From 011cd0e4f413aa91829f9df944902adfa0b45c61 Mon Sep 17 00:00:00 2001
From: "Sascha L. Teichmann" <sascha.teichmann@intevation.de>
Date: Sun, 23 Aug 2015 22:48:54 +0200
Subject: [PATCH] Be more defensive in decoding node id table in blocks.

---
 common/block.go | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/common/block.go b/common/block.go
index 18d95ad..cc9fbf2 100644
--- a/common/block.go
+++ b/common/block.go
@@ -176,11 +176,24 @@ func NewDecodedBlock(data []byte, colors *Colors) (db *DecodedBlock, err error)
 		offset++
 		numMappings := int(binary.BigEndian.Uint16(data[offset:]))
 		offset += 2
-		for i := 0; i < numMappings; i++ {
+		const outOfBounds = "Offset in node id table out of bounds. Ignored."
+		for i, n := 0, len(data); i < numMappings; i++ {
+			if offset+1 >= n {
+				log.Println(outOfBounds)
+				break
+			}
 			nodeId := int32(binary.BigEndian.Uint16(data[offset:]))
 			offset += 2
+			if offset+1 >= n {
+				log.Println(outOfBounds)
+				break
+			}
 			nameLen := int(binary.BigEndian.Uint16(data[offset:]))
 			offset += 2
+			if offset+nameLen-1 >= n {
+				log.Println(outOfBounds)
+				break
+			}
 			name := string(data[offset : offset+nameLen])
 			offset += nameLen
 			switch name {
@@ -191,7 +204,7 @@ func NewDecodedBlock(data []byte, colors *Colors) (db *DecodedBlock, err error)
 			default:
 				if index, found := colors.NameIndex[name]; found {
 					indexMap[nodeId] = index
-					if colors.IsTransparent(index) {
+					if !transparent && colors.IsTransparent(index) {
 						transparent = true
 					}
 				} else {