source: mainline/uspace/lib/sif/src/sif.c

/*
 * Copyright (c) 2024 Jiri Svoboda
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
/** @addtogroup libsif
 * @{
 */
/**
 * @file Structured Information Format
 *
 * Structured Information Format (SIF) is an API that allows an application
 * to maintain data in a persistent repository in a format that is
 * structured (and hence extensible).
 *
 * SIF is meant to be used as the basis for the storage backend used to
 * maintain application or configuration data. SIF is *not* a (relational)
 * database (not even close). The structure of a SIF repository is quite
 * similar to an XML document that contains just tags with attributes
 * (but no text).
 */

#include <adt/list.h>
#include <adt/odict.h>
#include <ctype.h>
#include <errno.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <str.h>
#include "../include/sif.h"
#include "../private/sif.h"

static errno_t sif_export_node(sif_node_t *, FILE *);
static errno_t sif_import_node(sif_node_t *, FILE *, sif_node_t **, bool *);
static sif_attr_t *sif_node_first_attr(sif_node_t *);
static sif_attr_t *sif_node_next_attr(sif_attr_t *);
static void sif_attr_delete(sif_attr_t *);
static void *sif_attr_getkey(odlink_t *);
static int sif_attr_cmp(void *, void *);

/** Determine if character can start a name.
 *
 * @param c Character
 * @return @c true iff the character can start a name
 */
static bool sif_is_name_start_char(char c)
{
        return isalpha(c) || c == '_';
}

/** Determine if character can continue a name.
 *
 * @param c Character
 * @return @c true iff the character can continue a name
 */
static bool sif_is_name_char(char c)
{
        return isalnum(c) || c == '-' || c == '.';
}

/** Create new SIF node.
 *
 * @param parent Parent node
 * @return Pointer to new node on success or @c NULL if out of memory
 */
static sif_node_t *sif_node_new(sif_node_t *parent)
{
        sif_node_t *node;

        node = calloc(1, sizeof(sif_node_t));
        if (node == NULL)
                return NULL;

        node->parent = parent;
        odict_initialize(&node->attrs, sif_attr_getkey, sif_attr_cmp);
        list_initialize(&node->children);

        return node;
}

/** Delete SIF node.
 *
 * Delete a SIF node that has been already unlinked from the tree.
 * This will also delete any attributes or child nodes.
 *
 * @param node Node
 */
static void sif_node_delete(sif_node_t *node)
{
        sif_attr_t *attr;
        sif_node_t *child;

        if (node == NULL)
                return;

        assert(!link_used(&node->lparent));

        if (node->ntype != NULL)
                free(node->ntype);

        attr = sif_node_first_attr(node);
        while (attr != NULL) {
                odict_remove(&attr->lattrs);
                sif_attr_delete(attr);
                attr = sif_node_first_attr(node);
        }

        child = sif_node_first_child(node);
        while (child != NULL) {
                list_remove(&child->lparent);
                sif_node_delete(child);
                child = sif_node_first_child(node);
        }

        free(node);
}

/** Create new SIF attribute.
 *
 * @param node Containing node
 * @return Pointer to new node on success or @c NULL if out of memory
 */
static sif_attr_t *sif_attr_new(sif_node_t *node)
{
        sif_attr_t *attr;

        attr = calloc(1, sizeof(sif_attr_t));
        if (attr == NULL)
                return NULL;

        attr->node = node;
        return attr;
}

/** Delete SIF attribute.
 *
 * Delete a SIF attribute that has been already unlinked from is node.
 *
 * @param attr Attribute
 */
static void sif_attr_delete(sif_attr_t *attr)
{
        if (attr == NULL)
                return;

        assert(!odlink_used(&attr->lattrs));

        if (attr->aname != NULL)
                free(attr->aname);
        if (attr->avalue != NULL)
                free(attr->avalue);

        free(attr);
}

/** Create SIF document.
 *
 * @param rdoc Place to store pointer to new document.
 *
 * @return EOK on success or error code
 */
errno_t sif_new(sif_doc_t **rdoc)
{
        sif_doc_t *doc;
        sif_node_t *root = NULL;
        errno_t rc;

        doc = calloc(1, sizeof(sif_doc_t));
        if (doc == NULL)
                return ENOMEM;

        root = sif_node_new(NULL);
        if (root == NULL) {
                rc = ENOMEM;
                goto error;
        }

        root->ntype = str_dup("sif");
        if (root->ntype == NULL) {
                rc = ENOMEM;
                goto error;
        }

        doc->root = root;

