pdfviewer: don't crash if the xref is corrupted.

experimental/PdfViewer/pdfparser/native/SkPdfNativeTokenizer.cpp

 
 #include "SkPdfNativeTokenizer.h"
 #include "SkPdfObject.h"
 #include "SkPdfConfig.h"
 
 #include "SkPdfStreamCommonDictionary_autogen.h"
 #include "SkPdfImageDictionary_autogen.h"
 
 // TODO(edisonn): perf!!!
 // there could be 0s between start and end! but not in the needle.
@@ skipping 273 matching lines @@
     } else {
         return start + (out - (const unsigned char*)NULL); // return where the string would end if we reuse the string
     }
 }
 
 static int readStringLength(int level, const unsigned char* start, const unsigned char* end) {
     return readString(level, start, end, NULL) - start;
 }
 
 static const unsigned char* readString(int level, const unsigned char* start, const unsigned char* end, SkPdfObject* str, SkPdfAllocator* allocator) {
+    if (!allocator) {
+        return end;
+    }
     int outLength = readStringLength(level, start, end);
     // TODO(edisonn): optimize the allocation, don't allocate new string, but put it in a preallocated buffer
     unsigned char* out = (unsigned char*)allocator->alloc(outLength);
     start = readString(level, start, end, out);
     SkPdfObject::makeString(out, out + outLength, str);
     TRACE_STRING(out, out + outLength);
     return start;  // consumed already ) at the end of the string
 }
 
 static const unsigned char* readHexString(int level, const unsigned char* start, const unsigned char* end, unsigned char* out) {
@@ skipping 123 matching lines @@
     } else {
         return start + (out - (const unsigned char*)NULL); // return where the string would end if we reuse the string
     }
 }
 
 static int readHexStringLength(int level, const unsigned char* start, const unsigned char* end) {
     return readHexString(level, start, end, NULL) - start;
 }
 
 static const unsigned char* readHexString(int level, const unsigned char* start, const unsigned char* end, SkPdfObject* str, SkPdfAllocator* allocator) {
+    if (!allocator) {
+        return end;
+    }
     int outLength = readHexStringLength(level, start, end);
     // TODO(edisonn): optimize the allocation, don't allocate new string, but put it in a preallocated buffer
     unsigned char* out = (unsigned char*)allocator->alloc(outLength);
     start = readHexString(level, start, end, out);
     SkPdfObject::makeHexString(out, out + outLength, str);
     TRACE_HEXSTRING(out, out + outLength);
     return start;  // consumed already > at the end of the string
 }
 
 // TODO(edisonn): before PDF 1.2 name could not have special characters, add version parameter
@@ skipping 102 matching lines @@
     } else {
         return start + (out - (const unsigned char*)NULL); // return where the string would end if we reuse the string
     }
 }
 
 static int readNameLength(int level, const unsigned char* start, const unsigned char* end) {
     return readName(level, start, end, NULL) - start;
 }
 
 static const unsigned char* readName(int level, const unsigned char* start, const unsigned char* end, SkPdfObject* name, SkPdfAllocator* allocator) {
+    if (!allocator) {
+        return end;
+    }
     int outLength = readNameLength(level, start, end);
     // TODO(edisonn): optimize the allocation, don't allocate new string, but put it in a preallocated buffer
     unsigned char* out = (unsigned char*)allocator->alloc(outLength);
     start = readName(level, start, end, out);
     SkPdfObject::makeName(out, out + outLength, name);
     TRACE_NAME(out, out + outLength);
     return start;
 }
 
 // TODO(edisonn): pdf spec let Length to be an indirect object define after the stream
@@ skipping 481 matching lines @@
             SkPdfObject* obj = fAllocator->allocObject();
             fUncompressedStream = nextObject(0, fUncompressedStream, fUncompressedStreamEnd, obj, fAllocator, fDoc);
             // TODO(edisonn): perf maybe we should not expand abreviation like this
             inlineImage->set(inlineImageKeyAbbreviationExpand(key),
                              inlineImageValueAbbreviationExpand(obj));
         }
     }
     // TODO(edisonn): report end of data with inline image without an EI
     return inlineImage;
 }