From 5ccd4c43035df90b493ebdfd40bf9afdc51579c0 Mon Sep 17 00:00:00 2001
From: Imanol-Mikel Barba Sabariego <imanol@imanolbarba.net>
Date: Sun, 31 May 2020 23:30:28 +0100
Subject: [PATCH] Fixed region and relative chunk calculation from coords. Fixed bug when chunks were not generated in region file. Fixed potential crash when header length is 0

---
 chunk.c       | 36 ++++++++++++++++++++++++++----------
 chunk.h       |  1 +
 compression.c |  2 +-
 3 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/chunk.c b/chunk.c
index 5fcde08..975ebed 100644
--- a/chunk.c
+++ b/chunk.c
@@ -8,8 +8,8 @@ ssize_t loadChunk(const char* regionFolder, ChunkID chunk, void** chunkData);
 
 RegionID translateChunkToRegion(int x, int z) {
     RegionID region;
-    region.x = x/CHUNKS_PER_REGION;
-    region.z = z/CHUNKS_PER_REGION;
+    region.x = floor((double)x/CHUNKS_PER_REGION);
+    region.z = floor((double)z/CHUNKS_PER_REGION);
     return region;
 }
 
@@ -20,16 +20,16 @@ RegionID translateCoordsToRegion(double x, double y, double z) {
 
 ChunkID translateCoordsToChunk(double x, double y, double z) {
     ChunkID chunk;
-    chunk.x = x/BLOCKS_PER_CHUNK;
-    chunk.z = z/BLOCKS_PER_CHUNK;
+    chunk.x = floor((double)x/BLOCKS_PER_CHUNK);
+    chunk.z = floor((double)z/BLOCKS_PER_CHUNK);
     return chunk;
 }
 
 int overwriteChunk(const char* regionFolder, ChunkID chunk, void* chunkData, size_t chunkLength) {
     RegionID region = translateChunkToRegion(chunk.x,chunk.z);
     ChunkID relativeChunk;
-    relativeChunk.x = chunk.x % 32;
-    relativeChunk.z = chunk.z % 32;
+    relativeChunk.x = chunk.x & 31;
+    relativeChunk.z = chunk.z & 31;
 
     char* regionFilename = calloc(MAX_REGION_FILENAME_LENGTH + strlen(regionFolder),sizeof(char));
     sprintf(regionFilename,"%s/r.%d.%d.mca",regionFolder,region.x,region.z);
@@ -110,8 +110,8 @@ int overwriteChunk(const char* regionFolder, ChunkID chunk, void* chunkData, siz
 ssize_t loadChunk(const char* regionFolder, ChunkID chunk, void** chunkData) {
     RegionID region = translateChunkToRegion(chunk.x,chunk.z);
     ChunkID relativeChunk;
-    relativeChunk.x = chunk.x % 32;
-    relativeChunk.z = chunk.z % 32;
+    relativeChunk.x = chunk.x & 31;
+    relativeChunk.z = chunk.z & 31;
 
     char* regionFilename = calloc(MAX_REGION_FILENAME_LENGTH + strlen(regionFolder),sizeof(char));
     sprintf(regionFilename,"%s/r.%d.%d.mca",regionFolder,region.x,region.z);
@@ -135,6 +135,11 @@ ssize_t loadChunk(const char* regionFolder, ChunkID chunk, void** chunkData) {
         return -3;
     }
     chunkHeaderOffset = (__bswap_32(chunkHeaderOffset & 0x00FFFFFF) >> 8) * CHUNK_SECTOR_SIZE;
+    if(chunkHeaderOffset == 0) {
+        // Chunk not present. Hasn't been generated
+        close(fd); 
+        return 0;
+    }
 
     if(lseek(fd,chunkHeaderOffset,SEEK_SET) == -1) {
         close(fd);
@@ -150,6 +155,16 @@ ssize_t loadChunk(const char* regionFolder, ChunkID chunk, void** chunkData) {
     }
     header.length = __bswap_32(header.length);
     ssize_t chunkLength = header.length;
+    if(header.compressionType != COMPRESSION_TYPE_ZLIB && header.compressionType != COMPRESSION_TYPE_GZIP) {
+        fprintf(stderr, "Invalid compression method. Proably reading the wrong data for the header\n");
+        close(fd); 
+        return -6;
+    }
+    if(header.length == 0) {
+        fprintf(stderr, "Header length is 0. Probably reading the wrong data for the header\n");
+        close(fd); 
+        return -7;
+    }
     
     void* compressedChunk = calloc(chunkLength,sizeof(char));
     ssize_t nRead = 0;
@@ -163,7 +178,7 @@ ssize_t loadChunk(const char* regionFolder, ChunkID chunk, void** chunkData) {
             fprintf(stderr,"Unable to read chunk: %s\n",strerror(errno));
             close(fd);
             free(compressedChunk);
-            return -6;
+            return -8;
         }
         totalRead += nRead;
     }
@@ -174,7 +189,8 @@ ssize_t loadChunk(const char* regionFolder, ChunkID chunk, void** chunkData) {
     
     if(chunkLength <= 0) {
         fprintf(stderr,"Error while decompressing chunk\n");
-        return -8;
+        free(compressedChunk);
+        return -9;
     }
     free(compressedChunk);
 
diff --git a/chunk.h b/chunk.h
index e369742..f45a4f3 100644
--- a/chunk.h
+++ b/chunk.h
@@ -9,6 +9,7 @@
 #include <stdint.h>
 #include <string.h>
 #include <byteswap.h>
+#include <math.h>
 
 #include "compression.h"
 
diff --git a/compression.c b/compression.c
index c87ed08..6edfd2e 100644
--- a/compression.c
+++ b/compression.c
@@ -45,7 +45,7 @@ ssize_t inflateGzip(void* compData, size_t compDataLen, void** unCompData, int h
         strm.avail_out = uncompLength - strm.total_out;
 
         // Inflate another chunk.
-        err = inflate (&strm, Z_SYNC_FLUSH);
+        err = inflate(&strm, Z_SYNC_FLUSH);
         if(err != Z_OK && err != Z_STREAM_END) {
             fprintf(stderr, "Error while inflating buffer: %d - %s.\n", err,strm.msg);
             inflateEnd(&strm);
--
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