Uri: the ":" separator omitted for an empty scheme

This patch changes slightly the grammar used by the Uri class. In the
previous version, the ":" separator following the schema was always
required. In the new grammar, the ":" separator is omitted for an empty
schema. As a result, the normalized representation of an empty Uri is an
empty string. This is more intuitive behavior than the previous one,
when empty Uri was represented by ":" string. All URIs accepted by the
old grammar are also accepted by the new one. Additionally, URIs
without scheme and without the ":" separator are also accepted now.

BUG=none
TEST=with unittests on my workstation

Change-Id: I4bc8875af4a5d05a227aca47863c7d659b8d4223
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2553529
Auto-Submit: Piotr Pawliczek <pawliczek@chromium.org>
Commit-Queue: Sean Kau <skau@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#831958}

chromeos/printing/uri.cc

@@ -180,6 +180,7 @@ std::string Uri::GetNormalized(bool always_print_port) const {
 
   // Output string. Adds Scheme.
   std::string out = pim_->scheme();
+  if (!out.empty())
     out.push_back(':');
 
   // Adds authority (Userinfo + Host + Port) if non-empty.

chromeos/printing/uri.h

@@ -50,7 +50,7 @@ namespace chromeos {
 //
 // 1. The grammar is simplified:
 //
-//    uri = Scheme ":" [ authority ] [ Path ] [ "?" Query ] [ "#" Fragment ]
+//    uri = [ Scheme ":" ] [ authority ] [ Path ] [ "?" Query ] [ "#" Fragment ]
 //
 //    authority = "//" [ Userinfo "@" ] Host [ ":" Port ]
 //
@@ -215,7 +215,7 @@ class CHROMEOS_EXPORT Uri {
     kInvalidPercentEncoding,    // cannot parse hex number after % sign
     kDisallowedASCIICharacter,  // non-printable ASCII character
     kInvalidUTF8Character,      // error when tried to parse UTF-8 character
-    kInvalidScheme,             // invalid Scheme format or no ':' in input
+    kInvalidScheme,             // invalid Scheme format
     kInvalidPortNumber,
     kRelativePathsNotAllowed,  // non-empty Path that does not start with '/'
     kEmptySegmentInPath,
@@ -279,8 +279,8 @@ class CHROMEOS_EXPORT Uri {
   // - Set*Encoded(...) methods
   const ParserError& GetLastParsingError() const;
 
-  // Returns the URL in the normalized form. It never returns empty string!
-  // When all components are empty, this method returns ":" (see the grammar).
+  // Returns the URL in the normalized form. It returns empty string if and only
+  // if all components are empty (see the grammar).
   // If the Port is specified (GetPort() != -1) and |always_print_port| is set
   // to true, a Port number is always included in the returned URI (even when
   // it equals to a Scheme's default port number).

chromeos/printing/uri_impl.cc

@@ -420,8 +420,10 @@ bool Uri::Pim::ParseUri(const Iter& begin, const Iter end) {
   parser_error_.parsed_strings = 0;
   parser_error_.parsed_chars = 0;
   Iter it1 = begin;
-  // The Scheme component ends at the first colon (":").
-  {
+  // The Scheme component starts from character different than slash ("/"),
+  // question mark ("?"), and number sign ("#"). Non-empty Scheme must be
+  // followed by the colon (":") character.
+  if (it1 < end && *it1 != '/' && *it1 != '?' && *it1 != '#') {
     auto it2 = std::find(it1, end, ':');
     if (it2 == end) {
       parser_error_.status = ParserStatus::kInvalidScheme;

chromeos/printing/uri_unittest.cc

@@ -84,7 +84,7 @@ void TestNormalization(const std::string& input_uri,
 
 TEST(UriTest, DefaultConstructor) {
   Uri uri;
-  EXPECT_EQ(uri.GetNormalized(), ":");
+  EXPECT_EQ(uri.GetNormalized(), "");
   EXPECT_EQ(uri.GetLastParsingError().status, Uri::ParserStatus::kNoErrors);
   EXPECT_EQ(uri.GetScheme(), "");
   EXPECT_EQ(uri.GetUserinfo(), "");
@@ -262,7 +262,7 @@ TEST(UriTest, ParsingOfUriWithLeadingAndTrailingWhitespaces) {
 
 // Empty components are accepted.
 TEST(UriTest, NormalizationOfEmptyUri) {
-  TestNormalization("://@:/?#", ":");
+  TestNormalization("://@:/?#", "");
 }
 
 TEST(UriTest, NormalizationOfUriWithoutAuthority) {

chromeos/printing/uri_unittest_consistency.cc

@@ -121,7 +121,9 @@ TEST_P(UriConsistencyTest, QueryBuilding) {
 // Build normalized URI from encoded components and make sure that it is
 // equal to the value returned by GetNormalized().
 TEST_P(UriConsistencyTest, UriBuilding) {
-  std::string scheme = uri_.GetScheme() + ":";
+  std::string scheme = uri_.GetScheme();
+  if (!scheme.empty())
+    scheme += ":";
 
   // Build a part of URI called Authority (Userinfo@Host:Port).
   std::string authority_encoded;