How to correctly response to HTTP request - c++

Question

I am trying to create simple server which will repond to every HTTP request with 200 OK. I write code below, but when I called the server with Postman I ended with wrong result. If I do NOT call closesocket(clientSocket), Postman is waiting infinitely long for response with Sending requst.... I i do call closesocket(clientSocket), Postman shows Error: socket hang up.
What I have to do to correctly close connection?
void main()
{
std::cout << "Start..." << std::endl;;
int port = 54000;
// Initialize WinSock
WSAData data;
WORD ver = MAKEWORD(2, 2);
int wsResult = WSAStartup(ver, &data);
if (wsResult != 0)
{
std::cout << "Can't start Winsock, Err #" << wsResult << std::endl;
return;
}
// Create socket
SOCKET sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock == INVALID_SOCKET)
{
std::cout << "Can't create socket, Err #" << WSAGetLastError() << std::endl;
WSACleanup();
return;
}
// Bind the ip address and port to a socket
sockaddr_in hint;
hint.sin_family = AF_INET;
hint.sin_port = htons(port);
hint.sin_addr.S_un.S_addr = INADDR_ANY;
bind(sock, (sockaddr*)&hint, sizeof(hint));
listen(sock, SOMAXCONN);
// Wait for a connection
sockaddr_in client;
int clientSize = sizeof(client);
// While loop: accept and echo message back to client
char buf[16384];
while (true)
{
SOCKET clientSocket = accept(sock, (sockaddr*)&client, &clientSize);
//print(client);
ZeroMemory(buf, 16384);
// Wait for client to send data
int bytesReceived = recv(clientSocket, buf, 16384, 0);
if (bytesReceived == SOCKET_ERROR)
{
std::cout << "Error in recv(). Quitting" << std::endl;
break;
}
const char* reply =
"HTTP/1.1 200 OK\n"
"Content-Type: text/html\n"
"Content-Length: 0\n"
"Keep - Alive: timeout=1, max=1\n"
"Accept-Ranges: bytes\n"
"Connection: close\n";
send(clientSocket, reply, strlen(reply), 0);
//closesocket(clientSocket);
} |
}
edit. Edited code. I corrected line endings, added better check for recv result and also I am checking number of sent bytes (and yes, all bytes are send). I also tried to add shutdown function, but result is still the same - infinite waiting or error. When I try to add do / while section, I will stuck in infinite waiting for another request. Do you have any other advice?
void main()
{
std::cout << "Start..." << std::endl;;
int port = 54000;
// Initialize WinSock
WSAData data;
WORD ver = MAKEWORD(2, 2);
int wsResult = WSAStartup(ver, &data);
if (wsResult != 0)
{
std::cout << "Can't start Winsock, Err #" << wsResult << std::endl;
return;
}
// Create socket
SOCKET sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock == INVALID_SOCKET)
{
std::cout << "Can't create socket, Err #" << WSAGetLastError() << std::endl;
WSACleanup();
return;
}
// Bind the ip address and port to a socket
sockaddr_in hint;
hint.sin_family = AF_INET;
hint.sin_port = htons(port);
hint.sin_addr.S_un.S_addr = INADDR_ANY;
bind(sock, (sockaddr*)&hint, sizeof(hint));
listen(sock, SOMAXCONN);
// Wait for a connection
sockaddr_in client;
int clientSize = sizeof(client);
// While loop: accept and echo message back to client
char buf[16384];
while (true)
{
SOCKET clientSocket = accept(sock, (sockaddr*)&client, &clientSize);
//print(client);
ZeroMemory(buf, 16384);
// Wait for client to send data
//do {
bytesReceived = recv(clientSocket, buf, 16384, 0);
if (bytesReceived > 0)
{
std::cout << std::string(buf, 0, bytesReceived) << std::endl;
}
else if (bytesReceived == 0)
{
std::cout << "Connection closed" << std::endl;
}
else
{
std::cout << "Error in recv(). Quitting = " << WSAGetLastError() << std::endl;
break;
}
//} while (bytesReceived > 0);
const char* reply =
"HTTP/1.1 200 OK\r\n"
"Content-Type: text/html\r\n"
"Content-Length: 0\r\n"
"Accept-Ranges: bytes\r\n"
"Connection: close";
bytesSent = send(clientSocket, reply, strlen(reply), 0);
if (bytesSent < 0)
{
std::cout << "Send failed = " << WSAGetLastError() << std::endl;
}
std::cout << "Sent: " << bytesSent << " (" << strlen(reply) << ")" << std::endl;
shutdown(clientSocket, SD_BOTH);
closesocket(clientSocket);
} |
}

Answer 1

const char* reply =
"HTTP/1.1 200 OK\n"
...
"Keep - Alive: timeout=1, max=1\n"
...
"Connection: close\n";
send(clientSocket, reply, strlen(reply), 0);
This is not a valid HTTP response for multiple reasons:
The line ending should be \r\n not \n.
The HTTP header should end with an additional \r\n (i.e. empty line). This means the HTTP response you send is not complete and thus Postman hangs on waiting for the rest.
The Keep - Alive header has not the valid syntax for a HTTP header. The field name is not allowed to contain spaces.
Apart from that,
send is not guaranteed to send everything in the given buffer, i.e. you should check the return code.
A Keep-Alive header makes no sense at all if Connection: close is used.
Note that HTTP is not an ad-hoc protocol but an actual standard. Implementations should follow the standard and thus the developers would need to study the actual standard and not blindly rely on (wrong) assumptions of how things might work. Even if it works with some client it might not work with another one, since some clients adhere more to the standard while others are more tolerant regarding errors.

Answer 2

There are multiple problems with the shown code.
int bytesReceived = recv(clientSocket, buf, 16384, 0);
On any TCP socket, HTTP or not, you get no guarantees whatsoever that whatever the other side of the socket sent you, it will get returned in a single recv() call.
If, for example, the client sent you the following HTTP request:
GET / HTTP/1.0<CR><LF>
Host: localhost<CR><LF>
<CR><LF>
Nobody is going to guarantee you that this recv() will return this entire thing to you. recv() could, for example, return only the "GET" part, and return the value of 3 to indicate that only 3 bytes were received. You are required to call recv() as many times as necessary to receive the complete message. The 2nd call to recv() could, theoretically, return " /" and the value of 2 to indicate that two more bytes were received.
You cannot completely ignore the return code from recv(), which tells you what was actually read, and you will need to implement appropriate logic to keep recv()ing until you received the entire message. Your code needs to understand that an HTTP message consists of a message line, an arbitrary list of headers, then a single blank line, all terminated by <CR><LF>, or "\r\n", and keep trying until it receives the complete message.
const char* reply =
"HTTP/1.1 200 OK\n"
"Content-Type: text/html\n"
"Content-Length: 0\n"
"Keep - Alive: timeout=1, max=1\n"
"Accept-Ranges: bytes\n"
"Connection: close\n";
HTTP uses <CR><LF> as the end of line terminator, all of these should be \r\n.
"Keep - Alive:" is not a valid HTTP header name. Header names cannot contain spaces.
A blank line, a single \r\n, should follow the last HTTP header. It is missing fom your response. Even though you're closing the socket immediately, without a well-formed HTTP response message the client can rightfully conclude that the HTTP server is faulty and did not send a valid response.
send(clientSocket, reply, strlen(reply), 0);
Like with recv(), you are not guaranteed that send() will transmit the requested number of bytes. Just like with recv() you must check the return value of send() to see how many bytes were sent, and then try again to send the remaining part of the message, if there's any, until you send the entire message.
You must fix all of these problems in order to properly implement HTTP over TCP.