Control automatic port forwarding with a devcontainer.json file

build.gradle.kts

@@ -11,6 +11,7 @@ plugins {
     alias(libs.plugins.changelog) // Gradle Changelog Plugin
     alias(libs.plugins.qodana) // Gradle Qodana Plugin
     alias(libs.plugins.kover) // Gradle Kover Plugin
+    kotlin("plugin.serialization") version "2.1.10"
 }
 
 group = properties("pluginGroup").get()
@@ -24,6 +25,12 @@ repositories {
 // Dependencies are managed with Gradle version catalog - read more: https://docs.gradle.org/current/userguide/platforms.html#sub:version-catalog
 dependencies {
 //    implementation(libs.annotations)
+    // We need kotlinx-serialization-json >= 1.7.0 to support allowComments, as
+    // devcontainer.json files often have comments and therefore use
+    // nonstandard JSON syntax. This dependency should be marked compileOnly
+    // once the minimum IDE version we support (pluginSinceBuild in
+    // gradle.properties) is at least 251, which includes version 1.7.2.
+    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.8.0")
 }
 
 // Set the JVM language level used to build the project.

src/main/kotlin/com/coder/jetbrains/matcher/PortMatcher.kt

@@ -0,0 +1,58 @@
+package com.coder.jetbrains.matcher
+
+class PortMatcher(private val rule: String) {
+    private sealed class MatchRule {
+        data class SinglePort(val port: Int) : MatchRule()
+        data class PortRange(val start: Int, val end: Int) : MatchRule()
+        data class RegexPort(val pattern: Regex) : MatchRule()
+    }
+
+    private val parsedRule: MatchRule = parseRule(rule)
+
+    fun matches(port: Int): Boolean {
+        return when (parsedRule) {
+            is MatchRule.SinglePort -> port == parsedRule.port
+            is MatchRule.PortRange -> port in parsedRule.start..parsedRule.end
+            is MatchRule.RegexPort -> parsedRule.pattern.matches(port.toString())
+        }
+    }
+
+    private fun parseRule(rule: String): MatchRule {
+        // Remove host part if present (e.g., "localhost:3000" -> "3000")
+        val portPart = rule.substringAfter(':').takeIf { ':' in rule } ?: rule
+
+        return when {
+            // Try parsing as single port
+            portPart.all { it.isDigit() } -> {
+                val port = portPart.toInt()
+                validatePort(port)
+                MatchRule.SinglePort(port)
+            }
+            // Try parsing as port range (e.g., "40000-55000")
+            portPart.matches("^\\d+\\s*-\\s*\\d+$".toRegex()) -> {
+                val (start, end) = portPart.split('-')
+                    .map { it.trim().toInt() }
+                validatePortRange(start, end)
+                MatchRule.PortRange(start, end)
+            }
+            // If not a single port or range, treat as regex
+            else -> {
+                try {
+                    MatchRule.RegexPort(portPart.toRegex())
+                } catch (e: Exception) {
+                    throw IllegalArgumentException("Invalid port rule format: $rule")
+                }
+            }
+        }
+    }
+
+    private fun validatePort(port: Int) {
+        require(port in 0..65535) { "Port number must be between 0 and 65535, got: $port" }
+    }
+
+    private fun validatePortRange(start: Int, end: Int) {
+        validatePort(start)
+        validatePort(end)
+        require(start <= end) { "Invalid port range: start must be less than or equal to end" }
+    }
+}

src/main/kotlin/com/coder/jetbrains/services/CoderPortForwardService.kt

@@ -1,5 +1,6 @@
 package com.coder.jetbrains.services
 
+import com.coder.jetbrains.matcher.PortMatcher
 import com.coder.jetbrains.scanner.listeningPorts
 import com.intellij.openapi.Disposable
 import com.intellij.openapi.components.serviceOrNull
@@ -15,6 +16,10 @@ import kotlinx.coroutines.delay
 import kotlinx.coroutines.isActive
 import kotlinx.coroutines.launch
 import kotlinx.coroutines.withContext
+import java.io.File
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.ExperimentalSerializationApi
+import com.coder.jetbrains.settings.CoderBackendSettings
 
 /**
  * Automatically forward ports that have something listening on them by scanning
@@ -29,15 +34,20 @@ class CoderPortForwardService(
     private val logger = thisLogger()
     private var poller: Job? = null
 
-    // TODO: Make customizable.
+    private data class PortRule(
+        val matcher: PortMatcher,
+        val autoForward: Boolean
+    )
     // TODO: I also see 63342, 57675, and 56830 for JetBrains.  Are they static?
     // TODO: If you have multiple IDEs, you will see 5991. 5992, etc.  Can we
     //       detect all of these and exclude them?
-    private val ignoreList = setOf(
-        22,   // SSH
-        5990, // JetBrains Gateway port.
+    private val rules = mutableListOf(
+        PortRule(PortMatcher("22"), false),
+        PortRule(PortMatcher("5990"), false),
     )
 
+    private var defaultForward = true
+
     init {
         logger.info("initializing port forwarding service")
         start()
@@ -47,13 +57,58 @@ class CoderPortForwardService(
         poller?.cancel()
     }
 
