feat(dag): add --local-only to dag export and import

- Export: only export blocks present locally; skip missing (partial CAR).
  --local-only with --offline. Support both binary and base58 link keys.
- Import: support partial CARs; --local-only with -- pin-roots=false (error if
  both --pin-roots and --local-only set).
- Fix cidFromBinString to accept base58 key format from link implementations.

Signed-off-by: Chayan Das <01chayandas@gmail.com>

Author: ChayanDass

core/commands/dag/dag.go

@@ -23,6 +23,7 @@ const (
 	statsOptionName           = "stats"
 	fastProvideRootOptionName = "fast-provide-root"
 	fastProvideWaitOptionName = "fast-provide-wait"
+	localOnlyOptionName       = "local-only"
 )
 
 // DagCmd provides a subset of commands for interacting with ipld dag objects
@@ -192,6 +193,9 @@ Note:
   currently present in the blockstore does not represent a complete DAG,
   pinning of that individual root will fail.
 
+  Use --local-only with --pin-roots=false when importing a partial CAR (e.g. from
+  'dag export --local-only').
+
 FAST PROVIDE OPTIMIZATION:
 
 Root CIDs from CAR headers are immediately provided to the DHT in addition
@@ -213,6 +217,7 @@ Specification of CAR formats: https://ipld.io/specs/transport/car/
 	},
 	Options: []cmds.Option{
 		cmds.BoolOption(pinRootsOptionName, "Pin optional roots listed in the .car headers after importing.").WithDefault(true),
+		cmds.BoolOption(localOnlyOptionName, "Import a partial CAR without pinning roots (for CARs from dag export --local-only)."),
 		cmds.BoolOption(silentOptionName, "No output."),
 		cmds.BoolOption(statsOptionName, "Output stats."),
 		cmds.BoolOption(fastProvideRootOptionName, "Immediately provide root CIDs to DHT in addition to regular queue, for faster discovery. Default: Import.FastProvideRoot"),
@@ -285,6 +290,7 @@ CAR file follows the CARv1 format: https://ipld.io/specs/transport/car/carv1/
 	},
 	Options: []cmds.Option{
 		cmds.BoolOption(progressOptionName, "p", "Display progress on CLI. Defaults to true when STDERR is a TTY."),
+		cmds.BoolOption(localOnlyOptionName, "If set, only blocks present locally are exported; missing blocks are skipped (partial CAR). Use with --offline for a local-only DAG walk."),
 	},
 	Run: dagExport,
 	PostRun: cmds.PostRunMap{

core/commands/dag/export.go

@@ -1,6 +1,7 @@
 package dagcmd
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -16,7 +17,10 @@ import (
 	"github.com/ipfs/kubo/core/commands/cmdutils"
 	iface "github.com/ipfs/kubo/core/coreiface"
 	gocar "github.com/ipld/go-car/v2"
+	"github.com/ipld/go-ipld-prime/datamodel"
+	"github.com/ipld/go-ipld-prime/linking"
 	cidlink "github.com/ipld/go-ipld-prime/linking/cid"
+	"github.com/ipld/go-ipld-prime/traversal"
 	selectorparse "github.com/ipld/go-ipld-prime/traversal/selector/parse"
 )
 
@@ -27,6 +31,7 @@ func dagExport(req *cmds.Request, res cmds.ResponseEmitter, env cmds.Environment
 		return err
 	}
 
+	localOnly, _ := req.Options[localOnlyOptionName].(bool)
 	api, err := cmdenv.GetApi(env, req)
 	if err != nil {
 		return err
@@ -51,7 +56,25 @@ func dagExport(req *cmds.Request, res cmds.ResponseEmitter, env cmds.Environment
 		}()
 
 		lsys := cidlink.DefaultLinkSystem()
-		lsys.SetReadStorage(&dagStore{dag: api.Dag(), ctx: req.Context})
+		ds := &dagStore{dag: api.Dag(), ctx: req.Context}
+		if localOnly {
+			lsys.StorageReadOpener = func(lctx linking.LinkContext, lnk datamodel.Link) (io.Reader, error) {
+				cl, ok := lnk.(cidlink.Link)
+				if !ok {
+					return nil, fmt.Errorf("unsupported link type: %T", lnk)
+				}
+				data, err := ds.Get(lctx.Ctx, cl.Cid.String())
+				if err != nil {
+					if ipld.IsNotFound(err) {
+						return nil, traversal.SkipMe{}
+					}
+					return nil, fmt.Errorf("local block read failed: %w", err)
+				}
+				return bytes.NewReader(data), nil
+			}
+		} else {
+			lsys.SetReadStorage(ds)
+		}
 
