update checker using github release page

src/net/torvald/terrarum/CheckUpdate.kt

@@ -0,0 +1,70 @@
+package net.torvald.terrarum
+
+import net.torvald.terrarum.App.printdbg
+import net.torvald.terrarum.App.printdbgerr
+import net.torvald.terrarum.savegame.ByteArray64GrowableOutputStream
+import net.torvald.terrarum.savegame.DiskSkimmer.Companion.read
+import java.io.*
+import java.net.MalformedURLException
+import java.net.URI
+import java.net.URL
+import java.net.http.HttpClient
+import java.net.http.HttpRequest
+import java.net.http.HttpResponse
+
+/**
+ * Created by minjaesong on 2023-10-03.
+ */
+object CheckUpdate {
+
+    private val versionNumFull = App.getVERSION_STRING()
+    private val versionNumOnly = String.format(
+        "%d.%d.%d",
+        App.VERSION_RAW ushr 48,
+        App.VERSION_RAW and 0xffff000000L ushr 24,
+        App.VERSION_RAW and 0xffffffL
+    )
+
+    private val checkUpdateURL = setOf(
+        "https://github.com/curioustorvald/Terrarum/releases/tag/v$versionNumOnly",
+        "https://github.com/curioustorvald/Terrarum/releases/tag/v$versionNumFull",
+    ).toList()
+
+    private fun wget(url: String): String? {
+        printdbg(this, "wget $url")
+
+        var ret: String? = null
+        var fail: Throwable? = null
+        try {
+            // check the http connection before we do anything to the fs
+            val client = HttpClient.newBuilder().build()
+            val request = HttpRequest.newBuilder().uri(URI.create(url)).build()
+            val response = client.send(request, HttpResponse.BodyHandlers.ofString())
+            ret = if (response.statusCode() >= 400) null else response.body()
+
+            printdbg(this, "HTTP ${response.statusCode()}")
+        }
+        catch (e: Throwable) {
+            fail = e
+            printdbgerr(this, "wget $url got error: ${e.stackTraceToString()}")
+        }
+        finally {
+        }
+
+        return ret
+    }
+
+    fun hasUpdate(): Boolean {
+        var allNull = true
+
+        val hasLatestAny = checkUpdateURL.any { url ->
+            val http = wget(url)
+            if (http != null) allNull = false
+            http?.contains("a href=\"/curioustorvald/Terrarum/releases/latest") ?: false
+        }
+
+        return if (allNull) false else !hasLatestAny
+    }
+
+
+}