Commits on Jul 16, 2018

1. importer: remove UnixfsNode from the balanced builder …

   The `UnixfsNode` structure has multiple pointers to many (non-complementary)
   mutually exclusive node types, only some of them are active (not-`nil`) at a
   given time in the code path which made the code too convoluted. Specifically,
   the most important distinction between node types was being hidden: leaf nodes
   vs internal (non-leaf) nodes.
   
   Remove entirely the use of `UnixfsNode` from the `balanced` package replacing it
   in turn with the newly created `FSNodeOverDag` structure that represents the
   UnixFS node encoded inside the DAG node, primarily used for internal node
   representations. Leaf nodes are handled exclusively in the `NewLeafDataNode`
   encapsulating its multiple representations (that we're previously exposed in
   `UnixfsNode` as conflicting pointers).
   
   The `builder.go` file has been completely rewritten, although the basic DAG
   creation algorithm has been preserved (extending a full DAG by creating a new
   root and linking the old one as its child), the most significant modification
   has been in the loop of `Layout` that now only handles internal nodes (i.e.,
   nodes with `depth` bigger than zero) to be able to adapt `fillNodeRec` to only
   that scenario (avoiding the replace logic of the zero `depth` case with the
   defective `Set` function, now removed). The `fillNodeRec` now explicitly returns
   the `ipld.Node` and the size of the file data it's storing to propagate it
   upwards into the DAG.
   
   The `DagBuilderHelper` was heavily extended to incorporate `ipld.Node` functions
   that would replace the `UnixfsNode` ones used by the balanced builder:
   `NewLeafNode()`, `NewLeafDataNode()` and `AddNodeAndClose()`. Also, the
   `ProcessFileStore` function was incorporated to encapsulate all the logic
   related to the Filestore support which was scattered throughout the builder
   logic, the `offset` that was being passed through most functions is now a part
   of the `DagBuilderHelper`.
   
   This has turned out to be a rather big commit, it should have been split into
   more smaller and logically cohesive commits, but the `UnixfsNode` was too
   entangled inside the logic and that would have required a progressive
   modification of the `UnixfsNode` structure as well, which wasn't possible as it
   is still being used by the balanced builder (the same reason why most of the
   `UnixfsNode`-related functions cannot yet be removed, leaving the `helpers.go`
   file mostly untouched).
   
   License: MIT
   Signed-off-by: Lucas Molas <schomatis@gmail.com>

   

   schomatis committed Jul 16, 2018
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