Nginx源码分析-数据结构之字符串string
Nginx 中封装了自定义的字符串类型和一系列字符串操作函数，定义在 ngx_string.c/h 中。
自定义字符串类型
ngx_str_t 是 nginx 的自定义字符串类型，包含一个字符串长度和不以 ‘\0’ 结尾的字符串。
typedef struct {
size_t len; //字符串长度
u_char *data; //字符串数据
} ngx_str_t;
自定义字符串的初始化和赋值是以宏的形式定义的，需要注意的是，两个宏中的参数 str 需要传一个常量字符串：
#define ngx_string(str) { sizeof(str) - 1, (u_char *) str } //此宏与下面 ngx_str_set 宏中str 需要传一个常量字符串
#define ngx_null_string { 0, NULL }
#define ngx_str_set(str, text) \
(str)->len = sizeof(text) - 1; (str)->data = (u_char *) text
#define ngx_str_null(str) (str)->len = 0; (str)->data = NULL
字符串操作函数
nginx 中封装了很多字符串操作函数，下面按其用途分类介绍并详细分析其中的一些重点函数：
字符串大小写转换
#define ngx_tolower(c) (u_char) ((c >= 'A' && c <= 'Z') ? (c | 0x20) : c) //转为小写
#define ngx_toupper(c) (u_char) ((c >= 'a' && c <= 'z') ? (c & ~0x20) : c) //转为大写
//将字符串转为小写
void ngx_strlow(u_char *dst, u_char *src, size_t n);
计算字符串长度
#define ngx_strlen(s) strlen((const char *) s)
//在n范围内计算字符串长度
size_t ngx_strnlen(u_char *p, size_t n);
在 n 的范围内计算字符串长度其实就是遍历字符串，直到出现 ‘\0’ 或到 n 的位置：
//在n范围内计算字符串长度
size_t
ngx_strnlen(u_char *p, size_t n)
{
size_t i;
for (i = 0; i < n; i++) {
if (p[i] == '\0') {
return i;
}
}
return n;
}
字符串包含
#define ngx_strstr(s1, s2) strstr((const char *) s1, (const char *) s2) //字符串包含字符串
#define ngx_strchr(s1, c) strchr((const char *) s1, (int) c) //字符串包含字符
//字符串某个范围内第一次出现字符c 的位置，没有返回NULL
static ngx_inline u_char * ngx_strlchr(u_char *p, u_char *last, u_char c)
u_char *ngx_strnstr(u_char *s1, char *s2, size_t n);
u_char *ngx_strstrn(u_char *s1, char *s2, size_t n);
//不区分大小写
u_char *ngx_strcasestrn(u_char *s1, char *s2, size_t n);
u_char *ngx_strlcasestrn(u_char *s1, u_char *last, u_char *s2, size_t n);
我们来看一下 ngx_strnstr 的实现，ngx_strstrn, ngx_strcasestrn, ngx_strlcasestrn 都与之类似。这个函数会先比较与 s2 字符串的第一个字符相等的位置，然后调用 strncmp 比较字符串是否相同。
u_char *
ngx_strnstr(u_char *s1, char *s2, size_t len)
{
u_char c1, c2;
size_t n;
c2 = *(u_char *) s2++;
n = ngx_strlen(s2);
do {
//先查找到第一个字符相等地位置，然后通过strncmp比较函数来判断字符串是否相同
do {
if (len-- == 0) {
return NULL;
}
c1 = *s1++;
if (c1 == 0) {
return NULL;
}
} while (c1 != c2);
if (n > len) {
return NULL;
}
} while (ngx_strncmp(s1, (u_char *) s2, n) != 0);
return --s1;
}
字符串拷贝与初始化
#define ngx_memzero(buf, n) (void) memset(buf, 0, n) //内存置0
#define ngx_memset(buf, c, n) (void) memset(buf, c, n) //内存置值c
//为防止编译器死区消除优化策略(dead store elimination optimization)，不要优化掉memset
void ngx_explicit_memzero(void *buf, size_t n);
//这两个区别在于返回值，ngx_memcpy 返回拷贝完的首地址，ngx_cpymem 返回拷贝完的结尾位置
#define ngx_memcpy(dst, src, n) (void) memcpy(dst, src, n)
