Stop counting POM retrievals before the response is released

src/main/java/rife/bld/dependencies/DependencyResolver.java

@@ -243,15 +243,24 @@ public class DependencyResolver {
      */
     public RepositoryArtifact transferIntoDirectory(File directory)
     throws DependencyTransferException {
+        DependencyTransferException transient_failure = null;
         for (var artifact : getTransferArtifacts()) {
             try {
                 if (retriever_.transferIntoDirectory(artifact, directory)) {
                     return artifact;
                 }
             } catch (IOException e) {
-                throw new DependencyTransferException(dependency_, artifact.location(), directory, e);
+                // a transient issue with this repository, try the next one
+                // before giving up
+                transient_failure = rememberFailure(transient_failure, new DependencyTransferException(dependency_, artifact.location(), directory, e));
             }
         }
+
+        // transient failures never degrade into a null not-found result,
+        // an artifact that couldn't be transferred might still exist
+        if (transient_failure != null) {
+            throw transient_failure;
+        }
         return null;
     }
 
@@ -370,46 +379,58 @@ public class DependencyResolver {
     }
 
     private MavenMetadata parseMavenMetadata(List<RepositoryArtifact> artifacts) {
-        RepositoryArtifact retrieved_artifact = null;
-        String metadata = null;
+        var retrieved = retrieveFirstAvailable(artifacts, "metadata locations");
+
+        var xml = new Xml2MavenMetadata();
+        if (!xml.processXml(retrieved.content())) {
+            throw new DependencyXmlParsingErrorException(dependency_, retrieved.artifact().location(), xml.getErrors());
+        }
+
+        return xml;
+    }
+
+    private record RetrievedArtifact(RepositoryArtifact artifact, String content) {
+    }
+
+    private RetrievedArtifact retrieveFirstAvailable(List<RepositoryArtifact> artifacts, String locationsDescription) {
+        ArtifactRetrievalErrorException transient_failure = null;
         for (var artifact : artifacts) {
             try {
-                var content = retriever_.readString(artifact);
-                if (content == null) {
-                    throw new ArtifactNotFoundException(dependency_, artifact.location());
-                }
-
-                retrieved_artifact = artifact;
-                metadata = content;
-
-                break;
+                return new RetrievedArtifact(artifact, retriever_.readString(artifact));
             } catch (FileUtilsErrorException e) {
                 if (e.getCause() instanceof FileNotFoundException) {
                     continue;
                 }
-                throw new ArtifactRetrievalErrorException(dependency_, artifact.location(), e);
+                // a transient issue with this repository, try the next one
+                // before giving up
+                transient_failure = rememberFailure(transient_failure, new ArtifactRetrievalErrorException(dependency_, artifact.location(), e));
             }
         }
 
-        if (metadata == null) {
-            var location = artifacts.stream().map(RepositoryArtifact::location).collect(Collectors.joining(", "));
-            if (location.isEmpty()) {
-                if (repositories_.isEmpty()) {
-                    location = "[no repositories defined]";
-                }
-                else {
-                    location = "[no metadata locations defined]";
-                }
+        // transient failures never degrade into not-found, an artifact
+        // that couldn't be retrieved might still exist
+        if (transient_failure != null) {
+            throw transient_failure;
+        }
+
+        var location = artifacts.stream().map(RepositoryArtifact::location).collect(Collectors.joining(", "));
+        if (location.isEmpty()) {
+            if (repositories_.isEmpty()) {
+                location = "[no repositories defined]";
+            }
+            else {
+                location = "[no " + locationsDescription + " defined]";
             }
-            throw new ArtifactNotFoundException(dependency_, location);
         }
+        throw new ArtifactNotFoundException(dependency_, location);
+    }
 
-        var xml = new Xml2MavenMetadata();
-        if (!xml.processXml(metadata)) {
-            throw new DependencyXmlParsingErrorException(dependency_, retrieved_artifact.location(), xml.getErrors());
+    private static <T extends Throwable> T rememberFailure(T remembered, T failure) {
+        if (remembered == null) {
+            return failure;
         }
-
-        return xml;
+        remembered.addSuppressed(failure);
+        return remembered;
     }
 
     private List<RepositoryArtifact> getPomLocations() {
@@ -426,50 +447,16 @@ public class DependencyResolver {
     }
 
     Xml2MavenPom getMavenPom(Dependency parent) {
-        RepositoryArtifact retrieved_artifact = null;
-        String pom = null;
-        var artifacts = getPomLocations();
-
-        for (var artifact : artifacts) {
-            try {
-                var content = retriever_.readString(artifact);
-                if (content == null) {
-                    throw new ArtifactNotFoundException(dependency_, artifact.location());
-                }
-
-                retrieved_artifact = artifact;
-                pom = content;
-
-                break;
-            } catch (FileUtilsErrorException e) {
-                if (e.getCause() instanceof FileNotFoundException) {
-                    continue;
-                }
-                throw new ArtifactRetrievalErrorException(dependency_, artifact.location(), e);
-            }
-        }
-
-        if (pom == null) {
-            var location = artifacts.stream().map(RepositoryArtifact::location).collect(Collectors.joining(", "));
-            if (location.isEmpty()) {
-                if (repositories_.isEmpty()) {
-                    location = "[no repositories defined]";
-                }
-                else {
-                    location = "[no pom locations defined]";
-                }
-            }
-            throw new ArtifactNotFoundException(dependency_, location);
-        }
+        var retrieved = retrieveFirstAvailable(getPomLocations(), "pom locations");
 
