Index: src/OFZIPArchive.h
==================================================================
--- src/OFZIPArchive.h
+++ src/OFZIPArchive.h
@@ -32,10 +32,15 @@
  * @brief A class for accessing and manipulating ZIP files.
  */
 @interface OFZIPArchive: OFObject
 {
 	OFSeekableStream *_stream;
+	enum {
+		OF_ZIP_ARCHIVE_MODE_READ,
+		OF_ZIP_ARCHIVE_MODE_WRITE,
+		OF_ZIP_ARCHIVE_MODE_APPEND
+	} _mode;
 	uint32_t _diskNumber, _centralDirectoryDisk;
 	uint64_t _centralDirectoryEntriesInDisk, _centralDirectoryEntries;
 	uint64_t _centralDirectorySize;
 	int64_t _centralDirectoryOffset;
 	OFString *_archiveComment;
@@ -52,44 +57,60 @@
 
 /*!
  * @brief Creates a new OFZIPArchive object with the specified seekable stream.
  *
  * @param stream A seekable stream from which the ZIP archive will be read
+ * @param mode The mode for the ZIP file. Valid modes are "r" for reading,
+ *	       "w" for creating a new file and "a" for appending to an existing
+ *	       file.
  * @return A new, autoreleased OFZIPArchive
  */
-+ (instancetype)archiveWithSeekableStream: (OFSeekableStream *)stream;
++ (instancetype)archiveWithSeekableStream: (OFSeekableStream *)stream
+				     mode: (OFString *)mode;
 
 #ifdef OF_HAVE_FILES
 /*!
  * @brief Creates a new OFZIPArchive object with the specified file.
  *
  * @param path The path to the ZIP file
+ * @param mode The mode for the ZIP file. Valid modes are "r" for reading,
+ *	       "w" for creating a new file and "a" for appending to an existing
+ *	       file.
  * @return A new, autoreleased OFZIPArchive
  */
-+ (instancetype)archiveWithPath: (OFString *)path;
++ (instancetype)archiveWithPath: (OFString *)path
+			   mode: (OFString *)mode;
 #endif
 
 - init OF_UNAVAILABLE;
 
 /*!
  * @brief Initializes an already allocated OFZIPArchive object with the
  *	  specified seekable stream.
  *
  * @param stream A seekable stream from which the ZIP archive will be read
+ * @param mode The mode for the ZIP file. Valid modes are "r" for reading,
+ *	       "w" for creating a new file and "a" for appending to an existing
+ *	       file.
  * @return An initialized OFZIPArchive
  */
-- initWithSeekableStream: (OFSeekableStream *)stream OF_DESIGNATED_INITIALIZER;
+- initWithSeekableStream: (OFSeekableStream *)stream
+		    mode: (OFString *)mode OF_DESIGNATED_INITIALIZER;
 
 #ifdef OF_HAVE_FILES
 /*!
  * @brief Initializes an already allocated OFZIPArchive object with the
  *	  specified file.
  *
  * @param path The path to the ZIP file
+ * @param mode The mode for the ZIP file. Valid modes are "r" for reading,
+ *	       "w" for creating a new file and "a" for appending to an existing
+ *	       file.
  * @return An initialized OFZIPArchive
  */
-- initWithPath: (OFString *)path;
+- initWithPath: (OFString *)path
+	  mode: (OFString *)mode;
 #endif
 
 /*!
  * @brief Returns the entries of the central directory of the archive as an
  * 	  array of objects of class @ref OFZIPArchiveEntry.
@@ -102,10 +123,12 @@
  */
 - (OFArray OF_GENERIC(OFZIPArchiveEntry *) *)entries;
 
 /*!
  * @brief Returns a stream for reading the specified file from the archive.
+ *
+ * This method is only available in read and append mode.
  *
  * @warning Calling @ref streamForReadingFile: will invalidate all streams
  *	    previously returned by @ref streamForReadingFile:! Reading from an
  *	    invalidated stream will throw an @ref OFReadFailedException!
  *

Index: src/OFZIPArchive.m
==================================================================
--- src/OFZIPArchive.m
+++ src/OFZIPArchive.m
@@ -135,35 +135,45 @@
 
 @implementation OFZIPArchive
 @synthesize archiveComment = _archiveComment;
 
 + (instancetype)archiveWithSeekableStream: (OFSeekableStream *)stream
+				     mode: (OFString *)mode
 {
-	return [[[self alloc] initWithSeekableStream: stream] autorelease];
+	return [[[self alloc] initWithSeekableStream: stream
+						mode: mode] autorelease];
 }
 
 #ifdef OF_HAVE_FILES
 + (instancetype)archiveWithPath: (OFString *)path
+			   mode: (OFString *)mode
 {
-	return [[[self alloc] initWithPath: path] autorelease];
+	return [[[self alloc] initWithPath: path
+				      mode: mode] autorelease];
 }
 #endif
 
 - init
 {
 	OF_INVALID_INIT_METHOD
 }
 
 - initWithSeekableStream: (OFSeekableStream *)stream
+		    mode: (OFString *)mode
 {
 	self = [super init];
 
 	@try {
 		_stream = [stream retain];
 
-		[self of_readZIPInfo];
-		[self of_readEntries];
+		if ([mode isEqual: @"r"]) {
+			_mode = OF_ZIP_ARCHIVE_MODE_READ;
+
+			[self of_readZIPInfo];
+			[self of_readEntries];
+		} else
+			@throw [OFInvalidArgumentException exception];
 	} @catch (id e) {
 		[self release];
 		@throw e;
 	}
 
@@ -170,15 +180,17 @@
 	return self;
 }
 
 #ifdef OF_HAVE_FILES
 - initWithPath: (OFString *)path
+	  mode: (OFString *)mode
 {
 	OFFile *file = [[OFFile alloc] initWithPath: path
-					       mode: @"r"];
+					       mode: mode];
 	@try {
-		self = [self initWithSeekableStream: file];
+		self = [self initWithSeekableStream: file
+					       mode: mode];
 	} @finally {
 		[file release];
 	}
 
 	return self;
@@ -327,11 +339,15 @@
 	void *pool = objc_autoreleasePoolPush();
 	OFZIPArchiveEntry *entry = [_pathToEntryMap objectForKey: path];
 	OFZIPArchive_LocalFileHeader *localFileHeader;
 	int64_t offset64;
 
-	if (entry == nil)
+	if (_mode != OF_ZIP_ARCHIVE_MODE_READ &&
+	    _mode != OF_ZIP_ARCHIVE_MODE_APPEND)
+		@throw [OFInvalidArgumentException exception];
+
+	if ((entry = [_pathToEntryMap objectForKey: path]) == nil)
 		@throw [OFOpenItemFailedException exceptionWithPath: path
 							       mode: @"r"
 							      errNo: ENOENT];
 
 	[_lastReturnedStream close];

Index: utils/ofzip/ZIPArchive.m
==================================================================
--- utils/ofzip/ZIPArchive.m
+++ utils/ofzip/ZIPArchive.m
@@ -65,11 +65,12 @@
 {
 	self = [super init];
 
 	@try {
 		_archive = [[OFZIPArchive alloc]
-		    initWithSeekableStream: stream];
+		    initWithSeekableStream: stream
+				      mode: @"r"];
 	} @catch (id e) {
 		[self release];
 		@throw e;
 	}