[英]Boost Asio incomplete write to socket
我正在使用 Boost Asio 編寫一個非常簡單的玩具鍵值存儲,並且發生了一些非常奇怪的事情。
基於字符串的協議是這樣的:
S <key> <value> // to set a key
G <key> // to get the key value
L // to list all key-value pairs
寫入是同步的,使用
boost::asio::write(socket_,boost::asio::buffer(resp, len));
其中 socket_ 是一個 boost::asio::ip::tcp::socket - 顯然,異步寫入故事不會改變。
問題是有時它不會將它應該寫入的所有字節寫入套接字,或者輸出以某種方式被破壞......
損壞列表 output 的示例(在本地主機上,使用 nc、echo 和 hexdump):
> echo S a 12 | nc localhost 5000
A
> echo S b 23 | nc localhost 5000
A
> echo L | nc localhost 5000 | hexdump -C
00000000 61 3a 20 31 32 3b 20 62 60 00 00 00 00 00 |a: 12; b`.....|
0000000e
> echo L | nc localhost 5000 | hexdump -C
00000000 61 3a 20 31 32 3b 20 62 3a 20 32 33 3b 20 |a: 12; b: 23; |
0000000e
我正在使用 Ubuntu 14.10 存儲庫中的 Boost 1.55。 遵循為客戶端服務的功能代碼。
提前感謝您的任何提示!
void ClientSession::handle_read(const boost::system::error_code& error, size_t bytes_transferred) {
if (!error) {
std::string cmd(data_, bytes_transferred);
cmd = trim_str(cmd);
const char* resp = NULL;
int len = 0;
switch(cmd.at(0)) {
case SET: {
std::size_t k_pos = cmd.find(" ") + 1;
std::size_t v_pos = cmd.find(" ", k_pos+1) + 1;
std::string key = trim_str(cmd.substr(k_pos, v_pos-3));
std::string value = trim_str(cmd.substr(v_pos, cmd.length()-1));
cout << "SET key " << key << ", value " << value << "*" <<endl;
kvs->db[key] = std::atoi(value.c_str());
resp = "A";
len = 1;
break;
}
case GET: {
std::size_t k_pos = cmd.find(" ") + 1;
std::string key = trim_str(cmd.substr(k_pos, cmd.length()));
cout << "GET key " << key << "*" << endl;
int value = kvs->db[key];
char str[5];
sprintf(str, "%d", value);
resp = (const char*) str;
len = strlen(resp);
break;
}
case LIST: {
ostringstream os;
for (std::map<string, int>::iterator iter = kvs->db.begin();
iter != kvs->db.end(); ++iter )
os << iter->first << ": " << iter->second << "; ";
cout << "list: " << os.str().c_str() << endl;
resp = os.str().c_str();
len = strlen(resp);
break;
}
case DEL: {
std::size_t k_pos = cmd.find(" ") + 1;
std::string key = trim_str(cmd.substr(k_pos, cmd.length()));
kvs->db.erase(key);
resp = "A";
len = 1;
break;
}
default: {
resp = "NACK.";
len = 5;
}
}
cout << "resp: " << resp << "*" << endl;
cout << "len: " << len << "*" << endl;
std::size_t written = boost::asio::write(socket_,
boost::asio::buffer(resp, len));
cout << "written: " << written << endl;
boost::system::error_code ignored_ec;
socket_.shutdown(boost::asio::ip::tcp::socket::shutdown_both, ignored_ec);
socket_.close();
} else
delete this;
至少你有未定義的行為,因為在case GET
懸空resp
指針:
{
// ...
char str[5];
resp = (const char*) str; // WHOOOOOOOOOOOPS
len = strlen(resp);
}
在case LIST
下完全相同:
{
std::ostringstream os;
// ....
resp = os.str().c_str(); // WHOOOOOOOOOOOPS
}
當你有Undefined Behavior時,所有關於程序的推理都不再有用。
修復這些問題(可能還有更多我沒有尋找的問題),然后重新測試。 在 valgrind 下運行。 使用static分析工具。
更新:單線程修復版本: https://gist.github.com/sehe/69379e17350fb718892f#comment-1428235
試運行 output:
$ for a in S{a..d}\ $RANDOM Gnonexisting L; do echo "$a -> $(netcat 127.0.0.1 5000 <<< "$a")"; done | nl
1 Sa 15936 -> A
2 Sb 3671 -> A
3 Sc 10550 -> A
4 Sd 7741 -> A
5 Gnonexisting -> 0
6 L -> 1: 1; 2: 2; a: 15936; asdasd: 0; b: 3671; c: 10550; d: 7741; nonexisting: 0;
handle_read
的代碼如下所示:
void ClientSession::handle_read(const boost::system::error_code& error, size_t bytes_transferred) {
if (!error) {
std::istringstream request(std::string(data_, bytes_transferred));
boost::asio::streambuf resp;
std::ostream os(&resp);
char cmd_char = 0;
std::string key;
int value;
if (request >> cmd_char) switch(cmd_char) {
case SET:
if (request >> key >> value)
kvs->db[key] = value;
os << "A";
break;
case GET:
if (request >> key)
os << kvs->db[key];
break;
case LIST:
for (auto const& e : kvs->db)
os << e.first << ": " << e.second << "; ";
break;
case DEL:
if (request >> key)
kvs->db.erase(key);
os << "A";
break;
default:
os << "NACK.";
}
cout << "resp: " << &resp << "*" << endl;
cout << "len: " << resp.size() << "*" << endl;
std::size_t written = boost::asio::write(socket_, resp);
cout << "written: " << written << endl;
boost::system::error_code ignored_ec;
socket_.shutdown(boost::asio::ip::tcp::socket::shutdown_both, ignored_ec);
socket_.close();
} else
delete this;
}
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