         var xml = new Xml2MavenPom(parent, resolution_, retriever_, repositories_);
         // first pass only extracts the properties from the pom
-        if (!xml.processXml(pom)) {
-            throw new DependencyXmlParsingErrorException(dependency_, retrieved_artifact.location(), xml.getErrors());
+        if (!xml.processXml(retrieved.content())) {
+            throw new DependencyXmlParsingErrorException(dependency_, retrieved.artifact().location(), xml.getErrors());
         }
         // second pass parses all the rest so that the properties are available anywhere
-        if (!xml.processXml(pom)) {
-            throw new DependencyXmlParsingErrorException(dependency_, retrieved_artifact.location(), xml.getErrors());
+        if (!xml.processXml(retrieved.content())) {
+            throw new DependencyXmlParsingErrorException(dependency_, retrieved.artifact().location(), xml.getErrors());
         }
 
         return xml;

src/main/java/rife/bld/wrapper/Wrapper.java

@@ -629,29 +629,32 @@ public class Wrapper {
 
     private void downloadDistribution(File file, String downloadUrl)
     throws IOException {
-        try {
-            System.out.print("Downloading: " + downloadUrl + " ... ");
-            System.out.flush();
-            var url = new URL(downloadUrl);
-            var readableByteChannel = Channels.newChannel(url.openStream());
-            try (var fileOutputStream = new FileOutputStream(file)) {
-                var fileChannel = fileOutputStream.getChannel();
-                fileChannel.transferFrom(readableByteChannel, 0, Long.MAX_VALUE);
+        retryOnTransientIoIssues(() -> {
+            try {
+                System.out.print("Downloading: " + downloadUrl + " ... ");
+                System.out.flush();
+                var url = new URL(downloadUrl);
+                var readableByteChannel = Channels.newChannel(url.openStream());
+                try (var fileOutputStream = new FileOutputStream(file)) {
+                    var fileChannel = fileOutputStream.getChannel();
+                    fileChannel.transferFrom(readableByteChannel, 0, Long.MAX_VALUE);
 
-                System.out.print("done");
+                    System.out.print("done");
+                }
+            } catch (FileNotFoundException e) {
+                System.err.println("not found");
+                System.err.println("Failed to download file " + file + ".");
+                throw e;
+            } catch (IOException e) {
+                System.err.println("error");
+                System.err.println("Failed to download file " + file + " due to I/O issue.");
+                Files.deleteIfExists(file.toPath());
+                throw e;
+            } finally {
+                System.out.println();
             }
-        } catch (FileNotFoundException e) {
-            System.err.println("not found");
-            System.err.println("Failed to download file " + file + ".");
-            throw e;
-        } catch (IOException e) {
-            System.err.println("error");
-            System.err.println("Failed to download file " + file + " due to I/O issue.");
-            Files.deleteIfExists(file.toPath());
-            throw e;
-        } finally {
-            System.out.println();
-        }
+            return null;
+        });
     }
 
     private void resolveExtensions() {
@@ -835,11 +838,48 @@ public class Wrapper {
 
     private String readString(String version, URL url)
     throws IOException {
-        var connection = url.openConnection();
-        connection.setUseCaches(false);
-        connection.setRequestProperty(HttpUtils.HEADER_USER_AGENT, Product.BLD.toUserAgent(version));
-        try (var in = connection.getInputStream()) {
-            return new String(in.readAllBytes(), StandardCharsets.UTF_8);
+        return retryOnTransientIoIssues(() -> {
+            var connection = url.openConnection();
+            connection.setUseCaches(false);
+            connection.setRequestProperty(HttpUtils.HEADER_USER_AGENT, Product.BLD.toUserAgent(version));
+            try (var in = connection.getInputStream()) {
+                return new String(in.readAllBytes(), StandardCharsets.UTF_8);
+            }
+        });
+    }
+
+    static final int DOWNLOAD_ATTEMPTS = 3;
+    static final long DOWNLOAD_RETRY_DELAY_MS = 2000L;
+
+    interface IoAction<T> {
+        T execute() throws IOException;
+    }
+
+    private static <T> T retryOnTransientIoIssues(IoAction<T> action)
+    throws IOException {
+        return retryOnTransientIoIssues(action, DOWNLOAD_ATTEMPTS, DOWNLOAD_RETRY_DELAY_MS);
+    }
+
+    static <T> T retryOnTransientIoIssues(IoAction<T> action, int attempts, long delayMs)
+    throws IOException {
+        for (var attempt = 1; ; ++attempt) {
+            try {
+                return action.execute();
+            } catch (FileNotFoundException e) {
+                // a resource that doesn't exist will not appear by retrying
+                throw e;
+            } catch (IOException e) {
+                if (attempt >= attempts) {
+                    throw e;
+                }
+                System.err.println("Download issue (" + e.getMessage() + "), retrying ...");
+                try {
+                    Thread.sleep(delayMs * attempt);
+                } catch (InterruptedException interrupted) {
+                    Thread.currentThread().interrupt();
+                    throw e;
+                }
+            }
         }
     }
 

src/test/java/rife/bld/dependencies/TestDependencyResolver.java

@@ -6,6 +6,7 @@ package rife.bld.dependencies;
 