#define ngx_cpymem(dst, src, n) (((u_char *) memcpy(dst, src, n)) + (n))
static ngx_inline u_char * ngx_copy(u_char *dst, u_char *src, size_t len)
//这两个区别与 ngx_memcpy 和 ngx_cpymem 相同，ngx_memmove 返回 dst 首地址，ngx_movemem 返回 dst 尾地址
#define ngx_memmove(dst, src, n) (void) memmove(dst, src, n)
#define ngx_movemem(dst, src, n) (((u_char *) memmove(dst, src, n)) + (n))
u_char *ngx_cpystrn(u_char *dst, u_char *src, size_t n);
//从内存池中申请内存并拷贝字符串，不包含结尾'\0' 字符
u_char *ngx_pstrdup(ngx_pool_t *pool, ngx_str_t *src);
字符串比较
#define ngx_strncmp(s1, s2, n) strncmp((const char *) s1, (const char *) s2, n) //字符串比较
#define ngx_strcmp(s1, s2) strcmp((const char *) s1, (const char *) s2) //字符串比较
ngx_int_t ngx_strcasecmp(u_char *s1, u_char *s2);
ngx_int_t ngx_strncasecmp(u_char *s1, u_char *s2, size_t n);
//字符串比较，从右侧字符开始
//这个函数与下一个函数ngx_rstrncasecmp都是从右侧开始比较，
//相等返回0，不相等返回从右侧开始第一个不相等字符的差值，
//ngx_rstrncasecmp是不区分大小写的比较
ngx_int_t ngx_rstrncmp(u_char *s1, u_char *s2, size_t n);
ngx_int_t ngx_rstrncasecmp(u_char *s1, u_char *s2, size_t n);
//给定两块内存及长度比较大小
ngx_int_t ngx_memn2cmp(u_char *s1, u_char *s2, size_t n1, size_t n2);
//给不同应用定制的字符串比较函数
ngx_int_t ngx_dns_strcmp(u_char *s1, u_char *s2);
ngx_int_t ngx_filename_cmp(u_char *s1, u_char *s2, size_t n);
格式化输出
u_char * ngx_cdecl ngx_sprintf(u_char *buf, const char *fmt, ...);
u_char * ngx_cdecl ngx_snprintf(u_char *buf, size_t max, const char *fmt, ...);
u_char * ngx_cdecl ngx_slprintf(u_char *buf, u_char *last, const char *fmt,
...);
u_char *ngx_vslprintf(u_char *buf, u_char *last, const char *fmt, va_list args);
#define ngx_vsnprintf(buf, max, fmt, args) \
ngx_vslprintf(buf, buf + (max), fmt, args)
格式化输出支持的输出格式在注释中有说明：
/*
* supported formats:
* %[0][width][x][X]O off_t
* %[0][width]T time_t
* %[0][width][u][x|X]z ssize_t/size_t
* %[0][width][u][x|X]d int/u_int
* %[0][width][u][x|X]l long
* %[0][width|m][u][x|X]i ngx_int_t/ngx_uint_t
* %[0][width][u][x|X]D int32_t/uint32_t
* %[0][width][u][x|X]L int64_t/uint64_t
* %[0][width|m][u][x|X]A ngx_atomic_int_t/ngx_atomic_uint_t
* %[0][width][.width]f double, max valid number fits to %18.15f
* %P ngx_pid_t
* %M ngx_msec_t
* %r rlim_t
* %p void *
* %[x|X]V ngx_str_t *
* %[x|X]v ngx_variable_value_t *
* %[x|X]s null-terminated string
* %*[x|X]s length and string
* %Z '\0'
* %N '\n'
* %c char
* %% %
*
* reserved:
* %t ptrdiff_t
* %S null-terminated wchar string
* %C wchar
*/
ngx_sprintf, ngx_snprintf, ngx_slprintf 通过调用 ngx_vslprintf 来实现字符串格式化，下面我的来看一下 ngx_vslprintf 的实现：
//格式化字符串输出，返回写入后的位置
u_char *
