net: prefer /etc/hosts over DNS when no /etc/nsswitch.conf is present

Do not mimic glibc behavior if /etc/nsswitch.conf is missing. This will will likely be missing on musl libc systems and glibc systems will likely always have it, resulting in localhost lookup being done over DNS rather than from /etc/hosts. Do what makes most sense rather than making any assumption about the libc. Fixes #35305 Change-Id: I20bd7e24131bba8eaa39a20c8950fe552364784d GitHub-Last-Rev: 1194098 GitHub-Pull-Request: #39685 Reviewed-on: https://go-review.googlesource.com/c/go/+/238629 Run-TryBot: Dan Peterson <[email protected]> TryBot-Result: Go Bot <[email protected]> Reviewed-by: Dan Peterson <[email protected]> Reviewed-by: Ian Lance Taylor <[email protected]> Trust: Emmanuel Odeke <[email protected]>
golang · Oct 25, 2020 · c800222 · c800222
1 parent 9488741
commit c800222
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Showing 2 changed files with 10 additions and 8 deletions.
diff --git a/src/net/conf.go b/src/net/conf.go
@@ -202,11 +202,6 @@ func (c *conf) hostLookupOrder(r *Resolver, hostname string) (ret hostLookupOrde
 			// illumos defaults to "nis [NOTFOUND=return] files"
 			return fallbackOrder
 		}
-		if c.goos == "linux" {
-			// glibc says the default is "dns [!UNAVAIL=return] files"
-			// https://www.gnu.org/software/libc/manual/html_node/Notes-on-NSS-Configuration-File.html.
-			return hostLookupDNSFiles
-		}
 		return hostLookupFilesDNS
 	}
 	if nss.err != nil {

diff --git a/src/net/conf_test.go b/src/net/conf_test.go
@@ -170,16 +170,23 @@ func TestConfHostLookupOrder(t *testing.T) {
 			},
 			hostTests: []nssHostTest{{"google.com", "myhostname", hostLookupDNSFiles}},
 		},
-		// glibc lacking an nsswitch.conf, per
-		// https://www.gnu.org/software/libc/manual/html_node/Notes-on-NSS-Configuration-File.html
 		{
 			name: "linux_no_nsswitch.conf",
 			c: &conf{
 				goos:   "linux",
 				nss:    &nssConf{err: fs.ErrNotExist},
 				resolv: defaultResolvConf,
 			},
-			hostTests: []nssHostTest{{"google.com", "myhostname", hostLookupDNSFiles}},
+			hostTests: []nssHostTest{{"google.com", "myhostname", hostLookupFilesDNS}},
+		},
+		{
+			name: "linux_empty_nsswitch.conf",
+			c: &conf{
+				goos:   "linux",
+				nss:    nssStr(""),
+				resolv: defaultResolvConf,
+			},
+			hostTests: []nssHostTest{{"google.com", "myhostname", hostLookupFilesDNS}},
 		},
 		{
 			name: "files_mdns_dns",