Update Gradle cache with the configurable plugin support (#114)

* feat(gradle): add request metrics for build cache handler

* Implement fallback handling for Gradle plugin requests and update tests

* refactor(gradle): simplify response handling and remove unused metrics assertions

* Add tests for Gradle plugin metadata fallback and refactor metadata handling

---------

Co-authored-by: Mateusz (Mati) Kepa <m.kepa@sportradar.com>

Author: matikepa

README.md

@@ -210,6 +210,18 @@ Add to your `~/.m2/settings.xml`:
 </settings>
 ```
 
+The `/maven/` endpoint uses Maven Central as primary upstream and falls back to the Gradle Plugin Portal for Gradle plugin marker metadata and related artifacts when the primary upstream returns not found.
+
+For Gradle plugin resolution via the same proxy endpoint:
+
+```kotlin
+pluginManagement {
+  repositories {
+    maven(url = "http://localhost:8080/maven/")
+  }
+}
+```
+
 ### Gradle HTTP Build Cache
 
 Configure in `settings.gradle(.kts)`:
@@ -386,6 +398,7 @@ sudo dnf update
 ## Configuration
 
 The proxy can be configured via:
+
 1. Command line flags (highest priority)
 2. Environment variables
 3. Configuration file (YAML or JSON)
@@ -977,6 +990,7 @@ The proxy will recreate the database on next start.
 ## Building from Source
 
 Requirements:
+
 - Go 1.25 or later
 
 ```bash

cmd/proxy/main.go

@@ -72,6 +72,8 @@
 //	PROXY_DATABASE_URL     - PostgreSQL connection URL
 //	PROXY_LOG_LEVEL        - Log level
 //	PROXY_LOG_FORMAT       - Log format
+//	PROXY_UPSTREAM_MAVEN   - Maven repository upstream URL
+//	PROXY_UPSTREAM_GRADLE_PLUGIN_PORTAL - Gradle Plugin Portal upstream URL
 //	PROXY_GRADLE_BUILD_CACHE_READ_ONLY       - Disable Gradle PUT uploads
 //	PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE - Max Gradle PUT request body size
 //	PROXY_GRADLE_BUILD_CACHE_MAX_AGE         - Gradle cache max age eviction
@@ -199,6 +201,8 @@ func runServe() {
 		fmt.Fprintf(os.Stderr, "  PROXY_DATABASE_URL     PostgreSQL connection URL\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_LOG_LEVEL        Log level\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_LOG_FORMAT       Log format\n")
+		fmt.Fprintf(os.Stderr, "  PROXY_UPSTREAM_MAVEN   Maven repository upstream URL\n")
+		fmt.Fprintf(os.Stderr, "  PROXY_UPSTREAM_GRADLE_PLUGIN_PORTAL Gradle Plugin Portal upstream URL\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_READ_ONLY       Disable Gradle PUT uploads\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE Max Gradle PUT request body size\n")
 		fmt.Fprintf(os.Stderr, "  PROXY_GRADLE_BUILD_CACHE_MAX_AGE         Gradle cache max age eviction\n")

config.example.yaml

@@ -71,6 +71,12 @@ upstream:
   # npm registry URL
   npm: "https://registry.npmjs.org"
 
+  # Maven repository URL (used by /maven endpoint)
+  maven: "https://repo1.maven.org/maven2"
+
+  # Gradle Plugin Portal Maven URL (fallback for plugin marker artifacts)
+  gradle_plugin_portal: "https://plugins.gradle.org/m2"
+
   # Cargo sparse index URL
   cargo: "https://index.crates.io"
 

docs/configuration.md

@@ -114,6 +114,8 @@ Override default upstream registry URLs:
 ```yaml
 upstream:
   npm: "https://registry.npmjs.org"
+  maven: "https://repo1.maven.org/maven2"
+  gradle_plugin_portal: "https://plugins.gradle.org/m2"
   cargo: "https://index.crates.io"
   cargo_download: "https://static.crates.io/crates"
 ```

internal/config/config.go

@@ -221,6 +221,15 @@ type UpstreamConfig struct {
 	// Default: https://registry.npmjs.org
 	NPM string `json:"npm" yaml:"npm"`
 
