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Expose basic text-based datamodel selector on retrieval
Syntaxt of selection is located at https://pkg.go.dev/github.com/ipld/go-ipld-selector-text-lite#SelectorSpecFromPath Example use, assuming that: - The root of the deal is a plain dag-pb unixfs directory - The directory is not sharded - The user wants to retrieve the first entry in that directory lotus client retrieve --miner f0XXXXX --datamodel-path-selector 'Links/0/Hash' bafyROOTCID ~/output
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,96 @@ | ||
| package utils | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "context" | ||
| "fmt" | ||
| "io" | ||
|
|
||
| // must be imported to init() raw-codec support | ||
| _ "github.com/ipld/go-ipld-prime/codec/raw" | ||
|
|
||
| "github.com/ipfs/go-cid" | ||
| mdagipld "github.com/ipfs/go-ipld-format" | ||
| dagpb "github.com/ipld/go-codec-dagpb" | ||
| "github.com/ipld/go-ipld-prime" | ||
| cidlink "github.com/ipld/go-ipld-prime/linking/cid" | ||
| basicnode "github.com/ipld/go-ipld-prime/node/basic" | ||
| "github.com/ipld/go-ipld-prime/traversal" | ||
| "github.com/ipld/go-ipld-prime/traversal/selector" | ||
| "github.com/ipld/go-ipld-prime/traversal/selector/builder" | ||
| ) | ||
|
|
||
| func TraverseDag( | ||
| ctx context.Context, | ||
| ds mdagipld.DAGService, | ||
| startFrom cid.Cid, | ||
| optionalSelector ipld.Node, | ||
| visitCallback traversal.AdvVisitFn, | ||
| ) error { | ||
|
|
||
| // If no selector is given - use *.* | ||
| // See discusion at https://github.com/ipld/go-ipld-prime/issues/171 | ||
| if optionalSelector == nil { | ||
| ssb := builder.NewSelectorSpecBuilder(basicnode.Prototype.Any) | ||
| optionalSelector = ssb.ExploreRecursive( | ||
| selector.RecursionLimitNone(), | ||
| ssb.ExploreUnion( | ||
| ssb.Matcher(), | ||
| ssb.ExploreAll(ssb.ExploreRecursiveEdge()), | ||
| ), | ||
| ).Node() | ||
| } | ||
|
|
||
| parsedSelector, err := selector.ParseSelector(optionalSelector) | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
|
||
| // not sure what this is for TBH... | ||
| linkContext := ipld.LinkContext{Ctx: ctx} | ||
|
|
||
| // this is what allows us to understand dagpb | ||
| nodePrototypeChooser := dagpb.AddSupportToChooser( | ||
| func(ipld.Link, ipld.LinkContext) (ipld.NodePrototype, error) { | ||
| return basicnode.Prototype.Any, nil | ||
| }, | ||
| ) | ||
|
|
||
| // this is how we implement GETs | ||
| linkSystem := cidlink.DefaultLinkSystem() | ||
| linkSystem.StorageReadOpener = func(_ ipld.LinkContext, lnk ipld.Link) (io.Reader, error) { | ||
| if cl, isCid := lnk.(cidlink.Link); !isCid { | ||
| return nil, fmt.Errorf("unexpected link type %#v", lnk) | ||
| } else { | ||
| node, err := ds.Get(context.TODO(), cl.Cid) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| return bytes.NewBuffer(node.RawData()), nil | ||
| } | ||
| } | ||
|
|
||
| // this is how we pull the start node out of the DS | ||
| startLink := cidlink.Link{Cid: startFrom} | ||
| startNodePrototype, err := nodePrototypeChooser(startLink, linkContext) | ||
| if err != nil { | ||
| return err | ||
| } | ||
| startNode, err := linkSystem.Load( | ||
| linkContext, | ||
| startLink, | ||
| startNodePrototype, | ||
| ) | ||
| if err != nil { | ||
| return err | ||
| } | ||
|
|
||
| // this is the actual execution, invoking the supplied callback | ||
| return traversal.Progress{ | ||
| Cfg: &traversal.Config{ | ||
| Ctx: ctx, | ||
| LinkSystem: linkSystem, | ||
| LinkTargetNodePrototypeChooser: nodePrototypeChooser, | ||
| }, | ||
| }.WalkAdv(startNode, parsedSelector, visitCallback) | ||
| } |
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