iOS development files (segmented) download

1 , HTTP HEAD Method

Nsmutableurlrequest *request = [nsmutableurlrequest requestwithurl:url cachepolicy:0 timeoutInterval:kTimeout];

Request. HttpMethod = @ "HEAD";

[Nsurlconnection sendasynchronousrequest:request queue:self.myQueue completionhandler:^ (Nsurlresponse *response, NSData *data, Nserror *connectionerror) {

NSLog (@ "%@", response);

NSLog (@ "---------------");

NSLog (@ "%@", data);

}];

Run the test code to discover that the Head method simply returns the resource information without returning the data body

Application Scenarios:

(1) Access to resources mimetype

(2) Get the resource file size for endpoint continuation or multi-threaded download

2 , using block code to get the network resource size method

-(void) Filesizewithurl: (nsurl *) URL completion: (void (^) (long long contentlength)) completion

{

Nsmutableurlrequest *request = [nsmutableurlrequest requestwithurl:url cachepolicy:0 timeoutInterval:kTimeout];

Request. HttpMethod = @ "HEAD";

Nsurlresponse *response = nil;

[Nsurlconnection sendsynchronousrequest:request returningresponse:&response Error:NULL];

Completion (RESPONSE.EXPECTEDCONTENTLENGTH);

}

3 , determine the pseudo-code implementation of each download packet

-(void) Downloadfilewithurl: (nsurl *) URL

{

[Self Filesizewithurl:url completion:^ (long long ContentLength) {

NSLog (@ "Total file size:%lld", contentlength);

Download files by size

while (ContentLength > Kdownloadbytes) {

NSLog (@ "Each download length:%lld", (Long Long) kdownloadbytes);

ContentLength-= kdownloadbytes;

}

NSLog (@ "Last downloaded bytes:%lld", contentlength);

}];

}

4 , HTTP Range The example

n Specify the size of each packet to be downloaded from the network by setting range

N Range Example

N bytes=0-499 from 0 to 499 of the first 500 bytes

N bytes=500-999 the second 500 bytes from 500 to 999

N bytes=500-all bytes from 500 bytes

n bytes=-500 last 500 bytes

n bytes=500-599,800-899 specify several ranges at the same time

N Range Summary

N-Used to separate

The number in front of P indicates the number of starting bytes

The array after p represents the number of cutoff bytes and does not represent to the end

n is used for grouping, you can specify more than one range at a time, but rarely

5 , segmented Range Code Implementation

Long long frombytes = 0;

Long long tobytes = 0;

while (ContentLength > Kdownloadbytes) {

Tobytes = frombytes + kDownloadBytes-1;

NSString *range = [NSString stringwithformat:@ "Bytes=%lld-%lld", Frombytes, tobytes];

NSLog (@ "range%@", range);

Frombytes + = Kdownloadbytes;

ContentLength-= kdownloadbytes;

}

Frombytes = frombytes + contentLength-1;

NSString *range = [NSString stringwithformat:@ "Bytes=%lld-%lld", Frombytes, tobytes];

NSLog (@ "range%@", range);

6 , segment Download File

/**nsurlrequestuseprotocolcachepolicy = 0//default cache policy, memory cache

Nsurlrequestreloadignoringlocalcachedata = 1//ignores local memory cache */

Nsmutableurlrequest *request = [nsmutableurlrequest requestwithurl:url cachepolicy: Nsurlrequestreloadignoringcachedata Timeoutinterval:ktimeout];

NSString *range = [NSString stringwithformat:@ "bytes=%lld-%lld", from, end];

[Request Setvalue:range forhttpheaderfield:@ "range"];

Nsurlresponse *response = nil;

NSData *data = [nsurlconnection sendsynchronousrequest:request returningresponse:&response Error:NULL];

NSLog (@ "%@-%@-%ld", Range, response, (unsigned long) data.length);

Tips:

If get contains a range request header, the response is returned as a status code of 206 (partialcontent) instead of a (OK)

7 , writing data to a file

-(void) AppendData: (NSData *) data

{

Open cache file

Nsfilehandle *FP =

[Nsfilehandle FileHandleForWritingAtPath:self.cachePath];

If the file does not exist, write the data directly

if (!FP) {

[Data WriteToFile:self.cachePath Atomically:yes];

} else {

    // move to end of file

[FP Seektoendoffile];

    // append a data file to the end of a file

[FP Writedata:data];

    // Close file handle

[FP CloseFile];

}

}

8 , Check File size

Determine if a file exists

if ([[[Nsfilemanager Defaultmanager] FileExistsAtPath:self.cachePath]) {

Nsdictionary *dict = [[Nsfilemanager Defaultmanager] AttributesOfItemAtPath:self.cachePath error:null];

return [dict[nsfilesize] longlongvalue];

} else {

return 0;

}

Tip: Because the data is appended, in order to avoid repeatedly downloading files from the network, before downloading

1. Determine if a file already exists in the cache path
2. Check file size if present
3. If the file size matches the size of the network resource, it is no longer downloaded

iOS development files (segmented) download