Index: src/OFTarArchive.h
==================================================================
--- src/OFTarArchive.h
+++ src/OFTarArchive.h
@@ -32,54 +32,77 @@
 #ifdef OF_TAR_ARCHIVE_ENTRY_M
 @public
 #endif
 	OFStream *_stream;
 @protected
+	enum {
+		OF_TAR_ARCHIVE_MODE_READ,
+		OF_TAR_ARCHIVE_MODE_WRITE,
+		OF_TAR_ARCHIVE_MODE_APPEND
+	} _mode;
 	OFTarArchiveEntry *_lastReturnedEntry;
 }
 
 /*!
  * @brief Creates a new OFTarArchive object with the specified stream.
  *
  * @param stream A stream from which the tar archive will be read
+ * @param mode The mode for the tar 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 OFTarArchive
  */
-+ (instancetype)archiveWithStream: (OFStream *)stream;
++ (instancetype)archiveWithStream: (OFStream *)stream
+			     mode: (OFString *)mode;
 
 #ifdef OF_HAVE_FILES
 /*!
  * @brief Creates a new OFTarArchive object with the specified file.
  *
  * @param path The path to the tar archive
+ * @param mode The mode for the tar 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 OFTarArchive
  */
-+ (instancetype)archiveWithPath: (OFString *)path;
++ (instancetype)archiveWithPath: (OFString *)path
+			   mode: (OFString *)mode;
 #endif
 
 /*!
  * @brief Initializes an already allocated OFTarArchive object with the
  *	  specified stream.
  *
  * @param stream A stream from which the tar archive will be read
+ * @param mode The mode for the tar file. Valid modes are "r" for reading,
+ *	       "w" for creating a new file and "a" for appending to an existing
+ *	       file.
  * @return An initialized OFTarArchive
  */
-- initWithStream: (OFStream *)stream OF_DESIGNATED_INITIALIZER;
+- initWithStream: (OFStream *)stream
+	    mode: (OFString *)mode OF_DESIGNATED_INITIALIZER;
 
 #ifdef OF_HAVE_FILES
 /*!
  * @brief Initializes an already allocated OFTarArchive object with the
  *	  specified file.
  *
  * @param path The path to the tar archive
+ * @param mode The mode for the tar file. Valid modes are "r" for reading,
+ *	       "w" for creating a new file and "a" for appending to an existing
+ *	       file.
  * @return An initialized OFTarArchive
  */
-- initWithPath: (OFString *)path;
+- initWithPath: (OFString *)path
+	  mode: (OFString *)mode;
 #endif
 
 /*!
  * @brief Returns the next entry from the tar archive or `nil` if all entries
  *	  have been read.
+ *
+ * This is only available in read mode.
  *
  * @warning Calling @ref nextEntry will invalidate all streams returned by the
  *	    previous entry! Reading from an invalidated stream will throw an
  *	    @ref OFReadFailedException!
  *

Index: src/OFTarArchive.m
==================================================================
--- src/OFTarArchive.m
+++ src/OFTarArchive.m
@@ -22,41 +22,59 @@
 #import "OFStream.h"
 #ifdef OF_HAVE_FILES
 # import "OFFile.h"
 #endif
 
+#import "OFInvalidArgumentException.h"
 #import "OFInvalidFormatException.h"
 
 @implementation OFTarArchive: OFObject
 + (instancetype)archiveWithStream: (OFStream *)stream
+			     mode: (OFString *)mode
 {
-	return [[[self alloc] initWithStream: stream] autorelease];
+	return [[[self alloc] initWithStream: 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
 
 - initWithStream: (OFStream *)stream
+	    mode: (OFString *)mode
 {
 	self = [super init];
 
-	_stream = [stream retain];
+	@try {
+		_stream = [stream retain];
+
+		if ([mode isEqual: @"r"])
+			_mode = OF_TAR_ARCHIVE_MODE_READ;
+		else
+			@throw [OFInvalidArgumentException exception];
+	} @catch (id e) {
+		[self release];
+		@throw e;
+	}
 
 	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 initWithStream: file];
+		self = [self initWithStream: file
+				       mode: mode];
 	} @finally {
 		[file release];
 	}
 
 	return self;
@@ -77,10 +95,13 @@
 		char c[512];
 		uint32_t u32[512 / sizeof(uint32_t)];
 	} buffer;
 	bool empty = true;
 
+	if (_mode != OF_TAR_ARCHIVE_MODE_READ)
+		@throw [OFInvalidArgumentException exception];
+
 	[_lastReturnedEntry of_skip];
 	[_lastReturnedEntry close];
 	[_lastReturnedEntry release];
 	_lastReturnedEntry = nil;
 

Index: utils/ofzip/TarArchive.m
==================================================================
--- utils/ofzip/TarArchive.m
+++ utils/ofzip/TarArchive.m
@@ -55,11 +55,12 @@
 - initWithStream: (OF_KINDOF(OFStream *))stream
 {
 	self = [super init];
 
 	@try {
-		_archive = [[OFTarArchive alloc] initWithStream: stream];
+		_archive = [[OFTarArchive alloc] initWithStream: stream
+							   mode: @"r"];
 	} @catch (id e) {
 		[self release];
 		@throw e;
 	}