Redis源码笔记一: sds

/* SDSLib, A C dynamic strings library
 *
 * Copyright (c) 2006-2010, Salvatore Sanfilippo <antirez at gmail dot com>
 * 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.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT OWNER OR CONTRIBUTORS 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.
 */

#ifndef __SDS_H
#define __SDS_H

#define SDS_MAX_PREALLOC (1024*1024)    /* 1M空间 */

#include <sys/types.h>
#include <stdarg.h>

/* sds抽象数据类型,底层实现由char*实现 */
typedef char *sds;

struct sdshdr {
    int len;    /* buf已占用长度 */
    int free;    /* buf剩余可用长度 */
    char buf[];    /* 实际保存字符串数据的地方 */
};

static inline size_t sdslen(const sds s) {
    /* s - (sizeof(struct sdshdr)) 表示将指针向前移动到struct sdshdr的起点，从而得出一个指向sdshdr结构的指针 */
    struct sdshdr *sh = (void*)(s-(sizeof(struct sdshdr)));
    
    /* 返回sds buf的已占用长度 */
    return sh->len;
}

static inline size_t sdsavail(const sds s) {
    struct sdshdr *sh = (void*)(s-(sizeof(struct sdshdr)));
 
     /* 返回sds buf的剩余可用长度 */
     return sh->free;
}

/* 创建一个指定长度的sds,接受一个C字符串作为初始值 */
sds sdsnewlen(const void *init, size_t initlen);

/* 根据给定C字符串,创建一个相应的sds */
sds sdsnew(const char *init);

/* 创建一个只包含空白字符串""的sds */
sds sdsempty();

/*  */
size_t sdslen(const sds s);

/* 复制给定sds */
sds sdsdup(const sds s);

/* 释放给定sds */
void sdsfree(sds s);

/*  */
size_t sdsavail(const sds s);

/* 将给定sds的buf扩展至指定长度,无内容的部分用\0填充 */
sds sdsgrowzero(sds s, size_t len);

/* 按给定长度对sds进行扩展,并将一个C字符串追加到sds的末尾 */
sds sdscatlen(sds s, const void *t, size_t len);

/* 将一个C字符串追加到sds的末尾 */
sds sdscat(sds s, const char *t);

/* 将一个sds追加到另一个sds的末尾 */
sds sdscatsds(sds s, const sds t);

/* 将一个C字符串的部分内容复制到另一个sds中,需要时对sds进行扩展 */
sds sdscpylen(sds s, const char *t, size_t len);

/* 将一个C字符串复制到sds */
sds sdscpy(sds s, const char *t);

/*  */
sds sdscatvprintf(sds s, const char *fmt, va_list ap);

#ifdef __GNUC__
sds sdscatprintf(sds s, const char *fmt, ...)
    __attribute__((format(printf, 2, 3)));
#else
sds sdscatprintf(sds s, const char *fmt, ...);
#endif

sds sdstrim(sds s, const char *cset);
sds sdsrange(sds s, int start, int end);

/* 更新给定sds所对应sdshdr结构的free和len */
void sdsupdatelen(sds s);

/* 清除给定sds的内容,将它初始化为"" */
void sdsclear(sds s);

/* 比较s1和s2字符,如果s1>s2,则返回>0;如果s1=s2,则返回0;如果s1<s2,则返回<0 */
int sdscmp(const sds s1, const sds s2);

sds *sdssplitlen(const char *s, int len, const char *sep, int seplen, int *count);
void sdsfreesplitres(sds *tokens, int count);

/* 将s转换成小写字符 */
void sdstolower(sds s);

/* 将s转换成大写字符 */
void sdstoupper(sds s);

sds sdsfromlonglong(long long value);
sds sdscatrepr(sds s, const char *p, size_t len);
sds *sdssplitargs(const char *line, int *argc);

/* 按指定长度遍历字符s,从from复制至to */
sds sdsmapchars(sds s, const char *from, const char *to, size_t setlen);

