gb vendor fetch github.com/matrix-org/gomatrixserverlib/

vendor/src/github.com/matrix-org/gomatrixserverlib/resolve.go

@@ -0,0 +1,108 @@
+/* Copyright 2016-2017 Vector Creations Ltd
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package gomatrixserverlib
+
+import (
+	"net"
+	"strconv"
+	"strings"
+)
+
+// A HostResult is the result of looking up the IP addresses for a host.
+type HostResult struct {
+	CName string   // The canonical name for the host.
+	Addrs []string // The IP addresses for the host.
+	Error error    // If there was an error getting the IP addresses.
+}
+
+// A DNSResult is the result of looking up a matrix server in DNS.
+type DNSResult struct {
+	SRVCName   string                // The canonical name for the SRV record in DNS
+	SRVRecords []*net.SRV            // List of SRV record for the matrix server.
+	SRVError   error                 // If there was an error getting the SRV records.
+	Hosts      map[string]HostResult // The results of looking up the SRV record targets.
+	Addrs      []string              // List of "<ip>:<port>" strings that the server is listening on. These strings can be passed to `net.Dial()`.
+}
+
+// LookupServer looks up a matrix server in DNS.
+func LookupServer(serverName string) (*DNSResult, error) {
+	var result DNSResult
+	result.Hosts = map[string]HostResult{}
+
+	hosts := map[string][]net.SRV{}
+	if strings.Index(serverName, ":") == -1 {
+		// If there isn't an explicit port set then try to look up the SRV record.
+		var err error
+		result.SRVCName, result.SRVRecords, err = net.LookupSRV("matrix", "tcp", serverName)
+		result.SRVError = err
+
+		if err != nil {
+			if dnserr, ok := err.(*net.DNSError); ok {
+				// If the error is a network timeout talking to the DNS server
+				// then give up now rather than trying to fallback.
+				if dnserr.Timeout() {
+					return nil, err
+				}
+				// If there isn't a SRV record in DNS then fallback to "serverName:8448".
+				hosts[serverName] = []net.SRV{net.SRV{
+					Target: serverName,
+					Port:   8448,
+				}}
+			}
+		} else {
+			// Group the SRV records by target host.
+			for _, record := range result.SRVRecords {
+				hosts[record.Target] = append(hosts[record.Target], *record)
+			}
+		}
+	} else {
+		// There is a explicit port set in the server name.
+		// We don't need to look up any SRV records.
+		host, portStr, err := net.SplitHostPort(serverName)
+		if err != nil {
+			return nil, err
+		}
+		var port uint64
+		port, err = strconv.ParseUint(portStr, 10, 16)
+		if err != nil {
+			return nil, err
+		}
+		hosts[host] = []net.SRV{net.SRV{
+			Target: host,
+			Port:   uint16(port),
+		}}
+	}
+	// Look up the IP addresses for each host.
+	for host, records := range hosts {
+		// Ignore any DNS errors when looking up the CNAME. We only are interested in it for debugging.
+		cname, _ := net.LookupCNAME(host)
+		addrs, err := net.LookupHost(host)
+		result.Hosts[host] = HostResult{
+			CName: cname,
+			Addrs: addrs,
+			Error: err,
+		}
+		// For each SRV record, for each IP address add a "<ip>:<port>" entry to the list of addresses.
+		for _, record := range records {
+			for _, addr := range addrs {
+				ipPort := net.JoinHostPort(addr, strconv.Itoa(int(record.Port)))
+				result.Addrs = append(result.Addrs, ipPort)
+			}
+		}
+	}
+
+	return &result, nil
+}