gateway: attempt to resolve hostname to ipfs path

This allows someone to host a static site by pointing a TXT record at their
content in IPFS, and a CNAME record at an IPFS gateway.

Note that such a setup technically violates RFC1912 (section 2.4; "A CNAME
record is not allowed to coexist with any other data."), but tends to work in
practice.

We may want to consider changing the DNS->IPFS resolution scheme to allow this
scenario to be RFC-compliant (e.g. store the mapping on a well-known subdomain
to allow CNAME records on the domain itself).

License: MIT
Signed-off-by: Kevin Wallace <kevin@pentabarf.net>

cmd/ipfs/daemon.go

@@ -178,7 +178,10 @@ func daemonFunc(req cmds.Request, res cmds.Response) {
 
 	if gatewayMaddr != nil {
 		go func() {
-			var opts = []corehttp.ServeOption{corehttp.GatewayOption(writable)}
+			var opts = []corehttp.ServeOption{
+				corehttp.IPNSHostnameOption(),
+				corehttp.GatewayOption(writable),
+			}
 			if rootRedirect != nil {
 				opts = append(opts, rootRedirect)
 			}

core/corehttp/ipns_hostname.go

@@ -0,0 +1,29 @@
+package corehttp
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/jbenet/go-ipfs/Godeps/_workspace/src/code.google.com/p/go.net/context"
+	"github.com/jbenet/go-ipfs/core"
+)
+
+// IPNSHostnameOption rewrites an incoming request if its Host: header contains
+// an IPNS name.
+// The rewritten request points at the resolved name on the gateway handler.
+func IPNSHostnameOption() ServeOption {
+	return func(n *core.IpfsNode, mux *http.ServeMux) (*http.ServeMux, error) {
+		childMux := http.NewServeMux()
+		mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+			ctx, cancel := context.WithCancel(n.Context())
+			defer cancel()
+
+			host := strings.SplitN(r.Host, ":", 2)[0]
+			if k, err := n.Namesys.Resolve(ctx, host); err == nil {
+				r.URL.Path = "/ipfs/" + k.Pretty() + r.URL.Path
+			}
+			childMux.ServeHTTP(w, r)
+		})
+		return childMux, nil
+	}
+}