hdf5/examples/h5_elink_unix2win.c

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright by The HDF Group.                                               *
 * All rights reserved.                                                      *
 *                                                                           *
 * This file is part of HDF5.  The full HDF5 copyright notice, including     *
 * terms governing use, modification, and redistribution, is contained in    *
 * the COPYING file, which can be found at the root of the source code       *
 * distribution tree, or in https://www.hdfgroup.org/licenses.               *
 * If you do not have access to either file, you may request a copy from     *
 * help@hdfgroup.org.                                                        *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/* This program demonstrates how to translate an external link created on
 * a Windows machine into a format that a *nix machine can read.
 * This is done by registering a new traversal function for external links.
 *
 * This example is designed to be run on Unix and will create an external
 * link with a Windows-style path.  Using the traversal function below,
 * the example then successfully follows the external link.
 *
 * The external link will create a  file called "u2w/u2w_target.h5".
 * The example will fail if the directory u2w does not exist.
 */

#include "hdf5.h"
#include <stdlib.h>
#include <string.h>

/* "Windows to Unix" traversal function for external links
 *
 * Translates a filename stored in Unix format to Windows format by replacing
 * forward slashes with backslashes.
 * Makes no attempt to handle Windows drive names (e.g., "C:\"), spaces within
 * file names, quotes, etc.  These are left as an exercise for the user. :)
 * Note that this may not be necessary on your system; many Windows systems can
 * understand Unix paths.
 */
static hid_t
elink_unix2win_trav(const char *link_name, hid_t cur_group, const void *udata, size_t udata_size,
                    hid_t lapl_id, hid_t dxpl_id)
{
    hid_t       fid;
    const char *file_name;
    const char *obj_name;
    char       *new_fname = NULL; /* Buffer allocated to hold Unix file path */
    ssize_t     prefix_len;       /* External link prefix length */
    size_t      fname_len;
    size_t      start_pos; /* Initial position in new_fname buffer */
    size_t      x;         /* Counter variable */
    hid_t       ret_value = -1;

    printf("Converting Unix path to Windows path.\n");

    if (H5Lunpack_elink_val(udata, udata_size, NULL, &file_name, &obj_name) < 0)
        goto error;
    fname_len = strlen(file_name);

    /* See if the external link prefix property is set */
    if ((prefix_len = H5Pget_elink_prefix(lapl_id, NULL, 0)) < 0)
        goto error;

    /* If so, prepend it to the filename.  We assume that the prefix
     * is in the correct format for the current file system.
     */
    if (prefix_len > 0) {
        /* Allocate a buffer to hold the filename plus prefix */
        new_fname = malloc(prefix_len + fname_len + 1);

        /* Copy the prefix into the buffer */
        if (H5Pget_elink_prefix(lapl_id, new_fname, (size_t)(prefix_len + 1)) < 0)
            goto error;

        start_pos = prefix_len;
    }
    else {
        /* Allocate a buffer to hold just the filename */
        new_fname = malloc(fname_len + 1);
        start_pos = 0;
    }

    /* We should now copy file_name into new_fname starting at position pos.
     * We'll convert '/' characters into '\' characters as we go.
     */
    for (x = 0; file_name[x] != '\0'; x++) {
        if (file_name[x] == '/')
            new_fname[x + start_pos] = '\\';
        else
            new_fname[x + start_pos] = file_name[x];
    }
    new_fname[x + start_pos] = '\0';

    /* Now open the file and object within it */
    if ((fid = H5Fopen(new_fname, H5F_ACC_RDWR, H5P_DEFAULT)) < 0)
        goto error;
    ret_value = H5Oopen(fid, obj_name, lapl_id); /* If this fails, our return value will be negative. */
    if (H5Fclose(fid) < 0)
        goto error;

    /* Free file name if it's been allocated */
    if (new_fname)
        free(new_fname);

    return ret_value;

error:
    /* Free file name if it's been allocated */
    if (new_fname)
        free(new_fname);
    return -1;
}

const H5L_class_t elink_unix2win_class[1] = {{
    H5L_LINK_CLASS_T_VERS,    /* H5L_class_t version       */
    H5L_TYPE_EXTERNAL,        /* Link type id number            */
    "unix2win external link", /* Link class name for debugging  */
    NULL,                     /* Creation callback              */
    NULL,                     /* Move callback                  */
    NULL,                     /* Copy callback                  */
    elink_unix2win_trav,      /* The actual traversal function  */
    NULL,                     /* Deletion callback              */
    NULL                      /* Query callback                 */
}};

/* The example function.
 * Creates a file named "unix2win.h5" with an external link pointing to
 * the file "u2w/u2w_target.h5".
 *
 * Registers a new traversal function for external links and then
 * follows the external link to open the target file.
 */
static int
unix2win_example(void)
{
    hid_t fid = (-1); /* File ID */
    hid_t gid = (-1); /* Group ID */

    /* Create the target file. */
#ifdef H5_HAVE_WIN32_API
    if ((fid = H5Fcreate("u2w\\u2w_target.h5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT)) < 0)
        goto error;
#else
    if ((fid = H5Fcreate("u2w/u2w_target.h5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT)) < 0)
        goto error;
#endif
    if (H5Fclose(fid) < 0)
        goto error;

    /* Create the source file with an external link in Windows format */
    if ((fid = H5Fcreate("unix2win.h5", H5F_ACC_TRUNC, H5P_DEFAULT, H5P_DEFAULT)) < 0)
        goto error;

    /* Create the external link */
    if (H5Lcreate_external("u2w/../u2w/u2w_target.h5", "/", fid, "ext_link", H5P_DEFAULT, H5P_DEFAULT) < 0)
        goto error;

        /* If we are not on Windows, assume we are on a Unix-y filesystem and
         * follow the external link normally.
         * If we are on Windows, register the unix2win traversal function so
         * that external links can be traversed.
         */

#ifdef H5_HAVE_WIN32_API
    /* Register the elink_unix2win class defined above to replace default
     * external links
     */
    if (H5Lregister(elink_unix2win_class) < 0)
        goto error;
#endif

    /* Now follow the link */
    if ((gid = H5Gopen2(fid, "ext_link", H5P_DEFAULT)) < 0)
        goto error;
    printf("Successfully followed external link.\n");

    /* Close the group and the file */
    if (H5Gclose(gid) < 0)
        goto error;
    if (H5Fclose(fid) < 0)
        goto error;

    return 0;

error:
    printf("Error!\n");
    H5E_BEGIN_TRY
    {
        H5Gclose(gid);
        H5Fclose(fid);
    }
    H5E_END_TRY
    return -1;
}

/* Main function
 *
 * Invokes the example function.
 */
int
main(void)
{
    int ret;

    printf("Testing unix2win external links.\n");
    ret = unix2win_example();

    return ret;
}