Make pix{Read,Write}MemJp2k work via direct memory access.

* On platforms lacking open_memstream(), pix{Read,Write}MemJp2k()
  worked via a temporary file, but this overhead is unnecessary
  as openjpeg2000's opj_stream allows one to read/write directly
  from a memory buffer by supplying it with appropriate callbacks.
* This commit makes pix{Read,Write}MemJp2k() use this more direct
  mechanism on all platforms.
* In addition, since pixReadStreamJp2k() always read the whole
  stream into memory when it called fgetJp2kResolution(),
  this commit saves a bit of compute resources by in effect making
  pixReadStreamJp2k() into a wrapper for pixReadMemJp2k().

src/allheaders.h

@@ -1070,6 +1070,7 @@ LEPT_DLL extern l_ok readHeaderJp2k ( const char *filename, l_int32 *pw, l_int32
 LEPT_DLL extern l_ok freadHeaderJp2k ( FILE *fp, l_int32 *pw, l_int32 *ph, l_int32 *pbps, l_int32 *pspp, l_int32 *pcodec );
 LEPT_DLL extern l_ok readHeaderMemJp2k ( const l_uint8 *data, size_t size, l_int32 *pw, l_int32 *ph, l_int32 *pbps, l_int32 *pspp, l_int32 *pcodec );
 LEPT_DLL extern l_int32 fgetJp2kResolution ( FILE *fp, l_int32 *pxres, l_int32 *pyres );
+LEPT_DLL extern l_ok readResolutionMemJp2k ( const l_uint8 *data, size_t size, l_int32 *pxres, l_int32 *pyres );
 LEPT_DLL extern PIX * pixReadJp2k ( const char *filename, l_uint32 reduction, BOX *box, l_int32 hint, l_int32 debug );
 LEPT_DLL extern PIX * pixReadStreamJp2k ( FILE *fp, l_uint32 reduction, BOX *box, l_int32 hint, l_int32 debug );
 LEPT_DLL extern l_ok pixWriteJp2k ( const char *filename, PIX *pix, l_int32 quality, l_int32 nlevels, l_int32 hint, l_int32 debug );

src/jp2kheader.c

@@ -274,35 +274,57 @@ fgetJp2kResolution(FILE     *fp,
                    l_int32  *pxres,
                    l_int32  *pyres)
 {
-l_uint8    xexp, yexp;
 l_uint8   *data;
+size_t     nbytes;
+l_ok       ok;
+
+    if (!fp)
+        return ERROR_INT("stream not opened", __func__, 1);
+
+    rewind(fp);
+    data = l_binaryReadStream(fp, &nbytes);
+    rewind(fp);
+
+    ok = readResolutionMemJp2k(data, nbytes, pxres, pyres);
+
+    LEPT_FREE(data);
+    return ok;
+}
+
+/*!
+ * \brief   readResolutionMemJp2k()
+ *
+ * \param[in]   data    const; jp2k-encoded
+ * \param[in]   size    of data
+ * \param[out]  pxres   [optional]
+ * \param[out]  pyres   [optional]
+ * \return  0 if OK, 1 on error
+ */
+l_ok
+readResolutionMemJp2k(const l_uint8  *data,
+                      size_t          nbytes,
+                      l_int32        *pxres,
+                      l_int32        *pyres)
+{
+l_uint8    xexp, yexp;
 l_uint16   xnum, ynum, xdenom, ydenom;  /* these jp2k fields are 2-byte */
 l_int32    loc, found;
 l_uint8    resc[4] = {0x72, 0x65, 0x73, 0x63};  /* 'resc' */
-size_t     nbytes;
 l_float64  xres, yres, maxres;
 
     if (pxres) *pxres = 0;
     if (pyres) *pyres = 0;
     if (!pxres || !pyres)
         return ERROR_INT("&xres and &yres not both defined", __func__, 1);
-    if (!fp)
-        return ERROR_INT("stream not opened", __func__, 1);
-
-    rewind(fp);
-    data = l_binaryReadStream(fp, &nbytes);
-    rewind(fp);
 
         /* Search for the start of the first capture resolution box: 'resc' */
     arrayFindSequence(data, nbytes, resc, 4, &loc, &found);
     if (!found) {
         L_WARNING("image resolution not found\n", __func__);
-        LEPT_FREE(data);
         return 1;
     }
     if (nbytes < 80 || loc >= nbytes - 13) {
         L_WARNING("image resolution found without enough space\n", __func__);
-        LEPT_FREE(data);
         return 1;
     }
 
@@ -318,7 +340,6 @@ l_float64  xres, yres, maxres;
     xdenom = convertOnLittleEnd16(xdenom);
     if (ydenom == 0 || xdenom == 0) {
         L_WARNING("bad data: ydenom or xdenom is 0\n", __func__);
-        LEPT_FREE(data);
         return 1;
     }
     yexp = data[loc + 12];
@@ -339,7 +360,6 @@ l_float64  xres, yres, maxres;
         *pxres = (l_int32)(xres + 0.5);
     }
 
-    LEPT_FREE(data);
     return 0;
 }
 

src/jp2kheaderstub.c

@@ -72,5 +72,13 @@ l_int32 fgetJp2kResolution(FILE *fp, l_int32 *pxres, l_int32 *pyres)
     return ERROR_INT("function not present", __func__, 1);
 }
 
+/* ----------------------------------------------------------------------*/
+
+l_ok readResolutionMemJp2k(const l_uint8 *data, size_t size,
+                           l_int32 *pxres, l_int32 *pyres)
+{
+    return ERROR_INT("function not present", __func__, 1);
+}
+
 /* --------------------------------------------*/
 #endif  /* !USE_JP2KHEADER */