client/asset/dcrd: spv block header confs is -1 for orphan

This fixes (*spvWallet).GetBlockHeader so that it correctly considers the
main chain status of the block when computing confirmations and
retrieving NextHash.

The new function matches the behavior of dcrd and dcrwallet's
getblockheader handlers.

client/asset/dcr/spv.go

@@ -587,23 +587,32 @@ func (w *spvWallet) GetBlockHeader(ctx context.Context, blockHash *chainhash.Has
 		return nil, err
 	}
 
-	_, tipHeight := w.MainChainTip(ctx)
-	if tipHeight < int32(hdr.Height) {
-		return nil, errors.New("sumpin's wrong with our tip")
-	}
-
+	// Get next block hash unless there are none.
 	var nextHash *chainhash.Hash
-	if tipHeight > int32(hdr.Height) {
-		nextHash, err = w.GetBlockHash(ctx, int64(hdr.Height)+1)
-		if err != nil {
-			return nil, fmt.Errorf("error getting next hash for block %q: %w", blockHash, err)
+	confirmations := int64(-1)
+	mainChainHasBlock, _, err := w.BlockInMainChain(ctx, blockHash)
+	if err != nil {
+		return nil, fmt.Errorf("error checking if block is in mainchain: %w", err)
+	}
+	if mainChainHasBlock {
+		_, tipHeight := w.MainChainTip(ctx)
+		if int32(hdr.Height) < tipHeight {
+			nextHash, err = w.GetBlockHash(ctx, int64(hdr.Height)+1)
+			if err != nil {
+				return nil, fmt.Errorf("error getting next hash for block %q: %w", blockHash, err)
+			}
+		}
+		if int32(hdr.Height) <= tipHeight {
+			confirmations = int64(tipHeight) - int64(hdr.Height) + 1
+		} else { // if tip is less, may be rolling back, so just mock dcrd/dcrwallet
+			confirmations = 0
 		}
 	}
 
 	return &BlockHeader{
 		BlockHeader:   hdr,
 		MedianTime:    medianTime,
-		Confirmations: int64(uint32(tipHeight)-hdr.Height) + 1,
+		Confirmations: confirmations,
 		NextHash:      nextHash,
 	}, nil
 }

client/asset/dcr/spv_test.go

@@ -518,6 +518,16 @@ func TestGetBlockHeader(t *testing.T) {
 		t.Fatal("wrong next hash")
 	}
 
+	dcrw.mainchainDontHave = true
+	hdr, err = w.GetBlockHeader(tCtx, &blockHash)
+	if err != nil {
+		t.Fatalf("initial success error: %v", err)
+	}
+	if hdr.Confirmations != -1 {
+		t.Fatalf("expected -1 confs for side chain block, got %d", hdr.Confirmations)
+	}
+	dcrw.mainchainDontHave = false
+
 	// BlockHeader error
 	dcrw.blockHeaderErr[blockHash] = tErr
 	if _, err := w.GetBlockHeader(tCtx, &blockHash); err == nil {
@@ -534,8 +544,10 @@ func TestGetBlockHeader(t *testing.T) {
 
 	// MainChainTip error
 	dcrw.tip.height = 3
-	if _, err := w.GetBlockHeader(tCtx, &blockHash); err == nil {
+	if hdr, err := w.GetBlockHeader(tCtx, &blockHash); err != nil {
 		t.Fatalf("invalid tip height not noticed")
+	} else if hdr.Confirmations != 0 {
+		t.Fatalf("confirmations not zero for lower tip height")
 	}
 	dcrw.tip.height = tipHeight