Change metadata write order for JPEG output to better follow most common order in JPEG streams. Addresses part of issues raised in #286.

Add new MAX_EXIF start-up parameter that enables control over whether and how EXIF data is embedded in tile requests. Default size is 65533 bytes. 0 = disable, -1 = always embed.

Author: ruven

ChangeLog

@@ -1,3 +1,10 @@
+27/05/2026:
+	- Change metadata write order for JPEG output to better follow most common order in JPEG streams.
+	  Addresses part of issues raised in https://github.com/ruven/iipsrv/issues/286.
+	- Add new MAX_EXIF start-up parameter that enables control over whether and how EXIF data is embedded in tile requests.
+	  Default size is 65533 bytes. 0 = disable, -1 = always embed.
+
+
 11/02/2026:
 	- Correct typos in AVIFCompressor class
 	- Remove obsolete calculateResolution() function from View class

README

@@ -453,6 +453,8 @@ CACHE_CONTROL: Set the HTTP Cache-Control header. See http://www.w3.org/Protocol
 
 MAX_ICC: Set the maximum ICC profile size in bytes that is allowed to be embedded within an output image. This is set by default to 65535 bytes. If set to -1, no limit is set and all profiles are embedded. If set to 0, no profiles are embedded.
 
+MAX_EXIF: Set the maximum EXIF size in bytes that is allowed to be embedded within an output image (when serving tiles). This is set by default to 65532 bytes. If set to -1, no limit is set and all EXIF metadata is embedded. If set to 0, no EXIF metadata is embedded.
+
 OMP_NUM_THREADS: Set the number of OpenMP threads to be used by the iipsrv image processing routines (See OpenMP specification for details). All available processor threads are used by default.
 
 KAKADU_READMODE: Set the Kakadu JPEG2000 read-mode. 0 for 'fast' mode with minimal error checking (default), 1 for 'fussy' mode with no error recovery, 2 for 'resilient' mode with maximum recovery from codestream errors. See the Kakadu documentation for further details.

src/Environment.h

@@ -1,7 +1,7 @@
 /*
     IIP Environment Variable Class
 
-    Copyright (C) 2006-2025 Ruven Pillay
+    Copyright (C) 2006-2026 Ruven Pillay
 
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -51,7 +51,8 @@
 #define CACHE_CONTROL "max-age=86400";  // 24 hours
 #define ALLOW_UPSCALING true
 #define URI_MAP ""
-#define MAX_ICC 65536 // Max ICC profile size of 65k
+#define MAX_ICC 65536  // Max ICC profile size of 65k
+#define MAX_EXIF 65533 // Maximum size possible in a single JPEG chunk (taking into account prefix)
 #define CODEC_PASSTHROUGH true
 #define KAKADU_READMODE 0
 #define IIIF_VERSION 3
@@ -393,6 +394,17 @@ class Environment {
   }
 
 
+  static int getMaxEXIF(){
+    const char* envpara = getenv( "MAX_EXIF" );
+    int max_exif;
+    if( envpara ){
+      max_exif = atoi( envpara );
+    }
+    else max_exif = MAX_EXIF;
+    return max_exif;
+  }
+
+
   static bool getCodecPassthrough(){
     const char* envpara = getenv( "CODEC_PASSTHROUGH" );
     bool codec_passthrough;

src/JPEGCompressor.cc

@@ -1,6 +1,6 @@
 /*  JPEG class wrapper to ijg jpeg library
 
-    Copyright (C) 2000-2024 Ruven Pillay
+    Copyright (C) 2000-2026 Ruven Pillay
 
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -220,18 +220,18 @@ void JPEGCompressor::InitCompression( const RawTile& rawtile, unsigned int strip
 
   jpeg_start_compress( &cinfo, TRUE );
 
-  // Add an identifying comment
-  const char *comment = "iipsrv/" VERSION;
-  jpeg_write_marker( &cinfo, JPEG_COM, (const JOCTET*) comment, strlen(comment) );
-
-  // Embed ICC profile if one is supplied
-  writeICCProfile();
+  // Add EXIF metadata
+  writeExifMetadata();
 
   // Add XMP metadata
   writeXMPMetadata();
 
-  // Add EXIF metadata
-  writeExifMetadata();
+  // Embed ICC profile if one is supplied
+  writeICCProfile();
+
+  // Add an identifying comment
+  const char *comment = "iipsrv/" VERSION;
+  jpeg_write_marker( &cinfo, JPEG_COM, (const JOCTET*) comment, strlen(comment) );
 
   // Copy the encoded JPEG header data to a separate buffer
   size_t datacount = dest->source_size - dest->pub.free_in_buffer;
@@ -370,20 +370,19 @@ unsigned int JPEGCompressor::Compress( RawTile& rawtile )
   jpeg_set_quality( &cinfo, Q, TRUE );
 
   jpeg_start_compress( &cinfo, TRUE );
-  
-  // Add an identifying comment
-  const char *comment = "iipsrv/" VERSION;
-  jpeg_write_marker( &cinfo, JPEG_COM, (const JOCTET*) comment, strlen(comment) );
 
-  // Embed ICC profile if one is supplied
-  writeICCProfile();
+  // Add EXIF metadata
+  writeExifMetadata();
 
   // Add XMP metadata
   writeXMPMetadata();
 
-  // Add EXIF metadata
-  writeExifMetadata();
+  // Embed ICC profile if one is supplied
+  writeICCProfile();
 
+  // Add an identifying comment
+  const char *comment = "iipsrv/" VERSION;
+  jpeg_write_marker( &cinfo, JPEG_COM, (const JOCTET*) comment, strlen(comment) );
 
   // Compress the image line by line
   JSAMPROW row[1];

src/JTL.cc

@@ -1,7 +1,7 @@
 /*
     IIP JTL Command Handler Class Member Function: Export a single tile
 
-    Copyright (C) 2006-2025 Ruven Pillay.
+    Copyright (C) 2006-2026 Ruven Pillay.
 
