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90 lines
2.9 KiB
C
90 lines
2.9 KiB
C
// Copyright (c) 2021 Cesanta Software Limited
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// All rights reserved
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//
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// Example that demonstrates how to send a large responses with limited memory.
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// We're going to send a JSON array of many integer values, s_data.
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// The idea is to send a response in small chunks, and let the client request
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// the next chunk.
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// Periodically, s_data changes, which is tracked by s_version.
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// Client requests a range and a version, to ensure data integrity.
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//
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// 1. Start this server, type `make`
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// 2. Open http://localhost:8000 in your browser
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#include "mongoose.h"
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static const char *s_listen_on = "http://localhost:8000";
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static const char *s_root_dir = "web_root";
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#define DATA_SIZE 10000 // Total number of elements
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#define CHUNK_SIZE 100 // Max number returned in one API call
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static int s_data[DATA_SIZE]; // Simulate some complex big data
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static long s_version = 0; // Data "version"
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static long getparam(struct mg_http_message *hm, const char *json_path) {
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double dv = 0;
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mg_json_get_num(hm->body, json_path, &dv);
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return dv;
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}
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static size_t printdata(mg_pfn_t out, void *ptr, va_list *ap) {
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unsigned start = va_arg(*ap, unsigned);
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unsigned max = start + CHUNK_SIZE;
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const char *comma = "";
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size_t n = 0;
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if (max > DATA_SIZE) max = DATA_SIZE;
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while (start < max) {
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n += mg_xprintf(out, ptr, "%s%d", comma, s_data[start]);
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comma = ",";
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start++;
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}
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return n;
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}
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static void fn(struct mg_connection *c, int ev, void *ev_data) {
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if (ev == MG_EV_HTTP_MSG) {
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struct mg_http_message *hm = ev_data;
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if (mg_match(hm->uri, mg_str("/api/data"), NULL)) {
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const char *headers = "content-type: text/json\r\n";
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long start = getparam(hm, "$.start");
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long version = getparam(hm, "$.version");
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MG_DEBUG(("%.*s", (int) hm->body.len, hm->body.buf));
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if (version > 0 && version != s_version) {
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// Version mismatch: s_data has changed while client fetches it
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// Tell client to restart
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mg_http_reply(c, 200, headers, "{%m:%m, %m:%ld}", MG_ESC("error"),
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MG_ESC("wrong version"), MG_ESC("version"), version);
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} else {
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// Return data, up to CHUNK_SIZE elements
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mg_http_reply(c, 200, headers, "{%m:%ld,%m:%ld,%m:[%M]}",
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MG_ESC("version"), s_version, MG_ESC("start"), start,
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MG_ESC("data"), printdata, start);
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}
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} else {
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struct mg_http_serve_opts opts = {0};
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opts.root_dir = s_root_dir;
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mg_http_serve_dir(c, hm, &opts);
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}
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}
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}
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static void timer_fn(void *arg) {
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for (int i = 0; i < DATA_SIZE; i++) {
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s_data[i] = rand();
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}
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s_version++;
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(void) arg;
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}
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int main(void) {
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struct mg_mgr mgr;
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mg_mgr_init(&mgr);
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srand(time(NULL));
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mg_timer_add(&mgr, 5000, MG_TIMER_REPEAT | MG_TIMER_RUN_NOW, timer_fn, NULL);
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mg_http_listen(&mgr, s_listen_on, fn, NULL);
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MG_INFO(("Listening on %s", s_listen_on));
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for (;;) mg_mgr_poll(&mgr, 1000);
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mg_mgr_free(&mgr);
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return 0;
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}
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