/* This function is used to iterate through all the zipmap elements.
*
* 这个函数用于遍历 zipmap 的所有元素。
*
* In the first call the first argument is the pointer to the zipmap + 1.
*
* 在第一次调用这个函数时， zm 参数的值为 zipmap + 1
* （也即是，指向 zipmap 的第一个节点）
*
* In the next calls what zipmapNext returns is used as first argument.
*
* 而在之后的调用中， zm 参数的值为之前调用 zipmapNext 时所返回的值。
*
* Example:
*
* 示例：
*
* unsigned char *i = zipmapRewind(my_zipmap);
* while((i = zipmapNext(i,&key,&klen,&value,&vlen)) != NULL) {
* printf("%d bytes key at $p\n", klen, key);
* printf("%d bytes value at $p\n", vlen, value);
* }
*
* T = O(1)
*/
unsigned char *zipmapNext(unsigned char *zm, unsigned char **key, unsigned int *klen, unsigned char **value, unsigned int *vlen) {
// 已到达列表末尾，停止迭代
if (zm[0] == ZIPMAP_END) return NULL;
// 取出键，并保存到 key 参数中
if (key) {
*key = zm;
*klen = zipmapDecodeLength(zm);
*key += ZIPMAP_LEN_BYTES(*klen);
}
// 越过键
zm += zipmapRawKeyLength(zm);
// 取出值，并保存到 value 参数中
if (value) {
*value = zm+1;
*vlen = zipmapDecodeLength(zm);
*value += ZIPMAP_LEN_BYTES(*vlen);
}
// 越过值
zm += zipmapRawValueLength(zm);
// 返回指向下一节点的指针
return zm;
}
/* This function is used to iterate through all the zipmap elements.
* In the first call the first argument is the pointer to the zipmap + 1.
* In the next calls what zipmapNext returns is used as first argument.
* Example:
*
* unsigned char *i = zipmapRewind(my_zipmap);
* while((i = zipmapNext(i,&key,&klen,&value,&vlen)) != NULL) {
* printf("%d bytes key at $p\n", klen, key);
* printf("%d bytes value at $p\n", vlen, value);
* }
*/
unsigned char *zipmapNext(unsigned char *zm, unsigned char **key, unsigned int *klen, unsigned char **value, unsigned int *vlen) {
if (zm[0] == ZIPMAP_END) return NULL;
if (key) {
*key = zm;
*klen = zipmapDecodeLength(zm);
*key += ZIPMAP_LEN_BYTES(*klen);
}
zm += zipmapRawKeyLength(zm);
if (value) {
*value = zm+1;
*vlen = zipmapDecodeLength(zm);
*value += ZIPMAP_LEN_BYTES(*vlen);
}
zm += zipmapRawValueLength(zm);
return zm;
}
/* Search a key and retrieve the pointer and len of the associated value.
* If the key is found the function returns 1, otherwise 0. */
int zipmapGet(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned char **value, unsigned int *vlen) {
unsigned char *p;
if ((p = zipmapLookupRaw(zm,key,klen,NULL)) == NULL) return 0;
p += zipmapRawKeyLength(p);
*vlen = zipmapDecodeLength(p);
*value = p + ZIPMAP_LEN_BYTES(*vlen) + 1;
return 1;
}
/* zipmap的迭代器式遍历函数，典型用法如下：
*
* unsigned char *i = zipmapRewind(my_zipmap);
* while((i = zipmapNext(i,&key,&klen,&value,&vlen)) != NULL) {
* printf("%d bytes key at $p\n", klen, key);
* printf("%d bytes value at $p\n", vlen, value);
* }
*/
unsigned char *zipmapNext(unsigned char *zm, unsigned char **key, unsigned int *klen, unsigned char **value, unsigned int *vlen) {
// 如果达到尾部，直接返回NULL
if (zm[0] == ZIPMAP_END) return NULL;
// 获取key
if (key) {
*key = zm;
