MS RFC 88: Saving MapServer Objects to Strings

Author:Tamas Szekeres
Contact:szekerest at
Status:Accepted (2013/03/02), Implemented
Version:MapServer 6.3-dev

1. Overview

This RFC provides the option to save map objects to strings as mapfile string fragments. This functionality will mainly be utilized in MapScript and a new method (convertToString) will be added to the corresponding objects. This new method will provide the inverse option for updateFromString that has already been added within the scope of RFC 31.

2. Proposed Solution

The solution will utilize the existing msIO machinery when writing mapfiles. The key point of the implementation is to replace all occurrences of fprintf with msIO_fprintf in mapfile.c and mapsymbol.c. This replacement will establish the option to redirect mapfile writes to a buffer.

3. Implementation Details

Assuming the replacement of fprintf is done, writing objects to strings could be implemented by adding a new function for each object type something like:

char* msWriteLayerToString(layerObj *layer)
  msIOContext  context;
  msIOBuffer buffer;

  context.label = NULL;
  context.write_channel = MS_TRUE;
  context.readWriteFunc = msIO_bufferWrite;
  context.cbData = &buffer; = NULL;
  buffer.data_len = 0;
  buffer.data_offset = 0;

  msIO_installHandlers( NULL, &context, NULL );

  writeLayer(stdout, 0, layer);
  msIO_bufferWrite( &buffer, "", 1 );

  msIO_installHandlers( NULL, NULL, NULL );


The owneship of the returned buffer is passed to the caller, so we should hook this function in layer.i as follows:

%newobject convertToString;
char* convertToString()
  return msWriteLayerToString(self);

In order to implement the writer for mapObj (msWriteMapToString) we will require to isolate the bulk of the writing code in a separate function writeMap from msSaveMap. In this regard msSaveMap will now look something like:

int msSaveMap(mapObj *map, char *filename)
  FILE *stream;
  char szPath[MS_MAXPATHLEN];

  if(!map) {
    msSetError(MS_MISCERR, "Map is undefined.", "msSaveMap()");

  if(!filename) {
    msSetError(MS_MISCERR, "Filename is undefined.", "msSaveMap()");

  stream = fopen(msBuildPath(szPath, map->mappath, filename), "w");
  if(!stream) {
    msSetError(MS_IOERR, "(%s)", "msSaveMap()", filename);

  writeMap(stream, 0, map);


As the result of this implementation the following new functions will be exposed in mapserver.h

MS_DLL_EXPORT char *msWriteLayerToString(layerObj *layer);
MS_DLL_EXPORT char *msWriteMapToString(layerObj *layer);
MS_DLL_EXPORT char *msWriteClassToString(classObj *_class);
MS_DLL_EXPORT char *msWriteStyleToString(styleObj *style);
MS_DLL_EXPORT char *msWriteLabelToString(labelObj *label)
MS_DLL_EXPORT char *msWriteWebToString(webObj *web)
MS_DLL_EXPORT char *msWriteScalebarToString(scalebarObj *scalebar)
MS_DLL_EXPORT char *msWriteQueryMapToString(queryMapObj *querymap)
MS_DLL_EXPORT char *msWriteReferenceMapToString(referenceMapObj *ref)
MS_DLL_EXPORT char *msWriteLegendToString(legendObj *legend)
MS_DLL_EXPORT char *msWriteClusterToString(clusterObj *cluster)

4. Files Affected

  • mapserver.h: Expose msWriteXXXToString methods
  • mapfile.c: Implement msWriteXXXToString methods
  • mapsymbol.c: Implement msWriteSymbolToString methods
  • mapscript/swiginc/map.i: Add convertToString method
  • mapscript/swiginc/layer.i: Add convertToString method
  • mapscript/swiginc/class.i: Add convertToString method
  • mapscript/swiginc/web.i: Add convertToString method
  • mapscript/swiginc/legend.i: Add convertToString method
  • mapscript/swiginc/scalebar.i: Add convertToString method
  • mapscript/swiginc/querymap.i: Add convertToString method
  • mapscript/swiginc/referencemap.i: Add convertToString method
  • mapscript/swiginc/cluster.i: Add convertToString method
  • mapscript/swiginc/label.i: Add convertToString method
  • mapscript/swiginc/style.i: Add convertToString method
  • mapscript/php/php_mapscript.h: Declare new functions
  • mapscript/php/mapscript_i.c: Add proxyes for new functions
  • mapscript/php/map.c: Add convertToString method
  • mapscript/php/layer.c: Add convertToString method
  • mapscript/php/class.c: Add convertToString method
  • mapscript/php/web.c: Add convertToString method
  • mapscript/php/legend.c: Add convertToString method
  • mapscript/php/scalebar.c: Add convertToString method
  • mapscript/php/querymap.c: Add convertToString method
  • mapscript/php/referencemap.c: Add convertToString method
  • mapscript/php/cluster.c: Add convertToString method
  • mapscript/php/label.c: Add convertToString method
  • mapscript/php/style.c: Add convertToString method

6. Backwards compatibility issues

None expected, new functionality.

7. MapScript changes

New function convertToString will be added to the corresponding objects.

8. Voting history

Tom Kralidis +1 Steve Lime +1 Jeff McKenna +1 Daniel Morissette +1 Umberto Nicoletti +1 Michael Smith +1 Tamas Szekeres +1 Stephen Woodbridge +1