Avoid heap allocations in IPAddress

net/base/ip_address.h

Index: net/base/ip_address.h
diff --git a/net/base/ip_address.h b/net/base/ip_address.h
index e326e78da6e08a75f97fc4647c2c7252d7bd321a..e2d3d18b789fd866c5fa65844a13e7180bbed4a2 100644
--- a/net/base/ip_address.h
+++ b/net/base/ip_address.h
@@ -8,6 +8,7 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include <array>
 #include <string>
 #include <vector>
 
@@ -21,6 +22,83 @@ 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. Zeros out all elements in [0, |size|).

[eroman, 2017/05/17 20:48:16]

This is not the same way that std::vector<>::resize() works.
If changing the behavior, why not rename the function to Resize() as well?

[Ryan Hamilton, 2017/05/17 23:32:37]

Ah, ok. Renamed to Resize().

+    void resize(size_t size) {
+      DCHECK_LE(size, 16u);
+      if (size != 0)
+        memset(bytes_.data(), 0, size);
+      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();
 
@@ -102,8 +180,11 @@ class NET_EXPORT IPAddress {
   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();
@@ -127,11 +208,20 @@ class NET_EXPORT IPAddress {
  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