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

For a much more elaborate example see the top of ./itests/deals_partial_retrieval_test.go

.circleci/config.yml

@@ -835,6 +835,11 @@ workflows:
           suite: itest-deals_padding
           target: "./itests/deals_padding_test.go"
       
+      - test:
+          name: test-itest-deals_partial_retrieval
+          suite: itest-deals_partial_retrieval
+          target: "./itests/deals_partial_retrieval_test.go"
+      
       - test:
           name: test-itest-deals_power
           suite: itest-deals_power

api/api_full.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/ipfs/go-cid"
+	textselector "github.com/ipld/go-ipld-selector-text-lite"
 	"github.com/libp2p/go-libp2p-core/peer"
 
 	"github.com/filecoin-project/go-address"
@@ -933,6 +934,7 @@ type RetrievalOrder struct {
 	// TODO: make this less unixfs specific
 	Root                  cid.Cid
 	Piece                 *cid.Cid
+	DatamodelPathSelector *textselector.Expression
 	Size                  uint64
 
 	FromLocalCAR string // if specified, get data from a local CARv2 file.

api/docgen/docgen.go

@@ -27,6 +27,7 @@ import (
 	filestore2 "github.com/filecoin-project/go-fil-markets/filestore"
 	"github.com/filecoin-project/go-fil-markets/retrievalmarket"
 	"github.com/filecoin-project/go-jsonrpc/auth"
+	textselector "github.com/ipld/go-ipld-selector-text-lite"
 
 	"github.com/filecoin-project/go-state-types/abi"
 	"github.com/filecoin-project/go-state-types/crypto"
@@ -90,6 +91,7 @@ func init() {
 	addExample(&pid)
 
 	storeIDExample := imports.ID(50)
+	textSelExample := textselector.Expression("Links/21/Hash/Links/42/Hash")
 
 	addExample(bitfield.NewFromSet([]uint64{5}))
 	addExample(abi.RegisteredSealProof_StackedDrg32GiBV1_1)
@@ -124,6 +126,7 @@ func init() {
 	addExample(&storeIDExample)
 	addExample(retrievalmarket.ClientEventDealAccepted)
 	addExample(retrievalmarket.DealStatusNew)
+	addExample(&textSelExample)
 	addExample(network.ReachabilityPublic)
 	addExample(build.NewestNetworkVersion)
 	addExample(map[string]int{"name": 42})

cli/client.go

@@ -26,6 +26,7 @@ import (
 	datatransfer "github.com/filecoin-project/go-data-transfer"
 	"github.com/ipfs/go-cid"
 	"github.com/ipfs/go-cidutil/cidenc"
+	textselector "github.com/ipld/go-ipld-selector-text-lite"
 	"github.com/libp2p/go-libp2p-core/peer"
 	"github.com/multiformats/go-multibase"
 	"github.com/urfave/cli/v2"
@@ -1047,6 +1048,10 @@ var clientRetrieveCmd = &cli.Command{
 			Name:  "miner",
 			Usage: "miner address for retrieval, if not present it'll use local discovery",
 		},
+		&cli.StringFlag{
+			Name:  "datamodel-path-selector",
+			Usage: "a rudimentary (DM-level-only) text-path selector, allowing for sub-selection within a deal",
+		},
 		&cli.StringFlag{
 			Name:  "maxPrice",
 			Usage: fmt.Sprintf("maximum price the client is willing to consider (default: %s FIL)", DefaultMaxRetrievePrice),
@@ -1182,6 +1187,10 @@ var clientRetrieveCmd = &cli.Command{
 			IsCAR: cctx.Bool("car"),
 		}
 