 import com.sun.net.httpserver.HttpServer;
 import org.junit.jupiter.api.Test;
+import rife.bld.testing.RetryTest;
 import rife.ioc.HierarchicalProperties;
 import rife.tools.FileUtils;
 import rife.tools.StringUtils;
@@ -41,38 +42,38 @@ public class TestDependencyResolver {
         assertEquals(new Dependency("com.uwyn.rife2", "rife2", new VersionNumber(1, 4, 0)), resolver.dependency());
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testNotFound() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.org.unknown", "voidthing"));
         assertFalse(resolver.exists());
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testCheckExistence() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.uwyn.rife2", "rife2"));
         assertTrue(resolver.exists());
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testCheckExistenceVersion() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.uwyn.rife2", "rife2", new VersionNumber(1, 4, 0)));
         assertTrue(resolver.exists());
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testCheckExistenceMissingVersion() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.uwyn.rife2", "rife2", new VersionNumber(1, 3, 9)));
         assertFalse(resolver.exists());
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testCheckVersionOverride() {
         var resolver = new DependencyResolver(new VersionResolution(new HierarchicalProperties().put(PROPERTY_OVERRIDE_PREFIX, "com.uwyn.rife2:rife2:1.8.0")),
             ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.uwyn.rife2", "rife2", new VersionNumber(1, 3, 9)));
         assertEquals(new VersionNumber(1, 8, 0), resolver.resolveVersion());
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testListVersions() {
         var resolver1 = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.uwyn.rife2", "rife2"));
         var versions1 = resolver1.listVersions();
@@ -91,7 +92,7 @@ public class TestDependencyResolver {
         assertTrue(versions2.contains(new VersionNumber(11, 0, 14)));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetLatestVersion() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(3), new Dependency("com.uwyn.rife2", "rife2"));
         var version = resolver.latestVersion();
@@ -99,7 +100,7 @@ public class TestDependencyResolver {
         assertTrue(version.compareTo(new VersionNumber(1, 4)) >= 0);
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetReleaseVersion() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(4), new Dependency("com.uwyn.rife2", "rife2"));
         var version = resolver.releaseVersion();
@@ -107,7 +108,7 @@ public class TestDependencyResolver {
         assertTrue(version.compareTo(new VersionNumber(1, 4)) >= 0);
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testMetadata() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(5), new Dependency("com.uwyn.rife2", "rife2", new VersionNumber(1, 4, 0)));
         var metadata = resolver.getMavenMetadata();
@@ -116,7 +117,7 @@ public class TestDependencyResolver {
         assertNull(resolver.getSnapshotMavenMetadata());
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testSnapshotMetadata() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), List.of(getNextRepository(), RIFE2_SNAPSHOTS), new Dependency("com.uwyn.rife2", "rife2", new VersionNumber(1, 9, 1, "SNAPSHOT")));
         var metadata = resolver.getSnapshotMavenMetadata();
@@ -125,7 +126,7 @@ public class TestDependencyResolver {
         assertEquals(4, metadata.getSnapshotBuildNumber());
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesRIFE2() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.uwyn.rife2", "rife2"));
         var dependencies = resolver.getDirectDependencies(compile);
@@ -133,7 +134,7 @@ public class TestDependencyResolver {
         assertEquals(0, dependencies.size());
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesRIFE2Snapshot() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), List.of(getNextRepository(), RIFE2_SNAPSHOTS), new Dependency("com.uwyn.rife2", "rife2", new VersionNumber(1, 9, 1, "SNAPSHOT")));
         var dependencies = resolver.getDirectDependencies(compile);
@@ -141,7 +142,7 @@ public class TestDependencyResolver {
         assertEquals(0, dependencies.size());
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesGoogleApi() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.google.apis", "google-api-services-youtube", new VersionGeneric("v3-rev20240514-2.0.0")));
         var dependencies = resolver.getDirectDependencies(compile);
@@ -151,7 +152,7 @@ public class TestDependencyResolver {
             com.google.api-client:google-api-client:2.5.0""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesJetty() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.eclipse.jetty", "jetty-server", new VersionNumber(11, 0, 14)));
         var dependencies = resolver.getDirectDependencies(compile);
@@ -164,7 +165,7 @@ public class TestDependencyResolver {
             org.slf4j:slf4j-api:2.0.5""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesAssertJ() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.assertj", "assertj-joda-time", new VersionNumber(2, 2, 0)));
         var dependencies = resolver.getDirectDependencies(compile);
@@ -174,7 +175,7 @@ public class TestDependencyResolver {
             org.assertj:assertj-core""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesSwagger() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("io.swagger.core.v3", "swagger-core", new VersionNumber(2,2,27)));
         var dependencies = resolver.getDirectDependencies(compile);
@@ -194,7 +195,7 @@ public class TestDependencyResolver {
             jakarta.validation:jakarta.validation-api:2.0.2""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesJettyOverride1() {
         var resolver = new DependencyResolver(new VersionResolution(new HierarchicalProperties().put(PROPERTY_OVERRIDE_PREFIX, "org.slf4j:slf4j-api:2.0.16")),
             ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.eclipse.jetty", "jetty-server", new VersionNumber(11, 0, 14)));
@@ -208,7 +209,7 @@ public class TestDependencyResolver {
             org.slf4j:slf4j-api:2.0.16""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesJettyOverride2() {
         var resolver = new DependencyResolver(new VersionResolution(new HierarchicalProperties().put(PROPERTY_OVERRIDE_PREFIX, "org.slf4j:slf4j-api:2.0.11,org.eclipse.jetty:jetty-io:11.0.13,org.eclipse.jetty:jetty-server:11.0.15")),
             ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.eclipse.jetty", "jetty-server", new VersionNumber(11, 0, 14)));
@@ -222,7 +223,7 @@ public class TestDependencyResolver {
             org.slf4j:slf4j-api:2.0.11""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileRuntimeDependenciesJunit() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.junit.jupiter", "junit-jupiter", new VersionNumber(5, 9, 2)));
         var dependencies_compile = resolver.getDirectDependencies(compile, runtime);
@@ -234,7 +235,7 @@ public class TestDependencyResolver {
             org.junit.jupiter:junit-jupiter-engine:5.9.2""", StringUtils.join(dependencies_compile, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesSpringBoot() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.springframework.boot", "spring-boot-starter", new VersionNumber(3, 0, 4)));
         var dependencies = resolver.getDirectDependencies(compile);
@@ -249,7 +250,7 @@ public class TestDependencyResolver {
