Envoy container's ENVIRONMENT VARIABLES.

I tried to use "environ_get" as mentioned here: https://github.com/envoyproxy/envoy/issues/14958 but the Bazel compilation fails.

Which is the correct way for reading ENVIRONMENT VARIABLES within a EnvoyFilter WASM (C++)?

score 0 · Answer 1 · answered Sep 21 '22 at 07:23

Code should be: myvar := os.Getenv("PATH")

Here is go language:

envoyfilter:

static_resources:
  listeners:
    - name: main
      address:
        socket_address:
          address: 0.0.0.0
          port_value: 18000
      filter_chains:
        - filters:
            - name: envoy.http_connection_manager
              typed_config:
                "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
                stat_prefix: ingress_http
                codec_type: auto
                route_config:
                  name: local_route
                  virtual_hosts:
                    - name: local_service
                      domains:
                        - "*"
                      routes:
                        - match:
                            prefix: "/"
                          route:
                            cluster: web_service
                http_filters:
                  - name: envoy.filters.http.wasm
                    typed_config:
                      "@type": type.googleapis.com/udpa.type.v1.TypedStruct
                      type_url: type.googleapis.com/envoy.extensions.filters.http.wasm.v3.Wasm
                      value:
                        config:
                          vm_config:
                            runtime: "envoy.wasm.runtime.v8"
                            code:
                              local:
                                filename: "./main.wasm"
                            environment_variables:
                                host_env_keys: ["HELLO_1", "VAR_2", "GITHUB_USER", "HOSTNAME", "PATH"] 
                  - name: envoy.filters.http.router
                    typed_config:
                      "@type": type.googleapis.com/envoy.extensions.filters.http.router.v3.Router

    - name: staticreply
      address:
        socket_address:
          address: 127.0.0.1
          port_value: 8099
      filter_chains:
        - filters:
            - name: envoy.http_connection_manager
              typed_config:
                "@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
                stat_prefix: ingress_http
                codec_type: auto
                route_config:
                  name: local_route
                  virtual_hosts:
                    - name: local_service
                      domains:
                        - "*"
                      routes:
                        - match:
                            prefix: "/"
                          direct_response:
                            status: 200
                            body:
                              inline_string: "example body\n"
                http_filters:
                  - name: envoy.filters.http.router
                    typed_config:
                      "@type": type.googleapis.com/envoy.extensions.filters.http.router.v3.Router

  clusters:
    - name: web_service
      connect_timeout: 0.25s
      type: STATIC
      lb_policy: ROUND_ROBIN
      load_assignment:
        cluster_name: mock_service
        endpoints:
          - lb_endpoints:
              - endpoint:
                  address:
                    socket_address:
                      address: 127.0.0.1
                      port_value: 8099

admin:
  access_log_path: "/dev/null"
  address:
    socket_address:
      address: 0.0.0.0
      port_value: 8001

Related code:

// Copyright 2020-2021 Tetrate
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package main

import (
    "github.com/tetratelabs/proxy-wasm-go-sdk/proxywasm"
    "github.com/tetratelabs/proxy-wasm-go-sdk/proxywasm/types"
        "os"
)

func main() {
    proxywasm.SetVMContext(&vmContext{})
}

type vmContext struct {
    // Embed the default VM context here,
    // so that we don't need to reimplement all the methods.
    types.DefaultVMContext
}

// Override types.DefaultVMContext.
func (*vmContext) NewPluginContext(contextID uint32) types.PluginContext {
    return &pluginContext{}
}

type pluginContext struct {
    // Embed the default plugin context here,
    // so that we don't need to reimplement all the methods.
    types.DefaultPluginContext
}



// Override types.DefaultPluginContext.
func (*pluginContext) NewHttpContext(contextID uint32) types.HttpContext {
    return &httpHeaders{contextID: contextID}
}

type httpHeaders struct {
    // Embed the default http context here,
    // so that we don't need to reimplement all the methods.
    types.DefaultHttpContext
    contextID uint32
}

// Override types.DefaultHttpContext.
func (ctx *httpHeaders) OnHttpRequestHeaders(numHeaders int, endOfStream bool) types.Action {
    err := proxywasm.ReplaceHttpRequestHeader("test", "best")
    if err != nil {
        proxywasm.LogCritical("failed to set request header: test")
    }

    myvar := os.Getenv("PATH")
    proxywasm.LogInfof("hello variable: %s",myvar)

    hs, err := proxywasm.GetHttpRequestHeaders()
    if err != nil {
        proxywasm.LogCriticalf("failed to get request headers: %v", err)
    }

    for _, h := range hs {
        proxywasm.LogInfof("request header --> %s: %s", h[0], h[1])
    }
    return types.ActionContinue
}

// Override types.DefaultHttpContext.
func (ctx *httpHeaders) OnHttpResponseHeaders(numHeaders int, endOfStream bool) types.Action {
    hs, err := proxywasm.GetHttpResponseHeaders()
    if err != nil {
        proxywasm.LogCriticalf("failed to get response headers: %v", err)
    }

    for _, h := range hs {
        proxywasm.LogInfof("response header <-- %s: %s", h[0], h[1])
    }
    return types.ActionContinue
}

// Override types.DefaultHttpContext.
func (ctx *httpHeaders) OnHttpStreamDone() {
    proxywasm.LogInfof("%d finished", ctx.contextID)
}

EnvoyFilter WASM (C++) - reading container's environment variables

1 Answers1