retry publish on all 5XX errors

ivy/src/main/scala/sbt/internal/librarymanagement/IvyUtil.scala

@@ -31,8 +31,14 @@ private[sbt] object IvyUtil {
     }
   }
 
+  /**
+   * Currently transient network errors are defined as:
+   *  - a network timeout
+   *  - all server errors (response code 5xx)
+   *  - rate limiting (response code 429)
+   */
   object TransientNetworkException {
-    private val _r = """.*HTTP response code: (503|429).*""".r
+    private val _r = """.*HTTP response code: (5\d{2}|408|429).*""".r
 
     @inline private def check(s: String): Boolean = {
       if (s == null) return false

ivy/src/test/scala/sbt/internal/librarymanagement/IvyUtilSpec.scala

@@ -0,0 +1,66 @@
+package sbt.internal.librarymanagement
+
+import java.io.IOException
+
+import org.scalatest.FunSuite
+import sbt.internal.librarymanagement.IvyUtil._
+
+class IvyUtilSpec extends FunSuite {
+  test("503 should be a TransientNetworkException") {
+    val statusCode503Exception =
+      new IOException("Server returned HTTP response code: 503 for URL:")
+    assert(TransientNetworkException(statusCode503Exception))
+  }
+
+  test("500 should be a TransientNetworkException") {
+    val statusCode500Exception =
+      new IOException("Server returned HTTP response code: 500 for URL:")
+    assert(TransientNetworkException(statusCode500Exception))
+  }
+
+  test("408 should be a TransientNetworkException") {
+    val statusCode408Exception =
+      new IOException("Server returned HTTP response code: 408 for URL:")
+    assert(TransientNetworkException(statusCode408Exception))
+  }
+
+  test("429 should be a TransientNetworkException") {
+    val statusCode429Exception =
+      new IOException(" Server returned HTTP response code: 429 for URL:")
+    assert(TransientNetworkException(statusCode429Exception))
+  }
+
+  test("404 should not be a TransientNetworkException") {
+    val statusCode404Exception =
+      new IOException("Server returned HTTP response code: 404 for URL:")
+    assert(!TransientNetworkException(statusCode404Exception))
+  }
+
+  test("IllegalArgumentException should not be a TransientNetworkException") {
+    val illegalArgumentException = new IllegalArgumentException()
+    assert(!TransientNetworkException(illegalArgumentException))
+  }
+
+  test("it should retry for 3 attempts") {
+    var i = 0
+    def f: Int = {
+      i += 1
+      if (i < 3) throw new RuntimeException() else i
+    }
+    // exception predicate retries on all exceptions for this test
+    val result = retryWithBackoff(f, _ => true, maxAttempts = 3)
+    assert(result == 3)
+  }
+
+  test("it should fail after maxAttempts") {
+    var i = 0
+    def f: Int = {
+      i += 1
+      throw new RuntimeException()
+    }
+    intercept[RuntimeException] {
+      retryWithBackoff(f, _ => true, maxAttempts = 3)
+    }
+    assert(i == 3)
+  }
+}