             org.yaml:snakeyaml:1.33""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesMaven() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.apache.maven", "maven-core", new VersionNumber(3, 9, 0)));
         var dependencies = resolver.getDirectDependencies(compile);
@@ -284,7 +285,7 @@ public class TestDependencyResolver {
             org.slf4j:slf4j-api:1.7.36""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesPlay() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.typesafe.play", "play_2.13", new VersionNumber(2, 8, 19)));
         var dependencies = resolver.getDirectDependencies(compile);
@@ -318,7 +319,7 @@ public class TestDependencyResolver {
             org.scala-lang.modules:scala-parser-combinators_2.13:1.1.2""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileDependenciesVaadin() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.vaadin", "vaadin", new VersionNumber(23, 3, 7)));
         var dependencies = resolver.getDirectDependencies(compile);
@@ -336,7 +337,7 @@ public class TestDependencyResolver {
             com.vaadin:collaboration-engine:5.3.0""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileRuntimeDependenciesBitly() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("net.thauvin.erik", "bitly-shorten", new VersionNumber(2, 0, 0)));
         var dependencies = resolver.getDirectDependencies(compile, runtime);
@@ -351,7 +352,7 @@ public class TestDependencyResolver {
             org.json:json:20250107""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesRIFE2() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.uwyn.rife2", "rife2"));
         var dependencies = resolver.getAllDependencies(compile);
@@ -361,7 +362,7 @@ public class TestDependencyResolver {
             com.uwyn.rife2:rife2""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesRIFE2Snapshot() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), List.of(getNextRepository(), RIFE2_SNAPSHOTS), new Dependency("com.uwyn.rife2", "rife2", new VersionNumber(1, 9, 1, "SNAPSHOT")));
         var dependencies = resolver.getAllDependencies(compile);
@@ -371,7 +372,7 @@ public class TestDependencyResolver {
             com.uwyn.rife2:rife2:1.9.1-SNAPSHOT""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesJetty() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.eclipse.jetty", "jetty-server", new VersionNumber(11, 0, 14)));
         var dependencies = resolver.getAllDependencies(compile);
@@ -386,7 +387,7 @@ public class TestDependencyResolver {
             org.eclipse.jetty:jetty-util:11.0.14""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesJettyExclusion() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(),
             new Dependency("org.eclipse.jetty", "jetty-server", new VersionNumber(11, 0, 14))
@@ -402,7 +403,7 @@ public class TestDependencyResolver {
             org.eclipse.jetty:jetty-util:11.0.14""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesJettyFullGroupExclusion() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(),
             new Dependency("org.eclipse.jetty", "jetty-server", new VersionNumber(11, 0, 14))
@@ -416,7 +417,7 @@ public class TestDependencyResolver {
             org.slf4j:slf4j-api:2.0.5""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesJettyFullArtifactExclusion() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(),
             new Dependency("org.eclipse.jetty", "jetty-server", new VersionNumber(11, 0, 14))
@@ -432,7 +433,7 @@ public class TestDependencyResolver {
             org.eclipse.jetty:jetty-util:11.0.14""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesJettyFullExclusion() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(),
             new Dependency("org.eclipse.jetty", "jetty-server", new VersionNumber(11, 0, 14))
@@ -444,7 +445,7 @@ public class TestDependencyResolver {
             org.eclipse.jetty:jetty-server:11.0.14""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesJettyAndSlfj() {
         var dependencies = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.eclipse.jetty", "jetty-server", new VersionNumber(11, 0, 14))).getAllDependencies(compile);
         var dependencies2 = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.slf4j", "slf4j-simple", new VersionNumber(2, 0, 6))).getAllDependencies(compile, runtime);
@@ -464,7 +465,7 @@ public class TestDependencyResolver {
             org.slf4j:slf4j-api:2.0.6""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileRuntimeTransitiveDependenciesJunit() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.junit.jupiter", "junit-jupiter", new VersionNumber(5, 9, 2)));
         var dependencies_compile = resolver.getAllDependencies(compile, runtime);
@@ -487,7 +488,7 @@ public class TestDependencyResolver {
             org.junit.jupiter:junit-jupiter-engine:5.9.2""", StringUtils.join(dependencies_runtime, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesSpringBoot() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.springframework.boot", "spring-boot-starter", new VersionNumber(3, 0, 4)));
         var dependencies = resolver.getAllDependencies(compile);
@@ -514,7 +515,7 @@ public class TestDependencyResolver {
             org.apache.logging.log4j:log4j-api:2.19.0""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesMaven() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.apache.maven", "maven-core", new VersionNumber(3, 9, 0)));
         var dependencies = resolver.getAllDependencies(compile);
@@ -555,7 +556,7 @@ public class TestDependencyResolver {
             org.codehaus.plexus:plexus-cipher:2.0""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesPlay() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.typesafe.play", "play_2.13", new VersionNumber(2, 8, 19)));
         var dependencies = resolver.getAllDependencies(compile);
@@ -612,7 +613,7 @@ public class TestDependencyResolver {
             com.thoughtworks.paranamer:paranamer:2.8""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileTransitiveDependenciesVaadin() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("com.vaadin", "vaadin", new VersionNumber(23, 3, 7)));
         var dependencies = resolver.getAllDependencies(compile);
@@ -709,7 +710,7 @@ public class TestDependencyResolver {
             com.google.code.findbugs:jsr305:3.0.2""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileRuntimeTransitiveDependenciesBitly() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("net.thauvin.erik", "bitly-shorten", new VersionNumber(2, 0, 0)));
         var dependencies = resolver.getAllDependencies(compile, runtime);
@@ -729,7 +730,7 @@ public class TestDependencyResolver {
             com.squareup.okio:okio-jvm:3.6.0""", StringUtils.join(dependencies, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetCompileRuntimeTransitiveDependenciesMariaDb() {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.mariadb.jdbc", "mariadb-java-client", new VersionNumber(3, 1, 3)));
         var dependencies_compile = resolver.getAllDependencies(compile, runtime);
@@ -752,7 +753,7 @@ public class TestDependencyResolver {
             org.mariadb.jdbc:mariadb-java-client:3.1.3""", StringUtils.join(dependencies_runtime, "\n"));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependency()
     throws Exception {
         var repos = getNextRepositories();
@@ -776,7 +777,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySources()
     throws Exception {
         var repos = getNextRepositories();
@@ -801,7 +802,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySourcesJavadoc()
     throws Exception {
         var repos = getNextRepositories();
