Add ip update mechanism

- check if external IP has been changed by ISP using miniupnpc
- remember new IP and send it to DNS provider
- add some description

README.md

@@ -4,4 +4,9 @@
 
 Using an external configuration file:
 
-`java -jar dnsupdater.jar --spring.config.additional-location=my.properties`
+`java -jar dnsupdater.jar --spring.config.additional-location=my.properties`
+
+
+Since you don't have an OpenWrt Router, there are limited ways to retrieve the external IP
+The way is to install https://github.com/transmission/miniupnpc on your server and call `external-ip`, which returns 
+the external ip of your plastic router. 

build.gradle.kts

@@ -23,6 +23,8 @@ dependencies {
     implementation("org.springframework.boot:spring-boot-starter")
     implementation("org.springframework.boot:spring-boot-starter-web")
     implementation("org.jetbrains.kotlin:kotlin-reflect")
+    implementation("io.github.microutils:kotlin-logging:3.0.5")
+
     testImplementation("org.springframework.boot:spring-boot-starter-test")
 }
 

src/componentTest/kotlin/net/flyingelectrons/dnsupdater/gateway/GandiClientTest.kt

@@ -23,11 +23,11 @@ internal class GandiClientTest {
         wireMockServer.start()
         WireMockConfiguration.options().notifier(ConsoleNotifier(true))
         configureFor("localhost", 8080)
-        stubFor(put(urlEqualTo("/api/v5/domains/foo.net/records/bar/A"))
+        stubFor(put(urlEqualTo("/api/v5/domains/foo.net/records/fqdn/A"))
             .willReturn(okJson("{\"keks\":\"dose\"}")))
 
         val ipAddress= "1.1.1.1"
-        val responseCode = gandiClient.doUpdateIpWithfqdn(ipAddress, "bar")
+        val responseCode = gandiClient.doUpdateIpWithfqdn(ipAddress, "fqdn")
         assertThat(responseCode.statusCode.value()).isEqualTo(200)
         wireMockServer.stop()
     }

src/main/kotlin/net/flyingelectrons/dnsupdater/service/ExternalIpRetrieverService.kt

@@ -0,0 +1,15 @@
+package net.flyingelectrons.dnsupdater.service
+
+import org.springframework.stereotype.Service
+
+@Service
+class ExternalIpRetrieverService(private val processExecutorService: ProcessExecutorService) {
+
+    fun getExternalIp(): String {
+        val execute = processExecutorService.execute("external-ip")
+        if (execute.isEmpty()) {
+            throw java.lang.IllegalArgumentException("external IP is empty")
+        }
+        return execute
+    }
+}

src/main/kotlin/net/flyingelectrons/dnsupdater/service/ProcessExecutorService.kt

@@ -0,0 +1,41 @@
+package net.flyingelectrons.dnsupdater.service
+
+import org.springframework.stereotype.Service
+import java.io.BufferedReader
+import java.io.InputStream
+import java.io.InputStreamReader
+import java.util.concurrent.Executors
+import java.util.function.Consumer
+
+@Service
+class ProcessExecutorService {
+
+    fun execute(unixCommand: String): String {
+        var out = ""
+        val process: Process = Runtime.getRuntime()
+            .exec(unixCommand)
+        val streamGobbler = StreamGobbler(
+            process.inputStream, fun(x: String?) {
+                println(x)
+                out = x.orEmpty()
+            }
+        )
+        Executors.newSingleThreadExecutor().submit(streamGobbler)
+        val exitCode = process.waitFor()
+        assert(exitCode == 0)
+        return out
+    }
+}
+
+private class StreamGobbler(private val inputStream: InputStream, consumer: Consumer<String>) :
+    Runnable {
+    private val consumer: Consumer<String>
+    override fun run() {
+        BufferedReader(InputStreamReader(inputStream)).lines()
+            .forEach(consumer)
+    }
+
+    init {
+        this.consumer = consumer
+    }
+}

src/main/kotlin/net/flyingelectrons/dnsupdater/service/UpdateDnsSchedulingService.kt

@@ -0,0 +1,32 @@
+package net.flyingelectrons.dnsupdater.service
+
+import mu.KotlinLogging
+import net.flyingelectrons.dnsupdater.gateway.GandiClient
+import org.springframework.beans.factory.annotation.Autowired
+import org.springframework.scheduling.annotation.Scheduled
+import org.springframework.stereotype.Service
+
+@Service
+class UpdateDnsSchedulingService @Autowired constructor(
+    private val externalIpRetrieverService: ExternalIpRetrieverService,
+    private val gandiClient: GandiClient,
+) {
+
+    private var savedIp = "noIpKnownYet"
+
+    @Scheduled(cron = "*/3 * * * * *")
+    fun updateDns() {
+        val externalIp: String = externalIpRetrieverService.getExternalIp()
+        LOGGER.info("running scheduler. get external ip: $externalIp")
+        if (externalIp != savedIp) {
+            val ipWithfqdn = gandiClient.doUpdateIpWithfqdn(externalIp, "myfqdn")
+            LOGGER.info("Updating myfqdn")
+            LOGGER.info(ipWithfqdn.body)
+            savedIp = externalIp
+        }
+    }
+
+    companion object {
+        private val LOGGER = KotlinLogging.logger { }
+    }
+}