        *rdoc = doc;
        return EOK;
error:
        sif_node_delete(root);
        free(doc);
        return rc;
}

/** Load SIF document.
 *
 * @param fname File name
 * @param rdoc Place to store pointer to new document.
 *
 * @return EOK on success or error code
 */
errno_t sif_load(const char *fname, sif_doc_t **rdoc)
{
        sif_doc_t *doc;
        sif_node_t *root = NULL;
        errno_t rc;
        bool endtag;
        FILE *f = NULL;

        doc = calloc(1, sizeof(sif_doc_t));
        if (doc == NULL)
                return ENOMEM;

        doc->fname = str_dup(fname);
        if (doc->fname == NULL) {
                rc = ENOMEM;
                goto error;
        }

        f = fopen(fname, "r");
        if (f == NULL) {
                rc = EIO;
                goto error;
        }

        rc = sif_import_node(NULL, f, &root, &endtag);
        if (rc != EOK || endtag == true)
                goto error;

        if (str_cmp(root->ntype, "sif") != 0) {
                rc = EIO;
                goto error;
        }

        fclose(f);
        doc->root = root;
        *rdoc = doc;
        return EOK;
error:
        sif_node_delete(root);
        free(doc);
        if (f != NULL)
                fclose(f);
        return rc;
}

/** Delete SIF document.
 *
 * @param doc SIF document
 * @return EOK on success or error code
 */
void sif_delete(sif_doc_t *doc)
{
        sif_node_delete(doc->root);
        free(doc);
}

/** Return root node.
 *
 * @param doc SIF document
 */
sif_node_t *sif_get_root(sif_doc_t *doc)
{
        return doc->root;
}

/** Get first child of a node.
 *
 * @param parent Parent node
 * @return First child node or @c NULL if @a parent has no children
 */
sif_node_t *sif_node_first_child(sif_node_t *parent)
{
        link_t *link;

        link = list_first(&parent->children);
        if (link == NULL)
                return NULL;

        return list_get_instance(link, sif_node_t, lparent);
}

/** Get next child of a node.
 *
 * @param current Current node
 * @return Next child (i.e. next sibling of @a current)
 */
sif_node_t *sif_node_next_child(sif_node_t *current)
{
        link_t *link;

        link = list_next(&current->lparent, &current->parent->children);
        if (link == NULL)
                return NULL;

        return list_get_instance(link, sif_node_t, lparent);
}

/** Get node type.
 *
 * @param node SIF node
 * @return Pointer to string, valid until next modification.
 */
const char *sif_node_get_type(sif_node_t *node)
{
        return node->ntype;
}

/** Get node attribute.
 *
 * @param node SIF node
 * @param aname Attribute name
 *
 * @return Attribute value or @c NULL if attribute is not set
 */
const char *sif_node_get_attr(sif_node_t *node, const char *aname)
{
        odlink_t *link;
        sif_attr_t *attr;

        link = odict_find_eq(&node->attrs, (void *)aname, NULL);
        if (link == NULL)
                return NULL;

        attr = odict_get_instance(link, sif_attr_t, lattrs);
        return attr->avalue;
}

/** Save SIF document to file.
 * *
 * @param doc SIF document
 * @param fname File name
 * @return EOK on success or error code
 */
errno_t sif_save(sif_doc_t *doc, const char *fname)
{
        FILE *f = NULL;
        errno_t rc;

        f = fopen(fname, "w");
        if (f == NULL) {
                rc = EIO;
                goto error;
        }

        rc = sif_export_node(doc->root, f);
        if (rc != EOK)
                goto error;

        if (fflush(f) == EOF) {
                rc = EIO;
                goto error;
        }

        fclose(f);
        return EOK;
error:
        if (f != NULL)
                fclose(f);
        return rc;
}