+		if sel := textselector.Expression(cctx.String("datamodel-path-selector")); sel != "" {
+			order.DatamodelPathSelector = &sel
+		}
+
 		updates, err := fapi.ClientRetrieveWithEvents(ctx, *order, ref)
 		if err != nil {
 			return xerrors.Errorf("error setting up retrieval: %w", err)

documentation/en/api-v0-methods.md

@@ -1467,6 +1467,7 @@ Inputs:
       "/": "bafy2bzacea3wsdh6y3a36tb3skempjoxqpuyompjbmfeyf34fi3uy6uue42v4"
     },
     "Piece": null,
+    "DatamodelPathSelector": "Links/21/Hash/Links/42/Hash",
     "Size": 42,
     "FromLocalCAR": "string value",
     "Total": "0",
@@ -1521,6 +1522,7 @@ Inputs:
       "/": "bafy2bzacea3wsdh6y3a36tb3skempjoxqpuyompjbmfeyf34fi3uy6uue42v4"
     },
     "Piece": null,
+    "DatamodelPathSelector": "Links/21/Hash/Links/42/Hash",
     "Size": 42,
     "FromLocalCAR": "string value",
     "Total": "0",

documentation/en/api-v1-unstable-methods.md

@@ -1531,6 +1531,7 @@ Inputs:
       "/": "bafy2bzacea3wsdh6y3a36tb3skempjoxqpuyompjbmfeyf34fi3uy6uue42v4"
     },
     "Piece": null,
+    "DatamodelPathSelector": "Links/21/Hash/Links/42/Hash",
     "Size": 42,
     "FromLocalCAR": "string value",
     "Total": "0",
@@ -1585,6 +1586,7 @@ Inputs:
       "/": "bafy2bzacea3wsdh6y3a36tb3skempjoxqpuyompjbmfeyf34fi3uy6uue42v4"
     },
     "Piece": null,
+    "DatamodelPathSelector": "Links/21/Hash/Links/42/Hash",
     "Size": 42,
     "FromLocalCAR": "string value",
     "Total": "0",

documentation/en/cli-lotus.md

@@ -547,6 +547,7 @@ OPTIONS:
    --from value                     address to send transactions from
    --car                            export to a car file instead of a regular file (default: false)
    --miner value                    miner address for retrieval, if not present it'll use local discovery
+   --datamodel-path-selector value  a rudimentary (DM-level-only) text-path selector, allowing for sub-selection within a deal
    --maxPrice value                 maximum price the client is willing to consider (default: 0.01 FIL)
    --pieceCid value                 require data to be retrieved from a specific Piece CID
    --allow-local                    (default: false)

go.mod

@@ -99,7 +99,9 @@ require (
 	github.com/ipfs/interface-go-ipfs-core v0.2.3
 	github.com/ipld/go-car v0.3.1-0.20210601190600-f512dac51e8e
 	github.com/ipld/go-car/v2 v2.0.3-0.20210811121346-c514a30114d7
+	github.com/ipld/go-codec-dagpb v1.3.0
 	github.com/ipld/go-ipld-prime v0.12.0
+	github.com/ipld/go-ipld-selector-text-lite v0.0.0-20210817134355-4c190a2bb825
 	github.com/kelseyhightower/envconfig v1.4.0
 	github.com/libp2p/go-buffer-pool v0.0.2
 	github.com/libp2p/go-eventbus v0.2.1