 		// Uncomment the following to support CARv2 output.
 		/*
@@ -189,12 +212,11 @@ func (ds *dagStore) Has(ctx context.Context, key string) (bool, error) {
 }
 
 func cidFromBinString(key string) (cid.Cid, error) {
-	l, k, err := cid.CidFromBytes([]byte(key))
-	if err != nil {
-		return cid.Undef, fmt.Errorf("dagStore: key was not a cid: %w", err)
+	if l, k, err := cid.CidFromBytes([]byte(key)); err == nil && l == len(key) {
+		return k, nil
 	}
-	if l != len(key) {
-		return cid.Undef, fmt.Errorf("dagSore: key was not a cid: had %d bytes leftover", len(key)-l)
+	if c, decodeErr := cid.Decode(key); decodeErr == nil {
+		return c, nil
 	}
-	return k, nil
+	return cid.Undef, fmt.Errorf("dagStore: key was not a cid (binary or base58)")
 }

core/commands/dag/import.go

@@ -49,7 +49,11 @@ func dagImport(req *cmds.Request, res cmds.ResponseEmitter, env cmds.Environment
 	}
 
 	doPinRoots, _ := req.Options[pinRootsOptionName].(bool)
+	localOnly, _ := req.Options[localOnlyOptionName].(bool)
 
+	if doPinRoots && localOnly {
+		return fmt.Errorf("cannot pass both --%s and --%s", pinRootsOptionName, localOnlyOptionName)
+	}
 	fastProvideRoot, fastProvideRootSet := req.Options[fastProvideRootOptionName].(bool)
 	fastProvideWait, fastProvideWaitSet := req.Options[fastProvideWaitOptionName].(bool)
 

go.mod

@@ -280,3 +280,5 @@ exclude (
 	github.com/ipfs/go-ipfs-cmds v2.0.1+incompatible
 	github.com/libp2p/go-libp2p v6.0.23+incompatible
 )
+
+replace github.com/ipld/go-car/v2 => ../go-car/v2

go.sum

@@ -458,8 +458,6 @@ github.com/ipfs/go-test v0.2.3 h1:Z/jXNAReQFtCYyn7bsv/ZqUwS6E7iIcSpJ2CuzCvnrc=
 github.com/ipfs/go-test v0.2.3/go.mod h1:QW8vSKkwYvWFwIZQLGQXdkt9Ud76eQXRQ9Ao2H+cA1o=
 github.com/ipfs/go-unixfsnode v1.10.3 h1:c8sJjuGNkxXAQH75P+f5ngPda/9T+DrboVA0TcDGvGI=
 github.com/ipfs/go-unixfsnode v1.10.3/go.mod h1:2Jlc7DoEwr12W+7l8Hr6C7XF4NHST3gIkqSArLhGSxU=
-github.com/ipld/go-car/v2 v2.16.0 h1:LWe0vmN/QcQmUU4tr34W5Nv5mNraW+G6jfN2s+ndBco=
-github.com/ipld/go-car/v2 v2.16.0/go.mod h1:RqFGWN9ifcXVmCrTAVnfnxiWZk1+jIx67SYhenlmL34=
 github.com/ipld/go-codec-dagpb v1.7.0 h1:hpuvQjCSVSLnTnHXn+QAMR0mLmb1gA6wl10LExo2Ts0=
 github.com/ipld/go-codec-dagpb v1.7.0/go.mod h1:rD3Zg+zub9ZnxcLwfol/OTQRVjaLzXypgy4UqHQvilM=
 github.com/ipld/go-ipld-prime v0.11.0/go.mod h1:+WIAkokurHmZ/KwzDOMUuoeJgaRQktHtEaLglS3ZeV8=