/** Prepend new child.
 *
 * Create a new child and prepend it at the beginning of children list of
 * @a parent.
 *
 * @param parent Parent node
 * @param ctype Child type
 * @param rchild Place to store pointer to new child
 *
 * @return EOK on success or ENOMEM if out of memory
 */
errno_t sif_node_prepend_child(sif_node_t *parent, const char *ctype,
    sif_node_t **rchild)
{
        sif_node_t *child;

        child = sif_node_new(parent);
        if (child == NULL)
                return ENOMEM;

        child->ntype = str_dup(ctype);
        if (child->ntype == NULL) {
                sif_node_delete(child);
                return ENOMEM;
        }

        list_prepend(&child->lparent, &parent->children);

        *rchild = child;
        return EOK;
}

/** Append new child.
 *
 * Create a new child and append it at the end of children list of @a parent.
 *
 * @param parent Parent node
 * @param ctype Child type
 * @param rchild Place to store pointer to new child
 *
 * @return EOK on success or ENOMEM if out of memory
 */
errno_t sif_node_append_child(sif_node_t *parent, const char *ctype,
    sif_node_t **rchild)
{
        sif_node_t *child;

        child = sif_node_new(parent);
        if (child == NULL)
                return ENOMEM;

        child->ntype = str_dup(ctype);
        if (child->ntype == NULL) {
                sif_node_delete(child);
                return ENOMEM;
        }

        list_append(&child->lparent, &parent->children);

        *rchild = child;
        return EOK;
}

/** Insert new child before existing child.
 *
 * Create a new child and insert it before an existing child.
 *
 * @param sibling Sibling before which to insert
 * @param ctype Child type
 * @param rchild Place to store pointer to new child
 *
 * @return EOK on success or ENOMEM if out of memory
 */
errno_t sif_node_insert_before(sif_node_t *sibling, const char *ctype,
    sif_node_t **rchild)
{
        sif_node_t *child;

        child = sif_node_new(sibling->parent);
        if (child == NULL)
                return ENOMEM;

        child->ntype = str_dup(ctype);
        if (child->ntype == NULL) {
                sif_node_delete(child);
                return ENOMEM;
        }

        list_insert_before(&child->lparent, &sibling->lparent);

        *rchild = child;
        return EOK;
}

/** Insert new child after existing child.
 *
 * Create a new child and insert it after an existing child.
 *
 * @param sibling Sibling after which to insert
 * @param ctype Child type
 * @param rchild Place to store pointer to new child
 *
 * @return EOK on success or ENOMEM if out of memory
 */
errno_t sif_node_insert_after(sif_node_t *sibling, const char *ctype,
    sif_node_t **rchild)
{
        sif_node_t *child;

        child = sif_node_new(sibling->parent);
        if (child == NULL)
                return ENOMEM;

        child->ntype = str_dup(ctype);
        if (child->ntype == NULL) {
                sif_node_delete(child);
                return ENOMEM;
        }

        list_insert_after(&child->lparent, &sibling->lparent);

        *rchild = child;
        return EOK;
}

/** Destroy SIF node.
 *
 * @param node Node to destroy
 */
void sif_node_destroy(sif_node_t *node)
{
        list_remove(&node->lparent);
        sif_node_delete(node);
}