go.sum

@@ -784,6 +784,7 @@ github.com/ipld/go-ipld-prime v0.0.2-0.20200428162820-8b59dc292b8e/go.mod h1:uVI
 github.com/ipld/go-ipld-prime v0.5.1-0.20200828233916-988837377a7f/go.mod h1:0xEgdD6MKbZ1vF0GC+YcR/C4SQCAlRuOjIJ2i0HxqzM=
 github.com/ipld/go-ipld-prime v0.5.1-0.20201021195245-109253e8a018/go.mod h1:0xEgdD6MKbZ1vF0GC+YcR/C4SQCAlRuOjIJ2i0HxqzM=
 github.com/ipld/go-ipld-prime v0.9.0/go.mod h1:KvBLMr4PX1gWptgkzRjVZCrLmSGcZCb/jioOQwCqZN8=
+github.com/ipld/go-ipld-prime v0.10.0/go.mod h1:KvBLMr4PX1gWptgkzRjVZCrLmSGcZCb/jioOQwCqZN8=
 github.com/ipld/go-ipld-prime v0.11.0/go.mod h1:+WIAkokurHmZ/KwzDOMUuoeJgaRQktHtEaLglS3ZeV8=
 github.com/ipld/go-ipld-prime v0.12.0 h1:JapyKWTsJgmhrPI7hfx4V798c/RClr85sXfBZnH1VIw=
 github.com/ipld/go-ipld-prime v0.12.0/go.mod h1:hy8b93WleDMRKumOJnTIrr0MbbFbx9GD6Kzxa53Xppc=
@@ -791,6 +792,8 @@ github.com/ipld/go-ipld-prime-proto v0.0.0-20191113031812-e32bd156a1e5/go.mod h1
 github.com/ipld/go-ipld-prime-proto v0.0.0-20200428191222-c1ffdadc01e1/go.mod h1:OAV6xBmuTLsPZ+epzKkPB1e25FHk/vCtyatkdHcArLs=
 github.com/ipld/go-ipld-prime-proto v0.0.0-20200922192210-9a2bfd4440a6/go.mod h1:3pHYooM9Ea65jewRwrb2u5uHZCNkNTe9ABsVB+SrkH0=
 github.com/ipld/go-ipld-prime-proto v0.1.0/go.mod h1:11zp8f3sHVgIqtb/c9Kr5ZGqpnCLF1IVTNOez9TopzE=
+github.com/ipld/go-ipld-selector-text-lite v0.0.0-20210817134355-4c190a2bb825 h1:sGlmVUuWEhuJpVsErFqCHWy9XTsIy511hZWRWI/Lc4I=
+github.com/ipld/go-ipld-selector-text-lite v0.0.0-20210817134355-4c190a2bb825/go.mod h1:U2CQmFb+uWzfIEF3I1arrDa5rwtj00PrpiwwCO+k1RM=
 github.com/ipsn/go-secp256k1 v0.0.0-20180726113642-9d62b9f0bc52 h1:QG4CGBqCeuBo6aZlGAamSkxWdgWfZGeE49eUOWJPA4c=
 github.com/ipsn/go-secp256k1 v0.0.0-20180726113642-9d62b9f0bc52/go.mod h1:fdg+/X9Gg4AsAIzWpEHwnqd+QY3b7lajxyjE1m4hkq4=
 github.com/jackpal/gateway v1.0.4/go.mod h1:lTpwd4ACLXmpyiCTRtfiNyVnUmqT9RivzCDQetPfnjA=

