Added metrics support with an example and corresponding tests.

src/main/java/io/roastedroot/proxywasm/impl/Imports.java

@@ -10,6 +10,7 @@
 import io.roastedroot.proxywasm.v1.Handler;
 import io.roastedroot.proxywasm.v1.LogLevel;
 import io.roastedroot.proxywasm.v1.MapType;
+import io.roastedroot.proxywasm.v1.MetricType;
 import io.roastedroot.proxywasm.v1.StreamType;
 import io.roastedroot.proxywasm.v1.WasmException;
 import io.roastedroot.proxywasm.v1.WasmResult;
@@ -889,4 +890,50 @@ int proxyCallForeignFunction(
             return e.result().getValue();
         }
     }
+
+    @WasmExport
+    int proxyDefineMetric(int metricType, int nameDataPtr, int nameSize, int returnMetricId) {
+        try {
+            MetricType type = MetricType.fromInt(metricType);
+            if (type == null) {
+                return WasmResult.BAD_ARGUMENT.getValue();
+            }
+
+            var name = string(readMemory(nameDataPtr, nameSize));
+            int metricId = handler.defineMetric(type, name);
+            putUint32(returnMetricId, metricId);
+            return WasmResult.OK.getValue();
+        } catch (WasmException e) {
+            return e.result().getValue();
+        }
+    }
+
+    @WasmExport
+    int proxyRecordMetric(int metricId, long value) {
+        WasmResult result = handler.recordMetric(metricId, value);
+        return result.getValue();
+    }
+
+    @WasmExport
+    int proxyRemoveMetric(int metricId) {
+        WasmResult result = handler.removeMetric(metricId);
+        return result.getValue();
+    }
+
+    @WasmExport
+    int proxyIncrementMetric(int metricId, long value) {
+        WasmResult result = handler.incrementMetric(metricId, value);
+        return result.getValue();
+    }
+
+    @WasmExport
+    int proxyGetMetric(int metricId, int returnValuePtr) {
+        try {
+            var result = handler.getMetric(metricId);
+            putUint32(returnValuePtr, (int) result);
+            return WasmResult.OK.getValue();
+        } catch (WasmException e) {
+            return e.result().getValue();
+        }
+    }
 }

src/main/java/io/roastedroot/proxywasm/v1/ChainedHandler.java

@@ -281,4 +281,29 @@ public int dispatchHttpCall(
     public byte[] callForeignFunction(String name, byte[] bytes) throws WasmException {
         return next().callForeignFunction(name, bytes);
     }
+
+    @Override
+    public int defineMetric(MetricType metricType, String name) throws WasmException {
+        return next().defineMetric(metricType, name);
+    }
+
+    @Override
+    public WasmResult removeMetric(int metricId) {
+        return next().removeMetric(metricId);
+    }
+
+    @Override
+    public WasmResult recordMetric(int metricId, long value) {
+        return next().recordMetric(metricId, value);
+    }
+
+    @Override
+    public WasmResult incrementMetric(int metricId, long value) {
+        return next().incrementMetric(metricId, value);
+    }
+
+    @Override
+    public long getMetric(int metricId) throws WasmException {
+        return next().getMetric(metricId);
+    }
 }

src/main/java/io/roastedroot/proxywasm/v1/Handler.java

@@ -410,4 +410,24 @@ default int dispatchHttpCall(
     default byte[] callForeignFunction(String name, byte[] bytes) throws WasmException {
         throw new WasmException(WasmResult.NOT_FOUND);
     }
+
+    default int defineMetric(MetricType metricType, String name) throws WasmException {
+        throw new WasmException(WasmResult.UNIMPLEMENTED);
+    }
+
+    default WasmResult removeMetric(int metricId) {
+        return WasmResult.UNIMPLEMENTED;
+    }
+
+    default WasmResult recordMetric(int metricId, long value) {
+        return WasmResult.UNIMPLEMENTED;
+    }
+
+    default WasmResult incrementMetric(int metricId, long value) {
+        return WasmResult.UNIMPLEMENTED;
+    }
+
+    default long getMetric(int metricId) throws WasmException {
+        throw new WasmException(WasmResult.UNIMPLEMENTED);
+    }
 }

src/main/java/io/roastedroot/proxywasm/v1/MetricType.java

@@ -0,0 +1,45 @@
+package io.roastedroot.proxywasm.v1;
+
+/**
+ * Represents the type of metric in proxy WASM.
+ */
+public enum MetricType {
+    COUNTER(0),
+    GAUGE(1),
+    HISTOGRAM(2);
+
+    private final int value;
+
+    /**
+     * Constructor for MetricType enum.
+     *
+     * @param value The integer value of the metric type
+     */
+    MetricType(int value) {
+        this.value = value;
+    }
+
+    /**
+     * Get the integer value of this metric type.
+     *
+     * @return The integer value
+     */
+    public int getValue() {
+        return value;
+    }
+
+    /**
+     * Convert an integer value to a MetricType.
+     *
+     * @param value The integer value to convert
+     * @return The corresponding MetricType or null if the value doesn't match any MetricType
+     */
+    public static MetricType fromInt(int value) {
+        for (MetricType type : values()) {
+            if (type.value == value) {
+                return type;
+            }
+        }
+        return null;
+    }
+}

src/test/go-examples/metrics/README.md

@@ -0,0 +1,5 @@
+## Attribution
+
+This example originally came from:
+https://github.com/proxy-wasm/proxy-wasm-go-sdk/blob/ab4161dcf9246a828008b539a82a1556cf0f2e24/examples/metrics
+```

