StreamWriter/StreamReader buffer size inconsistencies #118748
Description
Description
Default buffer size value
The StreamWriter constructor overload that takes FileStreamOptions uses a buffer size of DefaultFileStreamBufferSize (4096) for the StreamWriter char buffer, but all other StreamWriter overloads without a caller-specified buffer size use DefaultBufferSize (1024). This is clearly a mistake and that DefaultFileStreamBufferSize was only intended to be used as the default buffer size of the FileStream byte buffer, not the StreamWriter char buffer.
Compare with the StreamReader constructor overload that takes FileStreamOptions, which correctly uses a buffer size of DefaultBufferSize (1024).
It's not clear why the DefaultFileStreamBufferSize constant is even defined in StreamReader or StreamWriter. The default buffer size of FileStream itself is also 4096, so StreamWriter and StreamReader could just use the FileStream constructor overload that doesn't require a bufferSize and get the same result. Neither StreamWriter nor StreamReader reference DefaultFileStreamBufferSize when using FileStreamOptions anyway.
Also, the StreamWriter constructor docs are inaccurate, since the bufferSize description is "The buffer size, in bytes.", but it actually indicates the size of a char[], not a byte[].
The StreamReader constructor docs are better, though inconsistent. One of the StreamReader overloads gives the complete correct description of "The minimum buffer size, in number of 16-bit characters.", but the other overloads just say "The minimum buffer size." without specifying the unit.
ArgumentOutOfRangeException conditions
The StreamWriter and StreamReader constructors that take a Stream allow bufferSize to be explicitly passed as -1 to use the default buffer size, but the constructors that take a file path throw an ArgumentOutOfRangeException if -1 is passed as the buffer size. I can't think of a reason for this inconsistency.
The StreamWriter docs claim every constructor throws ArgumentOutOfRangeException when "bufferSize is negative.", which is incorrect because -1 is accepted for Stream-accepting overloads. Also, it fails to mention that ArgumentOutOfRangeException is also thrown when bufferSize is 0.
The StreamReader docs claim ArgumentOutOfRangeException is thrown when "bufferSize is less than or equal to zero.", which at least mentions that 0 throws, but it still doesn't mention that -1 doesn't throw for the Stream-accepting overloads. Also, the docs for one of the StreamReader constructors doesn't mention ArgumentOutOfRangeException at all.
Reproduction Steps
Default buffer size value
new StreamWriter(@"C:\temp\test.txt", new FileStreamOptions())ArgumentOutOfRangeException conditions
new StreamWriter(@"C:\temp\test.txt", append: false, Encoding.UTF8, -1)Expected behavior
Default buffer size value
Uses buffer size consistent with all other StreamWriter constructors (1024 chars)
ArgumentOutOfRangeException conditions
Uses default buffer size
Actual behavior
Default buffer size value
Uses buffer size inconsistent with all other StreamWriter constructors (4096 chars)
ArgumentOutOfRangeException conditions
Throws ArgumentOutOfRangeException
Regression?
No response
Known Workarounds
No response
Configuration
No response
Other information
No response