diff --git a/plugins/samples/ad_insertion/BUILD b/plugins/samples/ad_insertion/BUILD
index 4a2accaf..1daacb3c 100644
--- a/plugins/samples/ad_insertion/BUILD
+++ b/plugins/samples/ad_insertion/BUILD
@@ -2,6 +2,11 @@ load("//:plugins.bzl", "proxy_wasm_plugin_cpp", "proxy_wasm_plugin_rust", "proxy
licenses(["notice"]) # Apache 2
+proxy_wasm_plugin_go(
+ name = "plugin_go.wasm",
+ srcs = ["plugin.go"],
+)
+
proxy_wasm_plugin_rust(
name = "plugin_rust.wasm",
srcs = ["plugin.rs"],
@@ -22,6 +27,7 @@ proxy_wasm_tests(
name = "tests",
config = ":tests.config",
plugins = [
+ ":plugin_go.wasm",
":plugin_rust.wasm",
":plugin_cpp.wasm",
],
diff --git a/plugins/samples/ad_insertion/plugin.go b/plugins/samples/ad_insertion/plugin.go
new file mode 100644
index 00000000..2858ff04
--- /dev/null
+++ b/plugins/samples/ad_insertion/plugin.go
@@ -0,0 +1,280 @@
+// Copyright 2025 Google LLC
+//
+// 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.
+
+// [START serviceextensions_plugin_ad_insertion]
+package main
+
+import (
+ "fmt"
+ "sort"
+ "strings"
+
+ "github.com/proxy-wasm/proxy-wasm-go-sdk/proxywasm"
+ "github.com/proxy-wasm/proxy-wasm-go-sdk/proxywasm/types"
+)
+
+func main() {}
+
+func init() {
+ proxywasm.SetVMContext(&vmContext{})
+}
+
+type vmContext struct {
+ types.DefaultVMContext
+}
+
+type pluginContext struct {
+ types.DefaultPluginContext
+ adConfigs map[string]adConfig
+ gptLibraryURL string
+ injectGptLibrary bool
+}
+
+type httpContext struct {
+ types.DefaultHttpContext
+ pluginContext *pluginContext
+ shouldInsertAds bool
+ isAdRequest bool
+}
+
+type adConfig struct {
+ Slot string // GAM ad slot path (e.g., "/1234/header_ad")
+ Size string // Ad dimensions (e.g., "728x90")
+ Marker string // HTML tag to insert ads relative to
+ InsertBefore bool // Insert before (true) or after (false) the marker
+}
+
+type insertion struct {
+ pos int
+ content string
+}
+
+func (*vmContext) NewPluginContext(contextID uint32) types.PluginContext {
+ return &pluginContext{}
+}
+
+func (ctx *pluginContext) OnPluginStart(pluginConfigurationSize int) types.OnPluginStartStatus {
+ // Set default configurations for fallback and testing purposes.
+ ctx.gptLibraryURL = "https://securepubads.g.doubleclick.net/tag/js/gpt.js"
+ ctx.injectGptLibrary = true
+ ctx.adConfigs = map[string]adConfig{
+ "header": {
+ Slot: "/1234/header_ad",
+ Size: "728x90",
+ Marker: "",
+ InsertBefore: false,
+ },
+ "content": {
+ Slot: "/1234/content_ad",
+ Size: "300x250",
+ Marker: "",
+ InsertBefore: false,
+ },
+ "sidebar": {
+ Slot: "/1234/sidebar_ad",
+ Size: "160x600",
+ Marker: "",
+ InsertBefore: true,
+ },
+ }
+
+ if pluginConfigurationSize == 0 {
+ proxywasm.LogInfo("No configuration provided. Using default ad insertion config.")
+ return types.OnPluginStartStatusOK
+ }
+
+ config, err := proxywasm.GetPluginConfiguration()
+ if err != nil || len(config) == 0 {
+ return types.OnPluginStartStatusOK
+ }
+
+ // Clear default ad configs since we are loading custom ones
+ ctx.adConfigs = make(map[string]adConfig)
+
+ // Parse the CSV-like configuration format
+ for _, line := range strings.Split(string(config), "\n") {
+ line = strings.TrimSpace(line)
+ if len(line) == 0 || strings.HasPrefix(line, "#") {
+ continue // Skip empty lines and comments
+ }
+
+ parts := strings.Split(line, ",")
+ for i := range parts {
+ parts[i] = strings.TrimSpace(parts[i])
+ }
+
+ if parts[0] == "gpt_url" && len(parts) >= 2 {
+ ctx.gptLibraryURL = parts[1]
+ } else if parts[0] == "inject_gpt" && len(parts) >= 2 {
+ ctx.injectGptLibrary = parts[1] == "true"
+ } else if parts[0] == "ad" && len(parts) >= 6 {
+ position := parts[1]
+ ctx.adConfigs[position] = adConfig{
+ Slot: parts[2],
+ Size: parts[3],
+ InsertBefore: parts[4] == "true",
+ Marker: parts[5],
+ }
+ } else {
+ proxywasm.LogWarnf("Invalid configuration line: %s", line)
+ }
+ }
+
+ proxywasm.LogInfo("Ad Insertion plugin configured successfully from custom payload.")
