Add wasm plugin contribution introduction (#47)

plugins/wasm-go/extensions/hello-world/go.mod

@@ -0,0 +1,17 @@
+module github.com/alibaba/higress/plugins/wasm-go/extensions/hello-world
+
+go 1.18
+
+replace github.com/alibaba/higress/plugins/wasm-go => ../..
+
+require (
+	github.com/alibaba/higress/plugins/wasm-go v0.0.0
+	github.com/tetratelabs/proxy-wasm-go-sdk v0.19.1-0.20220822060051-f9d179a57f8c
+)
+
+require (
+	github.com/google/uuid v1.3.0 // indirect
+	github.com/tidwall/gjson v1.14.3 // indirect
+	github.com/tidwall/match v1.1.1 // indirect
+	github.com/tidwall/pretty v1.2.0 // indirect
+)

plugins/wasm-go/extensions/hello-world/go.sum

@@ -0,0 +1,14 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/google/uuid v1.3.0 h1:t6JiXgmwXMjEs8VusXIJk2BXHsn+wx8BZdTaoZ5fu7I=
+github.com/google/uuid v1.3.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/stretchr/testify v1.8.0 h1:pSgiaMZlXftHpm5L7V1+rVB+AZJydKsMxsQBIJw4PKk=
+github.com/tetratelabs/proxy-wasm-go-sdk v0.19.1-0.20220822060051-f9d179a57f8c h1:OCUFXVGixHLfNjg6/QYEhv+jHJ5mRGhpEUVFv9eWPJE=
+github.com/tetratelabs/proxy-wasm-go-sdk v0.19.1-0.20220822060051-f9d179a57f8c/go.mod h1:5t/pWFNJ9eMyu/K/Z+OeGhDJ9sN9eCo8fc2pyM/Qjg4=
+github.com/tidwall/gjson v1.14.3 h1:9jvXn7olKEHU1S9vwoMGliaT8jq1vJ7IH/n9zD9Dnlw=
+github.com/tidwall/gjson v1.14.3/go.mod h1:/wbyibRr2FHMks5tjHJ5F8dMZh3AcwJEMf5vlfC0lxk=
+github.com/tidwall/match v1.1.1 h1:+Ho715JplO36QYgwN9PGYNhgZvoUSc9X2c80KVTi+GA=
+github.com/tidwall/match v1.1.1/go.mod h1:eRSPERbgtNPcGhD8UCthc6PmLEQXEWd3PRB5JTxsfmM=
+github.com/tidwall/pretty v1.2.0 h1:RWIZEg2iJ8/g6fDDYzMpobmaoGh5OLl4AXtGUGPcqCs=
+github.com/tidwall/pretty v1.2.0/go.mod h1:ITEVvHYasfjBbM0u2Pg8T2nJnzm8xPwvNhhsoaGGjNU=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

plugins/wasm-go/extensions/hello-world/main.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2022 Alibaba Group Holding Ltd.
+//
+// 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"
+
+	"github.com/alibaba/higress/plugins/wasm-go/pkg/wrapper"
+)
+
+func main() {
+	wrapper.SetCtx(
+		"hello-world",
+		wrapper.ProcessRequestHeadersBy(onHttpRequestHeaders),
+	)
+}
+
+type HelloWorldConfig struct {
+}
+
+func onHttpRequestHeaders(ctx *wrapper.CommonHttpCtx[HelloWorldConfig], config HelloWorldConfig, needBody *bool, log wrapper.LogWrapper) types.Action {
+	err := proxywasm.AddHttpRequestHeader("hello", "world")
+	if err != nil {
+		log.Critical("failed to set request header")
+	}
+	proxywasm.SendHttpResponse(200, nil, []byte("hello world"), -1)
+	return types.ActionContinue
+}