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Use integer division trick to get exact base64 length #31442

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Merged
merged 2 commits into from
Apr 1, 2021
Merged

Use integer division trick to get exact base64 length #31442

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3b58acc
Use integer division trick to get exact base64 length and avoid modul…
gfoidl Mar 30, 2021
597ff0d
Use Base64.GetMaxEncodedToUtf8Length directly
gfoidl Apr 1, 2021
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17 changes: 1 addition & 16 deletions src/Http/Headers/src/ContentDispositionHeaderValue.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -541,27 +541,12 @@ private bool RequiresEncoding(StringSegment input)
return false;
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
private static int GetBase64Length(int inputLength)
{
// Copied from https://github.com/dotnet/runtime/blob/82ca681cbac89d813a3ce397e0c665e6c051ed67/src/libraries/System.Private.CoreLib/src/System/Convert.cs#L2530
long outlen = ((long)inputLength) / 3 * 4; // the base length - we want integer division here.
outlen += ((inputLength % 3) != 0) ? 4 : 0; // at most 4 more chars for the remainder

if (outlen > int.MaxValue)
{
throw new OutOfMemoryException();
}

return (int)outlen;
}

// Encode using MIME encoding
// And adds surrounding quotes, Encoded data must always be quoted, the equals signs are invalid in tokens
private string EncodeMimeWithQuotes(StringSegment input)
{
var requiredLength = MimePrefix.Length +
GetBase64Length(Encoding.UTF8.GetByteCount(input.AsSpan())) +
Base64.GetMaxEncodedToUtf8Length(Encoding.UTF8.GetByteCount(input.AsSpan())) +
MimeSuffix.Length;
Span<byte> buffer = requiredLength <= 256
? (stackalloc byte[256]).Slice(0, requiredLength)
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