Extend net/base/parse_number.h for parsing of negative numbers, and determining if there was overflo

net/base/parse_number.cc

 // Copyright 2016 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 "net/base/parse_number.h"
 
+#include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 
 namespace net {
 
-bool ParseNonNegativeDecimalInt(const base::StringPiece& input, int* output) {
-  if (input.empty() || input[0] > '9' || input[0] < '0')
+namespace {
+
+// The string to number conversion functions in //base include the type in the
+// name (like StringToInt64()). The following wrapper methods create a
+// consistent interface to StringToXXX() that calls the appropriate //base
+// version. This simplifies writing generic code with a template.
+
+bool StringToNumber(const base::StringPiece& input, int32_t* output) {
+  // This assumes ints are 32-bits (will fail compile if that ever changes).
+  return base::StringToInt(input, output);
+}
+
+bool StringToNumber(const base::StringPiece& input, uint32_t* output) {
+  // This assumes ints are 32-bits (will fail compile if that ever changes).
+  return base::StringToUint(input, output);
+}
+
+bool StringToNumber(const base::StringPiece& input, int64_t* output) {
+  return base::StringToInt64(input, output);
+}
+
+bool StringToNumber(const base::StringPiece& input, uint64_t* output) {
+  return base::StringToUint64(input, output);
+}
+
+bool SetError(ParseIntError error, ParseIntError* optional_error) {
+  if (optional_error)
+    *optional_error = error;
+  return false;
+}
+
+template <typename T>
+bool ParseIntHelper(const base::StringPiece& input,
+                    ParseIntFormat format,
+                    T* output,
+                    ParseIntError* optional_error) {
+  if (input.empty())
+    return SetError(ParseIntError::FAILED_PARSE, optional_error);
+
+  bool starts_with_negative = input[0] == '-';
+  bool starts_with_digit = input[0] >= '0' && input[0] <= '9';
+
+  // Numbers must start with either a digit or a negative sign
+  //
+  // Reject everything else to prevent the permissive behavior of
+  // StringToIntXXX() when it comes to accepting a leading '+'.
+  if (!starts_with_digit) {
+    if (format == ParseIntFormat::NON_NEGATIVE || !starts_with_negative)
+      return SetError(ParseIntError::FAILED_PARSE, optional_error);
+  }
+
+  // Dispatch to the appropriate flavor of base::StringToXXX() by calling one of
+  // the type-specific overloads.
+  T result;
+  if (StringToNumber(input, &result)) {
+    *output = result;
+    return true;
+  }
+
+  // Set an error that distinguishes between parsing/underflow/overflow errors.
+  //
+  // Note that base::StringToXXX() functions have a magical API that modify the
+  // output on failure to indicate whether underflow/overflow happened.
+  //
+  // You would think these can be used here, but unfortunately they return those

[mmenke, 2016/04/07 20:42:53]

nit:  Think it's best to avoid personal pronouns like "you".  Maybe just remove
that clause entirely, and merge with previous paragraph?

[eroman, 2016/04/08 18:57:32]

Done. I simplified the various comments in this function.

+  // magic values in multiple cases making it impossible to distinguish
+  // underflow/overflow from failed parsing due to leading/trailing whitespace.
+  //
+  // So instead look at the number to see if it was valid.
+
+  // Optimization: If the error is not going to be inspected, don't bother
+  // refining it.
+  if (!optional_error)
     return false;
 
-  int result;
-  if (!base::StringToInt(input, &result))
-    return false;
+  // Strip any leading negative sign off the number.
+  base::StringPiece numeric_portion =
+      starts_with_negative ? input.substr(1) : input;
 
-  *output = result;
-  return true;
+  // Test if |numeric_portion| is a valid non-negative integer.
+  if (!numeric_portion.empty() &&
+      numeric_portion.find_first_not_of("0123456789") == std::string::npos) {
+    // If it was, the failure must have been due to underflow/overflow.
+    return SetError(starts_with_negative ? ParseIntError::FAILED_UNDERFLOW
+                                         : ParseIntError::FAILED_OVERFLOW,
+                    optional_error);
+  }
+
+  // Otherwise it was a mundane parsing error.
+  return SetError(ParseIntError::FAILED_PARSE, optional_error);
+}
+
+}  // namespace
+
+bool ParseInt32(const base::StringPiece& input,
+                ParseIntFormat format,
+                int32_t* output,
+                ParseIntError* optional_error) {
+  return ParseIntHelper(input, format, output, optional_error);
+}
+
+bool ParseInt64(const base::StringPiece& input,
+                ParseIntFormat format,
+                int64_t* output,
+                ParseIntError* optional_error) {
+  return ParseIntHelper(input, format, output, optional_error);
+}
+
+bool ParseUint32(const base::StringPiece& input,
+                 uint32_t* output,
+                 ParseIntError* optional_error) {
+  return ParseIntHelper(input, ParseIntFormat::NON_NEGATIVE, output,
+                        optional_error);
+}
+
+bool ParseUint64(const base::StringPiece& input,
+                 uint64_t* output,
+                 ParseIntError* optional_error) {
+  return ParseIntHelper(input, ParseIntFormat::NON_NEGATIVE, output,
+                        optional_error);
 }
 
 }  // namespace net