@@ -827,7 +828,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySnapshot()
     throws Exception {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), List.of(getNextRepository(), RIFE2_SNAPSHOTS), new Dependency("com.uwyn.rife2", "rife2", new VersionNumber(1, 9, 1, "SNAPSHOT")));
@@ -849,7 +850,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySnapshotSources()
     throws Exception {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), List.of(getNextRepository(), RIFE2_SNAPSHOTS), new Dependency("com.uwyn.rife2", "rife2", new VersionNumber(1, 9, 1, "SNAPSHOT")));
@@ -873,7 +874,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySnapshotSourcesJavadoc()
     throws Exception {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), List.of(getNextRepository(), RIFE2_SNAPSHOTS), new Dependency("com.uwyn.rife2", "rife2", new VersionNumber(1, 9, 1, "SNAPSHOT")));
@@ -899,7 +900,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySourcesModule()
     throws Exception {
         var repos = getNextRepositories();
@@ -924,7 +925,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySourcesJavadocModule()
     throws Exception {
         var repos = getNextRepositories();
@@ -950,7 +951,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySnapshotModule()
     throws Exception {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), List.of(getNextRepository(), RIFE2_SNAPSHOTS), new Module("com.uwyn.rife2", "rife2", new VersionNumber(1, 9, 1, "SNAPSHOT")));
@@ -972,7 +973,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySnapshotSourcesModule()
     throws Exception {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), List.of(getNextRepository(), RIFE2_SNAPSHOTS), new Module("com.uwyn.rife2", "rife2", new VersionNumber(1, 9, 1, "SNAPSHOT")));
@@ -996,7 +997,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySnapshotSourcesJavadocModule()
     throws Exception {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), List.of(SONATYPE_SNAPSHOTS, RIFE2_SNAPSHOTS), new Module("com.uwyn.rife2", "rife2", new VersionNumber(1, 9, 1, "SNAPSHOT")));
@@ -1022,7 +1023,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyJetty()
     throws Exception {
         var repos = getNextRepositories();
@@ -1059,7 +1060,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyJettyModule()
     throws Exception {
         var repos = getNextRepositories();
@@ -1096,7 +1097,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySwagger()
     throws Exception {
         var repos = getNextRepositories();
@@ -1149,7 +1150,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyGoogleApi()
     throws Exception {
         var repos = getNextRepositories();
@@ -1222,7 +1223,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyGoogleApiModule()
     throws Exception {
         var repos = getNextRepositories();
@@ -1295,7 +1296,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyJettyOverriddenVersions()
     throws Exception {
         var repos = getNextRepositories();
@@ -1336,7 +1337,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyJettyOverriddenVersionsModule()
     throws Exception {
         var repos = getNextRepositories();
@@ -1377,7 +1378,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyJettySources()
     throws Exception {
         var repos = getNextRepositories();
@@ -1426,7 +1427,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyJettySourcesModule()
     throws Exception {
         var repos = getNextRepositories();
@@ -1475,7 +1476,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyJettySourcesJavadoc()
     throws Exception {
         var repos = getNextRepositories();
@@ -1536,7 +1537,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyJettySourcesJavadocModule()
     throws Exception {
         var repos = getNextRepositories();
@@ -1597,7 +1598,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependenciesJunit()
     throws Exception {
         var repos = getNextRepositories();
@@ -1638,7 +1639,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencySpringBoot()
     throws Exception {
         var repos = getNextRepositories();
@@ -1699,7 +1700,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyMaven()
     throws Exception {
         var repos = getNextRepositories();
@@ -1788,7 +1789,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyPlay()
     throws Exception {
         var repos = getNextRepositories();
@@ -1909,7 +1910,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyPlayOverriddenVersions()
     throws Exception {
         var repos = getNextRepositories();
@@ -2031,7 +2032,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferDependencyVaadin()
     throws Exception {
         var repos = getNextRepositories();
@@ -2231,7 +2232,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferCheckExisting()
     throws Exception {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Dependency("org.eclipse.jetty", "jetty-server", new VersionNumber(11, 0, 14)));
@@ -2289,7 +2290,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testTransferCheckExistingModule()
     throws Exception {
         var resolver = new DependencyResolver(VersionResolution.dummy(), ArtifactRetriever.instance(), getNextRepositories(), new Module("org.eclipse.jetty", "jetty-server", new VersionNumber(11, 0, 14)));
@@ -2347,7 +2348,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetAllDependenciesParallelPomPrefetching() throws Exception {
         var max_concurrent_retrievals = new AtomicInteger();
         var server = createPomServer(max_concurrent_retrievals);
@@ -2373,7 +2374,7 @@ public class TestDependencyResolver {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testGetAllDependenciesSequentialWithoutCachingRetriever() throws Exception {
         var max_concurrent_retrievals = new AtomicInteger();
         var server = createPomServer(max_concurrent_retrievals);
@@ -2405,19 +2406,23 @@ public class TestDependencyResolver {
             try {
                 // delay the response so that parallel retrievals overlap
                 Thread.sleep(100);
-
-                // serve the POM of the artifact in the request path
-                var segments = exchange.getRequestURI().getPath().split("/");
-                var artifact = segments[segments.length - 3];
-                var body = buildPom(artifact, graph.getOrDefault(artifact, List.of())).getBytes();
-                exchange.sendResponseHeaders(200, body.length);
-                exchange.getResponseBody().write(body);
-                exchange.close();
             } catch (InterruptedException e) {
                 Thread.currentThread().interrupt();
-            } finally {
-                active_retrievals.decrementAndGet();
             }
+
+            // serve the POM of the artifact in the request path
+            var segments = exchange.getRequestURI().getPath().split("/");
+            var artifact = segments[segments.length - 3];
+            var body = buildPom(artifact, graph.getOrDefault(artifact, List.of())).getBytes();
+
+            // stop counting before the response is released, a sequential
+            // client sends its next request the moment the response
+            // arrives, even while this handler is still finishing up
+            active_retrievals.decrementAndGet();
+
+            exchange.sendResponseHeaders(200, body.length);
+            exchange.getResponseBody().write(body);
+            exchange.close();
         });
         server.setExecutor(Executors.newCachedThreadPool());
         return server;