/* Low level functions exposed to the user API */
/* 对sds所对应的sdshdr结构的buf进行扩展 */
sds sdsMakeRoomFor(sds s, size_t addlen);

/* 对sds的buf的右端进行扩展(expand)或者修剪(trim) */
void sdsIncrLen(sds s, int incr);

/* 在不改动buf的情况系,将buf内多余的空间释放出去 */
sds sdsRemoveFreeSpace(sds s);

/* 计算给定sds的buf所占用的内存总数 */
size_t sdsAllocSize(sds s);

#endif

/* SDSLib, A C dynamic strings library
 *
 * Copyright (c) 2006-2012, Salvatore Sanfilippo <antirez at gmail dot com>
 * 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.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT OWNER OR CONTRIBUTORS 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.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>
#include "sds.h"
#include "zmalloc.h"

/* 创建一个指定长度的sds */
sds sdsnewlen(const void *init, size_t initlen) {
    struct sdshdr *sh;

    if (init) {    /* 如果init不为NULL的话,则分配内存空间 */
        sh = zmalloc(sizeof(struct sdshdr)+initlen+1);
    } else {    /* 如果init为NULL的话,则calloc()将分配的内存空间中的每一位都初始化为零 */
        sh = zcalloc(sizeof(struct sdshdr)+initlen+1);
    }

    /* 内存不足,分配失败 */
    if (sh == NULL) return NULL;

    /* 更新属性,sh->len(已占用长度),sh->free(剩余可用长度) */
    sh->len = initlen;    
    sh->free = 0;    

    if (initlen && init)
        memcpy(sh->buf, init, initlen);

    /* 加上终结符 */
    sh->buf[initlen] = '\0';

    /* 返回buf,而不是整个sdshdr */
    return (char*)sh->buf;
}

/* 创建一个包含空字符串""的sds */
sds sdsempty(void) {
    return sdsnewlen("",0);
}

/* 根据给定初始值init,创建sds */
sds sdsnew(const char *init) {
    /* 如果init为NULL,那么创建一个buf内只包含\0终结符的sds */
    size_t initlen = (init == NULL) ? 0 : strlen(init);
    return sdsnewlen(init, initlen);
}

/* 复制sds的一个副本 */
sds sdsdup(const sds s) {
    return sdsnewlen(s, sdslen(s));
}

/* 释放sds所对应的sdshdr结构的内容 */
void sdsfree(sds s) {
    if (s == NULL) return;
    zfree(s-sizeof(struct sdshdr));
}

/* 更新给定sds所对应的sdshdr结构的free和len属性 */
void sdsupdatelen(sds s) {
    /* s - (sizeof(struct sdshdr))表示将指针向前移动到struct sdshdr的起点,从而得出一个指向 sdshdr 结构的指针 */
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));

    /* 计算正确的buf长度 */
    int reallen = strlen(s);

    /* 更新free和len属性 */
    sh->free += (sh->len-reallen);
    sh->len = reallen;
}

/* 清除给定sds buf中的内容,让它只包含一个\0终结符 */
void sdsclear(sds s) {
    /* 使用指针运算，可以从sds值中计算出相应的sdshdr结构： */
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));

    /* 更新属性 */
    sh->free += sh->len;
    sh->len = 0;
    sh->buf[0] = '\0';
}

/* Enlarge the free space at the end of the sds string so that the caller
 * is sure that after calling this function can overwrite up to addlen
 * bytes after the end of the string, plus one more byte for nul term.
 * 
 * Note: this does not change the *size* of the sds string as returned
 * by sdslen(), but only the free buffer space we have. */
/* 对sds的buf进行扩展,扩展的长度不少于addlen */
sds sdsMakeRoomFor(sds s, size_t addlen) {
    struct sdshdr *sh, *newsh;
    size_t free = sdsavail(s);
    size_t len, newlen;

    /* 剩余空间可满足需求,无需扩展 */
    if (free >= addlen) return s;

    /* 目前buf长度 */
    len = sdslen(s);

    sh = (void*) (s-(sizeof(struct sdshdr)));

