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Add claims dictionary preallocation #3542

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Merged
MZOLN merged 2 commits into from
Jul 15, 2026
+94 −2
Merged

Add claims dictionary preallocation #3542

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2949efa
Add claims dictionary presizing
Jul 10, 2026
7fe0325
Add unit tests for edge cases
Jul 15, 2026
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2 changes: 1 addition & 1 deletion src/Microsoft.IdentityModel.JsonWebTokens/Json/JsonWebToken.HeaderClaimSet.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -37,7 +37,7 @@ internal JsonClaimSet CreateHeaderClaimSet(ReadOnlySpan<byte> byteSpan)
LogHelper.MarkAsNonPII(reader.CurrentDepth),
LogHelper.MarkAsNonPII(reader.BytesConsumed))));

Dictionary<string, object> claims = new();
Dictionary<string, object> claims = new(byteSpan.Length / AverageJsonClaimLengthInBytes);
while (true)
{
if (reader.TokenType == JsonTokenType.PropertyName)
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8 changes: 7 additions & 1 deletion src/Microsoft.IdentityModel.JsonWebTokens/Json/JsonWebToken.PayloadClaimSet.cs
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Expand Up @@ -12,6 +12,12 @@ namespace Microsoft.IdentityModel.JsonWebTokens
{
public partial class JsonWebToken
{
// Average number of UTF-8 bytes per JSON claim (property name + value + structural
// characters) observed in typical JWTs. Used only to seed the initial capacity of the
// claims dictionary so it can be sized close to what it would grow to anyway, avoiding
// the intermediate reallocations/rehashes of the default 0 -> 3 -> 7 -> 17 growth path.
internal const int AverageJsonClaimLengthInBytes = 32;

internal JsonClaimSet CreatePayloadClaimSet(byte[] bytes, int length)
{
return CreatePayloadClaimSet(bytes.AsSpan(0, length));
Expand All @@ -35,7 +41,7 @@ internal JsonClaimSet CreatePayloadClaimSet(ReadOnlySpan<byte> byteSpan)
LogHelper.MarkAsNonPII(reader.CurrentDepth),
LogHelper.MarkAsNonPII(reader.BytesConsumed))));

Dictionary<string, object> claims = [];
Dictionary<string, object> claims = new(byteSpan.Length / AverageJsonClaimLengthInBytes);
while (true)
{
if (reader.TokenType == JsonTokenType.PropertyName)
Expand Down
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