feat: Add HTTPClient option to PluginConfig for custom HTTP client support

extism.go

@@ -125,6 +125,7 @@ type Plugin struct {
 	MaxHttpResponseBytes int64
 	MaxVarBytes          int64
 	log                  func(LogLevel, string)
+	httpClient           *http.Client
 	hasWasi              bool
 	guestRuntime         guestRuntime
 	Adapter              *observe.AdapterBase

extism_test.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"log"
+	"net/http"
 	"os"
 	"strings"
 	"sync"
@@ -1508,3 +1509,40 @@ func uintToLEBytes(num uint) []byte {
 func uintFromLEBytes(bytes []byte) uint {
 	return uint(bytes[0]) | uint(bytes[1])<<8 | uint(bytes[2])<<16 | uint(bytes[3])<<24
 }
+
+func TestHTTP_customClient(t *testing.T) {
+	manifest := manifest("http.wasm")
+	manifest.AllowedHosts = []string{"jsonplaceholder.*.com"}
+
+	// Track whether our custom transport was used.
+	var transportUsed bool
+	customClient := &http.Client{
+		Transport: roundTripFunc(func(req *http.Request) (*http.Response, error) {
+			transportUsed = true
+			return http.DefaultTransport.RoundTrip(req)
+		}),
+	}
+
+	ctx := context.Background()
+	plugin, err := NewCompiledPlugin(ctx, manifest, PluginConfig{
+		EnableWasi: true,
+		HTTPClient: customClient,
+	}, nil)
+	require.NoError(t, err)
+
+	instance, err := plugin.Instance(ctx, wasiPluginConfig())
+	require.NoError(t, err)
+	defer instance.Close(context.Background())
+
+	exit, _, err := instance.Call("run_test", []byte{})
+	require.NoError(t, err)
+	assert.Equal(t, uint32(0), exit)
+	assert.True(t, transportUsed, "custom HTTP client transport should have been used")
+}
+
+// roundTripFunc allows using a function as an http.RoundTripper.
+type roundTripFunc func(*http.Request) (*http.Response, error)
+
+func (f roundTripFunc) RoundTrip(req *http.Request) (*http.Response, error) {
+	return f(req)
+}

host.go

@@ -569,7 +569,7 @@ func httpRequest(ctx context.Context, m api.Module, requestOffset uint64, bodyOf
 			req.Header.Set(key, value)
 		}
 
-		client := http.DefaultClient
+		client := plugin.httpClient
 		resp, err := client.Do(req)
 		if err != nil {
 			panic(err)

plugin.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net/http"
 	"os"
 	"strings"
 	"sync/atomic"
@@ -40,6 +41,7 @@ type CompiledPlugin struct {
 	maxHttp                   int64
 	maxVar                    int64
 	enableHttpResponseHeaders bool
+	httpClient                *http.Client
 }
 
 type PluginConfig struct {
@@ -49,6 +51,10 @@ type PluginConfig struct {
 	ObserveOptions            *observe.Options
 	EnableHttpResponseHeaders bool
 
+	// HTTPClient overrides the default HTTP client used for plugin HTTP requests.
+	// If nil, http.DefaultClient is used.
+	HTTPClient *http.Client
+
 	// ModuleConfig is only used when a plugins are built using the NewPlugin
 	// function. In this function, the plugin is both compiled, and an instance
 	// of the plugin is instantiated, and the ModuleConfig is passed to the
@@ -136,6 +142,11 @@ func NewCompiledPlugin(
 		}
 	}
 
+	httpClient := config.HTTPClient
+	if httpClient == nil {
+		httpClient = http.DefaultClient
+	}
+
 	p := CompiledPlugin{
 		manifest:                  manifest,
 		runtime:                   wazero.NewRuntimeWithConfig(ctx, runtimeConfig),
@@ -145,6 +156,7 @@ func NewCompiledPlugin(
 		modules:                   make(map[string]wazero.CompiledModule),
 		maxHttp:                   calculateMaxHttp(manifest),
 		maxVar:                    calculateMaxVar(manifest),
+		httpClient:                httpClient,
 	}
 
 	if config.EnableWasi {
@@ -399,6 +411,7 @@ func (p *CompiledPlugin) Instance(ctx context.Context, config PluginInstanceConf
 		close:                closers,
 		extism:               extism,
 		hasWasi:              p.hasWasi,
+		httpClient:           p.httpClient,
 		mainModule:           main,
 		modules:              instancedModules,
 		Timeout:              time.Duration(p.manifest.Timeout) * time.Millisecond,