CODEWITHSUNDEEP
javascriptjqueryajax
sand
sand

Reputation: 37

Reading a live log file from javascript

I am using following code to read data from a text log file which is continually growing.

setInterval(call, 1000);

function call() {
  $.ajax({
    type: "GET",
    url: "GenNumber.txt",
    dataType: "text",
    success: function(data) {
      readdata(data);
    },
  });
}

My query is , does ajax reads complete file in every call or the (new) added lines from last call. If it reads entire file in each call, it may crash when file size bigger and bigger. Is there any way to read only new lines from the last call and stop the program when file stops growing.

Thanks

Upvotes: 1

Views: 3876

Answers (2)

neuhaus
neuhaus

Reputation: 4094

You can use the headers parameter for the settings parameter to the ajax() function to set a Range HTTP header to limit what data you are receiving.

Some examples:

bytes=9500-

will start sending data at offset 9500.

bytes=-500

will send the last 500 bytes. This requires that the HTTP server supports ranges (most do).

The Range header is documented in RFC 7233.

Taking your example code:

$.ajax({ 
        type: "GET", 
        url: "GenNumber.txt", 
        dataType: "text", 
        success: function (data) { readdata(data); }, 
        headers: {
            "Range" : "bytes=-500"
        }
    });

Upvotes: 3

Gaël Barbin
Gaël Barbin

Reputation: 3919

In complement to the neuhaus answer, using the Range header, you can store from the client side the total bytes already read.
So at each request, you will receive only data appended since the last call. 

var byteRead=0;
setInterval(function(){

   $.ajax({ 
        type: "GET", 
        url: "GenNumber.txt",
        dataType: "text", 
        success: function (data) {  
            byteRead+= data.length;
            readdata(data);
        }, 
        headers: {
            "Range" : "bytes="+byteRead+"-"
        }
    });
},1000);

Upvotes: 1

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