Redis源码学习1-sds.c

/* 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"

/*
* 根据给定的初始化字符串 init 和字符串长度 initlen
* 创建一个新的 sds
*
* 参数
*  init ：初始化字符串指针
*  initlen ：初始化字符串的长度
*
* 返回值
*  sds ：创建成功返回 sdshdr 相对应的 sds
*        创建失败返回 NULL
*
* 复杂度
*  T = O(N)
*/
/* Create a new sds string with the content specified by the 'init' pointer
* and 'initlen'.
* If NULL is used for 'init' the string is initialized with zero bytes.
*
* The string is always null-termined (all the sds strings are, always) so
* even if you create an sds string with:
*
* mystring = sdsnewlen("abc",3");
*
* You can print the string with printf() as there is an implicit \0 at the
* end of the string. However the string is binary safe and can contain
* \0 characters in the middle, as the length is stored in the sds header. */
sds sdsnewlen(const void *init, size_t initlen) {

struct sdshdr *sh;

// 根据是否有初始化内容，选择适当的内存分配方式
// T = O(N)
if (init) {
// zmalloc 不初始化所分配的内存
sh = zmalloc(sizeof(struct sdshdr)+initlen+1);
} else {
// zcalloc 将分配的内存全部初始化为 0
sh = zcalloc(sizeof(struct sdshdr)+initlen+1);
}

// 内存分配失败，返回
if (sh == NULL) return NULL;

// 设置初始化长度
sh->len = initlen;
// 新 sds 不预留任何空间
sh->free = 0;
// 如果有指定初始化内容，将它们复制到 sdshdr 的 buf 中
// T = O(N)
if (initlen && init)
memcpy(sh->buf, init, initlen);
// 以 \0 结尾
sh->buf[initlen] = '\0';

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

/*
* 创建并返回一个只保存了空字符串 "" 的 sds
*
* 返回值
*  sds ：创建成功返回 sdshdr 相对应的 sds
*        创建失败返回 NULL
*
* 复杂度
*  T = O(1)
*/
/* Create an empty (zero length) sds string. Even in this case the string
* always has an implicit null term. */
sds sdsempty(void) {
return sdsnewlen("",0);
}

/*
* 根据给定字符串 init ，创建一个包含同样字符串的 sds
*
* 参数
*  init ：如果输入为 NULL ，那么创建一个空白 sds
*         否则，新创建的 sds 中包含和 init 内容相同字符串
*
* 返回值
*  sds ：创建成功返回 sdshdr 相对应的 sds
*        创建失败返回 NULL
*
* 复杂度
*  T = O(N)
*/
/* Create a new sds string starting from a null termined C string. */
sds sdsnew(const char *init) {
size_t initlen = (init == NULL) ? 0 : strlen(init);
return sdsnewlen(init, initlen);
}

/*
* 复制给定 sds 的副本
*
* 返回值
*  sds ：创建成功返回输入 sds 的副本
*        创建失败返回 NULL
*
* 复杂度
*  T = O(N)
*/
/* Duplicate an sds string. */
sds sdsdup(const sds s) {
return sdsnewlen(s, sdslen(s));
}

/*
* 释放给定的 sds
*
* 复杂度
*  T = O(N)
*/
/* Free an sds string. No operation is performed if 's' is NULL. */
void sdsfree(sds s) {
if (s == NULL) return;
zfree(s-sizeof(struct sdshdr));
}

// 未使用函数，可能已废弃
/* Set the sds string length to the length as obtained with strlen(), so
* considering as content only up to the first null term character.
*
* This function is useful when the sds string is hacked manually in some
* way, like in the following example:
*
* s = sdsnew("foobar");
* s[2] = '\0';
* sdsupdatelen(s);
* printf("%d\n", sdslen(s));
*
* The output will be "2", but if we comment out the call to sdsupdatelen()
* the output will be "6" as the string was modified but the logical length
* remains 6 bytes. */
void sdsupdatelen(sds s) {
struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
int reallen = strlen(s);
sh->free += (sh->len-reallen);
sh->len = reallen;
}

