From 74d0652125b16416b2fa52f85e6e4833f33302a3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ond=C5=99ej=20Fiala?= <temp.xanomes@volny.cz>
Date: Sat, 2 Jul 2022 06:59:16 +0200
Subject: [PATCH] gmnlm: prompt for redirects, make max redirects configurable

Redirects are currently the most reliable way of tracking users in
geminispace. To mitigate this, similar approach as used with server
certificates is adopted -- users are prompted by default, but this
can be easily overriden with a command line flag if convenience is
preferred to tracking-resistance.
---
 doc/gmnlm.scd |  3 +++
 src/gmnlm.c   | 50 +++++++++++++++++++++++++++++++++++++++++++++-----
 2 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/doc/gmnlm.scd b/doc/gmnlm.scd
index e0a368f..2c7eaef 100644
--- a/doc/gmnlm.scd
+++ b/doc/gmnlm.scd
@@ -22,6 +22,9 @@ gmnlm - Gemini line-mode browser
 *-P*
 	Disable pagination.
 
+*-R* _redirs_
+	Sets the maximum number of redirects, negative argument disables limit.
+
 *-U*
 	Disable conservative use of Unicode symbols to render Gemini layout
 	features.
diff --git a/src/gmnlm.c b/src/gmnlm.c
index 53ec416..884796c 100644
--- a/src/gmnlm.c
+++ b/src/gmnlm.c
@@ -33,9 +33,13 @@ struct history {
 	struct history *prev, *next;
 };
 
+#define REDIRS_UNLIMITED -1
+#define REDIRS_ASK -2
+
 struct browser {
 	bool pagination, unicode;
 	int max_width;
+	int max_redirs;
 	struct gemini_options opts;
 	struct gemini_tofu tofu;
 	enum tofu_action tofu_mode;
@@ -92,7 +96,7 @@ const char *help_msg =
 static void
 usage(const char *argv_0)
 {
-	fprintf(stderr, "usage: %s [-PU] [-j mode] [-W width] [gemini://...]\n", argv_0);
+	fprintf(stderr, "usage: %s [-PU] [-j mode] [-R redirs] [-W width] [gemini://...]\n", argv_0);
 }
 
 static void
@@ -368,7 +372,7 @@ do_requests(struct browser *browser, struct gemini_response *resp)
 	int nredir = 0;
 	bool requesting = true;
 	enum gemini_result res;
-		
+
 	char *scheme;
 	CURLUcode uc = curl_url_get(browser->url,
 		CURLUPART_SCHEME, &scheme, 0);
@@ -483,9 +487,40 @@ do_requests(struct browser *browser, struct gemini_response *resp)
 			free(new_url);
 			break;
 		case GEMINI_STATUS_CLASS_REDIRECT:
-			if (++nredir >= 5) {
+			if (browser->max_redirs == REDIRS_ASK) {
+again:
+				fprintf(browser->tty,
+					"The host %s is redirecting to:\n"
+					"%s\n\n"
+					"[f]ollow redirect; [a]bort\n"
+					"=> ", host, resp->meta);
+
+				size_t sz = 0;
+				char *line = NULL;
+				if (getline(&line, &sz, browser->tty) == -1) {
+					free(line);
+					requesting = false;
+					break;
+				}
+				if (line[1] != '\n') {
+					free(line);
+					goto again;
+				}
+
+				char c = line[0];
+				free(line);
+
+				if (c == 'a') {
+					requesting = false;
+					break;
+				} else if (c != 'f') {
+					goto again;
+				}
+			} else if (browser->max_redirs != REDIRS_UNLIMITED
+					&& ++nredir >= browser->max_redirs) {
 				requesting = false;
-				fprintf(stderr, "Error: maximum redirects (5) exceeded\n");
+				fprintf(stderr, "Error: maximum redirects (%d) exceeded\n",
+					browser->max_redirs);
 				break;
 			}
 			set_url(browser, resp->meta, NULL);
@@ -1185,10 +1220,11 @@ main(int argc, char *argv[])
 		.url = curl_url(),
 		.tty = fopen("/dev/tty", "w+"),
 		.meta = NULL,
+		.max_redirs = REDIRS_ASK,
 	};
 
 	int c;
-	while ((c = getopt(argc, argv, "hj:PUW:")) != -1) {
+	while ((c = getopt(argc, argv, "hj:PR:UW:")) != -1) {
 		switch (c) {
 		case 'h':
 			usage(argv[0]);
@@ -1208,6 +1244,10 @@ main(int argc, char *argv[])
 		case 'P':
 			browser.pagination = false;
 			break;
+		case 'R':;
+			int mr = strtol(optarg, NULL, 10);
+			browser.max_redirs = mr < 0 ? REDIRS_UNLIMITED : mr;
+			break;
 		case 'U':
 			browser.unicode = false;
 			break;