问题描述
我需要使用node.js将内容从客户端发送到远程服务器。 内容可以是任何内容(用户可以上传任何文件)。
zlib.deflate
压缩每个内容,然后将其发送到远程。
我不希望进行多次往返并一次发送全部内容。
要在每个内容之间进行分隔,我需要一个不能在压缩字符串中使用的字符,因此我可以在遥控器上安全地对其进行分割。
解决方法
没有这样的字符或字符序列。 zlib压缩数据可以包含任何个字节序列。
您可以对zlib压缩数据进行编码以避免一个字节值,从而稍微扩展压缩数据。然后,您可以将该一个字节值用作分隔符。
示例代码:
// Example of encoding binary data to a sequence of bytes with no zero values.
// The result is expanded slightly. On average,assuming random input,the
// expansion is less than 0.1%. The maximum expansion is less than 14.3%,which
// is reached only if the input is a sequence of bytes all with value 255.
#include <stdio.h>
// Encode binary data read from in,to a sequence of byte values in 1..255
// written to out. There will be no zero byte values in the output. The
// encoding is decoding a flat (equiprobable) Huffman code of 255 symbols.
void no_zeros_encode(FILE *in,FILE *out) {
unsigned buf = 0;
int bits = 0,ch;
do {
if (bits < 8) {
ch = getc(in);
if (ch != EOF) {
buf += (unsigned)ch << bits;
bits += 8;
}
else if (bits == 0)
break;
}
if ((buf & 127) == 127) {
putc(255,out);
buf >>= 7;
bits -= 7;
}
else {
unsigned val = buf & 255;
buf >>= 8;
bits -= 8;
if (val < 127)
val++;
putc(val,out);
}
} while (ch != EOF);
}
// Decode a sequence of byte values made by no_zeros_encode() read from in,to
// the original binary data written to out. The decoding is encoding a flat
// Huffman code of 255 symbols. no_zeros_encode() will not generate any zero
// byte values in its output (that's the whole point),but if there are any
// zeros in the input to no_zeros_decode(),they are ignored.
void no_zeros_decode(FILE *in,ch;
while ((ch = getc(in)) != EOF)
if (ch != 0) { // could flag any zeros as an error
if (ch == 255) {
buf += 127 << bits;
bits += 7;
}
else {
if (ch <= 127)
ch--;
buf += (unsigned)ch << bits;
bits += 8;
}
if (bits >= 8) {
putc(buf,out);
buf >>= 8;
bits -= 8;
}
}
}