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Fix min buffer sizes #76

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Merged
manigandham merged 4 commits into from
Jun 2, 2022
Merged

Fix min buffer sizes #76

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0256b8d
add new const for min buffer size
manigandham Jun 2, 2022
84a8930
use max stackalloc size const instead of numbers
manigandham Jun 2, 2022
7904219
switch to private var for min buffer in ctor
manigandham Jun 2, 2022
e721509
add new tests
manigandham Jun 2, 2022
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40 changes: 22 additions & 18 deletions src/Hashids.net/Hashids.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ public partial class Hashids : IHashids
public const string DEFAULT_ALPHABET = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
public const string DEFAULT_SEPS = "cfhistuCFHISTU";
public const int MIN_ALPHABET_LENGTH = 16;
public const int MAX_STACKALLOC_SIZE = 512;
private const int MAX_STACKALLOC_SIZE = 512;

private const double SEP_DIV = 3.5;
private const double GUARD_DIV = 12.0;
Expand All @@ -24,6 +24,7 @@ public partial class Hashids : IHashids
private readonly char[] _guards;
private readonly char[] _salt;
private readonly int _minHashLength;
private readonly int _minBufferSize;

// Creates the Regex in the first usage, speed up first use of non-hex methods
private static readonly Lazy<Regex> HexValidator = new(() => new Regex("^[0-9a-fA-F]+$", RegexOptions.Compiled));
Expand Down Expand Up @@ -61,6 +62,9 @@ public Hashids(
_minHashLength = minHashLength;
_alphabet = alphabet.ToCharArray().Distinct().ToArray();
_seps = seps.ToCharArray();

// use min buffer size of 20 which is 1 digit longer than the biggest 64-bit integer (long.MaxValue = 9223372036854775807)
_minBufferSize = Math.Max(20, minHashLength);

if (_alphabet.Length < MIN_ALPHABET_LENGTH)
throw new ArgumentException($"Alphabet must contain at least {MIN_ALPHABET_LENGTH:N0} unique characters.", paramName: nameof(alphabet));
Expand Down Expand Up @@ -142,8 +146,8 @@ public Hashids(
/// <returns>the hashed string</returns>
public string EncodeLong(long number)
{
var numberLength = _minHashLength > 20 ? _minHashLength : 20;
var result = numberLength < 512 ? stackalloc char[numberLength] : new char[numberLength];
var numberLength = _minBufferSize;
var result = numberLength < MAX_STACKALLOC_SIZE ? stackalloc char[numberLength] : new char[numberLength];
var length = GenerateHashFrom(number, ref result);
return length == -1 ? string.Empty : result.Slice(0, length).ToString();
}
Expand All @@ -155,8 +159,8 @@ public string EncodeLong(long number)
/// <returns>Encoded hash string.</returns>
public string EncodeLong(params long[] numbers)
{
var numbersLength = _minHashLength > 20 ? _minHashLength * numbers.Length : numbers.Length * 20;
var result = numbersLength < 512 ? stackalloc char[numbersLength] : new char[numbersLength];
var numbersLength = _minBufferSize * numbers.Length;
var result = numbersLength < MAX_STACKALLOC_SIZE ? stackalloc char[numbersLength] : new char[numbersLength];
var length = GenerateHashFrom(numbers, ref result);
return length == -1 ? string.Empty : result.Slice(0, length).ToString();
}
Expand Down Expand Up @@ -290,21 +294,20 @@ private int GenerateHashFrom(long number, ref Span<char> result)

var numberHashInt = number % 100;

var alphabet = _alphabet.Length < 512 ? stackalloc char[_alphabet.Length] : new char[_alphabet.Length];
var alphabet = _alphabet.Length < MAX_STACKALLOC_SIZE ? stackalloc char[_alphabet.Length] : new char[_alphabet.Length];
_alphabet.CopyTo(alphabet);

var lottery = alphabet[(int)(numberHashInt % _alphabet.Length)];
result[0] = lottery;

var shuffleBuffer = _alphabet.Length < 512 ? stackalloc char[_alphabet.Length] : new char[_alphabet.Length];
var shuffleBuffer = _alphabet.Length < MAX_STACKALLOC_SIZE ? stackalloc char[_alphabet.Length] : new char[_alphabet.Length];
shuffleBuffer[0] = lottery;
_salt.AsSpan().Slice(0, Math.Min(_salt.Length, _alphabet.Length - 1)).CopyTo(shuffleBuffer.Slice(1));

var startIndex = 1 + _salt.Length;
var length = _alphabet.Length - startIndex;

