When reading text file with StreamReader, FileStream position resets to 0 periodically creating endless loop in the reader

[jazzman55]

Library/API/IoT binding

System.IO.FileSystem, System.IO.Streams

Visual Studio version

VS2022

.NET nanoFramework extension version

No response

Target name(s)

ESP32_REV3

Firmware version

1.12.0.32

Device capabilities

No response

Description

Reading text file with StreamReader, the underlying FileStream resets its position to 0 every time StreamReader's buffer is filled up. This causes endless jumps to beginning of the file and thus the file can't be read to end.

How to reproduce

1. Upload text file to ESP32 config partition. The file must be longer than StreamReader's buffer size (512B).
2. Open the file and read it line-by-line with StreamReader.ReadLine().

Expected behaviour

File is correctly read line-by-line from start to end. When end of file is reached ReadLine() returns null.

Screenshots

Sample project or code

//The last line of loremipsum.txt is <END>
        [TestMethod]
        public void ReadText_StreamReader()
        {
            Debug.WriteLine(nameof(ReadText_StreamReader));
            string line;
            string text = "";
            using (var fs = new StreamReader(new FileStream(@"I:\loremipsum.txt", FileMode.Open, FileAccess.Read)))
            {
                line = fs.ReadLine();
                int i = 0;
                while (line != null && i++ < 50) //exit after reading 50 lines to avoid endless loop
                {
                    Debug.WriteLine(line);

                    line = fs.ReadLine();
                    if (line != null)
                        text = line;
                }
            }

            Assert.Equal("<END>", text);
        }
[loremipsum.txt](https://github.com/user-attachments/files/16523448/loremipsum.txt)

Flash to ESP32 with:

@echo off
set port=COM5
littlefs-python create ..\FileSystem %tmp%\config_image.bin --fs-size=262144 --block-size=4096
python %idf_path%\components\partition_table\parttool.py -p %port% write_partition -n config --input %tmp%\config_image.bin 
del %tmp%\config_image.bin 

Aditional information

Workaround: Track stream's position in a separate variable and set the stream position before each read: https://github.com/CShark-Hub/Mako-IoT.Device.Services.FileStorage/blob/main/src/MakoIoT.Device.Services.FileStorage/MakoStreamReader.cs#L525

Note: This was working OK with one of the previous versions of System.IO.FileSystem

[jazzman55]

The test file loremipsum.txt

[josesimoes]

The unit tests must not be covering this either because the content isn't large enough or the code there is missing this operation... 🤔

Anyway, not surprising that it had a different behavior before, as the Stream has been introduced only recently.

[Akshit018]

Subject: Request to Work on Good First Issue

Hi @jazzman55 ,

I noticed the issue with StreamReader and FileStream and believe it would be a great first issue for me to work on. I'm eager to contribute and would love the opportunity to tackle this.

May I take it on?

Thank you, Akshit

[josesimoes]

Hey @Akshit018! That's great that you're willing to tackle this one. 🥳 I'm assigning it to you now.

Please take a look at the contribution guide here. This will typically require a PR to the Sys.IO.FileSystem repo. We 💜 PRs so feel free to start one as early as you want so you can have early feedback.

If you have questions or want to discuss anything, suggest you head over to our Discord server and engage a conversation there.