/*
* 在不释放 SDS 的字符串空间的情况下，（通过惰性空间释放策略， SDS 避免了缩短字符串时所需的内存重分配操作， 并为将来可能有的增长操作提供了优化。）
  * 重置 SDS 所保存的字符串为空字符串。
*
* 复杂度
*  T = O(1)
*/
/* Modify an sds string on-place to make it empty (zero length).
* However all the existing buffer is not discarded but set as free space
* so that next append operations will not require allocations up to the
* number of bytes previously available. */
void sdsclear(sds s) {

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

// 重新计算属性
sh->free += sh->len;
sh->len = 0;

// 将结束符放到最前面（相当于惰性地删除 buf 中的内容）
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 *length* of the sds string as returned
* by sdslen(), but only the free buffer space we have. */
/*
* 对 sds 中 buf 的长度进行扩展，确保在函数执行之后，
* buf 至少会有 addlen + 1 长度的空余空间
* （额外的 1 字节是为 \0 准备的）
*
* 返回值
*  sds ：扩展成功返回扩展后的 sds
*        扩展失败返回 NULL
*
* 复杂度
*  T = O(N)
*/
sds sdsMakeRoomFor(sds s, size_t addlen) {

struct sdshdr *sh, *newsh;

// 获取 s 目前的空余空间长度
size_t free = sdsavail(s);

size_t len, newlen;

// s 目前的空余空间已经足够，无须再进行扩展，直接返回
if (free >= addlen) return s;

// 获取 s 目前已占用空间的长度
len = sdslen(s);
sh = (void*) (s-(sizeof(struct sdshdr)));

// s 最少需要的长度
newlen = (len+addlen);

// 根据新长度，为 s 分配新空间所需的大小
if (newlen < SDS_MAX_PREALLOC)
// 如果新长度小于 SDS_MAX_PREALLOC
// 那么为它分配两倍于所需长度的空间
newlen *= 2;
else
// 否则，分配长度为目前长度加上 SDS_MAX_PREALLOC
newlen += SDS_MAX_PREALLOC;
// T = O(N)
newsh = zrealloc(sh, sizeof(struct sdshdr)+newlen+1);

// 内存不足，分配失败，返回
if (newsh == NULL) return NULL;

// 更新 sds 的空余长度
newsh->free = newlen - len;

// 返回 sds
return newsh->buf;
}

/*
* 回收 sds 中的空闲空间，
* 回收不会对 sds 中保存的字符串内容做任何修改。
*
* 返回值
*  sds ：内存调整后的 sds
*
* 复杂度
*  T = O(N)
*/
/* 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.
*
* After the call, the passed sds string is no longer valid and all the
* references must be substituted with the new pointer returned by the call. */
sds sdsRemoveFreeSpace(sds s) {
struct sdshdr *sh;

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

// 进行内存重分配，让 buf 的长度仅仅足够保存字符串内容
// T = O(N)
sh = zrealloc(sh, sizeof(struct sdshdr)+sh->len+1);

// 空余空间为 0
sh->free = 0;

return sh->buf;
}

/*
* 返回给定 sds 分配的内存字节数
*
* 复杂度
*  T = O(1)
*/
/* Return the total size of the allocation of the specifed sds string,
* including:
* 1) The sds header before the pointer.
* 2) The string.
* 3) The free buffer at the end if any.
* 4) The implicit null term.
*/
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 according to 'incr'. Also set the null term
* in the new end of the string.
*
* 根据 incr 参数，增加 sds 的长度，缩减空余空间，
* 并将 \0 放到新字符串的尾端
*
* 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.
*
* 这个函数是在调用 sdsMakeRoomFor() 对字符串进行扩展，
* 然后用户在字符串尾部写入了某些内容之后，
* 用来正确更新 free 和 len 属性的。
*
* Note: it is possible to use a negative increment in order to
* right-trim the string.
*
* 如果 incr 参数为负数，那么对字符串进行右截断操作。
*
* Usage example:
*
* 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 without copying into an intermediate buffer:
*
* 以下是 sdsIncrLen 的用例：
*
* oldlen = sdslen(s);
* s = sdsMakeRoomFor(s, BUFFER_SIZE);
* nread = read(fd, s+oldlen, BUFFER_SIZE);
* ... check for nread <= 0 and handle it ...
* sdsIncrLen(s, nread);
*
* 复杂度
*  T = O(1)
*/
void sdsIncrLen(sds s, int incr) {
struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));

// 确保 sds 空间足够
assert(sh->free >= incr);

