michael@0: /*
michael@0:  * Copyright (C) 2013 Square, Inc.
michael@0:  *
michael@0:  * Licensed under the Apache License, Version 2.0 (the "License");
michael@0:  * you may not use this file except in compliance with the License.
michael@0:  * You may obtain a copy of the License at
michael@0:  *
michael@0:  *      http://www.apache.org/licenses/LICENSE-2.0
michael@0:  *
michael@0:  * Unless required by applicable law or agreed to in writing, software
michael@0:  * distributed under the License is distributed on an "AS IS" BASIS,
michael@0:  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
michael@0:  * See the License for the specific language governing permissions and
michael@0:  * limitations under the License.
michael@0:  */
michael@0: package com.squareup.picasso;
michael@0: 
michael@0: import java.io.BufferedInputStream;
michael@0: import java.io.IOException;
michael@0: import java.io.InputStream;
michael@0: 
michael@0: /**
michael@0:  * An input stream wrapper that supports unlimited independent cursors for
michael@0:  * marking and resetting. Each cursor is a token, and it's the caller's
michael@0:  * responsibility to keep track of these.
michael@0:  */
michael@0: final class MarkableInputStream extends InputStream {
michael@0:   private final InputStream in;
michael@0: 
michael@0:   private long offset;
michael@0:   private long reset;
michael@0:   private long limit;
michael@0: 
michael@0:   private long defaultMark = -1;
michael@0: 
michael@0:   public MarkableInputStream(InputStream in) {
michael@0:     if (!in.markSupported()) {
michael@0:       in = new BufferedInputStream(in);
michael@0:     }
michael@0:     this.in = in;
michael@0:   }
michael@0: 
michael@0:   /** Marks this place in the stream so we can reset back to it later. */
michael@0:   @Override public void mark(int readLimit) {
michael@0:     defaultMark = savePosition(readLimit);
michael@0:   }
michael@0: 
michael@0:   /**
michael@0:    * Returns an opaque token representing the current position in the stream.
michael@0:    * Call {@link #reset(long)} to return to this position in the stream later.
michael@0:    * It is an error to call {@link #reset(long)} after consuming more than
michael@0:    * {@code readLimit} bytes from this stream.
michael@0:    */
michael@0:   public long savePosition(int readLimit) {
michael@0:     long offsetLimit = offset + readLimit;
michael@0:     if (limit < offsetLimit) {
michael@0:       setLimit(offsetLimit);
michael@0:     }
michael@0:     return offset;
michael@0:   }
michael@0: 
michael@0:   /**
michael@0:    * Makes sure that the underlying stream can backtrack the full range from
michael@0:    * {@code reset} thru {@code limit}. Since we can't call {@code mark()}
michael@0:    * without also adjusting the reset-to-position on the underlying stream this
michael@0:    * method resets first and then marks the union of the two byte ranges. On
michael@0:    * buffered streams this additional cursor motion shouldn't result in any
michael@0:    * additional I/O.
michael@0:    */
michael@0:   private void setLimit(long limit) {
michael@0:     try {
michael@0:       if (reset < offset && offset <= this.limit) {
michael@0:         in.reset();
michael@0:         in.mark((int) (limit - reset));
michael@0:         skip(reset, offset);
michael@0:       } else {
michael@0:         reset = offset;
michael@0:         in.mark((int) (limit - offset));
michael@0:       }
michael@0:       this.limit = limit;
michael@0:     } catch (IOException e) {
michael@0:       throw new IllegalStateException("Unable to mark: " + e);
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   /** Resets the stream to the most recent {@link #mark mark}. */
michael@0:   @Override public void reset() throws IOException {
michael@0:     reset(defaultMark);
michael@0:   }
michael@0: 
michael@0:   /** Resets the stream to the position recorded by {@code token}. */
michael@0:   public void reset(long token) throws IOException {
michael@0:     if (offset > limit || token < reset) {
michael@0:       throw new IOException("Cannot reset");
michael@0:     }
michael@0:     in.reset();
michael@0:     skip(reset, token);
michael@0:     offset = token;
michael@0:   }
michael@0: 
michael@0:   /** Skips {@code target - current} bytes and returns. */
michael@0:   private void skip(long current, long target) throws IOException {
michael@0:     while (current < target) {
michael@0:       long skipped = in.skip(target - current);
michael@0:       if (skipped == 0) {
michael@0:         if (read() == -1) {
michael@0:           break; // EOF
michael@0:         } else {
michael@0:           skipped = 1;
michael@0:         }
michael@0:       }
michael@0:       current += skipped;
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   @Override public int read() throws IOException {
michael@0:     int result = in.read();
michael@0:     if (result != -1) {
michael@0:       offset++;
michael@0:     }
michael@0:     return result;
michael@0:   }
michael@0: 
michael@0:   @Override public int read(byte[] buffer) throws IOException {
michael@0:     int count = in.read(buffer);
michael@0:     if (count != -1) {
michael@0:       offset += count;
michael@0:     }
michael@0:     return count;
michael@0:   }
michael@0: 
michael@0:   @Override public int read(byte[] buffer, int offset, int length) throws IOException {
michael@0:     int count = in.read(buffer, offset, length);
michael@0:     if (count != -1) {
michael@0:       this.offset += count;
michael@0:     }
michael@0:     return count;
michael@0:   }
michael@0: 
michael@0:   @Override public long skip(long byteCount) throws IOException {
michael@0:     long skipped = in.skip(byteCount);
michael@0:     offset += skipped;
michael@0:     return skipped;
michael@0:   }
michael@0: 
michael@0:   @Override public int available() throws IOException {
michael@0:     return in.available();
michael@0:   }
michael@0: 
michael@0:   @Override public void close() throws IOException {
michael@0:     in.close();
michael@0:   }
michael@0: 
michael@0:   @Override public boolean markSupported() {
michael@0:     return in.markSupported();
michael@0:   }
michael@0: }