/** Set node attribute.
 *
 * @param node SIF node
 * @param aname Attribute name
 * @param value Attribute value
 *
 * @return EOK on success, ENOMEM if out of memory
 */
errno_t sif_node_set_attr(sif_node_t *node, const char *aname,
    const char *avalue)
{
        odlink_t *link;
        sif_attr_t *attr;
        char *cvalue;

        link = odict_find_eq(&node->attrs, (void *)aname, NULL);

        if (link != NULL) {
                attr = odict_get_instance(link, sif_attr_t, lattrs);
                cvalue = str_dup(avalue);
                if (cvalue == NULL)
                        return ENOMEM;

                free(attr->avalue);
                attr->avalue = cvalue;
        } else {
                attr = sif_attr_new(node);
                if (attr == NULL)
                        return ENOMEM;

                attr->aname = str_dup(aname);
                if (attr->aname == NULL) {
                        sif_attr_delete(attr);
                        return ENOMEM;
                }

                attr->avalue = str_dup(avalue);
                if (attr->avalue == NULL) {
                        sif_attr_delete(attr);
                        return ENOMEM;
                }

                odict_insert(&attr->lattrs, &node->attrs, NULL);
        }

        return EOK;
}

/** Unset node attribute.
 *
 * @param node Node
 * @param aname Attribute name
 */
void sif_node_unset_attr(sif_node_t *node, const char *aname)
{
        odlink_t *link;
        sif_attr_t *attr;

        link = odict_find_eq(&node->attrs, (void *)aname, NULL);
        if (link == NULL)
                return;

        attr = odict_get_instance(link, sif_attr_t, lattrs);
        odict_remove(link);
        sif_attr_delete(attr);
}

/** Export node name to file.
 *
 * Export node name to file.
 *
 * @param str String
 * @param f File
 * @return EOK on success, EIO on I/O error
 */
static errno_t sif_export_name(const char *str, FILE *f)
{
        if (fputs(str, f) == EOF)
                return EIO;

        return EOK;
}

/** Export string to file.
 *
 * Export string to file (the string is double-quoted and escaped).
 *
 * @param str String
 * @param f File
 * @return EOK on success, EIO on I/O error
 */
static errno_t sif_export_string(const char *str, FILE *f)
{
        const char *cp;

        if (fputc('"', f) == EOF)
                return EIO;

        cp = str;
        while (*cp != '\0') {
                if (*cp == '<') {
                        if (fputs("&lt;", f) == EOF)
                                return EIO;
                } else if (*cp == '"') {
                        if (fputs("&quot;", f) == EOF)
                                return EIO;
                } else {
                        if (fputc(*cp, f) == EOF)
                                return EIO;
                }

                ++cp;
        }

        if (fputc('"', f) == EOF)
                return EIO;

        return EOK;
}

/** Read characters from file, make sure they match the specified sequence.
 *
 * @param f File
 * @param chars Expected sequence of characters to be read
 *
 * @return EOK on success, EIO on I/O error or mismatch
 */
static errno_t sif_get_verify_chars(FILE *f, const char *chars)
{
        const char *cp;
        char c;

        cp = chars;
        while (*cp != '\0') {
                c = fgetc(f);
                if (c != *cp)
                        return EIO;
                ++cp;
        }

        return EOK;
}

/** Import name from file.
 * *
 * @param f File
 * @param rstr Place to store pointer to newly allocated string
 * @return EOK on success, EIO on I/O error
 */
static errno_t sif_import_name(FILE *f, char **rstr)
{
        char *str;
        char *nstr;
        size_t str_size;
        size_t sidx;
        int c;
        errno_t rc;

        str_size = 1;
        sidx = 0;
        str = malloc(str_size + 1);
        if (str == NULL)
                return ENOMEM;

        c = fgetc(f);
        if (!sif_is_name_start_char(c)) {
                rc = EIO;
                goto error;
        }

        while (true) {
                if (sidx >= str_size) {
                        str_size *= 2;
                        nstr = realloc(str, str_size + 1);
                        if (nstr == NULL) {
                                rc = ENOMEM;
                                goto error;
                        }

                        str = nstr;
                }

                str[sidx++] = c;

                c = fgetc(f);
                if (!sif_is_name_char(c))
                        break;
        }

        ungetc(c, f);

        str[sidx] = '\0';
        *rstr = str;
        return EOK;
error:
        free(str);
        return rc;
}

