Android: ADB(Android Debug Bridge)

http://blog.chinaunix.net/u1/38994/showart_1807376.html
http://blog.chinaunix.net/u1/38994/showart.php?id=1818785
http://blog.chinaunix.net/u1/38994/showart_1907747.html

system/core/adb/OVERVIEW.TXT
system/core/adb/SERVICES.TXT
system/core/adb/protocol.txt

Host: Server + Client
TARGET: Daemon(adbd) + Service

When use adb command, it is actually a client talk to server on host. The server handles "packet" between host/target. There is a smartsocket(PORT 5037) provide a easy way to use adb connection to target for its service. Just send "4 byte len + service name". Or you can just use following function to manipulate the smartsocket:

adb_connect
adb_read
adb_write
adb_close