itests/deals_partial_retrieval_test.go

@@ -0,0 +1,185 @@
+package itests
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/filecoin-project/go-fil-markets/storagemarket"
+	"github.com/filecoin-project/go-state-types/abi"
+	"github.com/filecoin-project/go-state-types/big"
+	"github.com/filecoin-project/lotus/api"
+	"github.com/filecoin-project/lotus/chain/actors/policy"
+	"github.com/filecoin-project/lotus/itests/kit"
+	blocks "github.com/ipfs/go-block-format"
+	"github.com/ipfs/go-cid"
+	"github.com/ipld/go-car"
+	textselector "github.com/ipld/go-ipld-selector-text-lite"
+	"github.com/stretchr/testify/require"
+)
+
+// use the mainnet carfile as text fixture: it will always be here
+// https://dweb.link/ipfs/bafy2bzacecnamqgqmifpluoeldx7zzglxcljo6oja4vrmtj7432rphldpdmm2/8/1/8/1/0/1/0
+var (
+	sourceCar      = "../build/genesis/mainnet.car"
+	carRoot, _     = cid.Parse("bafy2bzacecnamqgqmifpluoeldx7zzglxcljo6oja4vrmtj7432rphldpdmm2")
+	carCommp, _    = cid.Parse("baga6ea4seaqmrivgzei3fmx5qxtppwankmtou6zvigyjaveu3z2zzwhysgzuina")
+	carPieceSize   = abi.PaddedPieceSize(2097152)
+	textSelector   = textselector.Expression("8/1/8/1/0/1/0")
+	expectedResult = "fil/1/storagepower"
+)
+
+func TestPartialRetrieval(t *testing.T) {
+
+	ctx := context.Background()
+
+	policy.SetPreCommitChallengeDelay(2)
+	kit.EnableLargeSectors(t)
+	kit.QuietMiningLogs()
+	client, miner, ens := kit.EnsembleMinimal(t, kit.ThroughRPC(), kit.MockProofs(), kit.SectorSize(512<<20))
+	dh := kit.NewDealHarness(t, client, miner, miner)
+	ens.InterconnectAll().BeginMining(50 * time.Millisecond)
+
+	_, err := client.ClientImport(ctx, api.FileRef{Path: sourceCar, IsCAR: true})
+	require.NoError(t, err)
+
+	caddr, err := client.WalletDefaultAddress(ctx)
+	require.NoError(t, err)
+
+	// first test retrieval from local car, then do an actual deal
+	for _, fullCycle := range []bool{false, true} {
+
+		var retOrder api.RetrievalOrder
+
+		if !fullCycle {
+
+			retOrder.FromLocalCAR = sourceCar
+			retOrder.Root = carRoot
+
+		} else {
+
+			dp := dh.DefaultStartDealParams()
+			dp.Data = &storagemarket.DataRef{
+				// FIXME: figure out how to do this with an online partial transfer
+				TransferType: storagemarket.TTManual,
+				Root:         carRoot,
+				PieceCid:     &carCommp,
+				PieceSize:    carPieceSize.Unpadded(),
+			}
+			proposalCid := dh.StartDeal(ctx, dp)
+
+			// Wait for the deal to reach StorageDealCheckForAcceptance on the client
+			cd, err := client.ClientGetDealInfo(ctx, *proposalCid)
+			require.NoError(t, err)
+			require.Eventually(t, func() bool {
+				cd, _ := client.ClientGetDealInfo(ctx, *proposalCid)
+				return cd.State == storagemarket.StorageDealCheckForAcceptance
+			}, 30*time.Second, 1*time.Second, "actual deal status is %s", storagemarket.DealStates[cd.State])
+
+			err = miner.DealsImportData(ctx, *proposalCid, sourceCar)
+			require.NoError(t, err)
+
+			// Wait for the deal to be published, we should be able to start retrieval right away
+			dh.WaitDealPublished(ctx, proposalCid)
+
+			offers, err := client.ClientFindData(ctx, carRoot, nil)
+			require.NoError(t, err)
+			require.NotEmpty(t, offers, "no offers")
+
+			retOrder = offers[0].Order(caddr)
+		}
+
+		retOrder.DatamodelPathSelector = &textSelector
+
+		// test retrieval of either data or constructing a partial selective-car
+		for _, retrieveAsCar := range []bool{false, true} {
+			outFile, err := ioutil.TempFile(t.TempDir(), "ret-file")
+			require.NoError(t, err)
+			defer outFile.Close() //nolint:errcheck
+
+			require.NoError(t, testGenesisRetrieval(
+				ctx,
+				client,
+				retOrder,
+				&api.FileRef{
+					Path:  outFile.Name(),
+					IsCAR: retrieveAsCar,
+				},
+				outFile,
+			))
+
+			// UGH if I do not sleep here, I get things like:
+			/*
+				retrieval failed: Retrieve failed: there is an active retrieval deal with peer 12D3KooWK9fB9a3HZ4PQLVmEQ6pweMMn5CAyKtumB71CPTnuBDi6 for payload CID bafy2bzacecnamqgqmifpluoeldx7zzglxcljo6oja4vrmtj7432rphldpdmm2 (retrieval deal ID 1631259332180384709, state DealStatusFinalizingBlockstore) - existing deal must be cancelled before starting a new retrieval deal:
+					github.com/filecoin-project/lotus/node/impl/client.(*API).ClientRetrieve
+						/home/circleci/project/node/impl/client/client.go:774
+			*/
+			time.Sleep(time.Second)
+		}
+	}
+}
+
+func testGenesisRetrieval(ctx context.Context, client *kit.TestFullNode, retOrder api.RetrievalOrder, retRef *api.FileRef, outFile *os.File) error {
+
+	if retOrder.Total.Nil() {
+		retOrder.Total = big.Zero()
+	}
+	if retOrder.UnsealPrice.Nil() {
+		retOrder.UnsealPrice = big.Zero()
+	}
+
+	err := client.ClientRetrieve(ctx, retOrder, retRef)
+	if err != nil {
+		return err
+	}
+
+	var data []byte
+	if !retRef.IsCAR {
+
+		data, err = io.ReadAll(outFile)
+		if err != nil {
+			return err
+		}
+
+	} else {
+
+		cr, err := car.NewCarReader(outFile)
+		if err != nil {
+			return err
+		}
+
+		if len(cr.Header.Roots) != 1 {
+			return fmt.Errorf("expected a single root in result car, got %d", len(cr.Header.Roots))
+		} else if cr.Header.Roots[0].String() != carRoot.String() {
+			return fmt.Errorf("expected root cid '%s', got '%s'", carRoot.String(), cr.Header.Roots[0].String())
+		}
+
+		blks := make([]blocks.Block, 0)
+		for {
+			b, err := cr.Next()
+			if err == io.EOF {
+				break
+			} else if err != nil {
+				return err
+			}
+
+			blks = append(blks, b)
+		}
+
+		if len(blks) != 3 {
+			return fmt.Errorf("expected a car file with 3 blocks, got one with %d instead", len(blks))
+		}
+
+		data = blks[2].RawData()
+	}
+
+	if string(data) != expectedResult {
+		return fmt.Errorf("retrieved data mismatch: expected '%s' got '%s'", expectedResult, data)
+	}
+
+	return nil
+}