    /* 新buf长度 */
    newlen = (len+addlen);

    /* 如果新buf长度小于SDS_MAX_PREALLOC(1024*1024)长度时,将buf的长度设为新buf长度的两倍 */
    if (newlen < SDS_MAX_PREALLOC)
        newlen *= 2;
    else
        newlen += SDS_MAX_PREALLOC;
    newsh = zrealloc(sh, sizeof(struct sdshdr)+newlen+1);
    if (newsh == NULL) return NULL;

    newsh->free = newlen - len;    
    
    /* 只返回字符串部分 */
    return newsh->buf;
}

/* Reallocate the sds string so that it has no free space at the end. The
 * contained string remains not altered, but next concatenation operations
 * will require a reallocation. */
/* 在不改动sds buf内容的情况下,将buf内多余的空间释放出去。在对sds执行这个函数之后,下一次对这个sds的拼接操作必须需要一次内存分配 */
sds sdsRemoveFreeSpace(sds s) {
    struct sdshdr *sh;

    sh = (void*) (s-(sizeof(struct sdshdr)));
    sh = zrealloc(sh, sizeof(struct sdshdr)+sh->len+1);

    /* 修改buf长度为sh->len + 1,不保留任何多余空间 */
    sh->free = 0;
    return sh->buf;
}

/* 计算给定sds buf的内容长度(包括已使用和未使用的) */
size_t sdsAllocSize(sds s) {
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));

    return sizeof(*sh)+sh->len+sh->free+1;
}

/* Increment the sds length and decrements the left free space at the
 * end of the string accordingly to 'incr'. Also set the null term
 * in the new end of the string.
 *
 * This function is used in order to fix the string length after the
 * user calls sdsMakeRoomFor(), writes something after the end of
 * the current string, and finally needs to set the new length.
 *
 * Note: it is possible to use a negative increment in order to
 * right-trim the string.
 *
 * Using sdsIncrLen() and sdsMakeRoomFor() it is possible to mount the
 * following schema to cat bytes coming from the kernel to the end of an
 * sds string new things without copying into an intermediate buffer:
 *
 * oldlen = sdslen(s);
 * s = sdsMakeRoomFor(s, BUFFER_SIZE);
 * nread = read(fd, s+oldlen, BUFFER_SIZE);
 * ... check for nread <= 0 and handle it ...
 * sdsIncrLen(s, nhread);
 */
 /*
  * 在sds buf的右端添加incr个位置。
  * 如果incr为负数时,可作为right-trim使用
  * 
  * incr为正数的例子:
  * hdr = sdshdr {
  *              len  = 10;
  *            free = 10;
  *            buf  = "Hello Moto\0";
  *          };
  * sdsIncrLen(hdr->buf, 2);
  * hdr = sdshdr {
  *            len = 12;
  *         free = 8;
  *            buf = "Hello Moto\0[ ]\0"
  *         };
  * 这里的[ ]表示一个任意内容的byte.
  *
  * incr为负数的例子:
  * hdr = sdshdr {
  *            len = 10;
  *            free = 10;
  *            buf = "Hello Moto\0"
  *         };
  * sdsIncrLen(hdr->buf, -2);
  * hdr = sdshdr {
  *            len = 8;
  *            free = 12;
  *            buf = "Hello Mo\0"
  *          };
 */
void sdsIncrLen(sds s, int incr) {
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));

    assert(sh->free >= incr);
    sh->len += incr;
    sh->free -= incr;
    assert(sh->free >= 0);
    s[sh->len] = '\0';
}

/* Grow the sds to have the specified length. Bytes that were not part of
 * the original length of the sds will be set to zero. */
/* 将sds的buf扩展至给定长度,无内容部分用\0填充 */
sds sdsgrowzero(sds s, size_t len) {
    struct sdshdr *sh = (void*)(s-(sizeof(struct sdshdr)));
    size_t totlen, curlen = sh->len;

    /* 如果现有长度比给定长度要大,则无需扩展 */
    if (len <= curlen) return s;