*klen = zipmapDecodeLength(zm);
*key += ZIPMAP_LEN_BYTES(*klen);
}
zm += zipmapRawKeyLength(zm);
// 获取value
if (value) {
// +1是为了跳过free字段，该字段占用一个字节
*value = zm+1;
*vlen = zipmapDecodeLength(zm);
*value += ZIPMAP_LEN_BYTES(*vlen);
}
// 此时zm指向下一个键值对的首地址
zm += zipmapRawValueLength(zm);
return zm;
}
/* Encode the length 'l' writing it in 'p'. If p is NULL it just returns
* the amount of bytes required to encode such a length. */
static unsigned int zipmapEncodeLength(unsigned char *p, unsigned int len) {
if (p == NULL) {
return ZIPMAP_LEN_BYTES(len);
} else {
if (len < ZIPMAP_BIGLEN) {
p[0] = len;
return 1;
} else {
p[0] = ZIPMAP_BIGLEN;
memcpy(p+1,&len,sizeof(len));
return 1+sizeof(len);
}
}
}
/* 将长度len编码到p指针指向的内存空间 */
static unsigned int zipmapEncodeLength(unsigned char *p, unsigned int len) {
if (p == NULL) {
return ZIPMAP_LEN_BYTES(len);
} else {
if (len < ZIPMAP_BIGLEN) {
// 长度小于254，只需要1个字节表示
p[0] = len;
return 1;
} else {
// 长度大于等于254，第一个字节赋值为254，接下来的4歌字节才是真正的长度值
p[0] = ZIPMAP_BIGLEN;
memcpy(p+1,&len,sizeof(len));
memrev32ifbe(p+1);
return 1+sizeof(len);
}
}
}
/* Search a key and retrieve the pointer and len of the associated value.
* If the key is found the function returns 1, otherwise 0.
*
* 在 zipmap 中按 key 进行查找，
* 将值的指针保存到 *value 中，并将值的长度保存到 *vlen 中。
*
* 成功找到值时函数返回 1 ，没找到则返回 0 。
*
* T = O(N^2)
*/
int zipmapGet(unsigned char *zm, unsigned char *key, unsigned int klen, unsigned char **value, unsigned int *vlen) {
unsigned char *p;
// 在 zipmap 中按 key 查找
// 没找到直接返回 0
// T = O(N^2)
if ((p = zipmapLookupRaw(zm,key,klen,NULL)) == NULL) return 0;
// 越过键，指向值
p += zipmapRawKeyLength(p);
// 取出值的长度
*vlen = zipmapDecodeLength(p);
// 将 *value 指向值， +1 为越过 <free> 属性
*value = p + ZIPMAP_LEN_BYTES(*vlen) + 1;
// 找到，返回 1
return 1;
}
/* Search a key and retrieve the pointer and len of the associated value.
* If the key is found the function returns 1, otherwise 0. */
int zipmapXGet(unsigned char **zm, unsigned char *key, unsigned int klen,
unsigned char **value, unsigned int *vlen, unsigned int timestamp) {
unsigned char *p;
if ((p = zipmapXLookupRaw(*zm,key,klen,NULL,NULL)) == NULL) return 0;
p += zipmapRawKeyLength(p);
unsigned int ts = *(unsigned int*)p;
p += sizeof(unsigned int);
*vlen = zipmapDecodeLength(p);
*value = p + ZIPMAP_LEN_BYTES(*vlen) + 1;
if (ts < timestamp) {
*vlen = 0;
*value = NULL;
return 0;
}
return 1;
}
/* Encode the length 'l' writing it in 'p'. If p is NULL it just returns
* the amount of bytes required to encode such a length.
*
* 编码长度 l ，将它写入到 p 中，然后返回编码 l 所需的字节数。
* 如果 p 是 NULL ，那么函数只返回编码 l 所需的字节数，不进行任何写入。
*
* T = O(1)
*/
static unsigned int zipmapEncodeLength(unsigned char *p, unsigned int len) {
// 只返回编码所需的字节数
if (p == NULL) {
return ZIPMAP_LEN_BYTES(len);
// 编码，并写入，然后返回编码所需的字节数
} else {
if (len < ZIPMAP_BIGLEN) {
p[0] = len;
return 1;
} else {
p[0] = ZIPMAP_BIGLEN;
memcpy(p+1,&len,sizeof(len));
memrev32ifbe(p+1);
return 1+sizeof(len);
}
}
}