Problem
When running discobot macOS binary and trying to access a service preview with a subdomain of localhost (e.g., http://my-service.localhost:52865), Safari and Discobot/Tauri (WKWebView) fail to load the page. Chrome and curl work fine.
Root Cause
Chrome and curl resolve *.localhost to 127.0.0.1 — Chrome via its built-in resolver (per https://datatracker.ietf.org/doc/html/rfc6761#section-6.3), and curl via getaddrinfo() which macOS resolves at the OS level.
Safari and Tauri use Apple's CFNetwork / NSURLSession stack, which has its own DNS resolution path that does not special-case *.localhost subdomains. Instead, it sends a real DNS query, which fails because no upstream DNS server has a record for the subdomain.
This is a longstanding omission in Apple's networking stack. RFC 6761 recommends that localhost and its subdomains always resolve to loopback, but CFNetwork does not implement this.
Workaround
Install dnsmasq
brew install dnsmasq
Resolve all *.localhost to 127.0.0.1
echo "address=/localhost/127.0.0.1" >> $(brew --prefix)/etc/dnsmasq.conf
Start as a persistent service
sudo brew services start dnsmasq
Route .localhost DNS queries to the local resolver
sudo mkdir -p /etc/resolver
echo "nameserver 127.0.0.1" | sudo tee /etc/resolver/localhost
Problem
When running discobot macOS binary and trying to access a service preview with a subdomain of localhost (e.g., http://my-service.localhost:52865), Safari and Discobot/Tauri (WKWebView) fail to load the page. Chrome and curl work fine.
Root Cause
Chrome and curl resolve *.localhost to 127.0.0.1 — Chrome via its built-in resolver (per https://datatracker.ietf.org/doc/html/rfc6761#section-6.3), and curl via getaddrinfo() which macOS resolves at the OS level.
Safari and Tauri use Apple's CFNetwork / NSURLSession stack, which has its own DNS resolution path that does not special-case *.localhost subdomains. Instead, it sends a real DNS query, which fails because no upstream DNS server has a record for the subdomain.
This is a longstanding omission in Apple's networking stack. RFC 6761 recommends that localhost and its subdomains always resolve to loopback, but CFNetwork does not implement this.
Workaround
Install dnsmasq
brew install dnsmasq
Resolve all *.localhost to 127.0.0.1
echo "address=/localhost/127.0.0.1" >> $(brew --prefix)/etc/dnsmasq.conf
Start as a persistent service
sudo brew services start dnsmasq
Route .localhost DNS queries to the local resolver
sudo mkdir -p /etc/resolver
echo "nameserver 127.0.0.1" | sudo tee /etc/resolver/localhost