net: add mechanisms to force go or cgo lookup, and to debug default strategy
GODEBUG=netdns=1 prints a one-time strategy decision. (cgo or go DNS lookups)
GODEBUG=netdns=2 prints the per-lookup strategy as a function of the hostname.
The new "netcgo" build tag forces cgo DNS lookups.
GODEBUG=netdns=go (or existing build tag "netgo") forces Go DNS resolution.
GODEBUG=netdns=cgo (or new build tag "netcgo") forces libc DNS resolution.
Options can be combined with e.g. GODEBUG=netdns=go+1 or GODEBUG=netdns=2+cgo.
Fixes #11322
Fixes #11450
Change-Id: I7a67e9f759fd0a02320e7803f9ded1638b19e861
Reviewed-on: https://go-review.googlesource.com/11584
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/net/net.go b/src/net/net.go
index cd1372f..75510a2 100644
--- a/src/net/net.go
+++ b/src/net/net.go
@@ -46,6 +46,14 @@
"time"
)
+// netGo and netCgo contain the state of the build tags used
+// to build this binary, and whether cgo is available.
+// conf.go mirrors these into conf for easier testing.
+var (
+ netGo bool // set true in cgo_stub.go for build tag "netgo" (or no cgo)
+ netCgo bool // set true in conf_netcgo.go for build tag "netcgo"
+)
+
func init() {
sysInit()
supportsIPv4 = probeIPv4Stack()
