content: /*
   * Copyright (C) 2011 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.android.internal.util;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.io.InputStream;
  import java.net.ProtocolException;
  import java.nio.charset.StandardCharsets;
  
  /**
   * Reader that specializes in parsing {@code /proc/} files quickly. Walks
   * through the stream using a single space {@code ' '} as token separator, and
   * requires each line boundary to be explicitly acknowledged using
   * {@link #finishLine()}. Assumes {@link StandardCharsets#US_ASCII} encoding.
   * <p>
   * Currently doesn't support formats based on {@code \0}, tabs, or repeated
   * delimiters.
   */
  public class ProcFileReader implements Closeable {
      private final InputStream mStream;
      private final byte[] mBuffer;
  
      /** Write pointer in {@link #mBuffer}. */
      private int mTail;
      /** Flag when last read token finished current line. */
      private boolean mLineFinished;
  
      public ProcFileReader(InputStream stream) throws IOException {
          this(stream, 4096);
      }
  
      public ProcFileReader(InputStream stream, int bufferSize) throws IOException {
          mStream = stream;
          mBuffer = new byte[bufferSize];
  
          // read enough to answer hasMoreData
          fillBuf();
      }
  
      /**
       * Read more data from {@link #mStream} into internal buffer.
       */
      private int fillBuf() throws IOException {
          final int length = mBuffer.length - mTail;
          if (length == 0) {
              throw new IOException("attempting to fill already-full buffer");
          }
  
          final int read = mStream.read(mBuffer, mTail, length);
          if (read != -1) {
              mTail += read;
          }
          return read;
      }
  
      /**
       * Consume number of bytes from beginning of internal buffer. If consuming
       * all remaining bytes, will attempt to {@link #fillBuf()}.
       */
      private void consumeBuf(int count) throws IOException {
          // TODO: consider moving to read pointer, but for now traceview says
          // these copies aren't a bottleneck.
          System.arraycopy(mBuffer, count, mBuffer, 0, mTail - count);
          mTail -= count;
          if (mTail == 0) {
              fillBuf();
          }
      }
  
      /**
       * Find buffer index of next token delimiter, usually space or newline.
       * Fills buffer as needed.
       *
       * @return Index of next delimeter, otherwise -1 if no tokens remain on
       *         current line.
       */
      private int nextTokenIndex() throws IOException {
          if (mLineFinished) {
              return -1;
          }
  
          int i = 0;
          do {
              // scan forward for token boundary
              for (; i < mTail; i++) {
                  final byte b = mBuffer[i];
                  if (b == '\n') {
                      mLineFinished = true;
                      return i;
                  }
                  if (b == ' ') {
                      return i;
                  }
              }
          } while (fillBuf() > 0);
  
          throw new ProtocolException("End of stream while looking for token boundary");
      }
  
      /**
       * Check if stream has more data to be parsed.
       */
      public boolean hasMoreData() {
          return mTail > 0;
      }
  
      /**
       * Finish current line, skipping any remaining data.
       */
      public void finishLine() throws IOException {
          // last token already finished line; reset silently
          if (mLineFinished) {
              mLineFinished = false;
              return;
          }
  
          int i = 0;
          do {
              // scan forward for line boundary and consume
              for (; i < mTail; i++) {
                  if (mBuffer[i] == '\n') {
                      consumeBuf(i + 1);
                      return;
                  }
              }
          } while (fillBuf() > 0);
  
          throw new ProtocolException("End of stream while looking for line boundary");
      }
  
      /**
       * Parse and return next token as {@link String}.
       */
      public String nextString() throws IOException {
          final int tokenIndex = nextTokenIndex();
          if (tokenIndex == -1) {
              throw new ProtocolException("Missing required string");
          } else {
              return parseAndConsumeString(tokenIndex);
          }
      }
  
      /**
       * Parse and return next token as base-10 encoded {@code long}.
       */
      public long nextLong() throws IOException {
          final int tokenIndex = nextTokenIndex();
          if (tokenIndex == -1) {
              throw new ProtocolException("Missing required long");
          } else {
              return parseAndConsumeLong(tokenIndex);
          }
      }
  
      /**
       * Parse and return next token as base-10 encoded {@code long}, or return
       * the given default value if no remaining tokens on current line.
       */
      public long nextOptionalLong(long def) throws IOException {
          final int tokenIndex = nextTokenIndex();
          if (tokenIndex == -1) {
              return def;
          } else {
              return parseAndConsumeLong(tokenIndex);
          }
      }
  
      private String parseAndConsumeString(int tokenIndex) throws IOException {
          final String s = new String(mBuffer, 0, tokenIndex, StandardCharsets.US_ASCII);
          consumeBuf(tokenIndex + 1);
          return s;
      }
  
      private long parseAndConsumeLong(int tokenIndex) throws IOException {
          final boolean negative = mBuffer[0] == '-';
  
          // TODO: refactor into something like IntegralToString
          long result = 0;
          for (int i = negative ? 1 : 0; i < tokenIndex; i++) {
              final int digit = mBuffer[i] - '0';
              if (digit < 0 || digit > 9) {
                  throw invalidLong(tokenIndex);
              }
  
              // always parse as negative number and apply sign later; this
              // correctly handles MIN_VALUE which is "larger" than MAX_VALUE.
              final long next = result * 10 - digit;
              if (next > result) {
                  throw invalidLong(tokenIndex);
              }
              result = next;
          }
  
          consumeBuf(tokenIndex + 1);
          return negative ? result : -result;
      }
  
      private NumberFormatException invalidLong(int tokenIndex) {
          return new NumberFormatException(
                  "invalid long: " + new String(mBuffer, 0, tokenIndex, StandardCharsets.US_ASCII));
      }
  
      /**
       * Parse and return next token as base-10 encoded {@code int}.
       */
      public int nextInt() throws IOException {
          final long value = nextLong();
          if (value > Integer.MAX_VALUE || value < Integer.MIN_VALUE) {
              throw new NumberFormatException("parsed value larger than integer");
          }
          return (int) value;
      }
  
      @Override
      public void close() throws IOException {
          mStream.close();
      }
  }
  