Set directory icon on Mac

directory_icon.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <CoreServices/CoreServices.h>
#include "directory_icon.h"

int setDirectoryIcon(const char *dirName, const char *iconData, size_t iconSize)
{
    const int kResidIcon = -16455;
    const OSType kRsrcType = 'icns';
    const char *kIconName = "/Icon\r";
    
    OSErr oserr;
    
    /* Construct icon filename */
    size_t filenameLength = strlen(dirName) + strlen(kIconName);
    char *iconFilename = (char *)malloc(filenameLength + 1);
    strcpy(iconFilename, dirName);
    char *p = &iconFilename[strlen(dirName) - 1];
    while (*p == '/')
        *(p--) = '\0';
    strcat(iconFilename, kIconName);
    /* Make sure it exists */
    FILE *iconFile = fopen(iconFilename, "w");
    fclose(iconFile);
    
    /* Open or create resource fork */
    FSRef iconRef;
    FSPathMakeRef((StringPtr)iconFilename, &iconRef, NULL);
    free(iconFilename);
    short iconRefNum = FSOpenResFile(&iconRef, fsRdWrPerm);
    HFSUniStr255 forkName;
    if (ResError() == eofErr)
        if (FSGetResourceForkName(&forkName) == noErr)
            if (FSCreateResourceFork(&iconRef, forkName.length, forkName.unicode, 0) == noErr)
                iconRefNum = FSOpenResFile(&iconRef, fsRdWrPerm);
    if ((oserr = ResError()) != noErr)
        return oserr;
    
    /* Write icon data to resource fork */
    Handle hand;
    if (! GetResource(kRsrcType, kResidIcon))
        if (PtrToHand(iconData, &hand, iconSize) == noErr)
            AddResource(hand, kRsrcType, kResidIcon, (StringPtr)"\pApplication icons");
    CloseResFile(iconRefNum);
    if ((oserr = ResError()) != noErr)
        return oserr;
    
    /* Set icon file info */
    FSCatalogInfo catalogInfo;
    FileInfo *fileInfo;
    FSGetCatalogInfo(&iconRef, kFSCatInfoFinderInfo, &catalogInfo, NULL, NULL, NULL);
    fileInfo = (FileInfo *)&catalogInfo.finderInfo;
    fileInfo->finderFlags |= kIsInvisible;
    fileInfo->fileCreator ='MACS';
    fileInfo->fileType = 'icon';
    FSSetCatalogInfo(&iconRef, kFSCatInfoFinderInfo, &catalogInfo);
    
    /* Set directory has custom icon */
    FSRef dirRef;
    FSPathMakeRef((StringPtr)dirName, &dirRef, NULL);
    FSGetCatalogInfo(&dirRef, kFSCatInfoFinderInfo, &catalogInfo, NULL, NULL, NULL);
    fileInfo = (FileInfo *)&catalogInfo.finderInfo;
    fileInfo->finderFlags |= kHasCustomIcon;
    FSSetCatalogInfo(&dirRef, kFSCatInfoFinderInfo, &catalogInfo);
    
    return 0;
}

directory_icon.h

#ifndef directory_icon_h
#define directory_icon_h

int setDirectoryIcon(const char *dirName, const char *iconData, size_t iconSize);

#endif