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

// 这个 assert 其实可以忽略
// 因为前一个 assert 已经确保 sh->free - incr >= 0 了
assert(sh->free >= 0);

// 放置新的结尾符号
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.
*
* if the specified length is smaller than the current length, no operation
* is performed. */
/*
* 将 sds 扩充至指定长度，未使用的空间以 0 字节填充。
*
* 返回值
*  sds ：扩充成功返回新 sds ，失败返回 NULL
*
* 复杂度：
*  T = O(N)
*/
sds sdsgrowzero(sds s, size_t len) {
struct sdshdr *sh = (void*)(s-(sizeof(struct sdshdr)));
size_t totlen, curlen = sh->len;

// 如果 len 比字符串的现有长度小，
// 那么直接返回，不做动作
if (len <= curlen) return s;

// 扩展 sds
// T = O(N)
s = sdsMakeRoomFor(s,len-curlen);
// 如果内存不足，直接返回
if (s == NULL) return NULL;

/* Make sure added region doesn't contain garbage */
// 将新分配的空间用 0 填充，防止出现垃圾内容
// T = O(N)
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;

// 返回新的 sds
return s;
}

/*
* 将长度为 len 的字符串 t 追加到 sds 的字符串末尾
*
* 返回值
*  sds ：追加成功返回新 sds ，失败返回 NULL
*
* 复杂度
*  T = O(N)
*/
/* Append the specified binary-safe string pointed by 't' of 'len' bytes to the
* end of the specified sds string 's'.
*
* After the call, the passed sds string is no longer valid and all the
* references must be substituted with the new pointer returned by the call. */
sds sdscatlen(sds s, const void *t, size_t len) {

struct sdshdr *sh;

// 原有字符串长度
size_t curlen = sdslen(s);

// 扩展 sds 空间
// T = O(N)
s = sdsMakeRoomFor(s,len);

// 内存不足？直接返回
if (s == NULL) return NULL;

// 复制 t 中的内容到字符串后部
// T = O(N)
sh = (void*) (s-(sizeof(struct sdshdr)));
memcpy(s+curlen, t, len);

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

// 添加新结尾符号
s[curlen+len] = '\0';

// 返回新 sds
return s;
}

/*
* 将给定字符串 t 追加到 sds 的末尾
*
* 返回值
*  sds ：追加成功返回新 sds ，失败返回 NULL
*
* 复杂度
*  T = O(N)
*/
/* Append the specified null termianted C string to the sds string 's'.
*
* After the call, the passed sds string is no longer valid and all the
* references must be substituted with the new pointer returned by the call. */
sds sdscat(sds s, const char *t) {
return sdscatlen(s, t, strlen(t));
}

/*
* 将另一个 sds 追加到一个 sds 的末尾
*
* 返回值
*  sds ：追加成功返回新 sds ，失败返回 NULL
*
* 复杂度
*  T = O(N)
*/
/* Append the specified sds 't' to the existing sds 's'.
*
* After the call, the modified sds string is no longer valid and all the
* references must be substituted with the new pointer returned by the call. */
sds sdscatsds(sds s, const sds t) {
return sdscatlen(s, t, sdslen(t));
}

/*
* 将字符串 t 的前 len 个字符复制到 sds s 当中，
* 并在字符串的最后添加终结符。
*
* 如果 sds 的长度少于 len 个字符，那么扩展 sds
*
* 复杂度
*  T = O(N)
*
* 返回值
*  sds ：复制成功返回新的 sds ，否则返回 NULL
*/
/* Destructively modify the sds string 's' to hold the specified binary
* safe string pointed by 't' of length 'len' bytes. */
sds sdscpylen(sds s, const char *t, size_t len) {

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

// sds 现有 buf 的长度
size_t totlen = sh->free+sh->len;

// 如果 s 的 buf 长度不满足 len ，那么扩展它
if (totlen < len) {
// T = O(N)
s = sdsMakeRoomFor(s,len-sh->len);
if (s == NULL) return NULL;
sh = (void*) (s-(sizeof(struct sdshdr)));
totlen = sh->free+sh->len;
}

// 复制内容
// T = O(N)
memcpy(s, t, len);

// 添加终结符号
s[len] = '\0';