// use buffer size of 19 which is the length of the biggest 64-bit integer (long.MaxValue = 9223372036854775807)
Span<char> hashBuffer = stackalloc char[19];
Span<char> hashBuffer = stackalloc char[_minBufferSize];

if (length > 0)
alphabet.Slice(0, length).CopyTo(shuffleBuffer.Slice(startIndex));
Expand Down Expand Up @@ -409,8 +412,7 @@ private int GenerateHashFrom(ReadOnlySpan<long> numbers, ref Span<char> result)
var startIndex = 1 + _salt.Length;
var length = _alphabet.Length - startIndex;

// use buffer size of 19 which is the length of the biggest 64-bit integer (long.MaxValue = 9223372036854775807)
Span<char> hashBuffer = stackalloc char[19];
Span<char> hashBuffer = stackalloc char[_minBufferSize];

for (var i = 0; i < numbers.Length; i++)
{
Expand Down Expand Up @@ -495,8 +497,7 @@ private int BuildReversedHash(long input, ReadOnlySpan<char> alphabet, Span<char
hashBuffer[length] = alphabet[idx];
length += 1;
input /= _alphabet.Length;
}
while (input > 0);
} while (input > 0);

return length;
}
Expand Down Expand Up @@ -534,10 +535,10 @@ private long GetNumberFrom(string hash)

var hashBuffer = hashBreakdown.Slice(1);

Span<char> alphabet = _alphabet.Length < 512 ? stackalloc char[_alphabet.Length] : new char[_alphabet.Length];
Span<char> alphabet = _alphabet.Length < MAX_STACKALLOC_SIZE ? stackalloc char[_alphabet.Length] : new char[_alphabet.Length];
_alphabet.CopyTo(alphabet);

Span<char> buffer = _alphabet.Length < 512 ? stackalloc char[_alphabet.Length] : new char[_alphabet.Length];
Span<char> buffer = _alphabet.Length < MAX_STACKALLOC_SIZE ? stackalloc char[_alphabet.Length] : new char[_alphabet.Length];
buffer[0] = lottery;
_salt.AsSpan().Slice(0, Math.Min(_salt.Length, _alphabet.Length - 1)).CopyTo(buffer.Slice(1));

Expand All @@ -550,10 +551,12 @@ private long GetNumberFrom(string hash)
ConsistentShuffle(alphabet, buffer);
var result = Unhash(hashBuffer, alphabet);

Span<char> resultBuffer = stackalloc char[guardedHash.Length];
// regenerate hash from numbers and compare to given hash to ensure the correct parameters were used
// ensure buffer is big enough based on what was generated
var bufferSize = Math.Max(_minBufferSize, guardedHash.Length);
Span<char> resultBuffer = stackalloc char[bufferSize];
var hashLength = GenerateHashFrom(result, ref resultBuffer);
ReadOnlySpan<char> rehash = resultBuffer.Slice(0, hashLength);
// regenerate hash from numbers and compare to given hash to ensure the correct parameters were used
if (guardedHash.Equals(rehash, StringComparison.Ordinal))
return result;

Expand All @@ -564,10 +567,11 @@ private long[] GetNumbersFrom(string hash)
{
var result = NumbersFrom(hash);

Span<char> hashBuffer = hash.Length < 512 ? stackalloc char[hash.Length] : new char[hash.Length];
Span<char> hashBuffer = hash.Length < MAX_STACKALLOC_SIZE ? stackalloc char[hash.Length] : new char[hash.Length];
var hashLength = GenerateHashFrom(result, ref hashBuffer);
if (hashLength == -1)
return Array.Empty<long>();

ReadOnlySpan<char> rehash = hashBuffer.Slice(0, hashLength);
// regenerate hash from numbers and compare to given hash to ensure the correct parameters were used
if (hash.AsSpan().Equals(rehash, StringComparison.Ordinal))
Expand Down
23 changes: 22 additions & 1 deletion test/Hashids.net.test/IssueSpecificTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -65,5 +65,26 @@ void Issue_64_long_max_value_with_min_alphabet_length()

decoded.Should().Be(long.MaxValue);
}

[Fact]
void Issue75_1CharacterHashShouldNotThrowException()
{
var hashids = new Hashids("salt");
Assert.Throws<NoResultException>(() => hashids.DecodeSingle("a"));
}

[Fact]
void Issue75_TooShortHashShouldNotThrowException()
{
var hashids = new Hashids("salt");
Assert.Throws<NoResultException>(() => hashids.DecodeSingle("ab"));
}

[Fact]
void Issue75_TooShortHashWithLargerHashLengthShouldNotThrowException()
{
var hashids = new Hashids("salt", 40);
Assert.Throws<NoResultException>(() => hashids.DecodeSingle("ab"));
}
}
}
}
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