I am writing a simple HTTP server in C from the CodeCrafter challenge Build your Own HTTP server. The request i am addressing is the following:
The tester will then send two HTTP requests to your server.
First, the tester will send a GET request, with a random string as the path:
$ curl -v http://localhost:4221/abcdefg
Your server must respond to this request with a 404 response:
HTTP/1.1 404 Not Found\r\n\r\n
Then, the tester will send a GET request, with the path /:
$ curl -v http://localhost:4221
Your server must respond to this request with a 200 response:
HTTP/1.1 200 OK\r\n\r\n
To perform reading/writing i have used the Rio package written in the Computer Systems: A Programmer's perspective. The reading functions seem to work fine, as the client request is read correctly, however, the writing is not working.
The test is giving me back the following error:
remote: [tester::#IH0] Sent bytes: "GET /mango HTTP/1.1\r\nHost: localhost:4221\r\n\r\n"
remote: [your_program] Client connected
remote: [tester::#IH0] Failed to read response:
remote: [tester::#IH0] Received: "" (no content received)
remote: [tester::#IH0] ^ error
remote: [tester::#IH0] Error: Expected: HTTP-version, Received: ""
remote: [tester::#IH0] Test failed
The complete code:
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
# define BUF_SIZE 8192
# define MAX_LINE 4096
/* struct that defines an internal buffer where to read/write avoiding frequent traps to OS */
typedef struct {
int rio_fd;
int rio_cnt;
char buf[BUF_SIZE];
char *rio_bufptr;
} rio_t;
/* initialize rio_t internal buffer */
void rio_init (rio_t *riot, int fd) {
riot->rio_fd = fd;
riot->rio_cnt = 0;
riot->rio_bufptr = riot->buf;
}
/* buffered version of read(), reads from the internal buffer rio_t -> buf until is not completely consumed */
ssize_t rio_read (rio_t *riot, char *usrbuf, size_t n) {
int cnt;
while (riot->rio_cnt <= 0) {
riot->rio_cnt = read(riot->rio_fd, riot->buf, sizeof(riot->buf));
if (riot->rio_cnt < 0) {
if (errno != EINTR) { // sighandler
return -1;
}
} else if (riot->rio_cnt == 0) { // EOF
return 0;
} else {
// reset buffer
riot->rio_bufptr = riot->buf;
}
}
cnt = n;
if (riot->rio_cnt < n) {
cnt = riot->rio_cnt;
}
memcpy(usrbuf, riot->rio_bufptr, cnt);
riot->rio_bufptr += cnt;
riot->rio_cnt -= cnt;
return cnt;
}
/* improved version of read, avoids short count, reads until requested bytes are read (n) or EOF */
size_t rio_readnb (rio_t *riot, void *usrbuf, size_t n) {
size_t nleft = n;
ssize_t nread;
char *buf = usrbuf;
while (nleft > 0) {
nread = rio_read(riot, buf, nleft);
if (nread < 0) {
if (errno == EINTR) { // interrupted by sighandler, call read() again
nread = 0;
} else {
return -1; // error
}
} else if (nread == 0) { // EOF
break;
}
nleft -= nread;
buf += nread;
}
return (n - nleft);
}
/* buffered write, used to avoid dealing with short counts encountered in network applications due to network delay etc. */
ssize_t rio_writen (int fd, void *buf, size_t n) {
size_t nleft = n;
ssize_t nwritten;
char *bufp = buf;
printf("%s\n", bufp);
while (nleft > 0) {
if ((nwritten = write(fd, bufp, nleft)) <= 0) {
if (errno == EINTR) {
printf("EINTR.\n");
nwritten = 0;
} else {
printf("Write Error.\n");
return - 1;
}
}
nleft -= nwritten;
bufp += nwritten;
}
return n;
}
void parseRequest (char *requestBuf, char *responseBuf) {
char path[MAX_LINE];
int startPath = 0;
int i_request = 0;
int i_path = 0;
while (requestBuf[i_request] != '\0' && requestBuf[i_request] != '\r' && requestBuf[i_request] != '\n') {
if (requestBuf[i_request] == ' ') {
if (startPath) {
break; // end of path
}
} else {
if (requestBuf[i_request] == '/') startPath = 1;
if (startPath) path[i_path++] = requestBuf[i_request];
}
i_request++;
}
// null terminate
path[i_path] = '\0';
if (strcmp(path, "/") == 0) {
strcpy(responseBuf, "HTTP/1.1 200 OK\r\n\r\n");
}
else {
strcpy(responseBuf, "HTTP/1.1 404 Not Found\r\n\r\n");
}
}
int main () {
// Disable output buffering
setbuf(stdout, NULL);
setbuf(stderr, NULL);
// internal buffer to read from client
rio_t riot;
// number of bytes read
size_t n;
// buffer to read request
char bufRequest[MAX_LINE];
char bufResponse[MAX_LINE];
int server_fd, client_addr_len, conn_fd;
struct sockaddr_in client_addr;
server_fd = socket(AF_INET, SOCK_STREAM, 0);
if (server_fd == -1) {
printf("Socket creation failed: %s...\n", strerror(errno));
return 1;
}
// SO_REUSEADDR ensures that we don't run into 'Address already in use' errors
int reuse = 1;
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR, &reuse, sizeof(reuse)) < 0) {
printf("SO_REUSEADDR failed: %s \n", strerror(errno));
return 1;
}
struct sockaddr_in serv_addr = { .sin_family = AF_INET ,
.sin_port = htons(4221),
.sin_addr = { htonl(INADDR_ANY) },
};
if (bind(server_fd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) != 0) {
printf("Bind failed: %s \n", strerror(errno));
return 1;
}
int connection_backlog = 5;
if (listen(server_fd, connection_backlog) != 0) {
printf("Listen failed: %s \n", strerror(errno));
return 1;
}
printf("Waiting for a client to connect...\n");
client_addr_len = sizeof(client_addr);
conn_fd = accept(server_fd, (struct sockaddr *) &client_addr, &client_addr_len);
if (conn_fd == -1) {
printf("Client not connected, exiting...");
return 1;
}
printf("Client connected\n");
// initialize internal buffer to read from conn_fd
rio_init(&riot, conn_fd);
// read request into bufRequest
while ((n = rio_readnb(&riot, bufRequest, MAX_LINE - 1)) != 0)
printf("%d bytes read by the server.\n", n);
if (n < 0) {
printf("Reading failed...\n");
return 1;
}
printf ("The request path is: %s\n", bufRequest);
parseRequest(bufRequest, bufResponse);
ssize_t nres = rio_writen(conn_fd, bufResponse, strlen(bufResponse));
close(conn_fd);
close(server_fd);
return 0;
}
The principal error is that your code waits for the connection to close and only then starts processing the request.
This is not how HTTP works. The connection is kept open all the time. You need to find the end-of-request marker (\r\n\r\n) without waiting for the connection to close.
This means testing for it each time read returns a positive number of bytes.
Don't forget that read may return in the middle of receiving \r\n\r\n, so when you restart the search next time read returns, don't check only the new bytes.
Note, the \r\n\r\n technicaly is the end of the headers, not the end of a full request (which may include a body). It is a simplification for the purposes of the task at hand.