src/test/java/rife/bld/dependencies/TestRepositoryFallthrough.java

@@ -0,0 +1,248 @@
+/*
+ * Copyright 2001-2026 Geert Bevin (gbevin[remove] at uwyn dot com)
+ * Licensed under the Apache License, Version 2.0 (the "License")
+ */
+package rife.bld.dependencies;
+
+import com.sun.net.httpserver.HttpServer;
+import org.junit.jupiter.api.Test;
+import rife.bld.dependencies.exceptions.ArtifactNotFoundException;
+import rife.bld.dependencies.exceptions.ArtifactRetrievalErrorException;
+import rife.bld.dependencies.exceptions.DependencyTransferException;
+import rife.ioc.HierarchicalProperties;
+import rife.tools.FileUtils;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.nio.file.Files;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.Executors;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static rife.bld.dependencies.Scope.*;
+
+/**
+ * A repository that fails with a transient issue is skipped in favor of
+ * the next one, and transient failures never degrade into not-found.
+ */
+public class TestRepositoryFallthrough {
+    private DependencyResolver resolver(List<Repository> repositories, Dependency dependency) {
+        return new DependencyResolver(new VersionResolution(new HierarchicalProperties()), ArtifactRetriever.instance(), repositories, dependency);
+    }
+
+    @Test
+    void testMetadataFallsThroughTransientFailure() throws Exception {
+        var failing = createFailingServer();
+        var serving = createArtifactServer(Map.of("tool:1.0.0", pom("tool", "1.0.0", "")),
+            Map.of("tool", metadata("tool", "1.0.0")));
+        failing.start();
+        serving.start();
+        try {
+            var resolver = resolver(List.of(serverRepository(failing), serverRepository(serving)),
+                new Dependency("com.example", "tool"));
+            assertEquals(Version.parse("1.0.0"), resolver.latestVersion());
+        } finally {
+            failing.stop(0);
+            serving.stop(0);
+        }
+    }
+
+    @Test
+    void testMetadataAllTransientFailures() throws Exception {
+        var failing1 = createFailingServer();
+        var failing2 = createFailingServer();
+        failing1.start();
+        failing2.start();
+        try {
+            var resolver = resolver(List.of(serverRepository(failing1), serverRepository(failing2)),
+                new Dependency("com.example", "tool"));
+            var exception = assertThrows(ArtifactRetrievalErrorException.class, resolver::latestVersion);
+            // the failure of the second repository is preserved as suppressed
+            assertEquals(1, exception.getSuppressed().length);
+        } finally {
+            failing1.stop(0);
+            failing2.stop(0);
+        }
+    }
+
+    @Test
+    void testMetadataNotFoundStaysNotFound() throws Exception {
+        var empty1 = createArtifactServer(Map.of(), Map.of());
+        var empty2 = createArtifactServer(Map.of(), Map.of());
+        empty1.start();
+        empty2.start();
+        try {
+            var resolver = resolver(List.of(serverRepository(empty1), serverRepository(empty2)),
+                new Dependency("com.example", "tool"));
+            assertThrows(ArtifactNotFoundException.class, resolver::latestVersion);
+        } finally {
+            empty1.stop(0);
+            empty2.stop(0);
+        }
+    }
+
+    @Test
+    void testPomFallsThroughTransientFailure() throws Exception {
+        var failing = createFailingServer();
+        var serving = createArtifactServer(Map.of(
+            "tool:1.0.0", pom("tool", "1.0.0", dependency("liba", "1.1.0")),
+            "liba:1.1.0", pom("liba", "1.1.0", "")), Map.of());
+        failing.start();
+        serving.start();
+        try {
+            var resolver = resolver(List.of(serverRepository(failing), serverRepository(serving)),
+                new Dependency("com.example", "tool", new VersionNumber(1, 0, 0)));
+            var dependencies = resolver.getAllDependencies(compile);
+            assertEquals(2, dependencies.size());
+        } finally {
+            failing.stop(0);
+            serving.stop(0);
+        }
+    }
+
+    @Test
+    void testPomAllTransientFailures() throws Exception {
+        var failing = createFailingServer();
+        failing.start();
+        try {
+            var resolver = resolver(List.of(serverRepository(failing)),
+                new Dependency("com.example", "tool", new VersionNumber(1, 0, 0)));
+            assertThrows(ArtifactRetrievalErrorException.class, () -> resolver.getAllDependencies(compile));
+        } finally {
+            failing.stop(0);
+        }
+    }
+
+    @Test
+    void testTransferFallsThroughTransientFailure() throws Exception {
+        var failing = createFailingServer();
+        var serving = createArtifactServer(Map.of("tool:1.0.0", pom("tool", "1.0.0", "")), Map.of());
+        failing.start();
+        serving.start();
+        var tmp = Files.createTempDirectory("fallthrough").toFile();
+        try {
+            var resolver = resolver(List.of(serverRepository(failing), serverRepository(serving)),
+                new Dependency("com.example", "tool", new VersionNumber(1, 0, 0)));
+            var artifact = resolver.transferIntoDirectory(tmp);
+            assertNotNull(artifact);
+            assertTrue(new File(tmp, "tool-1.0.0.jar").exists());
+        } finally {