+ return types.OnPluginStartStatusOK
+}
+
+func (ctx *pluginContext) NewHttpContext(contextID uint32) types.HttpContext {
+ return &httpContext{pluginContext: ctx}
+}
+
+func (ctx *httpContext) OnHttpRequestHeaders(numHeaders int, endOfStream bool) types.Action {
+ // Skip ad insertion for ad requests to avoid infinite loops
+ path, err := proxywasm.GetHttpRequestHeader(":path")
+ if err == nil && strings.Contains(path, "/ads/") {
+ ctx.isAdRequest = true
+ }
+ return types.ActionContinue
+}
+
+func (ctx *httpContext) OnHttpResponseHeaders(numHeaders int, endOfStream bool) types.Action {
+ // Check if response is HTML and should process for ad insertion
+ contentType, err := proxywasm.GetHttpResponseHeader("Content-Type")
+ if err == nil && strings.Contains(contentType, "text/html") {
+ ctx.shouldInsertAds = true
+ // Remove Content-Length header since we'll modify the body
+ proxywasm.RemoveHttpResponseHeader("Content-Length")
+ }
+ return types.ActionContinue
+}
+
+func (ctx *httpContext) OnHttpResponseBody(bodySize int, endOfStream bool) types.Action {
+ if !ctx.shouldInsertAds || ctx.isAdRequest {
+ return types.ActionContinue
+ }
+
+ // Process HTML body and inject GAM ads
+ body, err := proxywasm.GetHttpResponseBody(0, bodySize)
+ if err != nil {
+ return types.ActionContinue
+ }
+
+ bodyStr := string(body)
+ modifiedBody := ctx.processBodyWithGAM(bodyStr)
+
+ proxywasm.ReplaceHttpResponseBody([]byte(modifiedBody))
+ return types.ActionContinue
+}
+
+func (ctx *httpContext) isGptAlreadyLoaded(body string) bool {
+ return strings.Contains(body, "googletag") ||
+ strings.Contains(body, "gpt.js") ||
+ strings.Contains(body, "doubleclick.net/tag/js/gpt")
+}
+
+func (ctx *httpContext) processBodyWithGAM(body string) string {
+ // Slice to store all insertions: (position, content)
+ insertions := []insertion{}
+
+ // 1. Prepare GPT library injection if needed and not already present
+ if ctx.pluginContext.injectGptLibrary && !ctx.isGptAlreadyLoaded(body) {
+ ctx.prepareGptLibraryInjection(body, &insertions)
+ }
+
+ // 2. Prepare all ad insertions in single pass
+ for position, config := range ctx.pluginContext.adConfigs {
+ ctx.prepareAdInsertion(body, position, config, &insertions)
+ }
+
+ // 3. Apply all insertions in reverse order (to maintain correct indices)
+ if len(insertions) > 0 {
+ return ctx.applyAllInsertions(body, insertions)
+ }
+
+ return body
+}
+
+func (ctx *httpContext) prepareGptLibraryInjection(body string, insertions *[]insertion) {
+ if headPos := strings.Index(body, ""); headPos != -1 {
+ gptScript := fmt.Sprintf("\n ", ctx.pluginContext.gptLibraryURL)
+ *insertions = append(*insertions, insertion{pos: headPos + 6, content: gptScript})
+ return
+ }
+
+ if bodyPos := strings.Index(body, ""); bodyPos != -1 {
+ gptScript := fmt.Sprintf("\n", ctx.pluginContext.gptLibraryURL)
+ *insertions = append(*insertions, insertion{pos: bodyPos, content: gptScript})
+ }
+}
+
+func (ctx *httpContext) prepareAdInsertion(body string, position string, config adConfig, insertions *[]insertion) {
+ markerPos := strings.Index(body, config.Marker)
+ if markerPos == -1 {
+ return
+ }
+
+ insertPos := markerPos
+ if !config.InsertBefore {
+ insertPos += len(config.Marker)
+ }
+
+ adHTML := ctx.generateGAMAdHTML(position, config)
+ *insertions = append(*insertions, insertion{pos: insertPos, content: adHTML})
+}
+
+func (ctx *httpContext) applyAllInsertions(body string, insertions []insertion) string {
+ // Sort insertions by position in DESCENDING order
+ // This ensures that later insertions don't affect positions of earlier ones
+ sort.Slice(insertions, func(i, j int) bool {
+ return insertions[i].pos > insertions[j].pos
+ })
+
+ // Apply all insertions
+ result := body
+ for _, ins := range insertions {
+ result = result[:ins.pos] + ins.content + result[ins.pos:]
+ }
+
+ return result
+}
+
+func (ctx *httpContext) generateGAMAdHTML(position string, config adConfig) string {
+ // GAM Ad HTML Template
+ return fmt.Sprintf(``, position, config.Slot, config.Slot, config.Size, position, position, position)
+}
+
+// [END serviceextensions_plugin_ad_insertion]