Add SOCKS proxy support (cyrilgdn#195)

* Add SOCKS proxy support

This copies the implentation from the Redshift provider:
brainly/terraform-provider-redshift#19.

It allows users to proxy the requests to the database server through a SOCKS
proxy, in case the database server cannot be reached directly.

* Mention SOCKS5 proxy support to usage documentation

As part of this I found out the format of the values in the environment
variables isn't standardized, so there only place we potentially could link to
about the format of the values would be the source code for
`golang.org/x/net/proxy`. I thought that was a bit much, so I've instead
included a simple example instead.

Co-authored-by: Cyril Gaudin <cyril.gaudin@gmail.com>

Author: Tenzer

go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/lib/pq v1.10.4
 	github.com/sean-/postgresql-acl v0.0.0-20161225120419-d10489e5d217
 	gocloud.dev v0.25.0
+	golang.org/x/net v0.0.0-20220401154927-543a649e0bdd
 )
 
 require (
@@ -70,7 +71,6 @@ require (
 	go.uber.org/multierr v1.8.0 // indirect
 	go.uber.org/zap v1.21.0 // indirect
 	golang.org/x/crypto v0.0.0-20220331220935-ae2d96664a29 // indirect
-	golang.org/x/net v0.0.0-20220401154927-543a649e0bdd // indirect
 	golang.org/x/oauth2 v0.0.0-20220309155454-6242fa91716a // indirect
 	golang.org/x/sys v0.0.0-20220330033206-e17cdc41300f // indirect
 	golang.org/x/text v0.3.7 // indirect

postgresql/config.go

@@ -250,7 +250,7 @@ func (c *Client) Connect() (*DBConnection, error) {
 		var db *sql.DB
 		var err error
 		if c.config.Scheme == "postgres" {
-			db, err = sql.Open("postgres", dsn)
+			db, err = sql.Open(proxyDriverName, dsn)
 		} else {
 			db, err = postgres.Open(context.Background(), dsn)
 		}

postgresql/proxy_driver.go

@@ -0,0 +1,35 @@
+package postgresql
+
+import (
+	"context"
+	"database/sql"
+	"database/sql/driver"
+	"net"
+	"time"
+
+	"github.com/lib/pq"
+	"golang.org/x/net/proxy"
+)
+
+const proxyDriverName = "postgresql-proxy"
+
+type proxyDriver struct{}
+
+func (d proxyDriver) Open(name string) (driver.Conn, error) {
+	return pq.DialOpen(d, name)
+}
+
+func (d proxyDriver) Dial(network, address string) (net.Conn, error) {
+	dialer := proxy.FromEnvironment()
+	return dialer.Dial(network, address)
+}
+
+func (d proxyDriver) DialTimeout(network, address string, timeout time.Duration) (net.Conn, error) {
+	ctx, cancel := context.WithTimeout(context.TODO(), timeout)
+	defer cancel()
+	return proxy.Dial(ctx, network, address)
+}
+
+func init() {
+	sql.Register(proxyDriverName, proxyDriver{})
+}

website/docs/index.html.markdown

@@ -194,4 +194,10 @@ resource postgresql_database "test_db" {
 }
 ```
 
+### SOCKS5 Proxy Support
+
+The provider supports connecting via a SOCKS5 proxy, but when the `postgres` scheme is used. It can be configured by setting the `ALL_PROXY` or `all_proxy` environment variable to a value like `socks5://127.0.0.1:1080`.
+
+The `NO_PROXY` or `no_proxy` environment can also be set to opt out of proxying for specific hostnames or ports.
+
 [libpq]: https://pkg.go.dev/github.com/lib/pq