GODRIVER-2897 Add SRV test with capital letters in hostnames. (#1550)

Author: qingyang-hu

testdata/initial-dns-seedlist-discovery/replica-set/uri-with-uppercase-hostname.json

@@ -0,0 +1,16 @@
+{
+  "uri": "mongodb+srv://TEST1.TEST.BUILD.10GEN.CC",
+  "seeds": [
+    "localhost.test.build.10gen.cc:27017",
+    "localhost.test.build.10gen.cc:27018"
+  ],
+  "hosts": [
+    "localhost:27017",
+    "localhost:27018",
+    "localhost:27019"
+  ],
+  "options": {
+    "ssl": true
+  },
+  "ping": true
+}

testdata/initial-dns-seedlist-discovery/replica-set/uri-with-uppercase-hostname.yml

@@ -0,0 +1,11 @@
+uri: "mongodb+srv://TEST1.TEST.BUILD.10GEN.CC"
+seeds:
+    - localhost.test.build.10gen.cc:27017
+    - localhost.test.build.10gen.cc:27018
+hosts:
+    - localhost:27017
+    - localhost:27018
+    - localhost:27019
+options:
+    ssl: true
+ping: true

x/mongo/driver/dns/dns.go

@@ -104,8 +104,8 @@ func (r *Resolver) fetchSeedlistFromSRV(host string, srvName string, stopOnErr b
 }
 
 func validateSRVResult(recordFromSRV, inputHostName string) error {
-	separatedInputDomain := strings.Split(inputHostName, ".")
-	separatedRecord := strings.Split(recordFromSRV, ".")
+	separatedInputDomain := strings.Split(strings.ToLower(inputHostName), ".")
+	separatedRecord := strings.Split(strings.ToLower(recordFromSRV), ".")
 	if len(separatedRecord) < 2 {
 		return errors.New("DNS name must contain at least 2 labels")
 	}