hash.c

boa：Linux系统中的轻量级Web服务

/*
 *  Boa, an http server
 *  Copyright (C) 1995 Paul Phillips <[e-mail]>
 *  Some changes Copyright (C) 1996 Larry Doolittle <[e-mail]>
 *  Some changes Copyright (C) 1997 Jon Nelson <[e-mail]>
 *
 *  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
 *  the Free Software Foundation; either version 1, or (at your option)
 *  any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 */

/* $Id: hash.c,v 1.14.4.4 2002/07/30 03:59:26 jnelson Exp $*/

#include "boa.h"
#include "parse.h"

/*
 * There are two hash tables used, each with a key/value pair
 * stored in a hash_struct.  They are:
 *
 * mime_hashtable:
 *     key = file extension
 *   value = mime type
 *
 * passwd_hashtable:
 *     key = username
 *   value = home directory
 *
 */

struct _hash_struct_ {
    char *key;
    char *value;
    struct _hash_struct_ *next;
};

typedef struct _hash_struct_ hash_struct;

static hash_struct *mime_hashtable[MIME_HASHTABLE_SIZE];
static hash_struct *passwd_hashtable[PASSWD_HASHTABLE_SIZE];

#ifdef WANT_ICKY_HASH
static unsigned four_char_hash(char *buf);
#define boa_hash four_char_hash
#else
#ifdef WANT_SDBM_HASH
static unsigned sdbm_hash(char *str);
#define boa_hash sdbm_hash
#else
static unsigned djb2_hash(char *str);
#define boa_hash djb2_hash
#endif
#endif

#ifdef WANT_ICKY_HASH
static unsigned four_char_hash(char *buf)
{
    unsigned int hash = (buf[0] +
                     (buf[1] ? buf[1] : 241 +
                     (buf[2] ? buf[2] : 251 +
                      (buf[3] ? buf[3] : 257))));
#ifdef DEBUG_HASH
    log_error_time();
    fprintf(stderr, "four_char_hash(%s) = %u\n", buf, hash);
#endif
    return hash;
}

/* The next two hashes taken from
 * http://www.cs.yorku.ca/~oz/hash.html
 *
 * In my (admittedly) very brief testing, djb2_hash performed
 * very slightly better than sdbm_hash.
 */

#else
#define MAX_HASH_LENGTH 4
#ifdef WANT_SDBM_HASH
static unsigned sdbm_hash(char *str)
{
    unsigned hash = 0;
    int c;
    short count = MAX_HASH_LENGTH;

#ifdef DEBUG_HASH
    log_error_time();
    fprintf(stderr, "sdbm_hash(%s) = ", str);
#endif

    while ((c = *str++) && count--)
        hash = c + (hash << 6) + (hash << 16) - hash;

#ifdef DEBUG_HASH
    fprintf(stderr, "%u\n", hash);
#endif
    return hash;
}
#else

static unsigned djb2_hash(char *str)
{
    unsigned hash = 5381;
    int c;
    short count = MAX_HASH_LENGTH;

#ifdef DEBUG_HASH
    log_error_time();
    fprintf(stderr, "djb2_hash(%s) = ", str);
#endif

    while ((c = *(str++)) && count--)
        hash = ((hash << 5) + hash) + c; /* hash * 33 + c */

#ifdef DEBUG_HASH
    fprintf(stderr, "%u\n", hash);
#endif
    return hash;
}
#endif
#endif

/*
 * Name: add_mime_type
 * Description: Adds a key/value pair to the mime_hashtable
 */

void add_mime_type(char *extension, char *type)
{
    unsigned int hash;
    hash_struct *current, *next;

    if (!extension)
        return;

    hash = get_mime_hash_value(extension);

    current = mime_hashtable[hash];

    while (current) {
        if (!strcmp(current->key, extension))
            return;         /* don't add extension twice */
        if (current->next)
            current = current->next;
        else
            break;
    }

    /* if here, we need to add a new one */
    next = (hash_struct *) malloc(sizeof (hash_struct));
    if (!next) {
        DIE("malloc of hash_struct failed!");
    }
    next->key = strdup(extension);
    if (!next->key)
        DIE("malloc of hash_struct->key failed!");
    next->value = strdup(type);
    if (!next->value)
        DIE("malloc of hash_struct->value failed!");
    next->next = NULL;

    if (!current) {
        mime_hashtable[hash] = next;
    } else {
        current->next = next;
    }
}