    /* 扩展sds */
    s = sdsMakeRoomFor(s,len-curlen);

    if (s == NULL) return NULL;

    /* Make sure added region doesn't contain garbage */
    /* 使用\0来填充空位,确保空位中不包含垃圾数据 */
    sh = (void*)(s-(sizeof(struct sdshdr)));
    memset(s+curlen,0,(len-curlen+1)); /* also set trailing \0 byte */

    /* 更新属性 */
    totlen = sh->len+sh->free;
    sh->len = len;
    sh->free = totlen-sh->len;

    return s;
}

/* 按给定长度扩展sds,并将t拼接到sds的末尾 */
sds sdscatlen(sds s, const void *t, size_t len) {
    struct sdshdr *sh;
    size_t curlen = sdslen(s);

    s = sdsMakeRoomFor(s,len);
    if (s == NULL) return NULL;
    sh = (void*) (s-(sizeof(struct sdshdr)));

    /* 将给定长度的t拼接到sds的末尾 */
    memcpy(s+curlen, t, len);

    /* 更新属性 */
    sh->len = curlen+len;
    sh->free = sh->free-len;

    /* 终结符 */
    s[curlen+len] = '\0';

    return s;
}

/* 将一个char数组拼接到sds末尾 */
sds sdscat(sds s, const char *t) {
    return sdscatlen(s, t, strlen(t));
}

/* 拼接两个sds */
sds sdscatsds(sds s, const sds t) {
    return sdscatlen(s, t, sdslen(t));
}

/* 将一个char数组的前len个字节复制至sds,如果sds的buf不足以容纳要复制的内容,那么扩展buf的长度,让buf的长度大于等于len */
sds sdscpylen(sds s, const char *t, size_t len) {
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
    size_t totlen = sh->free+sh->len;

    if (totlen < len) {/* 扩展buf的长度,让它的长度大于等于len */
        s = sdsMakeRoomFor(s,len-sh->len);
        if (s == NULL) return NULL;
        sh = (void*) (s-(sizeof(struct sdshdr)));
        totlen = sh->free+sh->len;
    }
    memcpy(s, t, len);
    s[len] = '\0';

    /* 更新属性 */
    sh->len = len;
    sh->free = totlen-len;

    return s;
}

/* 将一个char数组复制到sds */
sds sdscpy(sds s, const char *t) {
    return sdscpylen(s, t, strlen(t));
}

/* 因为类似printf操作,事先不知道源串长度,因此采用一种类似启发式的方法,从16byte开始,按照倍数递增的方法来猜测长度,猜测长度时,是在倒数第二个字节处打了个标记('\0'),然后判断操作前后是否保持一致来判断是否空间够。好好看while循环,挺有意思的 */
sds sdscatvprintf(sds s, const char *fmt, va_list ap) {
    va_list cpy;
    char *buf, *t;
    size_t buflen = 16;

    while(1) {
        buf = zmalloc(buflen);
        if (buf == NULL) return NULL;
        buf[buflen-2] = '\0';
        va_copy(cpy,ap);
        vsnprintf(buf, buflen, fmt, cpy);
        if (buf[buflen-2] != '\0') {
            zfree(buf);
            buflen *= 2;
            continue;
        }
        break;
    }
    t = sdscat(s, buf);
    zfree(buf);
    return t;
}

sds sdscatprintf(sds s, const char *fmt, ...) {
    va_list ap;
    char *t;
    va_start(ap, fmt);
    t = sdscatvprintf(s,fmt,ap);
    va_end(ap);
    return t;
}

sds sdstrim(sds s, const char *cset) {
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
    char *start, *end, *sp, *ep;
    size_t len;

    sp = start = s;
    
    /* 最后一个有意义的字节,非'\0' */
    ep = end = s+sdslen(s)-1;
    
