Fix failing RFC822.Mailbox test.

Reverting commit 1d8c4aea broke the mailbox class a bit. This fixes the
issue, introduces Ascii.last_index_of which is needed by Mailbox anyway,
and adds some test for it. Also 'optimises' Ascii.index_of bit as well.

src/engine/rfc822/rfc822-mailbox-address.vala

@@ -127,7 +127,7 @@ public class Geary.RFC822.MailboxAddress :
         this.source_route = null;
         this.address = address;
 
-        int atsign = Ascii.index_of(address, '@');
+        int atsign = Ascii.last_index_of(address, '@');
         if (atsign > 0) {
             this.mailbox = address[0:atsign];
             this.domain = address[atsign + 1:address.length];
@@ -136,7 +136,7 @@ public class Geary.RFC822.MailboxAddress :
             this.domain = "";
         }
     }
-    
+
     public MailboxAddress.imap(string? name, string? source_route, string mailbox, string domain) {
         this.name = (name != null) ? decode_name(name) : null;
         this.source_route = source_route;
@@ -173,12 +173,12 @@ public class Geary.RFC822.MailboxAddress :
         }
 
         string address = mailbox.get_addr();
-        int atsign = address.last_index_of_char('@');
+        int atsign = Ascii.last_index_of(address, '@');
         if (atsign == -1) {
             // No @ detected, try decoding in case a mailer (wrongly)
             // encoded the whole thing and re-try
             address = decode_address_part(address);
-            atsign = address.last_index_of_char('@');
+            atsign = Ascii.last_index_of(address, '@');
         }
 
         if (atsign >= 0) {

src/engine/util/util-ascii.vala

@@ -12,19 +12,36 @@ extern string g_ascii_strdown(string str, ssize_t len = -1);
 namespace Geary.Ascii {
 
 public int index_of(string str, char ch) {
+    // Use a pointer and explicit null check, since testing against
+    // the length of the string as in a traditional for loop will mean
+    // a call to strlen(), making the loop O(n^2)
+    int ret = -1;
     char *strptr = str;
-    int index = 0;
-    for (;;) {
-        char strch = *strptr++;
-        
-        if (strch == String.EOS)
-            return -1;
-        
-        if (strch == ch)
-            return index;
-        
-        index++;
+    int i = 0;
+    while (*strptr != String.EOS) {
+        if (*strptr++ == ch) {
+            ret = i;
+            break;
+        }
+        i++;
     }
+    return ret;
+}
+
+public int last_index_of(string str, char ch) {
+    // Use a pointer and explicit null check, since testing against
+    // the length of the string as in a traditional for loop will mean
+    // a call to strlen(), making the loop O(n^2)
+    int ret = -1;
+    char *strptr = str;
+    int i = 0;
+    while (*strptr != String.EOS) {
+        if (*strptr++ == ch) {
+            ret = i;
+        }
+        i++;
+    }
+    return ret;
 }
 
 public bool get_next_char(string str, ref int index, out char ch) {

test/CMakeLists.txt

@@ -36,6 +36,7 @@ set(TEST_ENGINE_SRC
   engine/rfc822-message-test.vala
   engine/rfc822-message-data-test.vala
   engine/rfc822-utils-test.vala
+  engine/util-ascii-test.vala
   engine/util-html-test.vala
   engine/util-idle-manager-test.vala
   engine/util-inet-test.vala

test/engine/util-ascii-test.vala

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2018 Michael Gratton <mike@vee.net>
+ *
+ * This software is licensed under the GNU Lesser General Public License
+ * (version 2.1 or later). See the COPYING file in this distribution.
+ */
+
+class Geary.Ascii.Test : TestCase {
+
+    public Test() {
+        base("Geary.Ascii.Test");
+        add_test("index_of", index_of);
+        add_test("last_index_of", last_index_of);
+    }
+
+    public void index_of() throws Error {
+        assert_int(-1, Ascii.index_of("", 'a'));
+        assert_int(0, Ascii.index_of("a", 'a'));
+        assert_int(0, Ascii.index_of("aa", 'a'));
+
+        assert_int(0, Ascii.index_of("abcabc", 'a'));
+        assert_int(1, Ascii.index_of("abcabc", 'b'));
+        assert_int(2, Ascii.index_of("abcabc", 'c'));
+
+        assert_int(0, Ascii.index_of("@", '@'));
+
+        assert_int(-1, Ascii.index_of("abc", 'd'));
+    }
+
+    public void last_index_of() throws Error {
+        assert_int(-1, Ascii.last_index_of("", 'a'));
+        assert_int(0, Ascii.last_index_of("a", 'a'));
+        assert_int(1, Ascii.last_index_of("aa", 'a'));
+
+        assert_int(3, Ascii.last_index_of("abcabc", 'a'));
+        assert_int(4, Ascii.last_index_of("abcabc", 'b'));
+        assert_int(5, Ascii.last_index_of("abcabc", 'c'));
+
+        assert_int(0, Ascii.last_index_of("@", '@'));
+
+        assert_int(-1, Ascii.last_index_of("abc", 'd'));
+    }
+
+}

test/meson.build

@@ -32,6 +32,7 @@ geary_test_engine_sources = [
   'engine/rfc822-message-test.vala',
   'engine/rfc822-message-data-test.vala',
   'engine/rfc822-utils-test.vala',
+  'engine/util-ascii-test.vala',
   'engine/util-html-test.vala',
   'engine/util-idle-manager-test.vala',
   'engine/util-inet-test.vala',

test/test-engine.vala

@@ -30,6 +30,7 @@ int main(string[] args) {
     engine.add_suite(new Geary.App.ConversationSetTest().get_suite());
     // Depends on ConversationTest and ConversationSetTest passing
     engine.add_suite(new Geary.App.ConversationMonitorTest().get_suite());
+    engine.add_suite(new Geary.Ascii.Test().get_suite());
     engine.add_suite(new Geary.HTML.UtilTest().get_suite());
     engine.add_suite(new Geary.Imap.DeserializerTest().get_suite());
     engine.add_suite(new Geary.Imap.CreateCommandTest().get_suite());