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

// 返回新的 sds
return s;
}

/*
* 将字符串复制到 sds 当中，
* 覆盖原有的字符。
*
* 如果 sds 的长度少于字符串的长度，那么扩展 sds 。
*
* 复杂度
*  T = O(N)
*
* 返回值
*  sds ：复制成功返回新的 sds ，否则返回 NULL
*/
/* Like sdscpylen() but 't' must be a null-termined string so that the length
* of the string is obtained with strlen(). */
sds sdscpy(sds s, const char *t) {
return sdscpylen(s, t, strlen(t));
}

/* Helper for sdscatlonglong() doing the actual number -> string
* conversion. 's' must point to a string with room for at least
* SDS_LLSTR_SIZE bytes.
*
* The function returns the lenght of the null-terminated string
* representation stored at 's'. */
#define SDS_LLSTR_SIZE 21
int sdsll2str(char *s, long long value) {
char *p, aux;
unsigned long long v;
size_t l;

/* Generate the string representation, this method produces
* an reversed string. */
v = (value < 0) ? -value : value;
p = s;
do {
*p++ = '0'+(v%10);
v /= 10;
} while(v);
if (value < 0) *p++ = '-';

/* Compute length and add null term. */
l = p-s;
*p = '\0';

/* Reverse the string. */
p--;
while(s < p) {
aux = *s;
*s = *p;
*p = aux;
s++;
p--;
}
return l;
}

/* Identical sdsll2str(), but for unsigned long long type. */
int sdsull2str(char *s, unsigned long long v) {
char *p, aux;
size_t l;

/* Generate the string representation, this method produces
* an reversed string. */
p = s;
do {
*p++ = '0'+(v%10);
v /= 10;
} while(v);

/* Compute length and add null term. */
l = p-s;
*p = '\0';

/* Reverse the string. */
p--;
while(s < p) {
aux = *s;
*s = *p;
*p = aux;
s++;
p--;
}
return l;
}

/* Create an sds string from a long long value. It is much faster than:
*
* sdscatprintf(sdsempty(),"%lld\n", value);
*/
// 根据输入的 long long 值 value ，创建一个 SDS
sds sdsfromlonglong(long long value) {
char buf[SDS_LLSTR_SIZE];
int len = sdsll2str(buf,value);

return sdsnewlen(buf,len);
}

/*
* 打印函数，被 sdscatprintf 所调用
*
* T = O(N^2)
*/
/* Like sdscatpritf() but gets va_list instead of being variadic. */
sds sdscatvprintf(sds s, const char *fmt, va_list ap) {
va_list cpy;
char staticbuf[1024], *buf = staticbuf, *t;
size_t buflen = strlen(fmt)*2;

/* We try to start using a static buffer for speed.
* If not possible we revert to heap allocation. */
if (buflen > sizeof(staticbuf)) {
buf = zmalloc(buflen);
if (buf == NULL) return NULL;
} else {
buflen = sizeof(staticbuf);
}

/* Try with buffers two times bigger every time we fail to
* fit the string in the current buffer size. */
while(1) {
buf[buflen-2] = '\0';
va_copy(cpy,ap);
// T = O(N)
vsnprintf(buf, buflen, fmt, cpy);
if (buf[buflen-2] != '\0') {
if (buf != staticbuf) zfree(buf);
buflen *= 2;
buf = zmalloc(buflen);
if (buf == NULL) return NULL;
continue;
}
break;
}

/* Finally concat the obtained string to the SDS string and return it. */
t = sdscat(s, buf);
if (buf != staticbuf) zfree(buf);
return t;
}

/*
* 打印任意数量个字符串，并将这些字符串追加到给定 sds 的末尾
*
* T = O(N^2)
*/
/* Append to the sds string 's' a string obtained using printf-alike format
* specifier.
*
* After the call, the modified sds string is no longer valid and all the
* references must be substituted with the new pointer returned by the call.
*
* Example:
*
* s = sdsempty("Sum is: ");
* s = sdscatprintf(s,"%d+%d = %d",a,b,a+b).
*
* Often you need to create a string from scratch with the printf-alike
* format. When this is the need, just use sdsempty() as the target string:
*
* s = sdscatprintf(sdsempty(), "... your format ...", args);
*/
sds sdscatprintf(sds s, const char *fmt, ...) {
va_list ap;
char *t;
va_start(ap, fmt);
// T = O(N^2)
t = sdscatvprintf(s,fmt,ap);
va_end(ap);
return t;
}