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -169,6 +169,25 @@ void JTL::send( Session* session, int resolution, int tile ){
   }
 
 
+  // Embed EXIF metadata if we have one and if embedding has been enabled at start-up
+  if( ( session->view->maxEXIF() != 0 ) != 0 && ( (*session->image)->getMetadata("exif").size() > 0 ) ){
+    // Only embed if EXIF is of an acceptable size or if acceptable size is unlimited (-1)
+    if( ( session->view->maxEXIF() == -1 ) || ( (*session->image)->getMetadata("exif").size() < (unsigned long)session->view->maxEXIF() ) ){
+      if( session->loglevel >= 3 ){
+	*(session->logfile) << "JTL :: Embedding EXIF metadata with size "
+			    << (*session->image)->getMetadata("exif").size() << " bytes" << endl;
+      }
+      compressor->embedExifMetadata( true );
+    }
+    else{
+      if( session->loglevel >= 3 ){
+	*(session->logfile) << "JTL :: EXIF metadata with size "
+			    << (*session->image)->getMetadata("exif").size() << " bytes is too large: Not embedding" << endl;
+      }
+    }
+  }
+
+
   RawTile rawtile = tilemanager.getTile( resolution, tile, session->view->xangle,
 					 session->view->yangle, session->view->getLayers(), ct );
 

src/Main.cc

@@ -1,7 +1,7 @@
 /*
     IIP FCGI server module - Main loop.
 
-    Copyright (C) 2000-2025 Ruven Pillay
+    Copyright (C) 2000-2026 Ruven Pillay
 
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -349,6 +349,10 @@ int main( int argc, char *argv[] )
   int max_icc = Environment::getMaxICC();
 
 
+  // Get the max EXIF size we allow to be embedded
+  int max_exif = Environment::getMaxEXIF();
+
+
   // Get codec passthrough setting
   IIPImage::codec_passthrough = Environment::getCodecPassthrough();
 
@@ -437,6 +441,9 @@ int main( int argc, char *argv[] )
     logfile << "Setting maximum ICC profile size to ";
     if( max_icc < 0 ) logfile << "unlimited" << endl;
     else logfile << max_icc << " bytes" << endl;
+    logfile << "Setting maximum EXIF size to ";
+    if( max_exif < 0 ) logfile << "unlimited" << endl;
+    else logfile << max_exif << " bytes" << endl;
     logfile << "Setting codec passthrough to " << (IIPImage::codec_passthrough? "true" : "false") << endl;
     if( !copyright.empty() ) logfile << "Setting default rights/copyright statement to '" << copyright << "'" << endl;
     logfile << "Setting up TIFF support via " << TPTImage::getCodecVersion() << endl;
@@ -666,6 +673,7 @@ int main( int argc, char *argv[] )
     if( max_layers != 0 ) view.setMaxLayers( max_layers );
     view.setAllowUpscaling( allow_upscaling );
     view.setMaxICC( max_icc );
+    view.setMaxEXIF( max_exif );
 
 
     // Create an IIPResponse object - we use this for the OBJ requests.

src/View.h

@@ -69,6 +69,7 @@ class View{
   bool maintain_aspect;                       ///< Indicate whether aspect ratio should be maintained
   bool allow_upscaling;                       ///< Indicate whether images may be served larger than the source file
   int max_icc;                                ///< Maximum ICC profile size we allow to be embedded
+  int max_exif;                               ///< Maximum EXIF size we allow to be embedded
   ImageEncoding output_format;                ///< Requested output format
   float contrast;                             ///< Contrast adjustment requested by CNT command
   float gamma;                                ///< Gamma adjustment requested by GAM command
@@ -95,6 +96,7 @@ class View{
     allow_upscaling = true;
     colorspace = ColorSpace::NONE;
     max_icc = -1;
+    max_exif = -1;
     output_format = ImageEncoding::JPEG;
     equalization = false;
     minmax = false;
@@ -142,6 +144,20 @@ class View{
   }
 
 
+  /// Set the maximum EXIF size we allow to be embedded
+  /** @param max maximum icc profile size
+   */
+  void setMaxEXIF( int max ){ max_exif = max; };
+
+
+  /// Get the maximum EXIF size we allow to be embedded
+  /** @return max EXIFsize
+   */
+  int maxEXIF(){
+    return max_exif;
+  }
+
+
   /// Set the maximum view port dimension
   /** @param r number of availale resolutions */
   void setMaxResolutions( unsigned int r ){ max_resolutions = r; resolution=r-1; };