public void installSnapshot()

in ratis-server/src/main/java/org/apache/ratis/server/storage/SnapshotManager.java [102:171]
54 lines of code
9 McCabe index (conditional complexity)

  public void installSnapshot(InstallSnapshotRequestProto request, StateMachine stateMachine) throws IOException {
    final InstallSnapshotRequestProto.SnapshotChunkProto snapshotChunkRequest = request.getSnapshotChunk();
    final long lastIncludedIndex = snapshotChunkRequest.getTermIndex().getIndex();

    // create a unique temporary directory
    final File tmpDir =  new File(this.snapshotTmpDir.get(), "snapshot-" + snapshotChunkRequest.getRequestId());
    FileUtils.createDirectories(tmpDir);
    tmpDir.deleteOnExit();

    LOG.info("Installing snapshot:{}, to tmp dir:{}",
        ServerStringUtils.toInstallSnapshotRequestString(request), tmpDir);

    // TODO: Make sure that subsequent requests for the same installSnapshot are coming in order,
    // and are not lost when whole request cycle is done. Check requestId and requestIndex here
    for (FileChunkProto chunk : snapshotChunkRequest.getFileChunksList()) {
      SnapshotInfo pi = stateMachine.getLatestSnapshot();
      if (pi != null && pi.getTermIndex().getIndex() >= lastIncludedIndex) {
        throw new IOException("There exists snapshot file "
            + pi.getFiles() + " in " + selfId
            + " with endIndex >= lastIncludedIndex " + lastIncludedIndex);
      }

      final File tmpSnapshotFile = new File(tmpDir, getRelativePath.apply(chunk));
      FileUtils.createDirectoriesDeleteExistingNonDirectory(tmpSnapshotFile.getParentFile());

      try (FileChannel out = open(chunk, tmpSnapshotFile)) {
        final ByteBuffer data = chunk.getData().asReadOnlyByteBuffer();
        digester.update(data.duplicate());

        int written = 0;
        for(; data.remaining() > 0; ) {
          written += out.write(data);
        }
        Preconditions.assertSame(chunk.getData().size(), written, "written");
      }

      // rename the temp snapshot file if this is the last chunk. also verify
      // the md5 digest and create the md5 meta-file.
      if (chunk.getDone()) {
        final MD5Hash expectedDigest =
            new MD5Hash(chunk.getFileDigest().toByteArray());
        // calculate the checksum of the snapshot file and compare it with the
        // file digest in the request
        final MD5Hash digest = new MD5Hash(digester.digest());
        if (!digest.equals(expectedDigest)) {
          LOG.warn("The snapshot md5 digest {} does not match expected {}",
              digest, expectedDigest);
          // rename the temp snapshot file to .corrupt
          String renameMessage;
          try {
            final File corruptedFile = FileUtils.move(tmpSnapshotFile, CORRUPT + StringUtils.currentDateTime());
            renameMessage = "Renamed temporary snapshot file " + tmpSnapshotFile + " to " + corruptedFile;
          } catch (IOException e) {
            renameMessage = "Tried but failed to rename temporary snapshot file " + tmpSnapshotFile
                + " to a " + CORRUPT + " file";
            LOG.warn(renameMessage, e);
            renameMessage += ": " + e;
          }
          throw new CorruptedFileException(tmpSnapshotFile,
              "MD5 mismatch for snapshot-" + lastIncludedIndex + " installation.  " + renameMessage);
        } else {
          MD5FileUtil.saveMD5File(tmpSnapshotFile, digest);
        }
      }
    }

    if (snapshotChunkRequest.getDone()) {
      rename(tmpDir, snapshotDir.get());
    }
  }