/* This function is similar to sdscatprintf, but much faster as it does
* not rely on sprintf() family functions implemented by the libc that
* are often very slow. Moreover directly handling the sds string as
* new data is concatenated provides a performance improvement.
*
* However this function only handles an incompatible subset of printf-alike
* format specifiers:
*
* %s - C String
* %S - SDS string
* %i - signed int
* %I - 64 bit signed integer (long long, int64_t)
* %u - unsigned int
* %U - 64 bit unsigned integer (unsigned long long, uint64_t)
* %% - Verbatim "%" character.
*/
sds sdscatfmt(sds s, char const *fmt, ...) {
struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
size_t initlen = sdslen(s);
const char *f = fmt;
int i;
va_list ap;

va_start(ap,fmt);
f = fmt;    /* Next format specifier byte to process. */
i = initlen; /* Position of the next byte to write to dest str. */
while(*f) {
char next, *str;
size_t l;
long long num;
unsigned long long unum;

/* Make sure there is always space for at least 1 char. */
if (sh->free == 0) {
s = sdsMakeRoomFor(s,1);
sh = (void*) (s-(sizeof(struct sdshdr)));
}

switch(*f) {
case '%':
next = *(f+1);
f++;
switch(next) {
case 's':
case 'S':
str = va_arg(ap,char*);
l = (next == 's') ? strlen(str) : sdslen(str);
if (sh->free < l) {
s = sdsMakeRoomFor(s,l);
sh = (void*) (s-(sizeof(struct sdshdr)));
}
memcpy(s+i,str,l);
sh->len += l;
sh->free -= l;
i += l;
break;
case 'i':
case 'I':
if (next == 'i')
num = va_arg(ap,int);
else
num = va_arg(ap,long long);
{
char buf[SDS_LLSTR_SIZE];
l = sdsll2str(buf,num);
if (sh->free < l) {
s = sdsMakeRoomFor(s,l);
sh = (void*) (s-(sizeof(struct sdshdr)));
}
memcpy(s+i,buf,l);
sh->len += l;
sh->free -= l;
i += l;
}
break;
case 'u':
case 'U':
if (next == 'u')
unum = va_arg(ap,unsigned int);
else
unum = va_arg(ap,unsigned long long);
{
char buf[SDS_LLSTR_SIZE];
l = sdsull2str(buf,unum);
if (sh->free < l) {
s = sdsMakeRoomFor(s,l);
sh = (void*) (s-(sizeof(struct sdshdr)));
}
memcpy(s+i,buf,l);
sh->len += l;
sh->free -= l;
i += l;
}
break;
default: /* Handle %% and generally %<unknown>. */
s[i++] = next;
sh->len += 1;
sh->free -= 1;
break;
}
break;
default:
s[i++] = *f;
sh->len += 1;
sh->free -= 1;
break;
}
f++;
}
va_end(ap);

/* Add null-term */
s[i] = '\0';
return s;
}

/*
* 对 sds 左右两端进行修剪，清除其中 cset 指定的所有字符
*
* 比如 sdsstrim(xxyyabcyyxy, "xy") 将返回 "abc"
*
* 复杂性：
*  T = O(M*N)，M 为 SDS 长度， N 为 cset 长度。
*/
/* Remove the part of the string from left and from right composed just of
* contiguous characters found in 'cset', that is a null terminted C string.
*
* After the call, the modified sds string is no longer valid and all the
* references must be substituted with the new pointer returned by the call.
*
* Example:
*
* s = sdsnew("AA...AA.a.aa.aHelloWorld     :::");
* s = sdstrim(s,"A. :");
* printf("%s\n", s);
*
* Output will be just "Hello World".
*/
sds sdstrim(sds s, const char *cset) {
struct sdshdr *sh = (void*) (s-(sizeof(struct sdshdr)));
char *start, *end, *sp, *ep;
size_t len;

// 设置和记录指针
sp = start = s;
ep = end = s+sdslen(s)-1;

// 修剪, T = O(N^2)
while(sp <= end && strchr(cset, *sp)) sp++;
while(ep > start && strchr(cset, *ep)) ep--;

// 计算 trim 完毕之后剩余的字符串长度
len = (sp > ep) ? 0 : ((ep-sp)+1);

