Update MemoryStream max capacity #119089

alinpahontu2912 · 2025-08-26T10:02:07Z

Updates MemoryStream to cap capacity at 0x7FFFFFC7 (the true max byte array length) and adds a test to check:

Capacity just under the max succeeds
Capacity above the max throws

Copilot

Pull Request Overview

This PR updates the MemoryStream maximum capacity from int.MaxValue to 0x7FFFFFC7 (the actual maximum byte array length supported by the CLR). This change aligns MemoryStream capacity limits with the underlying array implementation constraints.

Key changes:

Updated the maximum capacity constant to reflect the true CLR byte array limit
Added comprehensive boundary testing for capacity validation
Updated related comments and validation logic to use the new limit

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
`src/libraries/System.Private.CoreLib/src/System/IO/MemoryStream.cs`	Updates `MemStreamMaxLength` constant from `int.MaxValue` to `0x7FFFFFC7` and adjusts validation logic
`src/libraries/System.Runtime/tests/System.IO.Tests/MemoryStream/MemoryStreamTests.cs`	Adds test to verify capacity boundary behavior at the new maximum limit

src/libraries/System.Private.CoreLib/src/System/IO/MemoryStream.cs

…m.cs Co-authored-by: Copilot <[email protected]>

…ontu2912/runtime into fix_update_mode_max_size

teo-tsirpanis

Instead of hardcoding a constant, we can use the Array.MaxLength property.

src/libraries/System.Private.CoreLib/src/System/IO/MemoryStream.cs

src/libraries/System.Runtime/tests/System.IO.Tests/BinaryWriter/BinaryWriterTests.cs

src/libraries/System.Runtime/tests/System.IO.Tests/MemoryStream/MemoryStreamTests.cs

Co-authored-by: Theodore Tsirpanis <[email protected]>

alinpahontu2912 · 2025-08-26T13:20:51Z

Thanks for the input @teo-tsirpanis, I replaced the hardcoded value 👍

src/libraries/System.Private.CoreLib/src/System/IO/MemoryStream.cs

…ontu2912/runtime into fix_update_mode_max_size

jozkee

LGTM, thanks.

jozkee

Sorry for the comments post-merge but I think there's some items to address.
I will also mark this as breaking change since we are changing the exception type being thrown.

jozkee · 2025-09-03T15:18:06Z

src/libraries/System.Private.CoreLib/src/Resources/Strings.resx

  </data>
  <data name="ArgumentOutOfRange_StreamLength" xml:space="preserve">
-    <value>Stream length must be non-negative and less than 2^31 - 1 - origin.</value>
+    <value>Stream length must be non-negative and less than the maximum array length (0x7FFFFFC7) - origin.</value>


There's been efforts to not hardcode 0x7FFFFFC7 and instead use Array.MaxLength. Can we pass $"0x{Array.MaxLength:X}" using SR.Format?

Suggested change

<value>Stream length must be non-negative and less than the maximum array length (0x7FFFFFC7) - origin.</value>

<value>Stream length must be non-negative and less than the maximum array length {0} - origin.</value>

Should this do something like the following instead, to help clarify that the value may change over time:

maximum array length (currently 0x{0})

Perhaps we could just explicitly use the text Array.MaxLength instead?

jozkee · 2025-09-03T15:18:12Z

src/libraries/System.Private.CoreLib/src/System/IO/MemoryStream.cs

            // Origin wasn't publicly exposed above.
-            Debug.Assert(MemStreamMaxLength == int.MaxValue);  // Check parameter validation logic in this method if this fails.
-            if (value > (int.MaxValue - _origin))
+            Debug.Assert(MemStreamMaxLength == 0x7FFFFFC7);  // Check parameter validation logic in this method if this fails.


Suggested change

Debug.Assert(MemStreamMaxLength == 0x7FFFFFC7); // Check parameter validation logic in this method if this fails.

