Index: src/OFStream.h
==================================================================
--- src/OFStream.h
+++ src/OFStream.h
@@ -1050,10 +1050,34 @@
  * @brief Cancels all pending asyncronous requests on the stream.
  */
 - (void)cancelAsyncRequests;
 #endif
 
+/*!
+ * @brief "Reverses" a read operation, meaning the bytes from the specified
+ *	  buffer will be returned on the next read operation.
+ *
+ * This is useful for reading into a buffer, parsing the data and then giving
+ * back the data which does not need to be processed. This can be used to
+ * optimize situations in which the length of the data that needs to be
+ * processed is not known before all data has been processed - for example in
+ * decompression - in which it would otherwise be necessary to read byte by
+ * byte to avoid consuming bytes that need to be parsed by something else -
+ * for example the data descriptor in a ZIP archive which immediately follows
+ * the compressed data.
+ *
+ * If the stream is a file, this method does not change any data in the file.
+ *
+ * If the stream is seekable, a seek operation will discard any data that was
+ * unread.
+ *
+ * @param buffer The buffer to unread
+ * @param length The length of the buffer to unread
+ */
+- (void)unreadFromBuffer: (const void*)buffer
+		  length: (size_t)length;
+
 /*!
  * @brief Closes the stream.
  */
 - (void)close;
 

Index: src/OFStream.m
==================================================================
--- src/OFStream.m
+++ src/OFStream.m
@@ -40,10 +40,11 @@
 #import "OFRunLoop+Private.h"
 
 #import "OFInvalidArgumentException.h"
 #import "OFInvalidFormatException.h"
 #import "OFNotImplementedException.h"
+#import "OFOutOfRangeException.h"
 #import "OFSetOptionFailedException.h"
 
 #import "macros.h"
 #import "of_asprintf.h"
 
@@ -1553,10 +1554,25 @@
 - (void)cancelAsyncRequests
 {
 	[OFRunLoop OF_cancelAsyncRequestsForStream: self];
 }
 #endif
+
+- (void)unreadFromBuffer: (const void*)buffer
+		  length: (size_t)length
+{
+	if (length > SIZE_MAX - _readBufferLength)
+		@throw [OFOutOfRangeException exception];
+
+	_readBuffer = [self resizeMemory: _readBuffer
+				    size: _readBufferLength + length];
+
+	memmove(_readBuffer + length, _readBuffer, _readBufferLength);
+	memcpy(_readBuffer, buffer, length);
+
+	_readBufferLength += length;
+}
 
 - (void)close
 {
 	[self doesNotRecognizeSelector: _cmd];
 	abort();