FILE_WRITE replaces existing content in File on SD-Card in 2.5.1

[Flashmueller]

Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• I have filled out all fields below.

Platform

• Hardware: [ESP-12]
• Core Version: [latest git hash or date]
• Development Env: [Arduino IDE 1.8.9]
• Operating System: [MacOS]

Settings in IDE

• Module: [Generic ESP8266 Module and Adafruit Feather Huzzah]
• Flash Mode: [qio]
• Flash Size: [4MB/1MB]
• lwip Variant: [v1.4|v2 Lower Memory|Higher Bandwidth]
• Reset Method: [ck|nodemcu]
• Flash Frequency: [80Mhz]
• CPU Frequency: [80Mhz]
• Upload Using: [SERIAL]
• Upload Speed: [921600] (serial upload only)

Problem Description

After updating to 2.5.1, data that gets pushed to an existing file on the SD-Card via
file.println(data); gets no longer added below the last line in the file, but replaces the whole file content. So only the last data, that was pushed to the file, stays there.

I was not able to figure out whether the whole file is replaced or only the content.
Same issue with short and long file name.

Examples to reproduce the Error: SD/Datalogger or SD/ReadWrite

Or the one below.

Output on Serial Monitor at readout should be:

test.txt:
testing 1, 2, 3.
testing 4, 5, 6.

But only is:

test.txt:
testing 1, 2, 3.

#include <SPI.h>
#include <SD.h>

File myFile;

void setup() {
  Serial.begin(9600);
  while (!Serial) {
  }

  Serial.print("Initializing SD card...");

  if (!SD.begin(4)) {
    Serial.println("initialization failed!");
    return;
  }
  Serial.println("initialization done.");

  myFile = SD.open("test.txt", FILE_WRITE);

  if (myFile) {
    myFile.println("testing 1, 2, 3.");
    myFile.close();

    myFile.println("testing 4, 5, 6.");
    myFile.close();
    Serial.println("done.");
  } 
else {
    Serial.println("error opening test.txt");
  }

  // re-open the file for reading:
  myFile = SD.open("test.txt");
  if (myFile) {
    Serial.println("test.txt:");

    // read from the file until there's nothing else in it:
    while (myFile.available()) {
      Serial.write(myFile.read());
    }
    // close the file:
    myFile.close();
  } else {
    // if the file didn't open, print an error:
    Serial.println("error opening test.txt");
  }
}

void loop() {
  // nothing happens after setup
}

Debug Messages

none

[earlephilhower]

The listed example has the sequence which is guaranteed to fail:

    myFile.println("testing 1, 2, 3.");
    myFile.close();

    myFile.println("testing 4, 5, 6.");
    myFile.close();
    Serial.println("done.");

After the first close, the writing of the 2nd line will fail since the file is no longer opened.

[earlephilhower]

That said, upon looking at the code I do see the difference. The attached PR reverts to the old behavior. You can try it yourself in your code by simply adding | sdfat::O_APPEND to the define in the header.

[Flashmueller]

Oh sorry... of course. i was to ambitious cutting out unnecessary parts to provide a short example.
correct Code-Snippet to show the behavior with and without the already requested modification:

  myFile = SD.open("test.txt", FILE_WRITE);
  if (myFile) {
    myFile.println("testing 1, 2, 3.");
    myFile.close();
    Serial.println("1st write done");
  }

myFile = SD.open("test.txt", FILE_WRITE);
  if (myFile) {
    myFile.println("testing 4, 5, 6.");
    myFile.close();
    Serial.println("2nd write done");
  } 

THANK YOU FOR that quick fix!
I have tested it and can confirm that it solves the "problem" and makes the new wrapper work just like the old library in this case.

[earlephilhower]

Reopening to track the fix commit