Appending to LittleFS

Firmware
1

I’m trying to append strings into a single file in the LittleFS system but running into issues with reading back what was appended. My code is as follows:

/*
 * Project FS-Tester
 * Description:
 * Author:
 * Date:
 */
#include <sys/stat.h>
#include <vector>
#include <fcntl.h>

// Initilize logger
SerialLogHandler logHandler1(LOG_LEVEL_INFO);

const char* fsPath = "/littlefstest/text";

// setup() runs once, when the device is first turned on.
void setup() {
  // Put initialization like pinMode and begin functions here.
  Serial.begin();
  Particle.function("writeToFs",writeToFs);
  Particle.function("dumpFs",dumpFs);
}

// loop() runs over and over again, as quickly as it can execute.
void loop() {
  // The core of your code will likely live here.

}

int writeToFs(String command){
  Log.info("Got new fs content");
  Log.info(command);
  command = command + ",";
  int fd = open(fsPath, O_RDWR | O_CREAT | O_APPEND );
  if(fd == -1){
    Log.error("File failed to open");
    return -5;
  }
  const char* req_event = command.c_str();
  uint16_t size = strlen(req_event)+1;
  int retVal = write(fd, req_event,size);
  close(fd);
  return retVal;
}

std::vector<String> parseArguments(String argumentString, String delimiter, int length){
  char argumentBuf[length];
  argumentString.toCharArray(argumentBuf, length);

  std::vector<String> result;
  char * pch;

  pch = strtok (argumentBuf,delimiter);
  while (pch != NULL)
  {
    result.push_back(pch);
    pch = strtok (NULL,delimiter);
  }
  return result;
}

int dumpFs(String command){  
  //Get File Stats
  int fd = open(fsPath, O_RDWR );
  if(fd == -1){
    Log.error("File failed to open");
    return -5;
  }
  uint16_t len;
  struct stat fStatBuf;
  int fStatRetVal = stat(fsPath, &fStatBuf);
  if(fStatRetVal == -1 ){
    Log.error("fStat on offline cache failed");
    return SYSTEM_ERROR_FILE;
  } else {
    Log.info("Got stat, reading...");
    len = fStatBuf.st_size;
  }
  Log.info("File was of size: %ld",len);

  //Read and Parse File
  char offlineCacheString[len];
  int readRetVal = read(fd, offlineCacheString, sizeof(offlineCacheString));
  if(readRetVal <= 0){
    Log.error("read on offline cache failed");
    return SYSTEM_ERROR_FILE;
  }
  Log.info("Size of read: %ld",readRetVal);
  Log.info("File read:");
  Log.info(offlineCacheString);
  std::vector<String> entries = parseArguments(String(offlineCacheString),",",readRetVal);

  // Publish cached data vector
  for(int i=0; i< entries.size(); i++){
    Log.info(entries[i]);
  }

  truncate(fsPath,0);
  close(fd);
  return readRetVal;
}

If I send three commands to ‘writeToFs’ say ‘hello’ ‘world’ ‘test’. I would expect a call to ‘dumpFs’ to log “hello,world,test,” before reporting the parse version. When I run it, I only get back the “hello,” value. Any thoughts on why this is the case? I suspect I’m using the O_APPEND flag incorrectly or may need to use lseek but would appreciate some advice.

2

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