ngx_vslprintf(u_char *buf, u_char *last, const char *fmt, va_list args)
{
u_char *p, zero;
int d;
double f;
size_t slen;
int64_t i64;
uint64_t ui64, frac;
ngx_msec_t ms;
ngx_uint_t width, sign, hex, max_width, frac_width, scale, n;
ngx_str_t *v;
ngx_variable_value_t *vv;
while (*fmt && buf < last) {
/*
* "buf < last" means that we could copy at least one character:
* the plain character, "%%", "%c", and minus without the checking
*/
//当出现% 字符时进行格式判断，否则直接拷贝
if (*fmt == '%') {
i64 = 0;
ui64 = 0;
//各标志位初始化
zero = (u_char) ((*++fmt == '0') ? '0' : ' '); //占位字符为0还是空格，第一个格式控制信息
width = 0; //宽度
sign = 1; //是否有符号
hex = 0; //是否是十六进制
max_width = 0; //最大宽度
frac_width = 0; //小数点后宽度
slen = (size_t) -1; //字符串长度
//第二个格式控制信息，计算宽度
while (*fmt >= '0' && *fmt <= '9') {
width = width * 10 + (*fmt++ - '0');
}
//其它格式控制信息，是否无符号，最大宽度，十六进制，小数点位数，字符串长度，字符串长度由后面可变参数中获取
for ( ;; ) {
switch (*fmt) {
case 'u':
sign = 0;
fmt++;
continue;
case 'm':
max_width = 1;
fmt++;
continue;
case 'X':
hex = 2;
sign = 0;
fmt++;
continue;
case 'x':
hex = 1;
sign = 0;
fmt++;
continue;
case '.':
fmt++;
while (*fmt >= '0' && *fmt <= '9') {
frac_width = frac_width * 10 + (*fmt++ - '0');
}
break;
case '*':
slen = va_arg(args, size_t);
fmt++;
continue;
default:
break;
}
break;
}
switch (*fmt) {
case 'V':
v = va_arg(args, ngx_str_t *);
buf = ngx_sprintf_str(buf, last, v->data, v->len, hex);
fmt++;
continue;
case 'v':
vv = va_arg(args, ngx_variable_value_t *);
buf = ngx_sprintf_str(buf, last, vv->data, vv->len, hex);
fmt++;
continue;
case 's':
p = va_arg(args, u_char *);
buf = ngx_sprintf_str(buf, last, p, slen, hex);
fmt++;
continue;
case 'O':
i64 = (int64_t) va_arg(args, off_t);
sign = 1;
break;
case 'P':
i64 = (int64_t) va_arg(args, ngx_pid_t);
sign = 1;
break;
case 'T':
i64 = (int64_t) va_arg(args, time_t);
sign = 1;
break;
case 'M':
ms = (ngx_msec_t) va_arg(args, ngx_msec_t);
if ((ngx_msec_int_t) ms == -1) {
sign = 1;
i64 = -1;
} else {
sign = 0;
ui64 = (uint64_t) ms;
}
break;
case 'z':
if (sign) {
i64 = (int64_t) va_arg(args, ssize_t);
} else {
ui64 = (uint64_t) va_arg(args, size_t);
}
break;
case 'i':
if (sign) {
i64 = (int64_t) va_arg(args, ngx_int_t);
} else {
ui64 = (uint64_t) va_arg(args, ngx_uint_t);
}
if (max_width) {
width = NGX_INT_T_LEN;
}
break;
case 'd':
if (sign) {
i64 = (int64_t) va_arg(args, int);
} else {
ui64 = (uint64_t) va_arg(args, u_int);
}
break;
case 'l':
if (sign) {
i64 = (int64_t) va_arg(args, long);
} else {
ui64 = (uint64_t) va_arg(args, u_long);
}
break;
case 'D':
if (sign) {
i64 = (int64_t) va_arg(args, int32_t);
} else {