+	// Maven is the upstream Maven repository URL.
+	// Default: https://repo1.maven.org/maven2
+	Maven string `json:"maven" yaml:"maven"`
+
+	// GradlePluginPortal is the upstream Gradle Plugin Portal Maven URL.
+	// Used to resolve Gradle plugin marker artifacts.
+	// Default: https://plugins.gradle.org/m2
+	GradlePluginPortal string `json:"gradle_plugin_portal" yaml:"gradle_plugin_portal"`
+
 	// Cargo is the upstream cargo index URL.
 	// Default: https://index.crates.io
 	Cargo string `json:"cargo" yaml:"cargo"`
@@ -298,9 +307,11 @@ func Default() *Config {
 			Format: "text",
 		},
 		Upstream: UpstreamConfig{
-			NPM:           "https://registry.npmjs.org",
-			Cargo:         "https://index.crates.io",
-			CargoDownload: "https://static.crates.io/crates",
+			NPM:                "https://registry.npmjs.org",
+			Maven:              "https://repo1.maven.org/maven2",
+			GradlePluginPortal: "https://plugins.gradle.org/m2",
+			Cargo:              "https://index.crates.io",
+			CargoDownload:      "https://static.crates.io/crates",
 		},
 		Gradle: GradleConfig{
 			BuildCache: GradleBuildCacheConfig{
@@ -395,6 +406,12 @@ func (c *Config) LoadFromEnv() {
 	if v := os.Getenv("PROXY_LOG_FORMAT"); v != "" {
 		c.Log.Format = v
 	}
+	if v := os.Getenv("PROXY_UPSTREAM_MAVEN"); v != "" {
+		c.Upstream.Maven = v
+	}
+	if v := os.Getenv("PROXY_UPSTREAM_GRADLE_PLUGIN_PORTAL"); v != "" {
+		c.Upstream.GradlePluginPortal = v
+	}
 	if v := os.Getenv("PROXY_COOLDOWN_DEFAULT"); v != "" {
 		c.Cooldown.Default = v
 	}

internal/config/config_test.go

@@ -31,6 +31,12 @@ func TestDefault(t *testing.T) {
 	if cfg.Gradle.BuildCache.MaxAge != "168h" {
 		t.Errorf("Gradle.BuildCache.MaxAge = %q, want %q", cfg.Gradle.BuildCache.MaxAge, "168h")
 	}
+	if cfg.Upstream.Maven != "https://repo1.maven.org/maven2" {
+		t.Errorf("Upstream.Maven = %q, want %q", cfg.Upstream.Maven, "https://repo1.maven.org/maven2")
+	}
+	if cfg.Upstream.GradlePluginPortal != "https://plugins.gradle.org/m2" {
+		t.Errorf("Upstream.GradlePluginPortal = %q, want %q", cfg.Upstream.GradlePluginPortal, "https://plugins.gradle.org/m2")
+	}
 }
 
 func TestValidate(t *testing.T) {
@@ -264,6 +270,8 @@ func TestLoadFromEnv(t *testing.T) {
 	t.Setenv("PROXY_BASE_URL", "https://env.example.com")
 	t.Setenv("PROXY_STORAGE_PATH", "/env/cache")
 	t.Setenv("PROXY_LOG_LEVEL", testLevelDebug)
+	t.Setenv("PROXY_UPSTREAM_MAVEN", "https://maven.example.com/repository/maven-public")
+	t.Setenv("PROXY_UPSTREAM_GRADLE_PLUGIN_PORTAL", "https://plugins.example.com/m2")
 	t.Setenv("PROXY_GRADLE_BUILD_CACHE_READ_ONLY", "true")
 	t.Setenv("PROXY_GRADLE_BUILD_CACHE_MAX_UPLOAD_SIZE", "32MB")
 	t.Setenv("PROXY_GRADLE_BUILD_CACHE_MAX_AGE", "12h")
@@ -284,6 +292,12 @@ func TestLoadFromEnv(t *testing.T) {
 	if cfg.Log.Level != testLevelDebug {
 		t.Errorf("Log.Level = %q, want %q", cfg.Log.Level, testLevelDebug)
 	}
+	if cfg.Upstream.Maven != "https://maven.example.com/repository/maven-public" {
+		t.Errorf("Upstream.Maven = %q, want %q", cfg.Upstream.Maven, "https://maven.example.com/repository/maven-public")
+	}
+	if cfg.Upstream.GradlePluginPortal != "https://plugins.example.com/m2" {
+		t.Errorf("Upstream.GradlePluginPortal = %q, want %q", cfg.Upstream.GradlePluginPortal, "https://plugins.example.com/m2")
+	}
 	if !cfg.Gradle.BuildCache.ReadOnly {
 		t.Error("Gradle.BuildCache.ReadOnly = false, want true")
 	}