Implements seekDir and getNextFileName on FS Lib to improve performance

[Lucasczm]

Description of Change

Implemented two functions:

• getNextFileName: Get the next file name with better performance than getNextFile function. To improve file listing.
• seekDir: Set the position of directory for improve search.

Examples:

 File root = SD.open("/data");
 String filename;
 //Return true if have next file, false if not
 if (root.getNextFileName(filename)) {
     Serial.println(filename); //print "file1"
 }

Tests scenarios

Tested on PlatformIO and Arduino core v2.0.4 with ESP32 LILYGO PoE Board

Related links

#5002

[CLAassistant]

All committers have signed the CLA.

[me-no-dev]

For getNextFileName why don't you return the filename directly (or empty String if not available) instead?

[PilnyTomas]

Tested using this sketch confirming that the new function is way much faster:
new function ~0.24ms per folder read
old function openNextFile ~142ms per folder read

[PilnyTomas]

Apart from the requested changes looks good.

[Lucasczm]

Now its return String name directly or String empty

[tueddy]

The speed improvement is amazing! For a webserver SD filexplorer the time for listing is currently about 2 seconds (very blocking), with this PR only 20 msecs (hundreds of mp3 files on SD card). Works fine here!

But for the Javascript based file explorer tree i also need the information wether it's a file or directory. Is there a way to get it?
Suggestion: add a trailing slash in filename if it's a directory or add an overload function with out-param isDirectory.

`

String VFSFileImpl::getNextFileName()
{
...
name += fname;
// add trailing slash for detecting directory
if (file->d_type == DT_DIR) {
name = "/" + name;
}
return name;
}

`

Thank's!

[tueddy]

I made a speedtest example for PIO here https://github.com/tueddy/FS/tree/main/example
Tested my SD-cards with a lot of files in root directory:

Samsung Evo 32GB:
getNextFileName(), done reading root-directory 36 elemts in 18 ms = 0.50 ms/folder
openNextFile(), done reading root-directory 36 elements in 492 ms = 13.67 ms/elements

Kingston 8GB, a bit older card:
getNextFileName(), done reading root-directory 42 elemts in 29 ms = 0.69 ms/folder
openNextFile(), done reading root-directory 42 elements in 1119 ms = 26.64 ms/elements

Transcend 16GB:
getNextFileName(), done reading root-directory 84 elemts in 83 ms = 0.99 ms/folder
openNextFile(), done reading root-directory 84 elements in 6960 ms = 82.86 ms/elements

Scandisk 16GB:
getNextFileName(), done reading root-directory 151 elemts in 68 ms = 0.45 ms/folder
openNextFile(), done reading root-directory 151 elements in 6872 ms = 45.51 ms/elements

[me-no-dev]

@SuGlider waiting on your approval here :)

[vortigont]

a small hint for String's

[SuGlider]

@Lucasczm - Thanks for the PR! Very good.

[SuGlider]

@Lucasczm - I can't rebase it from here. Please do it in your end in order to be able to merge it. Thanks.

[Lucasczm]

@SuGlider updated!

[tueddy]

Can't test it just at the moment, but can I distinguish whether in the listing is a file or directory with this commit?
Made a comment above..

Thank's for your work!

[BlueAndi]

@tueddy The seekDir() implementation will only be useful if the other functions are available in FS and VFS too, see
https://github.com/espressif/esp-idf/blob/16a4ee7c36a848ca155791677ce011f3ca75c519/components/newlib/platform_include/sys/dirent.h#L51-L57

@Lucasczm How do you use seekDir() without the other functions?

[tueddy]

getNextFileName() works fine in 2.0.6, but how can i detect now if return value is a file or directory?

[nomis]

This behaviour is inconsistent with openNextFile() which skips to the next file.

It's not possible to tell the difference between "end of file list" and "something that is not a file or directory".

[nomis]

This is the "path", not the "name" of the file.

This results in more effort by users of this function to remove the directory name (which they already have) from every filename.

(The openNextFile() function returns a File so it's possible to use name() or path())