Method to detect conflicts?

[drpepper]

Hi, I'm very interested in using JsonDiffPatch, but can't find how to detect and spell out conflicts between patches. That is, I'm looking for a function that, given the original data and a list of patches, spits out any unresolvable conflicts between the patches.

Does such a function exist, or would it be easy to write? Thanks

[benjamine]

currently, patch conflicts will only arise (as exceptions) when you apply them. I'm doing a big refactoring on a separate branch that will add the capability to combine 2 (or more) patches, raising conflicts (and hopefully I want to add the option to specify custom conflict resolution). that might arrive in 2 or 3 weeks, but if finding conflicts might no be that hard to implement, here are some tips:

patches reflect the hierarchical structure of the diffed object, so first step is going recursively thru the patch objects, if at some path a member is only found on one patch, you can ignore it (no conflict there).

if at some path you find an array on both patches (arrays represent a change), that is almost for sure, a conflict.

the only exception are changes that might not conflict, like text diffs (array with 3 items: [theTextDiff, 0, 3]) that modify different lines in the text, that could be found out by parsing the line numbers.

Example code, that could get you started:

function findConflicts(patch1, patch2, path) {
  path = path || '/';
  if (typeof patch2 == 'undefined') return;
  if (typeof patch1 == 'undefined') return;
  if (Array.isArray(patch1) && Array.isArray(patch2) throw "conflict at " + path;
  for (var member in patch1) {
    if (typeof patch2[member] == 'undefined') continue;
    findConflicts(patch1[member], patch2[member], path + member + '/');
  }
}

[benjamine]

BTW, speaking of gaming, on the refactoring branch I'm moving to a pipes&filter pattern internally, that will make it easy to plugin different strategies for diffing, patching, serializing and conflict resolution, one of the things I wanted to plugin is the ability to support things like FPS client-side predicition for certain properties (eg. coordinates for position and speed).

[drpepper]

Looks good, thanks!

[ghost]

Noticed you finished the refactor, but how do you now combine multiple patches? That would be immensely useful for me.