Address issues with small exr files and header parse

If we know the file size, we should truncate the header parse to only
read the file at most. Otherwise, if the file size is unknown (stream)
then be conservative (and slower) and read 1 byte at a time for the
header parse. Once we know the file, that should be free to read chunks

Signed-off-by: Kimball Thurston <[email protected]>

Author: kdt3rd

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)
     {