+    companion object {
+    @OptIn(ExperimentalSerializationApi::class)
+        private val json = Json {
+            ignoreUnknownKeys = true
+            allowTrailingComma = true
+            allowComments = true
+        }
+    }
+
     private fun start() {
+        val devcontainerFile = CoderBackendSettings.getDevcontainerFile()
+        if (devcontainerFile.exists()) {
+            try {
+                val jsonContent = devcontainerFile.readText()
+                val config = json.decodeFromString<DevContainerConfig>(jsonContent)
+
+                // Process port attributes
+                config.portsAttributes.forEach { (spec, attrs) ->
+                    when (attrs.onAutoForward) {
+                        "ignore" -> {
+                            logger.info("found ignored port specification $spec in devcontainer.json")
+                            rules.add(0, PortRule(PortMatcher(spec), false))
+                        }
+                        "" -> {}
+                        else -> {
+                            logger.info("found auto-forward port specification $spec in devcontainer.json")
+                            rules.add(0, PortRule(PortMatcher(spec), true))
+                        }
+                    }
+                }
+
+                // Process other ports attributes
+                config.otherPortsAttributes?.let {
+                    if (it.onAutoForward == "ignore") {
+                        logger.info("found ignored setting for otherPortsAttributes in devcontainer.json")
+                        defaultForward = false
+                    }
+                }
+            } catch (e: Exception) {
+                logger.warn("Failed to parse devcontainer.json", e)
+            }
+        }
+
         logger.info("starting port scanner")
         poller = cs.launch {
             while (isActive) {
                 logger.debug("scanning for ports")
                 val listeningPorts = withContext(Dispatchers.IO) {
-                    listeningPorts().subtract(ignoreList)
+                    listeningPorts().filter { port ->
+                        val matchedRule = rules.firstOrNull { it.matcher.matches(port) }
+                        matchedRule?.autoForward ?: defaultForward
+                    }.toSet()
                 }
                 application.invokeLater {
                     val manager = serviceOrNull<GlobalPortForwardingManager>()

src/main/kotlin/com/coder/jetbrains/services/DevContainerConfig.kt

@@ -0,0 +1,24 @@
+package com.coder.jetbrains.services
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class DevContainerConfig(
+    @SerialName("portsAttributes")
+    val portsAttributes: Map<String, PortAttributes> = mapOf(),
+    @SerialName("otherPortsAttributes")
+    val otherPortsAttributes: OtherPortsAttributes? = null
+)
+
+@Serializable
+data class PortAttributes(
+    @SerialName("onAutoForward")
+    val onAutoForward: String = ""
+)
+
+@Serializable
+data class OtherPortsAttributes(
+    @SerialName("onAutoForward")
+    val onAutoForward: String = ""
+)

src/main/kotlin/com/coder/jetbrains/settings/CoderBackendSettings.kt

@@ -0,0 +1,10 @@
+package com.coder.jetbrains.settings
+
+import java.io.File
+
+object CoderBackendSettings {
+    fun getDevcontainerFile(): File {
+        // TODO: make path configurable?
+        return File(System.getProperty("user.home"), ".cache/JetBrains/devcontainer.json")
+    }
+}

src/test/kotlin/com/coder/jetbrains/matcher/PortMatcherTest.kt

@@ -0,0 +1,71 @@
+package com.coder.jetbrains.matcher
+
+import org.junit.Test
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Assert.assertThrows
+
+class PortMatcherTest {
+
+    @Test
+    fun `test single port`() {
+        val matcher = PortMatcher("3000")
+        assertTrue(matcher.matches(3000))
+        assertFalse(matcher.matches(2999))
+        assertFalse(matcher.matches(3001))
+    }
+
+    @Test
+    fun `test host colon port`() {
+        val matcher = PortMatcher("localhost:3000")
+        assertTrue(matcher.matches(3000))
+        assertFalse(matcher.matches(3001))
+    }
+
+    @Test
+    fun `test port range`() {
+        val matcher = PortMatcher("40000-55000")
+        assertFalse(matcher.matches(39999))
+        assertTrue(matcher.matches(40000))
+        assertTrue(matcher.matches(50000))
+        assertTrue(matcher.matches(55000))
+        assertFalse(matcher.matches(55001))
+    }
+
+    @Test
+    fun `test port range with whitespace`() {
+        val matcher = PortMatcher("20021  - 20024")
+        assertFalse(matcher.matches(20000))
+        assertTrue(matcher.matches(20022))
+    }
+
+    @Test
+    fun `test regex`() {
+        val matcher = PortMatcher("800[1-9]")
+        assertFalse(matcher.matches(8000))
+        assertTrue(matcher.matches(8001))
+        assertTrue(matcher.matches(8005))
+        assertTrue(matcher.matches(8009))
+        assertFalse(matcher.matches(8010))
+    }
+
+    @Test
+    fun `test invalid port numbers`() {
+        assertThrows(IllegalArgumentException::class.java) { PortMatcher("65536") }
+        assertThrows(IllegalArgumentException::class.java) { PortMatcher("0-65536") }
+        assertThrows(IllegalArgumentException::class.java) { PortMatcher("70000") }
+    }
+
+    @Test
+    fun `test edge case port numbers`() {
+        // These should work
+        PortMatcher("0")
+        PortMatcher("65535")
+        PortMatcher("0-65535")
+
+        // These combinations should work
+        val matcher = PortMatcher("0-65535")
+        assertTrue(matcher.matches(0))
+        assertTrue(matcher.matches(65535))
+    }
+}