fix: replacing crc32 by sha256 hash sum and making sure it doesn't re…

…turn a negative value (#42)

masquerade.go

@@ -1,9 +1,9 @@
 package fronted
 
 import (
+	"crypto/sha256"
 	"encoding/json"
 	"fmt"
-	"hash/crc32"
 	"net"
 	"net/http"
 	"sort"
@@ -125,18 +125,29 @@ func NewProvider(hosts map[string]string, testURL string, masquerades []*Masquer
 	}
 
 	for _, m := range masquerades {
-		var sni string
-		if d.SNIConfig != nil && d.SNIConfig.UseArbitrarySNIs {
-			// Ensure that we use a consistent SNI for a given combination of IP address and SNI set
-			crc32Hash := int(crc32.ChecksumIEEE([]byte(m.IpAddress)))
-			sni = d.SNIConfig.ArbitrarySNIs[crc32Hash%len(d.SNIConfig.ArbitrarySNIs)]
-		}
+		sni := generateSNI(d.SNIConfig, m)
 		d.Masquerades = append(d.Masquerades, &Masquerade{Domain: m.Domain, IpAddress: m.IpAddress, SNI: sni})
 	}
 	d.PassthroughPatterns = append(d.PassthroughPatterns, passthrough...)
 	return d
 }
 
+// generateSNI generates a SNI for the given domain and ip address
+func generateSNI(config *SNIConfig, m *Masquerade) string {
+	if config != nil && m != nil && config.UseArbitrarySNIs && len(config.ArbitrarySNIs) > 0 {
+		// Ensure that we use a consistent SNI for a given combination of IP address and SNI set
+		hash := sha256.New()
+		hash.Write([]byte(m.IpAddress))
+		checksum := int(hash.Sum(nil)[0])
+		// making sure checksum is positive
+		if checksum < 0 {
+			checksum = -checksum
+		}
+		return config.ArbitrarySNIs[checksum%len(config.ArbitrarySNIs)]
+	}
+	return ""
+}
+
 // Lookup the host alias for the given hostname for this provider
 func (p *Provider) Lookup(hostname string) string {
 	// only consider the host porition if given a port as well.

masquerade_test.go

@@ -0,0 +1,70 @@
+package fronted
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGenerateSNI(t *testing.T) {
+	emptyMasquerade := new(Masquerade)
+	var tests = []struct {
+		name            string
+		assert          func(t *testing.T, actual string)
+		givenConfig     *SNIConfig
+		givenMasquerade *Masquerade
+	}{
+		{
+			name:            "should return a empty string when given SNI config is nil",
+			givenConfig:     nil,
+			givenMasquerade: emptyMasquerade,
+			assert: func(t *testing.T, actual string) {
+				assert.Empty(t, actual)
+			},
+		},
+		{
+			name: "should return a empty string when given SNI config is not nil and UseArbitrarySNIs is false",
+			givenConfig: &SNIConfig{
+				UseArbitrarySNIs: false,
+			},
+			givenMasquerade: emptyMasquerade,
+			assert: func(t *testing.T, actual string) {
+				assert.Empty(t, actual)
+			},
+		},
+		{
+			name: "should return a empty SNI when the list of arbitrary SNIs is empty",
+			givenConfig: &SNIConfig{
+				UseArbitrarySNIs: true,
+				ArbitrarySNIs:    []string{},
+			},
+			givenMasquerade: &Masquerade{
+				IpAddress: "1.1.1.1",
+				Domain:    "randomdomain.net",
+			},
+			assert: func(t *testing.T, actual string) {
+				assert.Empty(t, actual)
+			},
+		},
+		{
+			name: "should return a SNI when given SNI config is not nil and UseArbitrarySNIs is true",
+			givenConfig: &SNIConfig{
+				UseArbitrarySNIs: true,
+				ArbitrarySNIs:    []string{"sni1.com", "sni2.com"},
+			},
+			givenMasquerade: &Masquerade{
+				IpAddress: "1.1.1.1",
+				Domain:    "randomdomain.net",
+			},
+			assert: func(t *testing.T, actual string) {
+				assert.NotEmpty(t, actual)
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			actual := generateSNI(tt.givenConfig, tt.givenMasquerade)
+			tt.assert(t, actual)
+		})
+	}
+}