markets/utils/selectors.go

@@ -0,0 +1,91 @@
+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"
+	selectorparse "github.com/ipld/go-ipld-prime/traversal/selector/parse"
+)
+
+func TraverseDag(
+	ctx context.Context,
+	ds mdagipld.DAGService,
+	startFrom cid.Cid,
+	optionalSelector ipld.Node,
+	visitCallback traversal.AdvVisitFn,
+) error {
+
+	var parsedSelector selector.Selector
+	if optionalSelector == nil {
+		parsedSelector = selectorparse.CommonSelector_MatchAllRecursively
+	} else {
+		var err error
+		parsedSelector, err = selector.ParseSelector(optionalSelector)
+		if err != nil {
+			return err
+		}
+	}
+
+	// not sure what this is for TBH: we also provide ctx in  &traversal.Config{}
+	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(lctx ipld.LinkContext, lnk ipld.Link) (io.Reader, error) {
+		cl, isCid := lnk.(cidlink.Link)
+		if !isCid {
+			return nil, fmt.Errorf("unexpected link type %#v", lnk)
+		}
+
+		node, err := ds.Get(lctx.Ctx, 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)
+}

node/impl/client/client.go

@@ -24,10 +24,15 @@ import (
 	"github.com/ipfs/go-cid"
 	offline "github.com/ipfs/go-ipfs-exchange-offline"
 	files "github.com/ipfs/go-ipfs-files"
+	logging "github.com/ipfs/go-log/v2"
 	"github.com/ipfs/go-merkledag"
+	"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"
+	textselector "github.com/ipld/go-ipld-selector-text-lite"
 	"github.com/libp2p/go-libp2p-core/host"
 	"github.com/libp2p/go-libp2p-core/peer"
 	"github.com/multiformats/go-multibase"
@@ -68,6 +73,8 @@ import (
 	"github.com/filecoin-project/lotus/node/repo"
 )
 
+var log = logging.Logger("client")
+
 var DefaultHashFunction = uint64(mh.BLAKE2B_MIN + 31)
 
