Implement a parser that parses the "Range" HTTP header...

net/http/http_byte_range.cc

Index: net/http/http_byte_range.cc
===================================================================
--- net/http/http_byte_range.cc	(revision 0)
+++ net/http/http_byte_range.cc	(revision 0)
@@ -0,0 +1,76 @@
+// Copyright (c) 2009 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.
+
+#include <algorithm>
+
+#include "net/http/http_byte_range.h"
+
+namespace {
+
+const int64 kPositionNotSpecified = -1;
+
+}  // namespace
+
+namespace net {
+
+HttpByteRange::HttpByteRange()
+    : first_byte_position_(kPositionNotSpecified),
+      last_byte_position_(kPositionNotSpecified),
+      suffix_length_(kPositionNotSpecified),
+      has_computed_bounds_(false) {
+}
+
+bool HttpByteRange::IsSuffixByteRange() const {
+  return suffix_length_ != kPositionNotSpecified;
+}
+
+bool HttpByteRange::HasFirstBytePosition() const {
+  return first_byte_position_ != kPositionNotSpecified;
+}
+
+bool HttpByteRange::HasLastBytePosition() const {
+  return last_byte_position_ != kPositionNotSpecified;
+}
+
+bool HttpByteRange::IsValid() const {
+  if (suffix_length_ > 0)
+    return true;
+  return first_byte_position_ >= 0 &&
+         (last_byte_position_ == kPositionNotSpecified ||
+          last_byte_position_ >= first_byte_position_);
+}
+
+bool HttpByteRange::ComputeBounds(int64 size) {
+  if (size < 0)
+    return false;
+  if (has_computed_bounds_)
+    return false;
+  has_computed_bounds_ = true;
+
+  // Empty values.
+  if (!HasFirstBytePosition() &&
+      !HasLastBytePosition() &&
+      !IsSuffixByteRange()) {
+      first_byte_position_ = 0;
+      last_byte_position_ = size - 1;
+      return true;
+  }
+  if (!IsValid())
+    return false;
+  if (IsSuffixByteRange()) {
+    first_byte_position_ = size - std::min(size, suffix_length_);
+    last_byte_position_ = size - 1;
+    return true;
+  }
+  if (first_byte_position_ < size) {
+    if (HasLastBytePosition())
+      last_byte_position_ = std::min(size - 1, last_byte_position_);
+    else
+      last_byte_position_ = size - 1;
+    return true;
+  }
+  return false;
+}
+
+}  // namespace net