+            failing.stop(0);
+            serving.stop(0);
+            FileUtils.deleteDirectory(tmp);
+        }
+    }
+
+    @Test
+    void testTransferAllTransientFailures() throws Exception {
+        var failing = createFailingServer();
+        failing.start();
+        var tmp = Files.createTempDirectory("fallthrough").toFile();
+        try {
+            var resolver = resolver(List.of(serverRepository(failing)),
+                new Dependency("com.example", "tool", new VersionNumber(1, 0, 0)));
+            // a transient failure surfaces as an exception, not as the
+            // null result that signals not-found
+            assertThrows(DependencyTransferException.class, () -> resolver.transferIntoDirectory(tmp));
+        } finally {
+            failing.stop(0);
+            FileUtils.deleteDirectory(tmp);
+        }
+    }
+
+    @Test
+    void testTransferNotFoundReturnsNull() throws Exception {
+        var empty = createArtifactServer(Map.of(), Map.of());
+        empty.start();
+        var tmp = Files.createTempDirectory("fallthrough").toFile();
+        try {
+            var resolver = resolver(List.of(serverRepository(empty)),
+                new Dependency("com.example", "tool", new VersionNumber(1, 0, 0)));
+            assertNull(resolver.transferIntoDirectory(tmp));
+        } finally {
+            empty.stop(0);
+            FileUtils.deleteDirectory(tmp);
+        }
+    }
+
+    private static Repository serverRepository(HttpServer server) {
+        return new Repository("http://localhost:" + server.getAddress().getPort() + "/");
+    }
+
+    private static HttpServer createFailingServer()
+    throws IOException {
+        var server = HttpServer.create(new InetSocketAddress("localhost", 0), 0);
+        server.createContext("/", exchange -> {
+            exchange.sendResponseHeaders(500, -1);
+            exchange.close();
+        });
+        server.setExecutor(Executors.newCachedThreadPool());
+        return server;
+    }
+
+    private static HttpServer createArtifactServer(Map<String, String> poms, Map<String, String> metadata)
+    throws IOException {
+        var server = HttpServer.create(new InetSocketAddress("localhost", 0), 0);
+        server.createContext("/", exchange -> {
+            var segments = exchange.getRequestURI().getPath().split("/");
+            var filename = segments[segments.length - 1];
+            byte[] body = null;
+            if (filename.endsWith(".pom") && segments.length >= 3) {
+                var content = poms.get(segments[segments.length - 3] + ":" + segments[segments.length - 2]);
+                if (content != null) {
+                    body = content.getBytes();
+                }
+            } else if (filename.endsWith(".jar") && segments.length >= 3) {
+                if (poms.containsKey(segments[segments.length - 3] + ":" + segments[segments.length - 2])) {
+                    body = "jar".getBytes();
+                }
+            } else if (filename.equals("maven-metadata.xml") && segments.length >= 2) {
+                var content = metadata.get(segments[segments.length - 2]);
+                if (content != null) {
+                    body = content.getBytes();
+                }
+            }
+            if (body == null) {
+                exchange.sendResponseHeaders(404, -1);
+            } else {
+                exchange.sendResponseHeaders(200, body.length);
+                exchange.getResponseBody().write(body);
+            }
+            exchange.close();
+        });
+        server.setExecutor(Executors.newCachedThreadPool());
+        return server;
+    }
+
+    private static String dependency(String artifact, String version) {
+        return "<dependency><groupId>com.example</groupId><artifactId>" + artifact + "</artifactId><version>" + version + "</version></dependency>";
+    }
+
+    private static String pom(String artifact, String version, String dependencies) {
+        return """
+            <?xml version="1.0" encoding="UTF-8"?>
+            <project>
+                <modelVersion>4.0.0</modelVersion>
+                <groupId>com.example</groupId>
+                <artifactId>%s</artifactId>
+                <version>%s</version>
+                <dependencies>%s</dependencies>
+            </project>""".formatted(artifact, version, dependencies);
+    }
+
+    private static String metadata(String artifact, String version) {
+        return """
+            <?xml version="1.0" encoding="UTF-8"?>
+            <metadata>
+                <groupId>com.example</groupId>
+                <artifactId>%s</artifactId>
+                <versioning>
+                    <latest>%s</latest>
+                    <release>%s</release>
+                    <versions><version>%s</version></versions>
+                </versioning>
+            </metadata>""".formatted(artifact, version, version, version);
+    }
+}

src/test/java/rife/bld/operations/TestDependencyTreeOperation.java

@@ -5,6 +5,7 @@
 package rife.bld.operations;
 
 import org.junit.jupiter.api.Test;
+import rife.bld.testing.RetryTest;
 import rife.bld.BldVersion;
 import rife.bld.WebProject;
 import rife.bld.dependencies.*;
@@ -14,6 +15,7 @@ import rife.tools.FileUtils;
 import rife.tools.StringUtils;
 
 import java.io.File;
+import java.io.IOException;
 import java.nio.file.Files;
 import java.util.List;
 