ui64 = (uint64_t) va_arg(args, uint32_t);
}
break;
case 'L':
if (sign) {
i64 = va_arg(args, int64_t);
} else {
ui64 = va_arg(args, uint64_t);
}
break;
case 'A':
if (sign) {
i64 = (int64_t) va_arg(args, ngx_atomic_int_t);
} else {
ui64 = (uint64_t) va_arg(args, ngx_atomic_uint_t);
}
if (max_width) {
width = NGX_ATOMIC_T_LEN;
}
break;
case 'f':
//浮点数单独做处理
f = va_arg(args, double);
if (f < 0) {
*buf++ = '-';
f = -f;
}
ui64 = (int64_t) f; //取浮点数整数部分
frac = 0;
if (frac_width) {
scale = 1;
for (n = frac_width; n; n--) {
scale *= 10;
}
//取小数点后的位置，+0.5 用于做四舍五入
frac = (uint64_t) ((f - (double) ui64) * scale + 0.5);
//如果四舍五入后小数点后为0, 则整数部分+1
if (frac == scale) {
ui64++;
frac = 0;
}
}
//写入整数部分
buf = ngx_sprintf_num(buf, last, ui64, zero, 0, width);
//写入小数部分
if (frac_width) {
if (buf < last) {
*buf++ = '.';
}
buf = ngx_sprintf_num(buf, last, frac, '0', 0, frac_width);
}
fmt++;
continue;
#if !(NGX_WIN32)
case 'r':
i64 = (int64_t) va_arg(args, rlim_t);
sign = 1;
break;
#endif
case 'p':
//十六进制显示指针
ui64 = (uintptr_t) va_arg(args, void *);
hex = 2;
sign = 0;
zero = '0';
width = 2 * sizeof(void *);
break;
case 'c':
//写入一个字符
d = va_arg(args, int);
*buf++ = (u_char) (d & 0xff);
fmt++;
continue;
case 'Z':
//写入\0
*buf++ = '\0';
fmt++;
continue;
case 'N':
//写入换行，windows下为\r\n，其它为\n
#if (NGX_WIN32)
*buf++ = CR;
if (buf < last) {
*buf++ = LF;
}
#else
*buf++ = LF;
#endif
fmt++;
continue;
case '%':
//写入%
*buf++ = '%';
fmt++;
continue;
default:
*buf++ = *fmt++;
continue;
}
if (sign) {
if (i64 < 0) {
*buf++ = '-';
ui64 = (uint64_t) -i64;
} else {
ui64 = (uint64_t) i64;
}
}
//按指定格式写入数字
buf = ngx_sprintf_num(buf, last, ui64, zero, hex, width);
fmt++;
} else {
*buf++ = *fmt++;
}
}
return buf;
}
static u_char *
ngx_sprintf_num(u_char *buf, u_char *last, uint64_t ui64, u_char zero,
ngx_uint_t hexadecimal, ngx_uint_t width)
{
u_char *p, temp[NGX_INT64_LEN + 1];
/*
* we need temp[NGX_INT64_LEN] only,
* but icc issues the warning
*/
size_t len;
uint32_t ui32;
static u_char hex[] = "0123456789abcdef";
static u_char HEX[] = "0123456789ABCDEF";
//先将格式化后的数据放到temp中
p = temp + NGX_INT64_LEN;
if (hexadecimal == 0) {
//分开成32位还是64位因为两者除法算法不同，区分开可以更快
if (ui64 <= (uint64_t) NGX_MAX_UINT32_VALUE) {
/*
* To divide 64-bit numbers and to find remainders
* on the x86 platform gcc and icc call the libc functions
* [u]divdi3() and [u]moddi3(), they call another function
* in its turn. On FreeBSD it is the qdivrem() function,
* its source code is about 170 lines of the code.
* The glibc counterpart is about 150 lines of the code.
