Revert "paper: fall back to VERSION env var when jar missing metadata (#422)"

This reverts commit 1898ff8.

Author: itzg

src/main/java/me/itzg/helpers/paper/InstallPaperCommand.java

@@ -5,6 +5,7 @@
 import java.net.URI;
 import java.nio.file.Path;
 import java.util.Collections;
+import java.util.Optional;
 import java.util.concurrent.Callable;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -162,45 +163,33 @@ private Result downloadCustom(URI downloadUrl) {
                 .handleStatus(Fetch.loggingDownloadStatusHandler(log))
                 .assemble()
                 .publishOn(Schedulers.boundedElastic())
-                .flatMap(serverJar -> processDownloadedJar(downloadUrl, serverJar))
+                .flatMap(serverJar -> {
+                    final String version;
+                    try {
+                        version = Optional.ofNullable(extractVersionFromJar(serverJar))
+                                .orElseGet(() -> {
+                                    log.warn("Version metadata {} was missing from server jar: {}", VERSION_METADATA_NAME, serverJar);
+                                    return "custom";
+                                });
+
+                    } catch (IOException e) {
+                        return Mono.error(new GenericException("Failed to extract version from custom server jar", e));
+                    }
+                    return Mono.just(Result.builder()
+                        .serverJar(serverJar)
+                        .newManifest(
+                            PaperManifest.builder()
+                                .customDownloadUrl(downloadUrl)
+                                .files(Collections.singleton(Manifests.relativize(outputDirectory, serverJar)))
+                                .build()
+                        )
+                        .version(version)
+                        .build());
+                })
                 .block();
         }
     }
 
-    private Mono<Result> processDownloadedJar(URI downloadUrl, Path serverJar) {
-        final String version;
-        try {
-            final String versionFromJar = extractVersionFromJar(serverJar);
-            if (versionFromJar != null) {
-                version = versionFromJar;
-            }
-            else {
-                log.warn("Version metadata {} was missing from server jar: {}", VERSION_METADATA_NAME, serverJar);
-                final String fromEnv = System.getenv("VERSION");
-                if (fromEnv != null) {
-                    version = fromEnv;
-                }
-                else {
-                    throw new GenericException("Set environment variable 'VERSION' due to missing version metadata");
-                }
-
-            }
-        } catch (IOException e) {
-            return Mono.error(new GenericException("Failed to extract version from custom server jar", e));
-        }
-
-        return Mono.just(Result.builder()
-            .serverJar(serverJar)
-            .newManifest(
-                PaperManifest.builder()
-                    .customDownloadUrl(downloadUrl)
-                    .files(Collections.singleton(Manifests.relativize(outputDirectory, serverJar)))
-                    .build()
-            )
-            .version(version)
-            .build());
-    }
-
     private String extractVersionFromJar(Path serverJar) throws IOException {
         final VersionMeta versionMeta = IoStreams.readFileFromZip(serverJar, VERSION_METADATA_NAME, in ->
             ObjectMappers.defaultMapper().readValue(in, VersionMeta.class)