public String readLine() throws IOException {
    synchronized (in) {
      if (buf == null) {
        throw new IOException("LineReader is closed");
      }

      // Read more data if we are at the end of the buffered data.
      // Though it's an error to read after an exception, we will let {@code fillBuf()}
      // throw again if that happens; thus we need to handle end == -1 as well as end == pos.
      if (pos >= end) {
        fillBuf();
      }
      // Try to find LF in the buffered data and return the line if successful.
      for (int i = pos; i != end; ++i) {
        if (buf[i] == LF) {
          int lineEnd = (i != pos && buf[i - 1] == CR) ? i - 1 : i;
          String res = new String(buf, pos, lineEnd - pos, charset.name());
          pos = i + 1;
          return res;
        }
      }

      // Let's anticipate up to 80 characters on top of those already read.
      ByteArrayOutputStream out = new ByteArrayOutputStream(end - pos + 80) {
        @Override
        public String toString() {
          int length = (count > 0 && buf[count - 1] == CR) ? count - 1 : count;
          try {
            return new String(buf, 0, length, charset.name());
          } catch (UnsupportedEncodingException e) {
            throw new AssertionError(e); // Since we control the charset this will never happen.
          }
        }
      };

      while (true) {
        out.write(buf, pos, end - pos);
        // Mark unterminated line in case fillBuf throws EOFException or IOException.
        end = -1;
        fillBuf();
        // Try to find LF in the buffered data and return the line if successful.
        for (int i = pos; i != end; ++i) {
          if (buf[i] == LF) {
            if (i != pos) {
              out.write(buf, pos, i - pos);
            }
            pos = i + 1;
            return out.toString();
          }
        }
      }
    }
  }
Reads the next line. A line ends with {@code "\n"} or {@code "\r\n"},
this end of line marker is not included in the result.

@return the next line from the input.
@throws IOException for underlying {@code InputStream} errors.
@throws EOFException for the end of source stream.
core/src/main/java/com/bumptech/glide/disklrucache/StrictLineReader.java