极品矮人王,西南之窗方言教育网,山大司考互助团
一、摘要
1.七牛上传文件，用hash来唯一标识七牛存储空间中的某个文件，该hash是以etag算法计算出的一段哈希值；
2.算法介绍：；
3.七牛的提供的实现语言中（），没有给出oc实现；
4.参考js代码：；
二、代码
我要评论- (void)test2 {
/*测试链接
http://yqq.file.mediportal.com.cn/yqq_5b911b43955f06317c6bd792/3974e8eaab11b2dd5b357e60e5a587d1 etag:ftfvrvsdpvf9t_tcfyvsvc-1p6aw
4m以上文件亲测正确
*/
nsurl *url = [nsurl urlwithstring:@"http://yqq.file.mediportal.com.cn/yqq_5b911b43955f06317c6bd792/3974e8eaab11b2dd5b357e60e5a587d1"];
nserror *error;
nsdata * data = [nsdata datawithcontentsofurl:url options:nsdatareadingmapped error:&error];
nsstring *etag = [self caculateetagwith:data];
nslog(@"etag------%@", etag);
}
//算法实现
- (nsstring *)caculateetagwith:(nsdata *)data
{
unsigned long blocksize = 4 * 1024 * 1024;
nsmutabledata *sha1data = [nsmutabledata data];
byte prefix = 0x16;
int blockcount = 0;
unsigned long buffersize = [data length];
//获取余数
unsigned long remainder = buffersize % blocksize;
//获取商
double fa = (double)buffersize / blocksize;
//向下取整
blockcount = floor(fa);
if (buffersize > blocksize) {//大于4m的文件
nsmutabledata *sha2data = [nsmutabledata data];
for (int i = 0; i < blockcount+1; i++) {
nsuinteger length = blocksize;
if (i == blockcount && remainder > 0) {
length = remainder;
}
//将每个块（包括4m块和小于4m的块）进行sha1加密并拼接起来
nsdata *subdata = [data subdatawithrange:nsmakerange(i * blocksize, length)];
[sha2data appenddata:[self sha1:subdata]];
}
//将拼接块进行二次sha1加密
[sha1data appenddata:[self sha1:sha2data]];
} else {
[sha1data appenddata:[self sha1:data]];
}
if (!sha1data.length) return @"fto5o-5ea0snmlw_75vggjcv2acj";
nsdata *sha1buffer = sha1data;
if (buffersize > blocksize) {
//大于4m，头部拼接0x96单个字节
prefix = 0x96;
}
byte prebyte[] = {prefix};
nsmutabledata *mutadata = [nsmutabledata datawithbytes:prebyte length:1];
[mutadata appenddata:sha1buffer];
//将长度为21个字节的二进制数据进行url_safe_base64计算
return [self safebase64withsha1str:mutadata];
}
/*
sha1加密（加密后的data长度为20）
*/
- (nsdata*)sha1:(nsdata *)data
{
//注：如果用以下代码，转换出的data长度为40
// const char *cstr = [sourcestr cstringusingencoding:nsutf8stringencoding];
// nsdata *data = [nsdata datawithbytes:cstr length:sourcestr.length];
// nsmutablestring* output = [nsmutablestring stringwithcapacity:cc_sha1_digest_length * 2];
// for(int i = 0; i < cc_sha1_digest_length; i++)
// [output appendformat:@"%02x", digest[i]];
// return output;
//sha1data长度为20（cc_sha1_digest_length系统设定为20）
uint8_t digest[cc_sha1_digest_length];
cc_sha1(data.bytes, (cc_long)data.length, digest);
nsdata * sha1data = [[nsdata alloc] initwithbytes:digest length:cc_sha1_digest_length];
return sha1data;
}
- (nsstring *)safebase64withsha1str:(nsdata *)base64
{
//base64编码中包含有"+,/,="不安全的url字符串，我们要对这些字符进行转换
nsstring *base64str = [gtmbase64 encodebase64data:base64];
nsmutablestring *safebase64str = [[nsmutablestring alloc] initwithstring:base64str];
safebase64str = (nsmutablestring *)[safebase64str stringbyreplacingoccurrencesofstring:@"+"withstring:@"-"];
safebase64str = (nsmutablestring *)[safebase64str stringbyreplacingoccurrencesofstring:@"/"withstring:@"_"];
safebase64str = (nsmutablestring *)[safebase64str stringbyreplacingoccurrencesofstring:@"="withstring:@""];
return safebase64str;
}
说明：url?stat可查看七牛文件的etag值（即hash值），如下：
http://yqq.file.mediportal.com.cn/yqq_5b911b43955f06317c6bd792/3974e8eaab11b2dd5b357e60e5a587d1?stat
{"fsize":687810,"uploaded":687810,"hash":"ftfvrvsdpvf9t_tcfyvsvc-1p6aw","mimetype":"image/jpeg"}
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