*
* For 32-bit numbers and some divisors gcc and icc use
* a inlined multiplication and shifts. For example,
* unsigned "i32 / 10" is compiled to
*
* (i32 * 0xCCCCCCCD) >> 35
*/
ui32 = (uint32_t) ui64;
do {
*--p = (u_char) (ui32 % 10 + '0');
} while (ui32 /= 10);
} else {
do {
*--p = (u_char) (ui64 % 10 + '0');
} while (ui64 /= 10);
}
} else if (hexadecimal == 1) {
do {
/* the "(uint32_t)" cast disables the BCC's warning */
*--p = hex[(uint32_t) (ui64 & 0xf)];
} while (ui64 >>= 4);
} else { /* hexadecimal == 2 */
do {
/* the "(uint32_t)" cast disables the BCC's warning */
*--p = HEX[(uint32_t) (ui64 & 0xf)];
} while (ui64 >>= 4);
}
/* zero or space padding */
len = (temp + NGX_INT64_LEN) - p;
//不够宽度在前面补0 或空格
while (len++ < width && buf < last) {
*buf++ = zero;
}
/* number safe copy */
//计算数字占用的长度，拷贝到buf 并返回拷贝后的位置
len = (temp + NGX_INT64_LEN) - p;
if (buf + len > last) {
len = last - buf;
}
return ngx_cpymem(buf, p, len);
}
//格式化输出，hexadecimal: 0-默认输出，1-十六进制小写输出，2-十六进制大写输出
//返回写入buf 后的位置
static u_char *
ngx_sprintf_str(u_char *buf, u_char *last, u_char *src, size_t len,
ngx_uint_t hexadecimal)
{
static u_char hex[] = "0123456789abcdef";
static u_char HEX[] = "0123456789ABCDEF";
if (hexadecimal == 0) {
if (len == (size_t) -1) {
while (*src && buf < last) {
*buf++ = *src++;
}
} else {
len = ngx_min((size_t) (last - buf), len);
buf = ngx_cpymem(buf, src, len);
}
} else if (hexadecimal == 1) {
if (len == (size_t) -1) {
while (*src && buf < last - 1) {
*buf++ = hex[*src >> 4];
*buf++ = hex[*src++ & 0xf];
}
} else {
while (len-- && buf < last - 1) {
*buf++ = hex[*src >> 4];
*buf++ = hex[*src++ & 0xf];
}
}
} else { /* hexadecimal == 2 */
if (len == (size_t) -1) {
while (*src && buf < last - 1) {
*buf++ = HEX[*src >> 4];
*buf++ = HEX[*src++ & 0xf];
}
} else {
while (len-- && buf < last - 1) {
*buf++ = HEX[*src >> 4];
*buf++ = HEX[*src++ & 0xf];
}
}
}
return buf;
}
字符串与其它类型转换
ngx_int_t ngx_atoi(u_char *line, size_t n); //字符串转int
ngx_int_t ngx_atofp(u_char *line, size_t n, size_t point); //float字符串转int，n-取字符串长度，point-小数点后取的位数
ssize_t ngx_atosz(u_char *line, size_t n); //字符串转size类型，与ngx_atoi基本相同，只对于最大值范围不同
off_t ngx_atoof(u_char *line, size_t n); //字符串转off_t
time_t ngx_atotm(u_char *line, size_t n); //字符串转time_t
ngx_int_t ngx_hextoi(u_char *line, size_t n); //十六进制字符串转int
//将src的值转为十六进制放到dst中
u_char *ngx_hex_dump(u_char *dst, u_char *src, size_t len);
下面是 ngx_atoi 实现代码，其它函数与之类似。
ngx_int_t
ngx_atoi(u_char *line, size_t n)
{
ngx_int_t value, cutoff, cutlim;
if (n == 0) {
return NGX_ERROR;
}
