Окончательный вариант кода

main.cpp

@@ -4,6 +4,8 @@
 #include "text.h"
 #include "svg.h"
 #include <curl/curl.h>
+#include <sstream>
+#include <string>
 using namespace std;
 
 struct Input {
@@ -33,13 +35,24 @@ Input input_data(istream& in, bool prompt) {
     return inp;
 }
 
-int main(int argc, char* argv[]) {
-    curl_global_init(CURL_GLOBAL_ALL);
-    if (argc > 1) {
+size_t
+write_data(void* items, size_t item_size, size_t item_count, void* ctx) {
+    stringstream* buffer = reinterpret_cast<stringstream*>(ctx);
+    size_t data_size = item_size * item_count;
+    (*buffer).write(reinterpret_cast<const char*>(items), data_size);
+    return data_size;
+}
+
+Input
+download(const string& adress){
+    stringstream buffer;
     CURL* curl = curl_easy_init();
     if(curl) {
+
         CURLcode res;
-            curl_easy_setopt(curl, CURLOPT_URL, argv[1]);
+        curl_easy_setopt(curl, CURLOPT_URL, adress.c_str());
+        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
+        curl_easy_setopt(curl, CURLOPT_WRITEDATA, &buffer);
         res = curl_easy_perform(curl);
         if (res != CURLE_OK){
             cerr << curl_easy_strerror(res);
@@ -47,9 +60,20 @@ int main(int argc, char* argv[]) {
         }
         curl_easy_cleanup(curl);
     }
+
+    return input_data(buffer, false);
 }
+int main(int argc, char* argv[]) {
+    Input input;
+    if (argc > 1) {
+        input = download(argv[1]);
+    } else {
+        input = input_data(cin, true);
+    }
+
     auto in = input_data(cin, true);
     auto bins = make_histogram(in.numbers, in.bin_count);
     show_histogram_svg(bins);
     return 0;
 }
+