我正在使用setxattr命令查看iOS和Mac文件的扩展文件属性。据我了解,我可以在那里存储任意数据,最高可达128kb。
如何像编写字典一样写和读扩展属性,而不是取消引用字符串指针?
到目前为止,我有这段代码试图设置单个属性。
NSString* filepath = [MyValueObject filepath];
const char *systemPath = [filepath fileSystemRepresentation];
const char *name = "special_value";
const char *value = "test string";
int result = setxattr(systemPath, name, &value, strlen(value), 0, 0);
如果我需要存储一小部分值(例如5个键值对),我会考虑:
使用我的属性创建一个NSDictionary
将字典转换为JSON字符串
将字符串转换为字符指针
将字符串写入扩展属性
要读回属性,我将读回字符串指针
转换为NSString
转换为JSON对象
创建字典
从字典中检索值
这看起来像是正确的方法吗?有没有更简单的方法将元数据存储在扩展属性中?也许NSObject上有一个类别可以处理xattr的指针操作?
最佳答案
I found a Cocoanetics/DTFoundation that allows reading/writing arbitrary strings to xattr:与其他帖子一起,我能够完成我想要的工作-编写/恢复字典
#import "Note+ExtendedAttribute.h"
#include <sys/xattr.h>
@implementation MyFile (ExtendedAttribute)
-(NSString*)dictionaryKey
{
return @"mydictionary";
}
-(BOOL)writeExtendedAttributeDictionary:(NSDictionary*)dictionary
{
NSError *error;
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dictionary
options:0
error:&error];
if (! jsonData) {
return NO;
}
NSString* jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
const char *filepath = [[self filepath] fileSystemRepresentation];
const char *key = [[self dictionaryKey] UTF8String];
const char *value = [jsonString UTF8String];
int result = setxattr(filepath, key, value, strlen(value), 0, 0);
if(result != 0)
{
return NO;
}
return YES;
}
阅读:
-(NSMutableDictionary*)readExtendedAttributeDictionary
{
const char *attrName = [[self dictionaryKey] UTF8String];
const char *filePath = [[self filepath] fileSystemRepresentation];
// get size of needed buffer
int bufferLength = getxattr(filePath, attrName, NULL, 0, 0, 0);
if(bufferLength<=0)
{
return nil;
}
// make a buffer of sufficient length
char *buffer = malloc(bufferLength);
// now actually get the attribute string
getxattr(filePath, attrName, buffer, bufferLength, 0, 0);
// convert to NSString
NSString *retString = [[NSString alloc] initWithBytes:buffer length:bufferLength encoding:NSUTF8StringEncoding];
// release buffer
free(buffer);
NSData *data = [retString dataUsingEncoding:NSUTF8StringEncoding];
if(data == nil || data.length == 0)
{
return nil;
}
NSError *error = nil;
id json = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error];
if([json isKindOfClass:[NSDictionary class]])
{
return [NSMutableDictionary dictionaryWithDictionary:json];
}
if(error)
{
return nil;
}
return json;
}
关于ios - iOS如何在文件的xattr中存储NSDictionary或JSON?,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/25408028/