caddyhttp: fix randString sameCase dictionary to match its docs

The doc comment says randString excludes confusing characters like
I, l, 1, 0, O. When sameCase is true, uppercase letters and the
characters l and o should be excluded. But the sameCase dictionary
still contained '0'. Drop it.

Signed-off-by: Mohammed Al Sahaf <msaa1990@gmail.com>

modules/caddyhttp/errors.go

@@ -93,7 +93,7 @@ func randString(n int, sameCase bool) string {
 	}
 	dict := []byte("abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRTUVWXY23456789")
 	if sameCase {
-		dict = []byte("abcdefghijkmnpqrstuvwxyz0123456789")
+		dict = []byte("abcdefghijkmnpqrstuvwxyz123456789")
 	}
 	b := make([]byte, n)
 	for i := range b {

modules/caddyhttp/errors_randstring_test.go

@@ -0,0 +1,33 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package caddyhttp
+
+import (
+	"strings"
+	"testing"
+)
+
+// TestRandString_SameCaseExcludesZero is the regression test for the
+// randString(sameCase=true) dictionary bug where '0' was still emitted
+// despite being called out as a confusing character in the doc comment.
+func TestRandString_SameCaseExcludesZero(t *testing.T) {
+	// A sample of 5000 characters makes a leaked '0' extremely unlikely
+	// to go unnoticed: the dictionary is 33 characters, so the expected
+	// count for any single character would be ~151 if it were present.
+	s := randString(5000, true)
+	if strings.ContainsRune(s, '0') {
+		t.Errorf("randString(n, sameCase=true) must not emit '0'; got %q", s)
+	}
+}