mongoose/examples/huge-response/main.c
2022-04-12 14:14:55 +01:00

88 lines
3.0 KiB
C

// Copyright (c) 2021 Cesanta Software Limited
// All rights reserved
//
// Example that demonstrates how to send a large responses with limited memory.
// We're going to send a JSON array of many integer values, s_data.
// The idea is to send a response in small chunks, and let the client request
// the next chunk.
// Periodically, s_data changes, which is tracked by s_version.
// Client requests a range and a version, to ensure data integrity.
//
// 1. Start this server, type `make`
// 2. Open http://localhost:8000 in your browser
#include "mjson.h"
#include "mongoose.h"
static const char *s_listen_on = "http://localhost:8000";
static const char *s_root_dir = "web_root";
#define DATA_SIZE 10000 // Total number of elements
#define CHUNK_SIZE 1000 // Max number returned in one API call
static int s_data[DATA_SIZE]; // Simulate some complex big data
static unsigned s_version = 0; // Data "version"
static double getparam(struct mg_http_message *hm, const char *json_path) {
double dv = 0;
mjson_get_number(hm->body.ptr, hm->body.len, json_path, &dv);
return dv;
}
static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
if (ev == MG_EV_HTTP_MSG) {
struct mg_http_message *hm = ev_data;
if (mg_http_match_uri(hm, "/api/data")) {
unsigned start = getparam(hm, "$.start");
unsigned version = getparam(hm, "$.version");
char *response = NULL;
if (version > 0 && version != s_version) {
// Version mismatch: s_data has changed while client fetches it
// Tell client to restart
response = mjson_aprintf("{%Q:%Q, %Q:%u}", "error", "wrong version",
"version", version);
} else {
// Return data, up to CHUNK_SIZE elements
unsigned max = start + CHUNK_SIZE;
const char *comma = "";
if (max > DATA_SIZE) max = DATA_SIZE;
mjson_printf(mjson_print_dynamic_buf, &response, "{%Q:%u,%Q:%u,%Q:[",
"version", s_version, "start", start, "data");
while (start < max) {
mjson_printf(mjson_print_dynamic_buf, &response, "%s%d", comma,
s_data[start]);
comma = ",";
start++;
}
mjson_printf(mjson_print_dynamic_buf, &response, "]}");
}
mg_http_reply(c, 200, "Content-Type: text/json\r\n", "%s", response);
free(response);
} else {
struct mg_http_serve_opts opts = {0};
opts.root_dir = s_root_dir;
mg_http_serve_dir(c, hm, &opts);
}
}
(void) fn_data;
}
static void timer_fn(void *arg) {
for (int i = 0; i < DATA_SIZE; i++) {
s_data[i] = rand();
}
s_version++;
(void) arg;
}
int main(void) {
struct mg_mgr mgr;
mg_mgr_init(&mgr);
srand(time(NULL));
mg_timer_add(&mgr, 1000, MG_TIMER_REPEAT | MG_TIMER_RUN_NOW, timer_fn, NULL);
mg_http_listen(&mgr, s_listen_on, fn, NULL);
MG_INFO(("Listening on %s", s_listen_on));
for (;;) mg_mgr_poll(&mgr, 1000);
mg_mgr_free(&mgr);
return 0;
}