Address issues with small exr files and header parse

src/lib/OpenEXR/ImfContextInit.cpp

@@ -118,9 +118,27 @@ istream_nonparallel_read (
             }
         }
 
+        int64_t stream_sz = s->size ();
+        int64_t nend = nread + (int64_t)sz;
+        if (stream_sz > 0 && nend > stream_sz)
+        {
+            sz = stream_sz - nend;
+        }
+
         try
         {
-            s->read (static_cast<char*> (buffer), static_cast<int> (sz));
+            if (s->isMemoryMapped ())
+            {
+                char* data = s->readMemoryMapped (static_cast<int> (sz));
+                // TODO: in a future release, pass this through to
+                // core directly
+                if (data)
+                    memcpy (buffer, data, sz);
+            }
+            else
+            {
+                s->read (static_cast<char*> (buffer), static_cast<int> (sz));
+            }
         }
         catch (...)
         {

src/lib/OpenEXRCore/parse_header.c

@@ -103,7 +103,7 @@ scratch_seq_read (struct _internal_exr_seq_scratch* scr, void* buf, uint64_t sz)
             outbuf += nCopy;
             nCopied += nCopy;
         }
-        else if (notdone > SCRATCH_BUFFER_SIZE)
+        else if (notdone >= SCRATCH_BUFFER_SIZE)
         {
             uint64_t nPages  = notdone / SCRATCH_BUFFER_SIZE;
             int64_t  nread   = 0;
@@ -126,10 +126,28 @@ scratch_seq_read (struct _internal_exr_seq_scratch* scr, void* buf, uint64_t sz)
         else
         {
             int64_t nread = 0;
-            rv            = scr->ctxt->do_read (
+            uint64_t toread = SCRATCH_BUFFER_SIZE;
+
+            if (scr->ctxt->file_size > 0)
+            {
+                if ((scr->fileoff + SCRATCH_BUFFER_SIZE) > scr->ctxt->file_size)
+                {
+                    toread = scr->ctxt->file_size - scr->fileoff;
+                }
+            }
+            else
+            {
+                /*
+                 * hrm, stream only with no known size, just read 1 byte at a
+                 * time to be safer
+                 */
+                toread = 1;
+            }
+
+            rv = scr->ctxt->do_read (
                 scr->ctxt,
                 scr->scratch,
-                SCRATCH_BUFFER_SIZE,
+                toread,
                 &(scr->fileoff),
                 &nread,
                 EXR_ALLOW_SHORT_READ);

src/lib/OpenEXRUtil/ImfCheckFile.cpp

@@ -975,6 +975,8 @@ class PtrIStream : public IStream
 
     virtual bool isMemoryMapped () const { return false; }
 
+    virtual int64_t size () { return end - base; }
+
     virtual char* readMemoryMapped (int n)
     {