Debug.Assert(MemStreamMaxLength == Array.MaxLength); // Check parameter validation logic in this method if this fails.

jozkee · 2025-09-03T15:35:57Z

src/libraries/System.Private.CoreLib/src/System/IO/MemoryStream.cs

-            if (value > (int.MaxValue - _origin))
+            Debug.Assert(MemStreamMaxLength == 0x7FFFFFC7);  // Check parameter validation logic in this method if this fails.
+            if (value > (MemStreamMaxLength - _origin))
                throw new ArgumentOutOfRangeException(nameof(value), SR.ArgumentOutOfRange_StreamLength);


I believe we will also need to update the ctor that takes capacity because it will keep throwing OOM while we throw OutOfRange everywhere else.

dotnet-policy-service · 2025-09-03T15:38:12Z

Added needs-breaking-change-doc-created label because this PR has the breaking-change label.

When you commit this breaking change:

Create and link to this PR and the issue a matching issue in the dotnet/docs repo using the breaking change documentation template, then remove this needs-breaking-change-doc-created label.
Ask a committer to mail the .NET Breaking Change Notification DL.

Tagging @dotnet/compat for awareness of the breaking change.

tannergooding · 2025-09-03T16:48:32Z

I will also mark this as breaking change since we are changing the exception type being thrown.

Where is the exception type being changed? Looks like it is still ArgumentOutOfRangeException

jkotas · 2025-09-03T17:33:00Z

Where is the exception type being changed? Looks like it is still ArgumentOutOfRangeException

new MemoryStream().SetLength(Int32.MaxValue) threw OutOfMemoryException before this change and throws ArgumentOutOfRangeException exception after this change.

tannergooding · 2025-09-03T17:54:32Z

new MemoryStream().SetLength(Int32.MaxValue) threw OutOfMemoryException before this change and throws ArgumentOutOfRangeException exception after this change.

Ah, I see. Because the old one was > int.MaxValue so it would've tried and failed previously

👍

* cap memory stream max length and add unit test for max capacity * Update src/libraries/System.Private.CoreLib/src/System/IO/MemoryStream.cs Co-authored-by: Copilot <[email protected]> * fix failing tests * Replace hardcoded value Co-authored-by: Theodore Tsirpanis <[email protected]> * update error message --------- Co-authored-by: Copilot <[email protected]> Co-authored-by: Theodore Tsirpanis <[email protected]>

ericstj · 2025-10-24T21:46:44Z

📋 Breaking Change Documentation Required

Create a breaking change issue with AI-generated content

Generated by Breaking Change Documentation Tool - 2025-10-24 14:46:42

cap memory stream max length and add unit test for max capacity

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alinpahontu2912 and others added 3 commits August 26, 2025 12:03

Update src/libraries/System.Private.CoreLib/src/System/IO/MemoryStrea…

7d3947a

…m.cs Co-authored-by: Copilot <[email protected]>

fix failing tests

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Merge branch 'fix_update_mode_max_size' of https://github.com/alinpah…

682275b

…ontu2912/runtime into fix_update_mode_max_size

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Replace hardcoded value

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Co-authored-by: Theodore Tsirpanis <[email protected]>

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alinpahontu2912 added 2 commits August 26, 2025 17:10

update error message

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Merge branch 'fix_update_mode_max_size' of https://github.com/alinpah…

0a7fe26

…ontu2912/runtime into fix_update_mode_max_size

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alinpahontu2912 requested a review from ericstj September 2, 2025 08:40

ericstj requested a review from jozkee September 2, 2025 15:08

jozkee approved these changes Sep 2, 2025

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jozkee merged commit f610923 into dotnet:main Sep 2, 2025
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alinpahontu2912 mentioned this pull request Sep 25, 2025

Update MemoryStream max capacity improvements #120091

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	<value>Stream length must be non-negative and less than the maximum array length (0x7FFFFFC7) - origin.</value>
	<value>Stream length must be non-negative and less than the maximum array length {0} - origin.</value>

	Debug.Assert(MemStreamMaxLength == 0x7FFFFFC7); // Check parameter validation logic in this method if this fails.
	Debug.Assert(MemStreamMaxLength == Array.MaxLength); // Check parameter validation logic in this method if this fails.

Update MemoryStream max capacity #119089

Update MemoryStream max capacity #119089

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📋 Breaking Change Documentation Required

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