/** Import string from file.
 *
 * Import string from file (the string in the file must be
 * properly quoted and escaped).
 *
 * @param f File
 * @param rstr Place to store pointer to newly allocated string
 * @return EOK on success, EIO on I/O error
 */
static errno_t sif_import_string(FILE *f, char **rstr)
{
        char *str;
        char *nstr;
        size_t str_size;
        size_t sidx;
        int c;
        errno_t rc;

        str_size = 1;
        sidx = 0;
        str = malloc(str_size + 1);
        if (str == NULL)
                return ENOMEM;

        c = fgetc(f);
        if (c != '"') {
                rc = EIO;
                goto error;
        }

        while (true) {
                c = fgetc(f);
                if (c == EOF) {
                        rc = EIO;
                        goto error;
                }

                if (c == '"')
                        break;

                if (c == '&') {
                        c = fgetc(f);
                        if (c == EOF) {
                                rc = EIO;
                                goto error;
                        }

                        if (c == 'q') {
                                rc = sif_get_verify_chars(f, "uot;");
                                if (rc != EOK)
                                        goto error;
                        } else if (c == 'l') {
                                rc = sif_get_verify_chars(f, "t;");
                                if (rc != EOK)
                                        goto error;
                        } else {
                                rc = EIO;
                                goto error;
                        }
                }

                if (sidx >= str_size) {
                        str_size *= 2;
                        nstr = realloc(str, str_size + 1);
                        if (nstr == NULL) {
                                rc = ENOMEM;
                                goto error;
                        }

                        str = nstr;
                }

                str[sidx++] = c;
        }

        str[sidx] = '\0';
        *rstr = str;
        return EOK;
error:
        free(str);
        return rc;
}

/** Import SIF attribute from file.
 *
 * @param node Node under which attribute shou
 * @param f File
 * @param rattr Place to store pointer to imported SIF attribute
 * @return EOK on success, EIO on I/O error
 */
static errno_t sif_import_attr(sif_node_t *node, FILE *f, sif_attr_t **rattr)
{
        errno_t rc;
        char *aname = NULL;
        char *avalue = NULL;
        sif_attr_t *attr;
        int c;

        rc = sif_import_name(f, &aname);
        if (rc != EOK)
                goto error;

        c = fgetc(f);
        if (c != '=') {
                rc = EIO;
                goto error;
        }

        rc = sif_import_string(f, &avalue);
        if (rc != EOK)
                goto error;

        attr = sif_attr_new(node);
        if (attr == NULL) {
                rc = ENOMEM;
                goto error;
        }

        attr->aname = aname;
        attr->avalue = avalue;

        *rattr = attr;
        return EOK;
error:
        if (aname != NULL)
                free(aname);
        if (avalue != NULL)
                free(avalue);
        return rc;
}

/** Export SIF attribute to file.
 *
 * @param attr SIF attribute
 * @param f File
 * @return EOK on success, EIO on I/O error
 */
static errno_t sif_export_attr(sif_attr_t *attr, FILE *f)
{
        errno_t rc;

        rc = sif_export_name(attr->aname, f);
        if (rc != EOK)
                return rc;

        if (fputc('=', f) == EOF)
                return EIO;

        rc = sif_export_string(attr->avalue, f);
        if (rc != EOK)
                return rc;

        return EOK;
}

/** Export SIF node to file.
 *
 * @param node SIF node
 * @param f File
 * @return EOK on success, EIO on I/O error
 */
static errno_t sif_export_node(sif_node_t *node, FILE *f)
{
        errno_t rc;
        sif_attr_t *attr;
        sif_node_t *child;

        if (fputc('<', f) == EOF)
                return EIO;

        rc = sif_export_name(node->ntype, f);
        if (rc != EOK)
                return rc;

        /* Attributes */

        attr = sif_node_first_attr(node);
        while (attr != NULL) {
                if (fputc(' ', f) == EOF)
                        return EIO;

                rc = sif_export_attr(attr, f);
                if (rc != EOK)
                        return rc;

                attr = sif_node_next_attr(attr);
        }

        if (fputs(">\n", f) == EOF)
                return EIO;