src/test/go-examples/metrics/go.mod

@@ -0,0 +1,5 @@
+module github.com/proxy-wasm/proxy-wasm-go-sdk/examples/metrics
+
+go 1.24
+
+require github.com/proxy-wasm/proxy-wasm-go-sdk v0.0.0-20250212164326-ab4161dcf924

src/test/go-examples/metrics/go.sum

@@ -0,0 +1,10 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/proxy-wasm/proxy-wasm-go-sdk v0.0.0-20250212164326-ab4161dcf924 h1:wTcK6gcyTKJMeDka69AMjZYvisdI8CBXzTEfZ+2pOxI=
+github.com/proxy-wasm/proxy-wasm-go-sdk v0.0.0-20250212164326-ab4161dcf924/go.mod h1:9mBRvh8I6Td6sg3CwEY+zGFE4DKaIoieCaca1kQnDBE=
+github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
+github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

src/test/go-examples/metrics/main.go

@@ -0,0 +1,85 @@
+// Copyright 2020-2024 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 (
+	"fmt"
+
+	"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{})
+}
+
+// vmContext implements types.VMContext.
+type vmContext struct {
+	// Embed the default VM context here,
+	// so that we don't need to reimplement all the methods.
+	types.DefaultVMContext
+}
+
+// NewPluginContext implements types.VMContext.
+func (*vmContext) NewPluginContext(contextID uint32) types.PluginContext {
+	return &metricPluginContext{}
+}
+
+// metricPluginContext implements types.PluginContext.
+type metricPluginContext struct {
+	// Embed the default plugin context here,
+	// so that we don't need to reimplement all the methods.
+	types.DefaultPluginContext
+}
+
+// NewHttpContext implements types.PluginContext.
+func (ctx *metricPluginContext) NewHttpContext(contextID uint32) types.HttpContext {
+	return &metricHttpContext{}
+}
+
+// metricHttpContext implements types.HttpContext.
+type metricHttpContext struct {
+	// Embed the default http context here,
+	// so that we don't need to reimplement all the methods.
+	types.DefaultHttpContext
+}
+
+const (
+	customHeaderKey         = "my-custom-header"
+	customHeaderValueTagKey = "value"
+)
+
+// counters is a map from custom header value to a counter metric.
+// Note that Proxy-Wasm plugins are single threaded, so no need to use a lock.
+var counters = map[string]proxywasm.MetricCounter{}
+
+// OnHttpRequestHeaders implements types.HttpContext.
+func (ctx *metricHttpContext) OnHttpRequestHeaders(numHeaders int, endOfStream bool) types.Action {
+	customHeaderValue, err := proxywasm.GetHttpRequestHeader(customHeaderKey)
+	if err == nil {
+		counter, ok := counters[customHeaderValue]
+		if !ok {
+			// This metric is processed as: custom_header_value_counts{value="foo",reporter="wasmgosdk"} n.
+			// The extraction rule is defined in envoy.yaml as a bootstrap configuration.
+			// See https://www.envoyproxy.io/docs/envoy/latest/api-v3/config/metrics/v3/stats.proto#config-metrics-v3-statsconfig.
+			fqn := fmt.Sprintf("custom_header_value_counts_%s=%s_reporter=wasmgosdk", customHeaderValueTagKey, customHeaderValue)
+			counter = proxywasm.DefineCounterMetric(fqn)
+			counters[customHeaderValue] = counter
+		}
+		counter.Increment(1)
+	}
+	return types.ActionContinue
+}

src/test/java/io/roastedroot/proxywasm/MetricsTest.java

@@ -0,0 +1,49 @@
+package io.roastedroot.proxywasm;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+import com.dylibso.chicory.wasm.Parser;
+import io.roastedroot.proxywasm.v1.Action;
+import io.roastedroot.proxywasm.v1.MetricType;
+import io.roastedroot.proxywasm.v1.ProxyWasm;
+import io.roastedroot.proxywasm.v1.StartException;
+import java.nio.file.Path;
+import java.util.Map;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Java port of https://github.com/proxy-wasm/proxy-wasm-go-sdk/blob/ab4161dcf9246a828008b539a82a1556cf0f2e24/examples/metrics/main_test.go
+ */
+public class MetricsTest {
+
+    @Test
+    public void testMetric() throws StartException {
+        var handler = new MockHandler();
+        var module = Parser.parse(Path.of("./src/test/go-examples/metrics/main.wasm"));
+        ProxyWasm.Builder builder = ProxyWasm.builder().withPluginHandler(handler);
+
+        try (var host = builder.build(module)) {
+            try (var context = host.createHttpContext(handler)) {
+                // Create headers with custom header
+                Map<String, String> headers = Map.of("my-custom-header", "foo");
+
+                // Call OnRequestHeaders multiple times
+                long expectedCount = 3;
+                for (int i = 0; i < expectedCount; i++) {
+                    handler.setHttpRequestHeaders(headers);
+                    Action action = context.callOnRequestHeaders(false);
+                    assertEquals(Action.CONTINUE, action);
+                }
+
+                // Check metrics
+                var metric =
+                        handler.getMetric(
+                                "custom_header_value_counts_value=foo_reporter=wasmgosdk");
+                assertNotNull(metric);
+                assertEquals(MetricType.COUNTER, metric.type);
+                assertEquals(expectedCount, metric.value);
+            }
+        }
+    }
+}