add DNS configuration for TCP fallback.

Signed-off-by: Jason Volk <jason@zemos.net>

conduwuit-example.toml

@@ -491,6 +491,9 @@ allow_profile_lookup_federation_requests = true
 # Number of retries after a timeout.
 #dns_attempts = 5
 
+# Fallback to TCP on DNS errors. Set this to false if unsupported by nameserver.
+#dns_tcp_fallback = true
+
 # Enable to query all nameservers until the domain is found. Referred to as "trust_negative_responses" in hickory_resolver.
 # This can avoid useless DNS queries if the first nameserver responds with NXDOMAIN or an empty NOERROR response.
 #

src/config/mod.rs

@@ -98,6 +98,8 @@ pub struct Config {
 	pub dns_attempts: u16,
 	#[serde(default = "default_dns_timeout")]
 	pub dns_timeout: u64,
+	#[serde(default = "true_fn")]
+	pub dns_tcp_fallback: bool,
 	#[serde(default)]
 	pub query_all_nameservers: bool,
 	#[serde(default = "default_max_request_size")]
@@ -494,6 +496,7 @@ impl fmt::Display for Config {
 			("DNS minimum nxdomain ttl", &self.dns_min_ttl_nxdomain.to_string()),
 			("DNS attempts", &self.dns_attempts.to_string()),
 			("DNS timeout", &self.dns_timeout.to_string()),
+			("DNS fallback to TCP", &self.dns_tcp_fallback.to_string()),
 			("Query all nameservers", &self.query_all_nameservers.to_string()),
 			("Maximum request size (bytes)", &self.max_request_size.to_string()),
 			("Maximum concurrent requests", &self.max_concurrent_requests.to_string()),

src/service/globals/resolver.rs

@@ -64,6 +64,7 @@ impl Resolver {
 		opts.positive_max_ttl = Some(Duration::from_secs(60 * 60 * 24 * 7));
 		opts.timeout = Duration::from_secs(config.dns_timeout);
 		opts.attempts = config.dns_attempts as usize;
+		opts.try_tcp_on_error = config.dns_tcp_fallback;
 		opts.num_concurrent_reqs = 1;
 		opts.shuffle_dns_servers = true;
 		opts.rotate = true;