Well, in addition to that, I advise you to check the socket validity first
( by uv_is_active) because in some rare cases, the OS may send some portion
of buffer, that means the return code is positive but not as equal to
buffer size. So, do both of them.
On Wed, Jul 22, 2020, 20:42 WILLIAM n SUSIE ENGELKE <engelk...@bellsouth.net>
wrote:
> Reza - good advice. To check connection status, I try to write to the
> socket and then check if the return code (# bytes written) is < 0 -
> correct? Or is there another status check that you are referring to?
>
> On Wednesday, July 22, 2020, 10:44:13 AM CDT, Reza Mahdi <
> rezamahd...@gmail.com> wrote:
>
>
> In fact, you may not relay on other program's behavior. Your app must be
> failed tolerant. So, after any event that may occur, check the status.
>
> Suppose the connection get dropped by a wire disconnect....
>
> Get ready for anything
>
> On Wed, Jul 22, 2020, 20:09 Bill Engelke <engelk...@bellsouth.net> wrote:
>
> Thanks for the feedback. A follow-up question: My heartbeat runs only
> once a minute (or even less); if I would like to let the server close the
> connection each time (and re-establish it the next time), could I just let
> it close the connection, and not change that?
>
> On Tuesday, July 21, 2020 at 10:01:57 AM UTC-5, Reza Mahdi wrote:
>
> Well, you are using HTTP 1.0
> In this version, after the server sends the response, it will close the
> connection.
> You may use HTTP 1.1 with "Connection: keep-alive" header, to signal the
> server not to close the connection.
>
> On Tue, Jul 21, 2020, 19:24 Bill Engelke <enge...@bellsouth.net> wrote:
>
> I need code that will send a "heartbeat" to a web service (say, once per
> minute), and receive a response. This works fine with a browser, so I know
> the server is reachable and responding correctly. I have tried a vast
> number of different ways of doing this using libuv and c code, and so far,
> partial success at best. I have been able to connect to the server and send
> a request; but only the first request would work, and further sends would
> not make it to the server. In my most recent attempts, even the connection
> request stopped working. I don't know if the problem is my incorrect use of
> libuv, or something in the networking part that I don't understand. I have
> put the code into a single app for testing below; can anyone offer any
> suggestions??
>
> ```
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <uv.h>
> #include <string.h>
> #include <unistd.h>
>
> typedef struct {
> uv_write_t req;
> uv_buf_t buf;
> } write_req_t;
>
> static uv_tcp_t* socket_central;
> static struct sockaddr_in central_dest;
>
> static void alloc_buffer(uv_handle_t* handle, size_t suggested_size,
> uv_buf_t* buf) {
> buf->base = malloc(suggested_size);
> buf->len = suggested_size;
> }
>
> uv_loop_t *loop;
>
> ///// Callback for after TCP stream is closed //////////////////
> void on_close(uv_handle_t * handle)
> {
> printf("uv close triggered\n");
> }
>
> // process response from central server
> void proc_central_response(uv_stream_t *central, ssize_t nread, const
> uv_buf_t *buf)
> {
> printf("RESPONSE from Central Control; nread=%li\n",nread);
>
> printf("---------------------------------------------------------------\n");
> if (nread > 0) {
> printf("buf='%s'\n",buf->base);
>
> printf("---------------------------------------------------------------\n");
> }
> if (nread < 0) {
> if (nread != UV_EOF)
> fprintf(stderr, "Read error %s\n", uv_err_name(nread));
> free(buf->base);
> uv_close((uv_handle_t*) central, on_close);
> return;
> }
> //uv_close((uv_handle_t*) central, on_close);
> free(buf->base);
> return;
> }
>
> // now connected; send http POST
> void on_central_connect(uv_connect_t* connection, int status)
> {
> uv_stream_t* stream;
> uv_write_t write_req;
> printf("Connected to Central Contro, status = %il\n",status);
> if (status < 0) {
> fprintf(stderr, "Error in in connecting to Central Control %s\n",
> uv_strerror(status));
> // error!
> return;
> }
> printf(" - - - - Connect to Central Control - - - ;\n");
> // get the handle to the stream passed in connection
> stream = connection->handle;
>
> // make ready to receive response from Central
> uv_read_start((uv_stream_t*) stream, alloc_buffer,
> proc_central_response);
>
> // Now, prepare a heartbeat message to send to Central Control
>
> struct timeval timeout;
> char message[1024];
> timeout.tv_sec = 10; // if Central Host doesn't respond, we ignore
> timeout.tv_usec = 0; // and will try again after the pause time
> char tbuf[30];
> struct timeval tv;
> time_t curtime;
>
> char mytoken[75];
> strcpy(mytoken,"T12345XYZ"); // hard code this for now
>
> gettimeofday(&tv, NULL);
> curtime = tv.tv_sec;
> strftime(tbuf, 30, "%m-%d-%Y-%T.",localtime(&curtime));
> printf("Heartbeat TOD: '%s' %ld\n",tbuf,tv.tv_usec);
> // write message to go to host
> // message contains identity token and time stamp
> sprintf(message,"POST /apikey/%s-%s HTTP/1.0\r\n\r\n",mytoken,tbuf);
> uv_buf_t buf = uv_buf_init(message,strlen(message));
> int r1 = uv_write(&write_req, stream, &buf, 1, NULL);
> }
>
> void heartbeat(void *arg) {
> while(1==1)
> {
> printf("alloc socket\n");
> socket_central = (uv_tcp_t*)malloc(sizeof(uv_tcp_t));\
> printf("tcp init\n");
> uv_tcp_init(loop, socket_central);
> printf("alloc connection\n");
> uv_connect_t* connect = (uv_connect_t*)malloc(sizeof(uv_connect_t));
> uv_ip4_addr("192.168.1.67", 4000, ¢ral_dest);
> printf("CONNECT TO CENTRAL\n");
> uv_tcp_connect(connect, socket_central, (const struct
> sockaddr*)¢ral_dest, on_central_connect);
> printf("CONNECTION REQUEST DONE\n");
> printf("sleep start\n");
> sleep(5);
> printf("sleep done\n");
> }
> }
>
> int main() {
> printf("start\n");
> loop = uv_default_loop();
>
> printf("alloc socket\n");
> socket_central = (uv_tcp_t*)malloc(sizeof(uv_tcp_t));\
> printf("tcp init\n");
> uv_tcp_init(loop, socket_central);
>
> uv_thread_t hb_id;
> printf("start thread\n");
> uv_thread_create(&hb_id, heartbeat, NULL);
> printf("past thread start\n");
>
> uv_run(loop, UV_RUN_DEFAULT);
>
> sleep(10);
>
> printf("Now quitting.\n");
>
> uv_loop_close(loop);
> //free(loop);
> return 0;
> }
> ```
>
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