chainimport: refactor header verification at target height

In this commit, we consolidate block header and filter header
verification logic into reusable verification functions at target
height.

The main motive behind is change is allowing flexibility when
adapting the appendMode parameter later

Author: mohamedawnallah

chainimport/headers_import.go

@@ -316,6 +316,28 @@ func (h *headersImport) verifyHeadersAtTargetHeight(height uint32) error {
 		height, headerMetadata.startHeight,
 	)
 
+	if err := h.verifyBlockHeadersAtTargetHeight(
+		height, importSourceIndex,
+	); err != nil {
+		return fmt.Errorf("failed to verify block headers at target "+
+			"height %d: %w", height, err)
+	}
+
+	if err := h.verifyFilterHeadersAtTargetHeight(
+		height, importSourceIndex,
+	); err != nil {
+		return fmt.Errorf("failed to verify filter headers at target "+
+			"height %d: %w", height, err)
+	}
+
+	return nil
+}
+
+// verifyBlockHeadersAtTargetHeight ensures block headers at the specified
+// height match exactly between import and target sources.
+func (h *headersImport) verifyBlockHeadersAtTargetHeight(height uint32,
+	importSourceIndex uint32) error {
+
 	importSourceHeader, err := h.blockHeadersImportSource.GetHeader(
 		importSourceIndex,
 	)
@@ -346,7 +368,17 @@ func (h *headersImport) verifyHeadersAtTargetHeight(height uint32) error {
 			sourceBlkHeaderHash, targetBlkHeaderHash)
 	}
 
-	importSourceHeader, err = h.filterHeadersImportSource.GetHeader(
+	log.Debugf("Block headers from import and target sources verified at "+
+		"height %d", height)
+	return nil
+}
+
+// verifyFilterHeadersAtTargetHeight ensures filter headers at the specified
+// height match exactly between import and target sources.
+func (h *headersImport) verifyFilterHeadersAtTargetHeight(height uint32,
+	importSourceIndex uint32) error {
+
+	importSourceHeader, err := h.filterHeadersImportSource.GetHeader(
 		importSourceIndex,
 	)
 	if err != nil {
@@ -376,10 +408,8 @@ func (h *headersImport) verifyHeadersAtTargetHeight(height uint32) error {
 			sourceFilterHeaderHash, targetFilterHeaderHash)
 	}
 
-	log.Debugf("Headers from %s (block) and %s (filter) verified at "+
-		"height %d", h.blockHeadersImportSource.GetURI(),
-		h.filterHeadersImportSource.GetURI(), height)
-
+	log.Debugf("Filter headers from import and target sources verified at "+
+		"height %d", height)
 	return nil
 }
 

chainimport/headers_import_test.go

@@ -2851,8 +2851,8 @@ func TestImportAndTargetSourcesChainContinuityConstraint(t *testing.T) {
 				}
 			},
 			expectErr: true,
-			expectErrMsg: "genesis header mismatch: block header " +
-				"mismatch at height 0",
+			expectErrMsg: "genesis header mismatch: failed to " +
+				"verify block headers at target height 0",
 		},
 		{
 			name: "ErrorOnGenesisFilterHeadersMismatch",
@@ -2920,8 +2920,8 @@ func TestImportAndTargetSourcesChainContinuityConstraint(t *testing.T) {
 				}
 			},
 			expectErr: true,
-			expectErrMsg: "genesis header mismatch: filter " +
-				"header mismatch at height 0",
+			expectErrMsg: "genesis header mismatch: failed to " +
+				"verify filter headers at target height 0",
 		},
 		{
 			name: "ValidateOnGenesisHeightSuccessfully",