        /* Child nodes */

        child = sif_node_first_child(node);
        while (child != NULL) {
                rc = sif_export_node(child, f);
                if (rc != EOK)
                        return rc;

                child = sif_node_next_child(child);
        }

        if (fputs("</", f) == EOF)
                return EIO;

        rc = sif_export_name(node->ntype, f);
        if (rc != EOK)
                return rc;

        if (fputs(">\n", f) == EOF)
                return EIO;

        return EOK;
}

/** Import SIF node from file.
 *
 * @param parent Parent node
 * @param f File
 * @param rnode Place to store pointer to imported node
 * @param rendtag Place to store @c true iff end tag is encountered
 * @return EOK on success, EIO on I/O error
 */
static errno_t sif_import_node(sif_node_t *parent, FILE *f, sif_node_t **rnode,
    bool *rendtag)
{
        errno_t rc;
        sif_node_t *node = NULL;
        sif_node_t *child;
        sif_attr_t *attr = NULL;
        bool endtag;
        bool cendtag;
        char *ntype;
        int c;

        node = sif_node_new(parent);
        if (node == NULL)
                return ENOMEM;

        c = fgetc(f);
        while (isspace(c))
                c = fgetc(f);

        if (c != '<') {
                rc = EIO;
                goto error;
        }

        c = fgetc(f);
        if (c == '/') {
                endtag = true;
        } else {
                endtag = false;
                ungetc(c, f);
        }

        rc = sif_import_name(f, &ntype);
        if (rc != EOK)
                goto error;

        node->ntype = ntype;

        /* Attributes */

        c = fgetc(f);
        if (c == EOF) {
                rc = EIO;
                goto error;
        }

        while (c != '>') {
                /* End tags cannot have attributes */
                if (endtag) {
                        rc = EIO;
                        goto error;
                }

                while (isspace(c))
                        c = fgetc(f);
                ungetc(c, f);

                rc = sif_import_attr(node, f, &attr);
                if (rc != EOK)
                        goto error;

                odict_insert(&attr->lattrs, &node->attrs, NULL);

                c = fgetc(f);
                if (c == EOF) {
                        rc = EIO;
                        goto error;
                }
        }

        /* Child nodes */

        if (!endtag) {
                while (true) {
                        rc = sif_import_node(node, f, &child, &cendtag);
                        if (rc != EOK)
                                goto error;

                        if (cendtag) {
                                sif_node_delete(child);
                                break;
                        }

                        list_append(&child->lparent, &node->children);
                }
        }

        *rnode = node;
        *rendtag = endtag;
        return EOK;
error:
        sif_node_delete(node);
        return rc;
}

/** Get first attribute or a node.
 *
 * @param node SIF node
 * @return First attribute or @c NULL if there is none
 */
static sif_attr_t *sif_node_first_attr(sif_node_t *node)
{
        odlink_t *link;

        link = odict_first(&node->attrs);
        if (link == NULL)
                return NULL;

        return odict_get_instance(link, sif_attr_t, lattrs);
}

/** Get next attribute or a node.
 *
 * @param cur Current attribute
 * @return Next attribute or @c NULL if there is none
 */
static sif_attr_t *sif_node_next_attr(sif_attr_t *cur)
{
        odlink_t *link;

        link = odict_next(&cur->lattrs, &cur->node->attrs);
        if (link == NULL)
                return NULL;

        return odict_get_instance(link, sif_attr_t, lattrs);
}

/** Get key callback for ordered dictionary of node attributes.
 *
 * @param link Ordered dictionary link of attribute
 * @return Pointer to attribute name
 */
static void *sif_attr_getkey(odlink_t *link)
{
        return (void *)odict_get_instance(link, sif_attr_t, lattrs)->aname;
}

/** Comparison callback for  ordered dictionary of node attributes.
 *
 * @param a Name of first attribute
 * @param b Name of second attribute
 * @return Less than zero, zero or greater than zero, if a < b, a == b, a > b,
 *         respectively.
 */
static int sif_attr_cmp(void *a, void *b)
{
        char *ca, *cb;

        ca = (char *)a;
        cb = (char *)b;

        return str_cmp(ca, cb);
}

/** @}
 */