tappsbt: add validating setters for AltLeaves

Author: jharveyb

tappsbt/interface.go

@@ -2,6 +2,7 @@ package tappsbt
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"net/url"
 
@@ -79,7 +80,12 @@ var (
 
 	// ErrInvalidVPacketVersion is an error returned when a VPacket version
 	// is invalid.
-	ErrInvalidVPacketVersion = fmt.Errorf("tappsbt: invalid version")
+	ErrInvalidVPacketVersion = errors.New("tappsbt: invalid version")
+
+	// ErrAltLeavesAlreadySet is returned when a VInput or VOutput already
+	// has some AltLeaves set, but a call was made to set the AltLeaves
+	// again.
+	ErrAltLeavesAlreadySet = errors.New("tappsbt: alt leaves already set")
 )
 
 // VPacketVersion is the version of the virtual transaction. This can signal
@@ -419,6 +425,27 @@ func (i *VInput) Asset() *asset.Asset {
 	return i.asset
 }
 
+// SetAltLeaves asserts that a set of AltLeaves are valid, and updates a VInput
+// to set the AltLeaves. Setting the input's AltLeaves twice is disallowed.
+func (i *VInput) SetAltLeaves(altLeafAssets []*asset.Asset) error {
+	// AltLeaves can be set exactly once on a VInput.
+	if len(i.AltLeaves) != 0 {
+		return fmt.Errorf("%w: input", ErrAltLeavesAlreadySet)
+	}
+
+	// Each asset must be a valid AltLeaf, and the set of AltLeaves must be
+	// valid, by not having overlapping keys in the AltCommitment.
+	altLeaves := asset.ToAltLeaves(altLeafAssets)
+	err := asset.ValidAltLeaves(altLeaves)
+	if err != nil {
+		return err
+	}
+
+	i.AltLeaves = asset.CopyAltLeaves(altLeaves)
+
+	return nil
+}
+
 // serializeScriptKey serializes the input asset's script key as the PSBT
 // derivation information on the virtual input.
 func (i *VInput) serializeScriptKey(key asset.ScriptKey, coinType uint32) {
@@ -657,6 +684,27 @@ func (o *VOutput) SetAnchorInternalKey(keyDesc keychain.KeyDescriptor,
 	)
 }
 
+// SetAltLeaves asserts that a set of AltLeaves are valid, and updates a VOutput
+// to set the AltLeaves. Setting the output's AltLeaves twice is disallowed.
+func (o *VOutput) SetAltLeaves(altLeafAssets []*asset.Asset) error {
+	// AltLeaves can be set exactly once on a VOutput.
+	if len(o.AltLeaves) != 0 {
+		return fmt.Errorf("%w: output", ErrAltLeavesAlreadySet)
+	}
+
+	// Each asset must be a valid AltLeaf, and the set of AltLeaves must be
+	// valid, by not having overlapping keys in the AltCommitment.
+	altLeaves := asset.ToAltLeaves(altLeafAssets)
+	err := asset.ValidAltLeaves(altLeaves)
+	if err != nil {
+		return err
+	}
+
+	o.AltLeaves = asset.CopyAltLeaves(altLeaves)
+
+	return nil
+}
+
 // AnchorKeyToDesc attempts to extract the key descriptor of the anchor output
 // from the anchor output BIP-0032 derivation information.
 func (o *VOutput) AnchorKeyToDesc() (keychain.KeyDescriptor, error) {