What algorithm does iOS use for Delta Updates -


  1. do use algorithm such ones used in gdiff program?
  2. do ship intermediate code user instead of ios binary?
  3. why not possible do delta update while updating ios on windows?

a delta update defined 'an update requires user download code has changed, not whole program.'

ios does, in fact, perform delta updates, , contradictory ralph's comment, know how works.

  • applications

for ios applications, delta updates used minimize download size of new versions, save internet traffic. usually, things give program of size static images , other media. during simple update such bug fix, these static images stay same, , there no reason send them on network again. thing sent actual mach-o binary containing code buggy, along whatever files have been changed.

so, delta updates run checksumming. when submit app update, apple checks checksum of files submitted using algorithm (most likley sha1 or md5) scan changes. if executable has changed, image or other file has not, image isn't packed update, users have downloaded it, , don't need download again. while method may not pertain definition of delta update, includes executables along other types of files, has similar concepts.

  • ota updates

apple uses delta updates in over-the-air updates ios well. visible on jailbroken ios device. updates downloaded /var/mobilesofwareupdate/softwareupdate.xxxx, xxxx presumbably build/release number. each software update contains image of root filesystem, not entire version of ios included. files have changed version user on need replaced, , files included in update package. method finding these changes likley same ios apps, checksumming finds changes in files.

  • algorithm

basically, answer question, apple's algorithm doesn't send differences between 2 individual files (similar see in git commit), sends entire updated file. 'algorithm' looks change @ between last version, , doesn't actual change itself. proven fact in ota update packages, complete files available, , not log of changes.


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