Gracefully handle corrupted manifest files (#337)

src/main/java/me/itzg/helpers/files/Manifests.java

@@ -1,5 +1,6 @@
 package me.itzg.helpers.files;
 
+import com.fasterxml.jackson.core.JsonProcessingException;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -10,9 +11,11 @@
 import java.util.function.Consumer;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
+import lombok.extern.slf4j.Slf4j;
 import me.itzg.helpers.json.ObjectMappers;
 import org.slf4j.Logger;
 
+@Slf4j
 public class Manifests {
 
     private static final String SUFFIX = ".json";
@@ -112,13 +115,17 @@ public static boolean allFilesPresent(Path basePath, BaseManifest manifest, List
      *
      * @param outputDir directory where manifest and other module files are based
      * @param id module identifier, such as "fabric"
+     * @return the loaded manifest file or null if it didn't exist or was invalid content
      */
     public static <M extends BaseManifest> M load(Path outputDir, String id, Class<M> manifestClass) {
         final Path manifestPath = buildManifestPath(outputDir, id);
         if (Files.exists(manifestPath)) {
             final M manifest;
             try {
                 manifest = ObjectMappers.defaultMapper().readValue(manifestPath.toFile(), manifestClass);
+            } catch (JsonProcessingException e) {
+                log.error("Failed to parse existing manifest file {}", manifestPath, e);
+                return null;
             } catch (IOException e) {
                 throw new ManifestException("Failed to load existing manifest from "+manifestPath, e);
             }

src/test/java/me/itzg/helpers/files/ManifestsTest.java

@@ -0,0 +1,36 @@
+package me.itzg.helpers.files;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Collections;
+import lombok.Getter;
+import lombok.experimental.SuperBuilder;
+import lombok.extern.jackson.Jacksonized;
+import org.apache.commons.lang3.RandomStringUtils;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+class ManifestsTest {
+
+    @TempDir
+    Path tempDir;
+
+    @Getter @SuperBuilder @Jacksonized
+    static class EmptyManifest extends BaseManifest {
+
+    }
+
+    @Test
+    void loadFailsGracefullyWhenInvalid() throws IOException {
+        final String id = RandomStringUtils.randomAlphabetic(5);
+
+        final Path manifestFile = tempDir.resolve(String.format(".%s-manifest.json", id));
+        Files.write(manifestFile, Collections.singletonList("not json"));
+
+        final EmptyManifest manifest = Manifests.load(tempDir, id, EmptyManifest.class);
+        assertThat(manifest).isNull();
+    }
+}