Javascript NULL character in string when writing with chrome fileSystem

Question

I used a filewriter in chrome packaged apps to save a json string. I followed the samples where the writer is set to truncate at the length of the blob, so files can be overwritten with shorter data.

this.writeLocalFile = function(){
        chrome.fileSystem.getWritableEntry(self.localFile, function(writableEntry){
            console.log(writableEntry);
            writableEntry.createWriter(function(writer) {
                writer.onerror = function(){
                    console.log("error");
                }
                writer.onwriteend = function(){
                    console.log("Write ended");
                }
                self.getData();
                blob = new Blob([self.data], {type: 'text/plain'});
                writer.truncate(blob.size);
                //writer.seek(0);
                writer.write(blob);
            }, function(error){
                console.log(error);
            });
        })
    }

the issue is that when I overwrite a longer file with shorter data, if i dont use truncate, the extra data is left and i cant read in a valid json on next load, if i do use truncate, all that extra space is weird null charcters when i look in sublime

So, the read string is still the length of the old longer file, but when i log it in console, the string is correct, and i can copy and paste the output and set it to another variable for the shorter length. But the object read directly is still the longer length and I cant figure out how to trim the null characters from the end

For example, if the file was 1200 chars, and I delete some data and resave so the json string is 800 chars, the last 400 chars in the file are now null. When I reread the data next load, the string is still 1200 chars, with the last 400 being ""

weirdstring[900]//""
weirdstring[900] == ""   // false
weirdstring[900] == null // false
weirdstring[900].length // 1
!weirdstring[900] // false
weirdstring.charCodeAt(900) // 0

is there a better to way to fix this than scan the string, check for charCodeAt==0 and removing the rest? Like, a better way to write to the file?

Do you know the index of your last char ...? – Prasath K Jul 23 '13 at 08:45 — Prasath K, Jul 23 '13 at 08:45
Yeah I just search for RegExp('\0') – user864572 Jul 23 '13 at 19:31 — user864572, Jul 23 '13 at 19:31

score 0 · Answer 1 · answered Jul 18 '19 at 20:17

0

I found this because I am also having this issue. In doing research, I believe we are both using truncate incorrectly.

I think this stackoverflow explains how to use truncate correctly: overwrite a file with HTML5 FileWriter

answered Jul 18 '19 at 20:17

DemiImp

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Javascript NULL character in string when writing with chrome fileSystem

1 Answers1