zlibを使ってNSDataに圧縮/展開機能を追加する

NSDataと言えばバイト配列を扱うデータホルダー的なクラスです。
データホルダーなら、保持するデータを圧縮する機能があっても良いはず。
ということでNSDataを拡張してzlib機能を追加してみましょう。

まずはインタフェース。

NSDataExt.h

#import <Foundation/Foundation.h>

@interface NSData (NSDataZlibExtension)
- (id)deflate:(int)compressionLevel;
- (id)inflate;
@end

そして実装です。

NSDataExt.m

#import "NSDataZlib.h"
#import <zlib.h>

@implementation NSData (NSDataZlibExtension)
- (z_stream)initialized_zStream {
  z_stream zStream;
  zStream.zalloc = Z_NULL;
  zStream.zfree = Z_NULL;
  zStream.opaque = Z_NULL;
  return zStream;
}

- (id)deflate:(int)compressionLevel {
  z_stream zStream = [self initialized_zStream];
  Bytef buffer[131072];
  deflateInit(&zStream, compressionLevel);
  zStream.next_in = (Bytef *)self.bytes;
  zStream.avail_in = (UInt)self.length;
  int retval = Z_OK;
  NSMutableData *ret = [NSMutableData dataWithCapacity:0];
  do {
    zStream.next_out = buffer;
    zStream.avail_out = sizeof(buffer);
    retval = deflate(&zStream, Z_FINISH);
    size_t length = sizeof(buffer) - zStream.avail_out;
    if (length > 0)
      [ret appendBytes:buffer length:length];
  } while (zStream.avail_out != sizeof(buffer));
  deflateEnd(&zStream);
  return ret;
}

- (id)inflate {
  z_stream zStream = [self initialized_zStream];
  Bytef buffer[131072];
  inflateInit(&zStream);
  zStream.next_in = (Bytef *)self.bytes;
  zStream.avail_in = (UInt)self.length;
  int retval = Z_OK;
  NSMutableData *ret = [NSMutableData dataWithCapacity:0];
  do {
    zStream.next_out = buffer;
    zStream.avail_out = sizeof(buffer);
    retval = inflate(&zStream, Z_FINISH);
    size_t length = sizeof(buffer) - zStream.avail_out;
    if (length > 0)
      [ret appendBytes:buffer length:length];
  } while (zStream.avail_out != sizeof(buffer));
  inflateEnd(&zStream);
  return ret;
}
@end