@@ -64,7 +66,7 @@ public class TestDependencyTreeOperation {
         assertTrue(operation3.repositories().contains(repository2));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testExecution()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();
@@ -137,7 +139,7 @@ public class TestDependencyTreeOperation {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testExecutionProvidedTest()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();
@@ -215,7 +217,7 @@ public class TestDependencyTreeOperation {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testFromProject()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();
@@ -292,7 +294,7 @@ public class TestDependencyTreeOperation {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testFromProjectProvidedTest()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();
@@ -367,7 +369,7 @@ public class TestDependencyTreeOperation {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testFromProjectExtensions()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();

src/test/java/rife/bld/operations/TestDownloadOperation.java

@@ -5,12 +5,14 @@
 package rife.bld.operations;
 
 import org.junit.jupiter.api.Test;
+import rife.bld.testing.RetryTest;
 import rife.bld.WebProject;
 import rife.bld.dependencies.*;
 import rife.bld.dependencies.Module;
 import rife.tools.FileUtils;
 
 import java.io.File;
+import java.io.IOException;
 import java.nio.file.Files;
 import java.util.List;
 
@@ -120,7 +122,7 @@ public class TestDownloadOperation {
         assertTrue(operation3.repositories().contains(repository2));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testExecution()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();
@@ -208,7 +210,7 @@ public class TestDownloadOperation {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testExecutionAdditionalSourcesJavadoc()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();
@@ -352,7 +354,7 @@ public class TestDownloadOperation {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testFromProject()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();
@@ -460,7 +462,7 @@ public class TestDownloadOperation {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testFromProject2()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();

src/test/java/rife/bld/operations/TestPurgeOperation.java

@@ -5,12 +5,14 @@
 package rife.bld.operations;
 
 import org.junit.jupiter.api.Test;
+import rife.bld.testing.RetryTest;
 import rife.bld.WebProject;
 import rife.bld.dependencies.*;
 import rife.bld.dependencies.Module;
 import rife.tools.FileUtils;
 
 import java.io.File;
+import java.io.IOException;
 import java.nio.file.Files;
 import java.util.List;
 
@@ -115,7 +117,7 @@ public class TestPurgeOperation {
         assertTrue(operation3.repositories().contains(repository2));
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testExecution()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();
@@ -325,7 +327,7 @@ public class TestPurgeOperation {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testExecutionAdditionalSourcesJavadoc()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();
@@ -798,7 +800,7 @@ public class TestPurgeOperation {
         }
     }
 
-    @Test
+    @RetryTest(value = 3, delay = 2, withExceptions = IOException.class)
     void testFromProject()
     throws Exception {
         var tmp = Files.createTempDirectory("test").toFile();

src/test/java/rife/bld/wrapper/TestWrapperRetry.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2001-2026 Geert Bevin (gbevin[remove] at uwyn dot com)
+ * Licensed under the Apache License, Version 2.0 (the "License")
+ */
+package rife.bld.wrapper;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class TestWrapperRetry {
+    @Test
+    void testSucceedsWithoutRetry() throws Exception {
+        var attempts = new AtomicInteger();
+        var result = Wrapper.retryOnTransientIoIssues(() -> {
+            attempts.incrementAndGet();
+            return "ok";
+        }, 3, 1);
+        assertEquals("ok", result);
+        assertEquals(1, attempts.get());
+    }
+
+    @Test
+    void testRetriesTransientIoIssues() throws Exception {
+        // the first two attempts fail with a transient issue, the third
+        // succeeds
+        var attempts = new AtomicInteger();
+        var result = Wrapper.retryOnTransientIoIssues(() -> {
+            if (attempts.incrementAndGet() < 3) {
+                throw new IOException("Connection timed out");
+            }
+            return "ok";
+        }, 3, 1);
+        assertEquals("ok", result);
+        assertEquals(3, attempts.get());
+    }
+
+    @Test
+    void testThrowsAfterExhaustedAttempts() {
+        var attempts = new AtomicInteger();
+        var exception = assertThrows(IOException.class, () ->
+            Wrapper.retryOnTransientIoIssues(() -> {
+                attempts.incrementAndGet();
+                throw new IOException("Connection timed out");
+            }, 3, 1));
+        assertEquals("Connection timed out", exception.getMessage());
+        assertEquals(3, attempts.get());
+    }
+
+    @Test
+    void testDoesntRetryMissingResources() {
+        // a 404 is not transient, retrying it would only slow down the
+        // fallback paths that rely on a quick failure
+        var attempts = new AtomicInteger();
+        assertThrows(FileNotFoundException.class, () ->
+            Wrapper.retryOnTransientIoIssues(() -> {
+                attempts.incrementAndGet();
+                throw new FileNotFoundException("http://localhost/absent");
+            }, 3, 1));
+        assertEquals(1, attempts.get());
+    }
+}