// 如果有需要，前移字符串内容
// T = O(N)
if (sh->buf != sp) memmove(sh->buf, sp, len);

// 添加终结符
sh->buf[len] = '\0';

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

// 返回修剪后的 sds
return s;
}

/*
* 按索引对截取 sds 字符串的其中一段
* start 和 end 都是闭区间（包含在内）
*
* 索引从 0 开始，最大为 sdslen(s) - 1
* 索引可以是负数， sdslen(s) - 1 == -1
*
* 复杂度
*  T = O(N)
*/
/* Turn the string into a smaller (or equal) string containing only the
* substring specified by the 'start' and 'end' indexes.
*
* start and end can be negative, where -1 means the last character of the
* string, -2 the penultimate character, and so forth.
*
* The interval is inclusive, so the start and end characters will be part
* of the resulting string.
*
* The string is modified in-place.
*
* Example:
*
* s = sdsnew("Hello World");
* sdsrange(s,1,-1); => "ello World"
*/
void 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;
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;
}

// 如果有需要，对字符串进行移动
// T = O(N)
if (start && newlen) memmove(sh->buf, sh->buf+start, newlen);

// 添加终结符
sh->buf[newlen] = 0;

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

/*
* 将 sds 字符串中的所有字符转换为小写
*
* T = O(N)
*/
/* Apply tolower() to every character of the sds string 's'. */
void sdstolower(sds s) {
int len = sdslen(s), j;

for (j = 0; j < len; j++) s[j] = tolower(s[j]);
}

/*
* 将 sds 字符串中的所有字符转换为大写
*
* T = O(N)
*/
/* Apply toupper() to every character of the sds string 's'. */
void sdstoupper(sds s) {
int len = sdslen(s), j;

for (j = 0; j < len; j++) s[j] = toupper(s[j]);
}

/*
* 对比两个 sds ， strcmp 的 sds 版本
*
* 返回值
*  int ：相等返回 0 ，s1 较大返回正数， s2 较大返回负数
*
* T = O(N)
*/
/* Compare two sds strings s1 and s2 with memcmp().
*
* Return value:
*
*     1 if s1 > s2.
*    -1 if s1 < s2.
*     0 if s1 and s2 are exactly the same binary string.
*
* If two strings share exactly the same prefix, but one of the two has
* additional characters, the longer string is considered to be greater than
* the smaller one. */
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.
*
* 使用分隔符 sep 对 s 进行分割，返回一个 sds 字符串的数组。
* *count 会被设置为返回数组元素的数量。
*
* On out of memory, zero length string, zero length
* separator, NULL is returned.
*
* 如果出现内存不足、字符串长度为 0 或分隔符长度为 0
* 的情况，返回 NULL
*
* 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".
*
* 注意分隔符可以的是包含多个字符的字符串
*
* This version of the function is binary-safe but
* requires length arguments. sdssplit() is just the
* same function but for zero-terminated strings.
*
* 这个函数接受 len 参数，因此它是二进制安全的。
* （文档中提到的 sdssplit() 已废弃）
*
* T = O(N^2)
*/
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;

tokens = zmalloc(sizeof(sds)*slots);
if (tokens == NULL) return NULL;

if (len == 0) {
*count = 0;
return tokens;
}

// T = O(N^2)
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 */
// T = O(N)
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;
}
}

/*
* 释放 tokens 数组中 count 个 sds
*
* T = O(N^2)
*/
/* Free the result returned by sdssplitlen(), or do nothing if 'tokens' is NULL. */
void sdsfreesplitres(sds *tokens, int count) {
if (!tokens) return;
while(count--)
sdsfree(tokens[count]);
zfree(tokens);
}

