Better identify web links by trimming irrelevant charschromium/3107

Sometimes, web links are written with other text such as punctuations
which makes the extracted web links invalid. We improve this by trimming
invalid chars at the end of host name only URLs. For example, host names
never ends with ';' or ','.

BUG=chromium:720578

Change-Id: Id619025b2153531376d268a69a3a89c3d49fce08
Reviewed-on: https://pdfium-review.googlesource.com/5692
Commit-Queue: Wei Li <weili@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

1 files changed, 81 insertions, 19 deletions

diff --git a/core/fpdftext/cpdf_linkextract.cpp b/core/fpdftext/cpdf_linkextract.cpp
index 56a3ab4ec7..315cff12a0 100644
--- a/core/fpdftext/cpdf_linkextract.cpp
+++ b/core/fpdftext/cpdf_linkextract.cpp
@@ -13,6 +13,54 @@
 #include "core/fxcrt/fx_string.h"
 #include "core/fxcrt/fx_system.h"
 
+namespace {
+
+// Find the end of a web link starting from offset |start|.
+// The purpose of this function is to separate url from the surrounding context
+// characters, we do not intend to fully validate the url.
+// |str| contains lower case characters only.
+FX_STRSIZE FindWebLinkEnding(const CFX_WideString& str, FX_STRSIZE start) {
+  FX_STRSIZE end = str.GetLength() - 1;
+  if (str.Find(L'/', start) != -1) {
+    // When there is a path and query after '/', most ASCII chars are allowed.
+    // We don't sanitize in this case.
+    return end;
+  }
+
+  // When there is no path, it only has IP address or host name.
+  // Port is optional at the end.
+  if (str[start] == L'[') {
+    // IPv6 reference.
+    // Find the end of the reference.
+    end = str.Find(L']', start + 1);
+    if (end != -1 && end > start + 1) {  // Has content inside brackets.
+      FX_STRSIZE len = str.GetLength();
+      FX_STRSIZE off = end + 1;
+      if (off < len && str[off] == L':') {
+        off++;
+        while (off < len && str[off] >= L'0' && str[off] <= L'9')
+          off++;
+        if (off > end + 2 && off <= len)  // At least one digit in port number.
+          end = off - 1;  // |off| is offset of the first invalid char.
+      }
+    }
+    return end;
+  }
+
+  // According to RFC1123, host name only has alphanumeric chars, hyphens,
+  // and periods. Hyphen should not at the end though.
+  // Non-ASCII chars are ignored during checking.
+  while (end > start && str[end] < 0x80) {
+    if ((str[end] >= L'0' && str[end] <= L'9') ||
+        (str[end] >= L'a' && str[end] <= L'z') || str[end] == L'.')
+      break;
+    end--;
+  }
+  return end;
+}
+
+}  // namespace
+
 CPDF_LinkExtract::CPDF_LinkExtract(const CPDF_TextPage* pTextPage)
     : m_pTextPage(pTextPage) {}
 
@@ -71,6 +119,8 @@ void CPDF_LinkExtract::ParseLink() {
             break;
           }
         }
+        // Check for potential web URLs and email addresses.
+        // Ftp address, file system links, data, blob etc. are not checked.
         if (nCount > 5 &&
             (CheckWebLink(strBeCheck) || CheckMailLink(strBeCheck))) {
           m_LinkArray.push_back({start, nCount, strBeCheck});
@@ -87,28 +137,40 @@ void CPDF_LinkExtract::ParseLink() {
 }
 
 bool CPDF_LinkExtract::CheckWebLink(CFX_WideString& strBeCheck) {
+  static const wchar_t kHttpScheme[] = L"http";
+  static const FX_STRSIZE kHttpSchemeLen = FXSYS_len(kHttpScheme);
+  static const wchar_t kWWWAddrStart[] = L"www.";
+  static const FX_STRSIZE kWWWAddrStartLen = FXSYS_len(kWWWAddrStart);
+
   CFX_WideString str = strBeCheck;
   str.MakeLower();
-  if (str.Find(L"http://www.") != -1) {
-    strBeCheck = strBeCheck.Right(str.GetLength() - str.Find(L"http://www."));
-    return true;
-  }
-  if (str.Find(L"http://") != -1) {
-    strBeCheck = strBeCheck.Right(str.GetLength() - str.Find(L"http://"));
-    return true;
-  }
-  if (str.Find(L"https://www.") != -1) {
-    strBeCheck = strBeCheck.Right(str.GetLength() - str.Find(L"https://www."));
-    return true;
-  }
-  if (str.Find(L"https://") != -1) {
-    strBeCheck = strBeCheck.Right(str.GetLength() - str.Find(L"https://"));
-    return true;
+
+  FX_STRSIZE len = str.GetLength();
+  // First, try to find the scheme.
+  FX_STRSIZE start = str.Find(kHttpScheme);
+  if (start != -1) {
+    FX_STRSIZE off = start + kHttpSchemeLen;  // move after "http".
+    if (len > off + 4) {                      // At least "://<char>" follows.
+      if (str[off] == L's')                   // "https" scheme is accepted.
+        off++;
+      if (str[off] == L':' && str[off + 1] == L'/' && str[off + 2] == L'/') {
+        FX_STRSIZE end = FindWebLinkEnding(str, off + 3);
+        if (end > off + 3) {  // Non-empty host name.
+          strBeCheck = strBeCheck.Mid(start, end - start + 1);
+          return true;
+        }
+      }
+    }
   }
-  if (str.Find(L"www.") != -1) {
-    strBeCheck = strBeCheck.Right(str.GetLength() - str.Find(L"www."));
-    strBeCheck = L"http://" + strBeCheck;
-    return true;
+
+  // When there is no scheme, try to find url starting with "www.".
+  start = str.Find(kWWWAddrStart);
+  if (start != -1 && len > start + kWWWAddrStartLen) {
+    FX_STRSIZE end = FindWebLinkEnding(str, start);
+    if (end > start + kWWWAddrStartLen) {
+      strBeCheck = L"http://" + strBeCheck.Mid(start, end - start + 1);
+      return true;
+    }
   }
   return false;
 }