    /* strchr()函数功能为:查找字符串s中首次出现字符c的位置;返回值:返回首次出现c位置的指针,返回的地址是字符串在内存中随机分配的地址再加上你搜索的字符在字符串的位置,如果不存在c则返回NULL */
    /* 将头尾出现在字符串cset中的字符都删干净,*sp和*ep都是字符而非字符指针 */
    while(sp <= end && strchr(cset, *sp)) sp++;
    while(ep > start && strchr(cset, *ep)) ep--;

    len = (sp > ep) ? 0 : ((ep-sp)+1);
    if (sh->buf != sp)     memmove(sh->buf, sp, len);/* 因为sp和sh->buf有可能重叠,所以用了memmove */
    sh->buf[len] = '\0';

    /* 更新属性 */
    sh->free = sh->free+(sh->len-len);
    sh->len = len;
    
    /* 删除特定空间后,并不释放内存,只是增大sh->free */
    return s;
}

sds sdsrange(sds s, int start, int end) {
    struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
    size_t newlen, len = sdslen(s);

    if (len == 0) return s;
    if (start < 0) {
        start = len+start;
        if (start < 0) start = 0;
    }
    if (end < 0) {
        end = len+end;
        if (end < 0) end = 0;
    }
    newlen = (start > end) ? 0 : (end-start)+1;
    if (newlen != 0) {
        if (start >= (signed)len) {
            newlen = 0;
        } else if (end >= (signed)len) {
            end = len-1;
            newlen = (start > end) ? 0 : (end-start)+1;
        }
    } else {
        start = 0;
    }
    if (start && newlen) memmove(sh->buf, sh->buf+start, newlen);
    sh->buf[newlen] = 0;

    /* 更新属性 */
    sh->free = sh->free+(sh->len-newlen);
    sh->len = newlen;

    return s;
}

void sdstolower(sds s) {
    int len = sdslen(s), j;
    
    /* 逐个字符转为小写 */
    for (j = 0; j < len; j++) s[j] = tolower(s[j]);
}

void sdstoupper(sds s) {
    int len = sdslen(s), j;
    
    /* 逐个字符转为大写 */
    for (j = 0; j < len; j++) s[j] = toupper(s[j]);
}

/* 比较两个sds */
int sdscmp(const sds s1, const sds s2) {
    size_t l1, l2, minlen;
    int cmp;

    l1 = sdslen(s1);
    l2 = sdslen(s2);
    minlen = (l1 < l2) ? l1 : l2;
    cmp = memcmp(s1,s2,minlen);
    if (cmp == 0) return l1-l2;
    return cmp;
}

/* Split 's' with separator in 'sep'. An array
 * of sds strings is returned. *count will be set
 * by reference to the number of tokens returned.
 *
 * On out of memory, zero length string, zero length
 * separator, NULL is returned.
 *
 * Note that 'sep' is able to split a string using
 * a multi-character separator. For example
 * sdssplit("foo_-_bar","_-_"); will return two
 * elements "foo" and "bar".
 *
 * This version of the function is binary-safe but
 * requires length arguments. sdssplit() is just the
 * same function but for zero-terminated strings.
 */
sds *sdssplitlen(const char *s, int len, const char *sep, int seplen, int *count) {
    int elements = 0, slots = 5, start = 0, j;
    sds *tokens;
    
    if (seplen < 1 || len < 0) return NULL;
    
    /* 先假设有5个tokens供返回。在这个函数里返回值叫tokens,但在后续的sdssplitargs里返回值被起名为vector,而且类型一个时sds*,一个是char*,本质一样 */
    tokens = zmalloc(sizeof(sds)*slots);
    if (tokens == NULL) return NULL;

    if (len == 0) {
        *count = 0;
        return tokens;
    }
    for (j = 0; j < (len-(seplen-1)); j++) {
        /* make sure there is room for the next element and the final one */
        if (slots < elements+2) {
            sds *newtokens;

