An Emacs minor mode that displays log files formatted as JSON Lines in a more human-friendly format.

While JSON Lines format is easy to parse by machines, it is not very human friendly due to the extra punctuation and keys. This mode tries to make it easier to read by

• hiding the punctuation and keys;
• pretty printing the line at cursor in an associated side window.

Below are screenshots of viewing a MongoDB log file without and with this mode.

• Before the structured-log-mode is enabled:

• After the structured-log-mode is enabled:

• Emacs 29.1 or later

  This package uses the Emacs built-in packages treesit and the json-ts-mode, which are available since Emacs 29.1. Too double check if your Emacs has built in treesit support, please evaluate (treesit-available-p).

1. Git clone or download this repository.

2. Edit your Emacs init file to load it.

   If you are using use-package, you can add the following code to your init file:

    ``` emacs-lisp
    (use-package structured-log-mode
      :load-path "/path/to/structured-log-mode"
      :commands structured-log-mode)
   
    (use-package json-ts-mode
      :mode "\\.jsonl?\\'" "mongod*\\.log"
      )
    ```
   

   Note that the second use-package is optional. It tells Emacs to open MongoDB log files using json-ts-mode.

   If you are not using use-package, please add the following code to your init file:

    ``` emacs-lisp
    (add-to-list 'load-path "/path/to/structured-log-mode")
    (require 'structured-log-mode)
    ```
   

3. If haven't done yet, install the corresponding tree-sitter grammar by running M-x treesit-install-grammars and selecting json from the list.

4. Restart Emacs or run M-x load-file on your init file.

This mode processes the contents in the current window only. Hence, it is able to handle large files. On my laptop, after disabling any features which could potentially slow down Emacs, at the least, it is able to handle a 1GB mongod log file without issues.

I put the following configuration in my init.el to ensure that Emacs loads large files with minimal features to prevent Emacs from slowing or freezing.

  (defun lgf-huge-file-hook ()
    "Open huge files with minimum features.

Huge files (normally log files) can make Emacs sluggish or even
freeze. This hook tells Emacs to open such files with the
`fundamental-mode' and turn off any extra features which cannot
handle large files. In addition, it makes the buffer read only to
avoid accidental modifications."
    (when (> (buffer-size) (* 1024 1024 16)) ; 16 MB
      (fundamental-mode)
      (buffer-disable-undo)
      (which-function-mode -1)
      (if (fboundp 'highlight-parentheses-mode) (highlight-parentheses-mode -1))
      (setq buffer-read-only t)
      ))
  (add-hook 'find-file-hook 'lgf-huge-file-hook)

1. Open a log file that is formatted as JSON Lines.

2. Enable the structured-log-mode by running M-x structured-log-mode.

3. The log file should now be displayed in a more human-friendly format.

   Note If some lines in the window are not processed, please press Ctrl-l (or evaluate (recenter-top-bottom)) to refresh.

4. Move the cursor to a line to see the corresponding JSON data in the side window.

5. Press c-c c-s to show all the original contents. Press c-s c-h to hide again.

6. Run M-x structured-log-mode again to disable the mode.

• structlog-timer-delay - the idle time (delay in seconds) before updating the side window.

• Better whitespace handling.
• Highlight according to log level.
• Add customization options.