Avoid overstepping bounds in config file parsing

Our configuration files are not security relevant, but having a parser
which avoids crashing on them even if they are seriously messed up is
not a bad idea anyway. It is also a good opportunity to brush up the
code a bit avoiding a few small string copies with our string_view.

1 files changed, 26 insertions, 0 deletions

diff --git a/apt-pkg/contrib/string_view.h b/apt-pkg/contrib/string_view.h
index 05aad3327..04f6ff115 100644
--- a/apt-pkg/contrib/string_view.h
+++ b/apt-pkg/contrib/string_view.h
@@ -39,6 +39,10 @@ public:
     StringView(const char *data) : data_(data), size_(strlen(data)) {}
     StringView(std::string const & str): data_(str.data()), size_(str.size()) {}
 
+    /* Modifiers */
+    void remove_prefix(size_t n) { data_ += n; size_ -= n; }
+    void remove_suffix(size_t n) { size_ -= n; }
+    void clear() { size_ = 0; }
 
     /* Viewers */
     constexpr StringView substr(size_t pos, size_t n = npos) const {
@@ -76,6 +80,28 @@ public:
         return found - data_;
     }
 
+    size_t find(APT::StringView const needle) const {
+       if (needle.empty())
+	  return npos;
+       if (needle.length() == 1)
+	  return find(*needle.data());
+       size_t found = 0;
+       while ((found = find(*needle.data(), found)) != npos) {
+	  if (compare(found, needle.length(), needle) == 0)
+	     return found;
+	  ++found;
+       }
+       return found;
+    }
+    size_t find(APT::StringView const needle, size_t pos) const {
+       if (pos == 0)
+	  return find(needle);
+       size_t const found = substr(pos).find(needle);
+       if (found == npos)
+	  return npos;
+       return pos + found;
+    }
+
     /* Conversions */
     std::string to_string() const {
         return std::string(data_, size_);