Improve error message when seeking to negative position in FileStream (#120626)

Copilot · stephentoub · web-flow · commit 0b9f7349bfca · 2025-10-12T22:06:15.000-07:00
Fixes #112112 Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
diff --git a/src/libraries/System.Private.CoreLib/src/System/IO/Strategies/OSFileStreamStrategy.cs b/src/libraries/System.Private.CoreLib/src/System/IO/Strategies/OSFileStreamStrategy.cs
@@ -158,8 +158,8 @@ public sealed override long Seek(long offset, SeekOrigin origin)
             }
             else
             {
-                // keep throwing the same exception we did when seek was causing actual offset change
-                FileStreamHelpers.ThrowInvalidArgument(_fileHandle);
+                // keep throwing the same exception type we did when seek was causing actual offset change
+                throw new IOException(SR.IO_SeekBeforeBegin);
             }
 
             // Prevent users from overwriting data in a file that was opened in append mode.

Original file line number	Diff line number	Diff line change
`@@ -158,8 +158,8 @@ public sealed override long Seek(long offset, SeekOrigin origin)`
`158`	`158`	`}`
`159`	`159`	`else`
`160`	`160`	`{`
`161`		`- // keep throwing the same exception we did when seek was causing actual offset change`
`162`		`- FileStreamHelpers.ThrowInvalidArgument(_fileHandle);`
	`161`	`+ // keep throwing the same exception type we did when seek was causing actual offset change`
	`162`	`+ throw new IOException(SR.IO_SeekBeforeBegin);`
`163`	`163`	`}`
`164`	`164`
`165`	`165`	`// Prevent users from overwriting data in a file that was opened in append mode.`