/*
 * Name: get_mime_hash_value
 *
 * Description: adds the ASCII values of the file extension letters
 * and mods by the hashtable size to get the hash value
 */

unsigned get_mime_hash_value(char *extension)
{
    unsigned int hash = 0;

    if (extension == NULL || extension[0] == '\0') {
        /* FIXME */
        log_error_time();
        fprintf(stderr, "Attempt to hash NULL or empty string!\n");
        return 0;
    }

    hash = boa_hash(extension);
    hash %= MIME_HASHTABLE_SIZE;

    return hash;
}

/*
 * Name: get_mime_type
 *
 * Description: Returns the mime type for a supplied filename.
 * Returns default type if not found.
 */

char *get_mime_type(char *filename)
{
    char *extension;
    hash_struct *current;

    unsigned int hash;

    extension = strrchr(filename, '.');

    if (!extension || *extension++ == '\0')
        return default_type;

    hash = get_mime_hash_value(extension);
    current = mime_hashtable[hash];

    while (current) {
        if (!strcmp(current->key, extension)) /* hit */
            return current->value;
        current = current->next;
    }

    return default_type;
}

/*
 * Name: get_homedir_hash_value
 *
 * Description: adds the ASCII values of the username letters
 * and mods by the hashtable size to get the hash value
 */

unsigned get_homedir_hash_value(char *name)
{
    unsigned int hash = 0;

    if (name == NULL || name[0] == '\0') {
        /* FIXME */
        log_error_time();
        fprintf(stderr, "Attempt to hash NULL or empty string!\n");
        return 0;
    }

    hash = boa_hash(name);
    hash %= PASSWD_HASHTABLE_SIZE;

    return hash;
}


/*
 * Name: get_home_dir
 *
 * Description: Returns a point to the supplied user's home directory.
 * Adds to the hashtable if it's not already present.
 *
 */

char *get_home_dir(char *name)
{
    struct passwd *passwdbuf;

    hash_struct *current, *next;
    unsigned int hash;

    /* first check hash table -- if username is less than four characters,
       just hash to zero (this should be very rare) */

    hash = get_homedir_hash_value(name);

    for(current = passwd_hashtable[hash];current;current = current->next) {
        if (!strcmp(current->key, name)) /* hit */
            return current->value;
        if (!current->next)
            break;
    }

    /* if here, we have to add a new one */

    passwdbuf = getpwnam(name);

    if (!passwdbuf)         /* does not exist */
        return NULL;

    next = (hash_struct *) malloc(sizeof (hash_struct));
    if (!next) {
        WARN("malloc of hash_struct for passwd_hashtable failed!");
        return NULL;
    }

    next->key = strdup(name);
    if (!next->key) {
        WARN("malloc of passwd_hashtable[hash]->key failed!");
        free(next);
        return NULL;
    }
    next->value = strdup(passwdbuf->pw_dir);
    if (!next->value) {
        WARN("malloc of passwd_hashtable[hash]->value failed!");
        free(next->key);
        free(next);
        return NULL;
    }
    next->next = NULL;

    if (!current) {
        passwd_hashtable[hash] = next;
    } else {
        current->next = next;
    }
    return next->value;
}

void dump_mime(void)
{
    int i;
    hash_struct *temp;
    for (i = 0; i < MIME_HASHTABLE_SIZE; ++i) { /* these limits OK? */
        temp = mime_hashtable[i];
        while (temp) {
            hash_struct *temp_next;

            temp_next = temp->next;
            free(temp->key);
            free(temp->value);
            free(temp);

            temp = temp_next;
        }
        mime_hashtable[i] = NULL;
    }
}

void dump_passwd(void)
{
    int i;
    hash_struct *temp;
    for (i = 0; i < PASSWD_HASHTABLE_SIZE; ++i) { /* these limits OK? */
        temp = passwd_hashtable[i];
        while (temp) {
            hash_struct *temp_next;

            temp_next = temp->next;
            free(temp->key);
            free(temp->value);
            free(temp);

            temp = temp_next;
        }
        passwd_hashtable[i] = NULL;
    }
}

void show_hash_stats(void)
{
    int i;
    hash_struct *temp;
    int total = 0;
    int count;

    for (i = 0; i < MIME_HASHTABLE_SIZE; ++i) { /* these limits OK? */
        if (mime_hashtable[i]) {
            count = 0;
            temp = mime_hashtable[i];
            while (temp) {
                temp = temp->next;
                ++count;
            }
#ifdef NOISY_SIGALRM
            log_error_time();
            fprintf(stderr, "mime_hashtable[%d] has %d entries\n",
                    i, count);
#endif
            total += count;
        }
    }
    log_error_time();
    fprintf(stderr, "mime_hashtable has %d total entries\n",
            total);

    total = 0;
    for (i = 0; i < PASSWD_HASHTABLE_SIZE; ++i) { /* these limits OK? */
        if (passwd_hashtable[i]) {
            temp = passwd_hashtable[i];
            count = 0;
            while (temp) {
                temp = temp->next;
                ++count;
            }
#ifdef NOISY_SIGALRM
            log_error_time();
            fprintf(stderr, "passwd_hashtable[%d] has %d entries\n",
                    i, count);
#endif
            total += count;
        }
    }

    log_error_time();
    fprintf(stderr, "passwd_hashtable has %d total entries\n",
            total);

}