sort the generic config.Params in the DSN

AUTHORS

@@ -33,6 +33,7 @@ ICHINOSE Shogo <shogo82148 at gmail.com>
 INADA Naoki <songofacandy at gmail.com>
 Jacek Szwec <szwec.jacek at gmail.com>
 James Harr <james.harr at gmail.com>
+Jeff Hodges <jeff at somethingsimilar.com>
 Jian Zhen <zhenjl at gmail.com>
 Joshua Prunier <joshua.prunier at gmail.com>
 Julien Lefevre <julien.lefevr at gmail.com>

dsn.go

@@ -15,6 +15,7 @@ import (
 	"fmt"
 	"net"
 	"net/url"
+	"sort"
 	"strconv"
 	"strings"
 	"time"
@@ -257,7 +258,12 @@ func (cfg *Config) FormatDSN() string {
 
 	// other params
 	if cfg.Params != nil {
-		for param, value := range cfg.Params {
+		var params []string
+		for param := range cfg.Params {
+			params = append(params, param)
+		}
+		sort.Strings(params)
+		for _, param := range params {
 			if hasParam {
 				buf.WriteByte('&')
 			} else {
@@ -267,7 +273,7 @@ func (cfg *Config) FormatDSN() string {
 
 			buf.WriteString(param)
 			buf.WriteByte('=')
-			buf.WriteString(url.QueryEscape(value))
+			buf.WriteString(url.QueryEscape(cfg.Params[param]))
 		}
 	}
 

dsn_test.go

@@ -220,6 +220,22 @@ func TestDSNUnsafeCollation(t *testing.T) {
 	}
 }
 
+func TestParamsAreSorted(t *testing.T) {
+	expected := "/dbname?interpolateParams=true&foobar=baz&quux=loo"
+	dsn := &Config{
+		DBName:            "dbname",
+		InterpolateParams: true,
+		Params: map[string]string{
+			"quux":   "loo",
+			"foobar": "baz",
+		},
+	}
+	actual := dsn.FormatDSN()
+	if actual != expected {
+		t.Errorf("generic Config.Params were not sorted: want %#v, got %#v", expected, actual)
+	}
+}
+
 func BenchmarkParseDSN(b *testing.B) {
 	b.ReportAllocs()