web服务器的一个问题

[pigeon0411]

在做简单的HTTP SERVER时，用TCP传输简单的HTTP信息头，
抓包发现TCP传输到客户端总是会在数据后自动加一个NUL，请问是怎么回事？
因为被多添加了一个NUL，所以浏览器端总是显示不出图片来。
下面标注为红色的地方：

TCP - Transport Control Protocol
Source Port: 80 http [34-35]
Destination Port: 2094 nbx-au [36-37]
Sequence Number: 70528 [38-41]
Ack Number: 1782436267 [42-45]
TCP Offset: 5 (20 bytes) [46 Mask 0xF0]
Reserved: %0000 [46 Mask 0x0F]
TCP Flags: %00011000 ...AP... [47]
0... .... (No Congestion Window Reduction)
.0.. .... (No ECN-Echo)
..0. .... (No Urgent pointer)
...1 .... Ack
.... 1... Push
.... .0.. (No Reset)
.... ..0. (No SYN)
.... ...0 (No FIN)

Window: 3778 [48-49]
TCP Checksum: 0x5353 [50-51]
Urgent Pointer: 0 [52-53]
No TCP Options
HTTP - Hyper Text Transfer Protocol
HTTP Version: HTTP/1.0 [54-61]
HTTP Status: 200 [62-64]
HTTP Reason: OK<CR><LF> [66-67]
Date: Mon, 24 Nov 2003 01:24:17 GMT<CR><LF> [71-104]
Server: microHttp/1.0 Zlgmcu Corporation<CR><LF> [108-146]
Accept-Ranges: bytes<CR><LF> [150-168]
Connection: Keep-Close<CR><LF> [172-192]
Content-Type: image/bmp<CR><LF><CR><LF><NUL> [196-217]
FCS - Frame Check Sequence
FCS: 0x3F3DB3CF Calculated

[pigeon0411]

顶起来