PersistedFile loadTelemetriesFromDisk()

in agent/agent-tooling/src/main/java/com/microsoft/applicationinsights/agent/internal/localstorage/LocalFileLoader.java [69:140]
60 lines of code
9 McCabe index (conditional complexity)

  PersistedFile loadTelemetriesFromDisk() {
    String filenameToBeLoaded = localFileCache.poll();
    if (filenameToBeLoaded == null) {
      return null;
    }

    // when reading a file from the disk, loader renames the source file to "*.tmp" to prevent other
    // threads from processing the same file over and over again. this will prevent same data gets
    // sent to Application Insights more than once. after reading raw bytes from the .tmp file,
    // loader will delete the temp file when http
    // response confirms it is sent successfully; otherwise, temp file will get renamed back to the
    // source file extension.
    File tempFile;
    File sourceFile;
    try {
      sourceFile = new File(telemetryFolder, filenameToBeLoaded);
      if (!sourceFile.exists()) {
        return null;
      }

      tempFile =
          new File(
              telemetryFolder,
              FilenameUtils.getBaseName(filenameToBeLoaded) + TEMPORARY_FILE_EXTENSION);
      FileUtils.moveFile(sourceFile, tempFile);
    } catch (IOException e) {
      operationLogger.recordFailure(
          "Failed to change "
              + filenameToBeLoaded
              + " to have "
              + TEMPORARY_FILE_EXTENSION
              + " extension: ",
          e);
      incrementReadFailureCount();
      return null;
    }

    if (tempFile.length() <= 36) {
      if (LocalStorageUtils.deleteFileWithRetries(tempFile)) {
        operationLogger.recordFailure(
            "Fail to delete a corrupted persisted file: length is  " + tempFile.length());
      }
      return null;
    }

    byte[] ikeyBytes = new byte[36];
    int rawByteLength = (int) tempFile.length() - 36;
    byte[] telemetryBytes = new byte[rawByteLength];
    String instrumentationKey;
    try (FileInputStream fileInputStream = new FileInputStream(tempFile)) {
      readFully(fileInputStream, ikeyBytes, 36);
      instrumentationKey = new String(ikeyBytes, UTF_8);
      if (!isInstrumentationKeyValid(instrumentationKey)) {
        fileInputStream.close(); // need to close FileInputStream before delete
        if (!LocalStorageUtils.deleteFileWithRetries(tempFile)) {
          operationLogger.recordFailure(
              "Fail to delete the old persisted file with an invalid instrumentation key "
                  + tempFile.getName());
        }
        return null;
      }

      readFully(fileInputStream, telemetryBytes, rawByteLength);
    } catch (IOException ex) {
      operationLogger.recordFailure("Fail to read telemetry from " + tempFile.getName(), ex);
      incrementReadFailureCount();
      return null;
    }

    operationLogger.recordSuccess();
    return new PersistedFile(tempFile, instrumentationKey, ByteBuffer.wrap(telemetryBytes));
  }