            slots *= 2;
            newtokens = zrealloc(tokens,sizeof(sds)*slots);
            if (newtokens == NULL) goto cleanup;
            tokens = newtokens;
        }
        /* search the separator */
        if ((seplen == 1 && *(s+j) == sep[0]) || (memcmp(s+j,sep,seplen) == 0)) {
            tokens[elements] = sdsnewlen(s+start,j-start);
            if (tokens[elements] == NULL) goto cleanup;
            elements++;
            start = j+seplen;
            j = j+seplen-1; /* skip the separator */
        }
    }
    /* Add the final element. We are sure there is room in the tokens array. */
    tokens[elements] = sdsnewlen(s+start,len-start);
    if (tokens[elements] == NULL) goto cleanup;
    elements++;
    *count = elements;
    return tokens;

cleanup:
    {
        int i;
        for (i = 0; i < elements; i++) sdsfree(tokens[i]);
        zfree(tokens);
        *count = 0;
        return NULL;
    }
}

void sdsfreesplitres(sds *tokens, int count) {
    if (!tokens) return;
    while(count--)
        sdsfree(tokens[count]);
    zfree(tokens);
}

/* 将long long转成字符串 */
sds sdsfromlonglong(long long value) {
    char buf[32], *p;
    unsigned long long v;

    v = (value < 0) ? -value : value;
    p = buf+31; /* point to the last character */
    do {
        *p-- = '0'+(v%10);
        v /= 10;
    } while(v);
    if (value < 0) *p-- = '-';
    p++;
    return sdsnewlen(p,32-(p-buf));
}

/* 将参数p原封不动(做过处理的,时计算机认为合法的),保存在一个sds里,用于协议交换 */
sds sdscatrepr(sds s, const char *p, size_t len) {
    s = sdscatlen(s,"\"",1);
    while(len--) {
        switch(*p) {
        case '\\':
        case '"':
            s = sdscatprintf(s,"\\%c",*p);
            break;
        case '\n': s = sdscatlen(s,"\\n",2); break;
        case '\r': s = sdscatlen(s,"\\r",2); break;
        case '\t': s = sdscatlen(s,"\\t",2); break;
        case '\a': s = sdscatlen(s,"\\a",2); break;
        case '\b': s = sdscatlen(s,"\\b",2); break;
        default:
            if (isprint(*p))
                s = sdscatprintf(s,"%c",*p);
            else
                s = sdscatprintf(s,"\\x%02x",(unsigned char)*p);
            break;
        }
        p++;
    }
    return sdscatlen(s,"\"",1);
}

/* Helper function for sdssplitargs() that returns non zero if 'c'
 * is a valid hex digit. */
int is_hex_digit(char c) {
    return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') ||
           (c >= 'A' && c <= 'F');
}

/* Helper function for sdssplitargs() that converts an hex digit into an
 * integer from 0 to 15 */
 /* 十六进制转换成十进制 */
int hex_digit_to_int(char c) {
    switch(c) {
    case '0': return 0;
    case '1': return 1;
    case '2': return 2;
    case '3': return 3;
    case '4': return 4;
    case '5': return 5;
    case '6': return 6;
    case '7': return 7;
    case '8': return 8;
    case '9': return 9;
    case 'a': case 'A': return 10;
    case 'b': case 'B': return 11;
    case 'c': case 'C': return 12;
    case 'd': case 'D': return 13;
    case 'e': case 'E': return 14;
    case 'f': case 'F': return 15;
    default: return 0;
    }
}

/* Split a line into arguments, where every argument can be in the
 * following programming-language REPL-alike form:
 *
 * foo bar "newline are supported\n" and "\xff\x00otherstuff"
 *
 * The number of arguments is stored into *argc, and an array
 * of sds is returned.
 *
 * The caller should free the resulting array of sds strings with
 * sdsfreesplitres().
 *
 * Note that sdscatrepr() is able to convert back a string into
 * a quoted string in the same format sdssplitargs() is able to parse.
 *
 * The function returns the allocated tokens on success, even when the
 * input string is empty, or NULL if the input contains unbalanced
 * quotes or closed quotes followed by non space characters
 * as in: "foo"bar or "foo'
 */
sds *sdssplitargs(const char *line, int *argc) {
    const char *p = line;
    char *current = NULL;
    char **vector = NULL;

