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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