 // 8 days ~=  SealDuration + PreCommit + MaxProveCommitDuration + 8 hour buffer
@@ -500,7 +507,7 @@ func (a *API) ClientImport(ctx context.Context, ref api.FileRef) (res *api.Impor
 	}
 
 	if ref.IsCAR {
-		// user gave us a CAR fil, use it as-is
+		// user gave us a CAR file, use it as-is
 		// validate that it's either a carv1 or carv2, and has one root.
 		f, err := os.Open(ref.Path)
 		if err != nil {
@@ -835,6 +842,29 @@ func (a *API) clientRetrieve(ctx context.Context, order api.RetrievalOrder, ref
 	}
 
 	sel := shared.AllSelector()
+	if order.DatamodelPathSelector != nil {
+
+		ssb := builder.NewSelectorSpecBuilder(basicnode.Prototype.Any)
+
+		selspec, err := textselector.SelectorSpecFromPath(
+
+			*order.DatamodelPathSelector,
+
+			// URGH - this is a direct copy from https://github.com/filecoin-project/go-fil-markets/blob/v1.12.0/shared/selectors.go#L10-L16
+			// Unable to use it because we need the SelectorSpec, and markets exposes just a reified node
+			ssb.ExploreRecursive(
+				selector.RecursionLimitNone(),
+				ssb.ExploreAll(ssb.ExploreRecursiveEdge()),
+			),
+		)
+		if err != nil {
+			finish(xerrors.Errorf("failed to parse text-selector '%s': %w", *order.DatamodelPathSelector, err))
+			return
+		}
+
+		sel = selspec.Node()
+		log.Infof("partial retrieval of datamodel-path-selector %s/*", *order.DatamodelPathSelector)
+	}
 
 	// summary:
 	// 1. if we're retrieving from an import, FromLocalCAR will be set.
@@ -961,8 +991,8 @@ func (a *API) clientRetrieve(ctx context.Context, order api.RetrievalOrder, ref
 	// Are we outputting a CAR?
 	if ref.IsCAR {
 
-		// not IPFS - just extract the CARv1 from the CARv2 we stored the retrieval in
+		// not IPFS and we do full selection - just extract the CARv1 from the CARv2 we stored the retrieval in
-		if !retrieveIntoIPFS {
+		if !retrieveIntoIPFS && order.DatamodelPathSelector == nil {
 			finish(carv2.ExtractV1File(carPath, ref.Path))
 			return
 		}
@@ -995,6 +1025,40 @@ func (a *API) clientRetrieve(ctx context.Context, order api.RetrievalOrder, ref
 	ds := merkledag.NewDAGService(blockservice.New(retrievalBs, offline.Exchange(retrievalBs)))
 	root := order.Root
 
+	// if we used a selector - need to find the sub-root the user actually wanted to retrieve
+	if order.DatamodelPathSelector != nil {
+
+		var subRootFound bool
+
+		// no err check - we just compiled this before starting, but now we do not wrap a `*`
+		selspec, _ := textselector.SelectorSpecFromPath(*order.DatamodelPathSelector, nil) //nolint:errcheck
+		if err := utils.TraverseDag(
+			ctx,
+			ds,
+			root,
+			selspec.Node(),
+			func(p traversal.Progress, n ipld.Node, r traversal.VisitReason) error {
+				if r == traversal.VisitReason_SelectionMatch {
+					cidLnk, castOK := p.LastBlock.Link.(cidlink.Link)
+					if !castOK {
+						return xerrors.Errorf("cidlink cast unexpectedly failed on '%s'", p.LastBlock.Link.String())
+					}
+					root = cidLnk.Cid
+					subRootFound = true
+				}
+				return nil
+			},
+		); err != nil {
+			finish(xerrors.Errorf("Finding partial retrieval sub-root: %w", err))
+			return
+		}
+
+		if !subRootFound {
+			finish(xerrors.Errorf("Path selection '%s' does not match a node within %s", order.DatamodelPathSelector, root))
+			return
+		}
+	}
+
 	nd, err := ds.Get(ctx, root)
 	if err != nil {
 		finish(xerrors.Errorf("ClientRetrieve: %w", err))