cf: log warning rather than failing when unknown file hash algo (#459)

Author: itzg

src/main/java/me/itzg/helpers/curseforge/CurseForgeInstaller.java

@@ -807,7 +807,7 @@ private Mono<ResolveResult> downloadOrResolveFile(InstallContext context, CurseF
 
         if (locatedFile != null) {
             log.info("Mod file {} already exists", locatedFile);
-            return FileHashVerifier.verify(locatedFile, cfFile.getHashes())
+            return verifyHash(cfFile, locatedFile)
                 .map(ResolveResult::new);
         }
         else {
@@ -817,7 +817,7 @@ private Mono<ResolveResult> downloadOrResolveFile(InstallContext context, CurseF
             }
 
             return context.cfApi.download(cfFile, outputFile, modFileDownloadStatusHandler(this.outputDir, log))
-                .flatMap(path -> FileHashVerifier.verify(path, cfFile.getHashes()))
+                .flatMap(path -> verifyHash(cfFile, path))
                 .map(ResolveResult::new)
                 .onErrorResume(
                     e -> e instanceof FailedRequestException
@@ -827,6 +827,16 @@ private Mono<ResolveResult> downloadOrResolveFile(InstallContext context, CurseF
         }
     }
 
+    private static Mono<Path> verifyHash(CurseForgeFile cfFile, Path path) {
+        return FileHashVerifier.verify(path, cfFile.getHashes())
+            .onErrorResume(IllegalArgumentException.class::isInstance,
+                e -> {
+                    log.warn("Unable to process hash for mod {}: {}", cfFile, e.getMessage());
+                    return Mono.just(path);
+                }
+            );
+    }
+
     private Mono<ResolveResult> handleFileNeedingManualDownload(CurseForgeMod modInfo, boolean isWorld, CurseForgeFile cfFile,
         Path outputFile
     ) {

src/main/java/me/itzg/helpers/curseforge/FileHashVerifier.java

@@ -24,6 +24,10 @@ public class FileHashVerifier {
         algos.put(HashAlgo.Sha1, ChecksumAlgo.SHA1);
     }
 
+    /**
+     * @return Mono.error with {@link FileHashInvalidException}
+     * or {@link IllegalArgumentException} when compatible checksum algorithm can't be found
+     */
     public static Mono<Path> verify(Path file, List<FileHash> hashes) {
         if (hashes.isEmpty()) {
             return Mono.just(file);