/*
* 将长度为 len 的字符串 p 以带引号（quoted）的格式
* 追加到给定 sds 的末尾
*
* T = O(N)
*/
/* Append to the sds string "s" an escaped string representation where
* all the non-printable characters (tested with isprint()) are turned into
* escapes in the form "\n\r\a...." or "\x<hex-number>".
*
* After the call, the modified sds string is no longer valid and all the
* references must be substituted with the new pointer returned by the call. */
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. */
/*
* 如果 c 为十六进制符号的其中一个，返回正数
*
* T = O(1)
*/
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 a hex digit into an
* integer from 0 to 15 */
/*
* 将十六进制符号转换为 10 进制
*
* T = O(1)
*/
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:
*
* 将一行文本分割成多个参数，每个参数可以有以下的类编程语言 REPL 格式：
*
* foo bar "newline are supported\n" and "\xff\x00otherstuff"
*
* The number of arguments is stored into *argc, and an array
* of sds is returned.
*
* 参数的个数会保存在 *argc 中，函数返回一个 sds 数组。
*
* The caller should free the resulting array of sds strings with
* sdsfreesplitres().
*
* 调用者应该使用 sdsfreesplitres() 来释放函数返回的 sds 数组。
*
* Note that sdscatrepr() is able to convert back a string into
* a quoted string in the same format sdssplitargs() is able to parse.
*
* sdscatrepr() 可以将一个字符串转换为一个带引号（quoted）的字符串，
* 这个带引号的字符串可以被 sdssplitargs() 分析。
*
* 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'
*
* 即使输入出现空字符串， NULL ，或者输入带有未对应的括号，
* 函数都会将已成功处理的字符串先返回。
*
* 这个函数主要用于 config.c 中对配置文件进行分析。
* 例子：
*  sds *arr = sdssplitargs("timeout 10086\r\nport 123321\r\n");
* 会得出
*  arr[0] = "timeout"
*  arr[1] = "10086"
*  arr[2] = "port"
*  arr[3] = "123321"
*
* T = O(N^2)
*/
sds *sdssplitargs(const char *line, int *argc) {
const char *p = line;
char *current = NULL;
char **vector = NULL;

*argc = 0;
while(1) {

/* skip blanks */
// 跳过空白
// T = O(N)
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();

// T = O(N)
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 */
// T = O(N)
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.
*
* 将字符串 s 中，
* 所有在 from 中出现的字符，替换成 to 中的字符
*
* For instance: sdsmapchars(mystring, "ho", "01", 2)
* will have the effect of turning the string "hello" into "0ell1".
*
* 比如调用 sdsmapchars(mystring, "ho", "01", 2)
* 就会将 "hello" 转换为 "0ell1"
*
* The function returns the sds string pointer, that is always the same
* as the input pointer since no resize is needed.
* 因为无须对 sds 进行大小调整，
* 所以返回的 sds 输入的 sds 一样
*
* T = O(N^2)
*/
sds sdsmapchars(sds s, const char *from, const char *to, size_t setlen) {
size_t j, i, l = sdslen(s);

// 遍历输入字符串
for (j = 0; j < l; j++) {
// 遍历映射
for (i = 0; i < setlen; i++) {
// 替换字符串
if (s[j] == from[i]) {
s[j] = to[i];
break;
}
}
}
return s;
}

/* Join an array of C strings using the specified separator (also a C string).
* Returns the result as an sds string. */
sds sdsjoin(char **argv, int argc, char *sep) {
sds join = sdsempty();
int j;

for (j = 0; j < argc; j++) {
join = sdscat(join, argv[j]);
if (j != argc-1) join = sdscat(join,sep);
}
return join;
}

#ifdef SDS_TEST_MAIN
#include <stdio.h>
#include "testhelp.h"
#include "limits.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 = sdsnew("--");
x = sdscatfmt(x, "Hello %s World %I,%I--", "Hi!", LLONG_MIN,LLONG_MAX);
test_cond("sdscatfmt() seems working in the base case",
sdslen(x) == 60 &&
memcmp(x,"--Hello Hi! World -9223372036854775808,"
"9223372036854775807--",60) == 0)

sdsfree(x);
x = sdsnew("--");
x = sdscatfmt(x, "%u,%U--", UINT_MAX, ULLONG_MAX);
test_cond("sdscatfmt() seems working with unsigned numbers",
sdslen(x) == 35 &&
memcmp(x,"--4294967295,18446744073709551615--",35) == 0)

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

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

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

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

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

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

sdsfree(y);
y = sdsdup(x);
sdsrange(y,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)

sdsfree(y);
sdsfree(x);
x = sdsnewlen("\a\n\0foo\r",7);
y = sdscatrepr(sdsempty(),x,sdslen(x));
test_cond("sdscatrepr(...data...)",
memcmp(y,"\"\\a\\n\\x00foo\\r\"",15) == 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