    *argc = 0;
    while(1) {
        /* skip blanks */
        while(*p && isspace(*p)) p++;
        if (*p) {
            /* get a token */
            int inq=0;  /* set to 1 if we are in "quotes" */
            int insq=0; /* set to 1 if we are in 'single quotes' */
            int done=0;

            if (current == NULL) current = sdsempty();
            while(!done) {
                if (inq) {
                    if (*p == '\\' && *(p+1) == 'x' &&
                                             is_hex_digit(*(p+2)) &&
                                             is_hex_digit(*(p+3)))
                    {
                        unsigned char byte;

                        byte = (hex_digit_to_int(*(p+2))*16)+
                                hex_digit_to_int(*(p+3));
                        current = sdscatlen(current,(char*)&byte,1);
                        p += 3;
                    } else if (*p == '\\' && *(p+1)) {
                        char c;

                        p++;
                        switch(*p) {
                        case 'n': c = '\n'; break;
                        case 'r': c = '\r'; break;
                        case 't': c = '\t'; break;
                        case 'b': c = '\b'; break;
                        case 'a': c = '\a'; break;
                        default: c = *p; break;
                        }
                        current = sdscatlen(current,&c,1);
                    } else if (*p == '"') {
                        /* closing quote must be followed by a space or
                         * nothing at all. */
                        if (*(p+1) && !isspace(*(p+1))) goto err;
                        done=1;
                    } else if (!*p) {
                        /* unterminated quotes */
                        goto err;
                    } else {
                        current = sdscatlen(current,p,1);
                    }
                } else if (insq) {
                    if (*p == '\\' && *(p+1) == '\'') {
                        p++;
                        current = sdscatlen(current,"'",1);
                    } else if (*p == '\'') {
                        /* closing quote must be followed by a space or
                         * nothing at all. */
                        if (*(p+1) && !isspace(*(p+1))) goto err;
                        done=1;
                    } else if (!*p) {
                        /* unterminated quotes */
                        goto err;
                    } else {
                        current = sdscatlen(current,p,1);
                    }
                } else {
                    switch(*p) {
                    case ' ':
                    case '\n':
                    case '\r':
                    case '\t':
                    case '\0':
                        done=1;
                        break;
                    case '"':
                        inq=1;
                        break;
                    case '\'':
                        insq=1;
                        break;
                    default:
                        current = sdscatlen(current,p,1);
                        break;
                    }
                }
                if (*p) p++;
            }
            /* add the token to the vector */
            vector = zrealloc(vector,((*argc)+1)*sizeof(char*));
            vector[*argc] = current;
            (*argc)++;
            current = NULL;
        } else {
            /* Even on empty input string return something not NULL. */
            if (vector == NULL) vector = zmalloc(sizeof(void*));
            return vector;
        }
    }

err:
    while((*argc)--)
        sdsfree(vector[*argc]);
    zfree(vector);
    if (current) sdsfree(current);
    *argc = 0;
    return NULL;
}

/* Modify the string substituting all the occurrences of the set of
 * characters specified in the 'from' string to the corresponding character
 * in the 'to' array.
 *
 * For instance: sdsmapchars(mystring, "ho", "01", 2)
 * will have the effect of turning the string "hello" into "0ell1".
 *
 * The function returns the sds string pointer, that is always the same
 * as the input pointer since no resize is needed. */
/* 遍历字符 */
sds sdsmapchars(sds s, const char *from, const char *to, size_t setlen) {
    size_t j, i, l = sdslen(s);

    for (j = 0; j < l; j++) {
        for (i = 0; i < setlen; i++) {
            if (s[j] == from[i]) {
                s[j] = to[i];
                break;
            }
        }
    }
    return s;
}

