Flask Logfile Live Logging

Issues on Windows

• The Browser when running on the local machine updates late or not. On remote machine it is instantanious!

Features

Display and live update of logfiles.

Scroll windows

Scrolls automatically along the end of the file. When the scrollbar is moved more than 60pixels from the end, then automatic scrolling stops.

The scroll window detects when

• A file is missing: Wait for a file to appear.
• A file has been created: Logging starts.
• A file dissapeared: The file will remains on the page.

Scroll update is done very efficiently in as big as possible chuncks. This may be a entire file or just a part of the line - for example when pytest draws a '.' for each successful test.

File select form

This optional form allows to select from a given list of files.

Renderer Log

Display a logfile and mark the lines which contain ERROR, WARINING, INFO.

Renderer Ansi2Html

Takes a ansi file as input (pytest --color=yes).

Renderer LIVELOG_MOCK

For testing: Slowly sends line by line to demonstrate updating and scrolling.

Generator generator_file

This generator redirects a file. It detects when a file appears and dissapears.

Generator generator_pipe

This generator starts a command, in the following example dmesg and redirects the output (Only tested on linux).

Technical implementation

Html

Based on HTML5 and flexboxes.

Live update

Uses Server-Sent Events described in HTML5. This is very efficient one-way channel from flask to the scrollable html-container.

File events

Detection of files to appear, dissapear and data written to the file is done very rudimentary polling using functionality found in pathlib.

There are libraries which monitor operating system events which would do the job much nicer: Watchdog, Blog. To avoid additional dependencies I did not use them.

Demo

Start Flask:

export FLASK_APP=app/webapp.py
export FLASK_ENV=development
flask run

Start Flask and open http://localhost:5000/:

You may observe how the page is filled and scrolled. Please note the form to the top right.

This shows the logfile-renderer. Note that this example does not show the form in the top right.

This shows the ansi-color-renderer.

In this view you may

• Remove the file and reload the page:

• Run ./run_pytests.sh:

User Guide

Integrate in your application

This repository shows how to integrate livelog:

• You need to copy app/livelog.py and app/templates/livelog.html to your flask directory.

• Add these lines to your webapp.py:

provider = livelog.LogfileProvider(DIRECTORY_OF_THIS_FILE.parent, '**/*')
livelog.LiveLog(app, provider)

• Create a link to the livelog-page. You find examples in app/templates/index.html.

Links for the technical stuff this library is based on

• How to make a scrollable container with dynamic height using Flexbox
• You can also create a scrollable modal that allows scroll the modal body by adding
• Make a scrollable container with dynamic height using flexbox

Ansi2color

AHA: C Implementation available on Linux

ANSI2HTML: Python Implementation used for this project

These are commands I was playing around using unbuffered output of pytest on linux.

stdbuf -oL pytest --html=report.html --self-contained-html --verbose --capture=no --color=yes | stdbuf -oL aha --no-header > log_pytest.html

stdbuf -oL pytest --html=report.html --self-contained-html --verbose --color=yes | stdbuf -oL aha --no-header > log_pytest.html

stdbuf -oL pytest --color=yes | stdbuf -oL aha --no-header > log_pytest.html

stdbuf -oL pytest --color=yes | stdbuf -oL ansi2html --partial --inline > log_pytest.html