//NGX_MAX_INT_T_VALUE 最大的int 值
cutoff = NGX_MAX_INT_T_VALUE / 10;
cutlim = NGX_MAX_INT_T_VALUE % 10;
for (value = 0; n--; line++) {
if (*line < '0' || *line > '9') {
return NGX_ERROR;
}
//这里是关于int 最大值的判断
if (value >= cutoff && (value > cutoff || *line - '0' > cutlim)) {
return NGX_ERROR;
}
value = value * 10 + (*line - '0');
}
return value;
}
字符串编解码
Base64 编解码相关，URL 的base64与普通base64算法基本类似，只是URL里有三个字符 ‘+’, ‘/’, ‘=’有特殊含义，因此在 URL 的 base64 算法中这三个字符会被替换掉，’+’ 替换为 ‘-‘，’/’ 替换为 ‘_‘，’=’ 省略，详见RFC4684-Base16, Base32, 和 Base64 数据编码-中文翻译
//计算base64编解码后的长度
#define ngx_base64_encoded_length(len) (((len + 2) / 3) * 4)
#define ngx_base64_decoded_length(len) (((len + 3) / 4) * 3)
void ngx_encode_base64(ngx_str_t *dst, ngx_str_t *src);
void ngx_encode_base64url(ngx_str_t *dst, ngx_str_t *src);
ngx_int_t ngx_decode_base64(ngx_str_t *dst, ngx_str_t *src);
ngx_int_t ngx_decode_base64url(ngx_str_t *dst, ngx_str_t *src);
utf8 编解码：
uint32_t ngx_utf8_decode(u_char **p, size_t n);
size_t ngx_utf8_length(u_char *p, size_t n);
u_char *ngx_utf8_cpystrn(u_char *dst, u_char *src, size_t n, size_t len);
uri 转码相关：
//这几个函数都使用位来标识字符是否需要转码
uintptr_t ngx_escape_uri(u_char *dst, u_char *src, size_t size,
ngx_uint_t type);
void ngx_unescape_uri(u_char **dst, u_char **src, size_t size, ngx_uint_t type);
uintptr_t ngx_escape_html(u_char *dst, u_char *src, size_t size);
uintptr_t ngx_escape_json(u_char *dst, u_char *src, size_t size);
其它函数
//字符串红黑树的插入与查找，红黑树节点应为ngx_str_node_t结构
void ngx_str_rbtree_insert_value(ngx_rbtree_node_t *temp,
ngx_rbtree_node_t *node, ngx_rbtree_node_t *sentinel); //插入
ngx_str_node_t *ngx_str_rbtree_lookup(ngx_rbtree_t *rbtree, ngx_str_t *name,
uint32_t hash); //查找
//排序，base- 列表基地址，n- 列表排序个数，size- 列表元素大小，cmp- 排序比较函数
//这个排序用的是插入排序，稳定排序
void ngx_sort(void *base, size_t n, size_t size,
ngx_int_t (*cmp)(const void *, const void *));
#define ngx_qsort qsort
ngx_sort 使用插入排序，详见排序算法之-插入排序，下面是其实现代码：
void
ngx_sort(void *base, size_t n, size_t size,
ngx_int_t (*cmp)(const void *, const void *))
{
u_char *p1, *p2, *p;
//申请一个临时变量
p = ngx_alloc(size, ngx_cycle->log);
if (p == NULL) {
return;
}
//使用插入排序
//这里从第 2 个元素开始遍历列表元素
for (p1 = (u_char *) base + size;
p1 < (u_char *) base + n * size;
p1 += size)
{
ngx_memcpy(p, p1, size);
//与已排序好的元素进行比较，找到合适的位置
for (p2 = p1;
p2 > (u_char *) base && cmp(p2 - size, p) > 0;
p2 -= size)
{
ngx_memcpy(p2, p2 - size, size);
}
//插入元素到已排序列表
ngx_memcpy(p2, p, size);
}
ngx_free(p);
}
nginx源码基于nginx-1.22.0版本
参考：
nginx平台初探
nginx开发_字符串操作函数
Nginx源码分析 - 基础数据结构篇 - 字符串结构 ngx_string.c（08）
- 版权声明：
