Avoid heap allocations in IPAddress

net/base/ip_address.h

 // Copyright (c) 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_BASE_IP_ADDRESS_H_
 #define NET_BASE_IP_ADDRESS_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
+#include <array>
 #include <string>
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "base/strings/string_piece.h"
 #include "net/base/net_export.h"
 
 namespace net {
 
 class NET_EXPORT IPAddress {
  public:
   enum : size_t { kIPv4AddressSize = 4, kIPv6AddressSize = 16 };
 
+  // Helper class to represent the sequence of bytes in an IP address.
+  // A vector<uint8_t> would be simpler but incurs heap allocation, so
+  // IPAddressBytes uses a fixed size array
+  class IPAddressBytes {
+   public:
+    IPAddressBytes();
+    IPAddressBytes(const uint8_t* data, size_t data_len);
+    IPAddressBytes(const IPAddressBytes& other);
+    ~IPAddressBytes();
+
+    // Returns the number of elements in the underlying array.
+    size_t size() const { return size_; }
+
+    // Sets the size to be |size|. Does not actually change the size
+    // of the underlying array.
+    void resize(size_t size) {

[eroman, 2017/05/15 22:15:23]

I presume this exists to make existing code (which was using std::vector<>)
continue to work without changes? Does it then need to adhere to the same
contract as std::vector::resize?

In particular:

   x.resize(0);
   x.resize(16);

Previously this would result in the address being all zeros. Whereas now the
address bytes have whatever value they previously had.

My suggestion is to rename this to "Resize()" if you want it to behave
differently. Otherwise if there are lots of callers of resize() and you need to
preserve that API, then make it match by zeroing out the new bytes lest this
leads to subtle issues.

[Ryan Hamilton, 2017/05/17 18:26:42]

Yeah, specifically the code in ParseIPLiteralToBytes which passes in the array
to url::IPv6AddressToNumber or url::IPv4AddressToNumber, which works on a
vanilla unsigned char[].
Done.

+      DCHECK_LE(size, 16);
+      size_ = static_cast<uint8_t>(size);
+    }
+
+    // Returns true if the underlying array is empty.
+    bool empty() const { return size_ == 0; }
+
+    // Returns a pointer to the underlying array of bytes.
+    const uint8_t* data() const { return bytes_.data(); }
+    uint8_t* data() { return bytes_.data(); }
+
+    // Returns a pointer to the first element.
+    const uint8_t* begin() const { return data(); }
+
+    // Returns a pointer past the last element.
+    const uint8_t* end() const { return data() + size_; }
+
+    // Returns a reference to the last element.
+    uint8_t& back() {
+      DCHECK(!empty());
+      return bytes_[size_ - 1];
+    }
+    const uint8_t& back() const {
+      DCHECK(!empty());
+      return bytes_[size_ - 1];
+    }
+
+    // Appends |val| to the end and increments the size.
+    void push_back(uint8_t val) {
+      DCHECK_GT(16, size_);
+      bytes_[size_++] = val;
+    }
+
+    // Returns a reference to the byte at index |pos|.
+    uint8_t& operator[](size_t pos) {
+      DCHECK_LT(pos, size_);
+      return bytes_[pos];
+    }
+    const uint8_t& operator[](size_t pos) const {
+      DCHECK_LT(pos, size_);
+      return bytes_[pos];
+    }
+
+   private:
+    friend bool operator>(const IPAddressBytes& lhs, const IPAddressBytes& rhs);
+    friend bool operator<(const IPAddressBytes& lhs, const IPAddressBytes& rhs);
+    friend bool operator!=(const IPAddressBytes& lhs,
+                           const IPAddressBytes& rhs);
+    friend bool operator==(const IPAddressBytes& lhs,
+                           const IPAddressBytes& rhs);
+
+    // Underlying sequence of bytes
+    std::array<uint8_t, kIPv6AddressSize> bytes_;
+
+    // Number of elements in |bytes_|. Should be either kIPv4AddressSize
+    // or kIPv6AddressSize or 0.
+    uint8_t size_;
+  };
+
   // Creates a zero-sized, invalid address.
   IPAddress();
 
   // Copies the input address to |ip_address_|. The input is expected to be in
   // network byte order.
   explicit IPAddress(const std::vector<uint8_t>& address);
 
   IPAddress(const IPAddress& other);
 
   // Copies the input address to |ip_address_|. The input is expected to be in
@@ skipping 61 matching lines @@
   // Returns the canonical string representation of an IP address.
   // For example: "192.168.0.1" or "::1". Returns the empty string when
   // |ip_address_| is invalid.
   std::string ToString() const;
 
   // Parses an IP address literal (either IPv4 or IPv6) to its numeric value.
   // Returns true on success and fills |ip_address_| with the numeric value.
   bool AssignFromIPLiteral(const base::StringPiece& ip_literal)
       WARN_UNUSED_RESULT;
 
-  // Returns the underlying byte vector.
-  const std::vector<uint8_t>& bytes() const { return ip_address_; };
+  // Returns the underlying bytes.
+  const IPAddressBytes& bytes() const { return ip_address_; };
+
+  // Returns the underlying bytes as a vector.
+  std::vector<uint8_t> BytesAsVector() const;
 
   // Returns an IPAddress instance representing the 127.0.0.1 address.
   static IPAddress IPv4Localhost();
 
   // Returns an IPAddress instance representing the ::1 address.
   static IPAddress IPv6Localhost();
 
   // Returns an IPAddress made up of |num_zero_bytes| zeros.
   static IPAddress AllZeros(size_t num_zero_bytes);
 
   // Returns an IPAddress instance representing the 0.0.0.0 address.
   static IPAddress IPv4AllZeros();
 
   // Returns an IPAddress instance representing the :: address.
   static IPAddress IPv6AllZeros();
 
   bool operator==(const IPAddress& that) const;
   bool operator!=(const IPAddress& that) const;
   bool operator<(const IPAddress& that) const;
 
  private:
   // IPv4 addresses will have length kIPv4AddressSize, whereas IPv6 address
   // will have length kIPv6AddressSize.
-  std::vector<uint8_t> ip_address_;
+  IPAddressBytes ip_address_;
 
   // This class is copyable and assignable.
 };
 
+bool operator>(const IPAddress::IPAddressBytes& lhs,
+               const IPAddress::IPAddressBytes& rhs);
+bool operator<(const IPAddress::IPAddressBytes& lhs,
+               const IPAddress::IPAddressBytes& rhs);
+bool operator!=(const IPAddress::IPAddressBytes& lhs,
+                const IPAddress::IPAddressBytes& rhs);
+bool operator==(const IPAddress::IPAddressBytes& lhs,
+                const IPAddress::IPAddressBytes& rhs);
+
 using IPAddressList = std::vector<IPAddress>;
 
 // Returns the canonical string representation of an IP address along with its
 // port. For example: "192.168.0.1:99" or "[::1]:80".
 NET_EXPORT std::string IPAddressToStringWithPort(const IPAddress& address,
                                                  uint16_t port);
 
 // Returns the address as a sequence of bytes in network-byte-order.
 NET_EXPORT std::string IPAddressToPackedString(const IPAddress& address);
 
@@ skipping 54 matching lines @@
 template <size_t N>
 bool IPAddressStartsWith(const IPAddress& address, const uint8_t (&prefix)[N]) {
   if (address.size() < N)
     return false;
   return std::equal(prefix, prefix + N, address.bytes().begin());
 }
 
 }  // namespace net
 
 #endif  // NET_BASE_IP_ADDRESS_H_