1 files changed, 146 insertions, 0 deletions
diff --git a/url_handler/handler.cpp b/url_handler/handler.cpp
new file mode 100644
index 0000000..b202d5b
--- /dev/null
+++ b/url_handler/handler.cpp
@@ -0,0 +1,146 @@
+#include <fstream>
+#include <filesystem>
+#include <unordered_map>
+#include <mutex>
+#include <thread>
+#include <memory>
+#include <cstdlib>
+#include "handler.h"
+
+using namespace std;
+
+
+static string shell_escape(const string &str) {
+	string res;
+	res.reserve(str.size() + 16);
+	res += '\'';
+
+	for (char c : str) {
+		if (c == '\'') res += "'\"'\"'";
+		else res += c;
+	}
+
+	res += '\'';
+	return res;
+}
+
+static string read_file(const string &fname) {
+	ifstream f(fname);
+	if (!f) return {};
+
+	string contents;
+	char buffer[4096];
+	while (true) {
+		f.read(buffer, sizeof buffer);
+		contents.insert(contents.size(), buffer, f.gcount());
+		if (!f) break;
+	}
+
+	return contents;
+}
+
+static string download_url(const string &url) {
+	string tempdir_name = "/tmp/tmp.url_handler.XXXXXX";
+	if (mkdtemp(tempdir_name.data()) == nullptr) {
+		perror("mkdtemp");
+		return {};
+	}
+
+	string tempfile_name = tempdir_name + "/file";
+
+	string cmd = "curl -sL " + shell_escape(url) + " >" + shell_escape(tempfile_name);
+	// fprintf(stderr, "cmd = %s\n", cmd.data());
+
+	system(cmd.data());
+
+	string response = read_file(tempfile_name);
+	filesystem::remove_all(tempdir_name);
+
+	fprintf(stderr, "Received response for url '%s'\n", url.data());
+
+	return response;
+}
+
+struct State {
+	string url;
+
+	thread download_thread;
+
+	// mutex protects 'response' and 'response_present'; the download thread
+	// sets 'response_present' to true and simultaneously 'response' to the
+	// right value. After 'response_present' can be observed to be true by the
+	// main thread, the download thread doesn't touch anything anymore.
+	mutex res_mt;
+	bool response_present = false;
+	string response;
+
+	// owned by host thread
+	size_t rescur = 0;
+};
+
+static unordered_map<uint32_t, unique_ptr<State>> state_map;
+
+uint16_t handle_icmp(uint32_t source_addr, const array<uint8_t, 16> &payload) {
+	auto state_it = state_map.find(source_addr);
+	if (state_it == state_map.end()) {
+		state_it = state_map.emplace(source_addr, make_unique<State>()).first;
+	}
+	State &state = *state_it->second;
+
+	switch (payload[0]) {
+		case 100:  // url fragment
+			// fprintf(stderr, "msg(%u): url fragment\n", source_addr);
+			{
+				lock_guard<mutex> guard(state.res_mt);
+				if (state.response_present) return 0;
+			}
+			for (size_t i = 1; i < 16; i++) {
+				if (payload[i] == '\0') {
+					fprintf(stderr, "URL received: <%s>\n", state.url.data());
+					state.download_thread = thread([&state]() {
+						string response = download_url(state.url);
+
+						{
+							lock_guard<mutex> guard(state.res_mt);
+							state.response = move(response);
+							state.response_present = true;
+						}
+
+						// fprintf(stderr, "[dlth] response received: <%s>\n", state.response.data());
+					});
+					break;
+				}
+				state.url.push_back(payload[i]);
+			}
+			return 1;
+
+		case 101: {  // query whether response is ready
+			// fprintf(stderr, "msg(%u): ready query\n", source_addr);
+			lock_guard<mutex> guard(state.res_mt);
+			return state.response_present ? 1 : 0;
+		}
+
+		case 102: {  // get response
+			// fprintf(stderr, "msg(%u): get_response\n", source_addr);
+			{
+				lock_guard<mutex> guard(state.res_mt);
+				if (!state.response_present) return 0;
+			}
+
+			uint16_t retval = 0;
+			for (size_t i = 0; i < 2 && state.rescur < state.response.size(); i++) {
+				retval |= (uint16_t)state.response[state.rescur] << (8 * i);
+				state.rescur++;
+			}
+
+			if (state.rescur == state.response.size()) {
+				state.download_thread.join();  // should already have exited
+				state_map.erase(state_it);
+			}
+			// fprintf(stderr, "  -> retval %016X\n", (unsigned)retval);
+			return retval;
+		}
+	}
+
+	return 0;
+}