#ifdef SDS_TEST_MAIN
#include <stdio.h>
#include "testhelp.h"

int main(void) {
    {
        struct sdshdr *sh;
        sds x = sdsnew("foo"), y;

        test_cond("Create a string and obtain the length",
            sdslen(x) == 3 && memcmp(x,"foo\0",4) == 0)

        sdsfree(x);
        x = sdsnewlen("foo",2);
        test_cond("Create a string with specified length",
            sdslen(x) == 2 && memcmp(x,"fo\0",3) == 0)

        x = sdscat(x,"bar");
        test_cond("Strings concatenation",
            sdslen(x) == 5 && memcmp(x,"fobar\0",6) == 0);

        x = sdscpy(x,"a");
        test_cond("sdscpy() against an originally longer string",
            sdslen(x) == 1 && memcmp(x,"a\0",2) == 0)

        x = sdscpy(x,"xyzxxxxxxxxxxyyyyyyyyyykkkkkkkkkk");
        test_cond("sdscpy() against an originally shorter string",
            sdslen(x) == 33 &&
            memcmp(x,"xyzxxxxxxxxxxyyyyyyyyyykkkkkkkkkk\0",33) == 0)

        sdsfree(x);
        x = sdscatprintf(sdsempty(),"%d",123);
        test_cond("sdscatprintf() seems working in the base case",
            sdslen(x) == 3 && memcmp(x,"123\0",4) ==0)

        sdsfree(x);
        x = sdstrim(sdsnew("xxciaoyyy"),"xy");
        test_cond("sdstrim() correctly trims characters",
            sdslen(x) == 4 && memcmp(x,"ciao\0",5) == 0)

        y = sdsrange(sdsdup(x),1,1);
        test_cond("sdsrange(...,1,1)",
            sdslen(y) == 1 && memcmp(y,"i\0",2) == 0)

        sdsfree(y);
        y = sdsrange(sdsdup(x),1,-1);
        test_cond("sdsrange(...,1,-1)",
            sdslen(y) == 3 && memcmp(y,"iao\0",4) == 0)

        sdsfree(y);
        y = sdsrange(sdsdup(x),-2,-1);
        test_cond("sdsrange(...,-2,-1)",
            sdslen(y) == 2 && memcmp(y,"ao\0",3) == 0)

        sdsfree(y);
        y = sdsrange(sdsdup(x),2,1);
        test_cond("sdsrange(...,2,1)",
            sdslen(y) == 0 && memcmp(y,"\0",1) == 0)

        sdsfree(y);
        y = sdsrange(sdsdup(x),1,100);
        test_cond("sdsrange(...,1,100)",
            sdslen(y) == 3 && memcmp(y,"iao\0",4) == 0)

        sdsfree(y);
        y = sdsrange(sdsdup(x),100,100);
        test_cond("sdsrange(...,100,100)",
            sdslen(y) == 0 && memcmp(y,"\0",1) == 0)

        sdsfree(y);
        sdsfree(x);
        x = sdsnew("foo");
        y = sdsnew("foa");
        test_cond("sdscmp(foo,foa)", sdscmp(x,y) > 0)

        sdsfree(y);
        sdsfree(x);
        x = sdsnew("bar");
        y = sdsnew("bar");
        test_cond("sdscmp(bar,bar)", sdscmp(x,y) == 0)

        sdsfree(y);
        sdsfree(x);
        x = sdsnew("aar");
        y = sdsnew("bar");
        test_cond("sdscmp(bar,bar)", sdscmp(x,y) < 0)

        {
            int oldfree;

            sdsfree(x);
            x = sdsnew("0");
            sh = (void*) (x-(sizeof(struct sdshdr)));
            test_cond("sdsnew() free/len buffers", sh->len == 1 && sh->free == 0);
            x = sdsMakeRoomFor(x,1);
            sh = (void*) (x-(sizeof(struct sdshdr)));
            test_cond("sdsMakeRoomFor()", sh->len == 1 && sh->free > 0);
            oldfree = sh->free;
            x[1] = '1';
            sdsIncrLen(x,1);
            test_cond("sdsIncrLen() -- content", x[0] == '0' && x[1] == '1');
            test_cond("sdsIncrLen() -- len", sh->len == 2);
            test_cond("sdsIncrLen() -- free", sh->free == oldfree-1);
        }
    }
    test_report()
    return 0;
}
#endif