feat: support proxy set buffer bytes

[wimspaargaren]

Resolve #45

We've tested the set buffer bytes function deployed in Istio and it seems to be working as expected.

Filter built tiny go version:

tinygo version  
tinygo version 0.16.0-dev darwin/amd64 (using go version go1.15 and LLVM version 10.0.1)

Built using:

tinygo build -o ./filters/myfilter/filter.wasm -target=wasi -wasm-abi=generic ./myfilter.go

Istio version

istioctl version                                                                                                                
client version: 1.7.0
control plane version: 1.7.0
data plane version: 1.7.0 (10 proxies)

Example usage:

        body := []byte(`{ "data": "my new body" }`)
	bufferData := &body[0]
	res := rawhostcall.ProxySetBufferBytes(types.BufferTypeHttpRequestBody, 0, len(body), bufferData, len(body))
	if res != types.StatusOK {
		// handle error
	}
	err = proxywasm.SetHttpRequestHeader("content-length", fmt.Sprintf("%d", len(body)))
	if err != nil {
		// handle error
	}

Envoy filter description:

Name:         wasm-myfilter
Namespace:    mycluster
Labels:       app.kubernetes.io/managed-by=Helm
Annotations:  meta.helm.sh/release-name: mycluster-cluster-config
              meta.helm.sh/release-namespace: mycluster
API Version:  networking.istio.io/v1alpha3
Kind:         EnvoyFilter
Metadata:
  Creation Timestamp:  2020-10-09T07:59:52Z
  Generation:          1
  Managed Fields:
    API Version:  networking.istio.io/v1alpha3
    Fields Type:  FieldsV1
    fieldsV1:
      f:metadata:
        f:annotations:
          .:
          f:meta.helm.sh/release-name:
          f:meta.helm.sh/release-namespace:
        f:labels:
          .:
          f:app.kubernetes.io/managed-by:
      f:spec:
        .:
        f:configPatches:
        f:workloadSelector:
          .:
          f:labels:
            .:
            f:wasm_filter_myfilter:
    Manager:         Go-http-client
    Operation:       Update
    Time:            2020-10-09T07:59:52Z
  Resource Version:  2806
  Self Link:         /apis/networking.istio.io/v1alpha3/namespaces/mycluster/envoyfilters/wasm-myfilter
  UID:               fb324c3b-80aa-476a-9ab6-ecb2a5bbdf55
Spec:
  Config Patches:
    Apply To:  HTTP_FILTER
    Match:
      Context:  SIDECAR_INBOUND
      Listener:
        Filter Chain:
          Filter:
            Name:  envoy.http_connection_manager
            Sub Filter:
              Name:   autopseudo_filter
        Port Number:  80
      Proxy:
        Proxy Version:  ^1\.7.*
    Patch:
      Operation:  INSERT_BEFORE
      Value:
        Name:  myfilter_filter
        typed_config:
          @type:     type.googleapis.com/udpa.type.v1.TypedStruct
          type_url:  type.googleapis.com/envoy.extensions.filters.http.wasm.v3.Wasm
          Value:
            Config:
              Configuration:
                @type:  type.googleapis.com/google.protobuf.StringValue
                Value:  /gql
              root_id:  myfilter_root_id
              vm_config:
                Code:
                  Local:
                    Filename:  /var/local/lib/wasm-filters/myfilter/filter.wasm
                Runtime:       envoy.wasm.runtime.v8
                vm_id:         myfilter_filter
  Workload Selector:
    Labels:
      wasm_filter_myfilter:  enabled
Events:                       <none>

[mathetake]

@wimspaargaren thanks for this and looks fine!

Could you please add the high level apis in proxywasm package using this raw hostcall like these? https://github.com/tetratelabs/proxy-wasm-go-sdk/blob/main/proxywasm/hostcall.go#L145-L160

[mathetake]

Almost fine, but one thing left I would like to have is e2e test like this: https://github.com/tetratelabs/proxy-wasm-go-sdk/blob/main/e2e/e2e_test.go#L96-L119

[mathetake]

should we assert string(r.Body) == "{ "another": "body" }"?

[wimspaargaren]

well I wasn't sure on how to verify that. What we're doing is replacing the request body and the result is the response body from the staticreply filter. So the r.Body contains example body

[mathetake]

ah, you are right. It seems fine as it is now 👍

[mathetake]

Thanks:)

[wimspaargaren]

No problem, saves quite some time :)

[mathetake]

Thanks @wimspaargaren for your contribution 🎖️ 💯