* Allow render HTML with css/js external links

* Fix bug because of filename escape chars

* Fix lint

* Update docs about new configuration item

* Fix bug of render HTML in sub directory

* Add CSP head for displaying iframe in rendering file

* Fix test

* Apply suggestions from code review

Co-authored-by: delvh <dev.lh@web.de>

* Some improvements

* some improvement

* revert change in SanitizerDisabled of external renderer

* Add sandbox for iframe and support allow-scripts and allow-same-origin

* refactor

* fix

* fix lint

* fine tune

* use single option RENDER_CONTENT_MODE, use sandbox=allow-scripts

* fine tune CSP

* Apply suggestions from code review

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

* gofumpt -w -l .

* gofumpt -w -l -extra .

* Add linter

* manual fix

* change make fmt

* Fixes #16558 CSV delimiter determiner

* Fixes #16558 - properly determine CSV delmiiter

* Moves quoteString to a new function

* Adds big test with lots of commas for tab delimited csv

* Adds comments

* Shortens the text of the test

* Removes single quotes from regexp as only double quotes need to be searched

* Fixes spelling

* Fixes check of length as it probalby will only be 1e4, not greater

* Makes sample size a const, properly removes truncated line

* Makes sample size a const, properly removes truncated line

* Fixes comment

* Fixes comment

* tests for FormatError() function

* Adds logic to find the limiter before or after a quoted value

* Simplifies regex

* Error tests

* Error tests

* Update modules/csv/csv.go

Co-authored-by: delvh <dev.lh@web.de>

* Update modules/csv/csv.go

Co-authored-by: delvh <dev.lh@web.de>

* Adds comments

* Update modules/csv/csv.go

Co-authored-by: delvh <dev.lh@web.de>

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: delvh <dev.lh@web.de>

* Fixes #16559 - Do not trim leading spaces for tab delimited

* Adds back semicolon delimited test

* Fixes linting

* Adds nolint directive to test because uses strings starting with spaces

Co-authored-by: zeripath <art27@cantab.net>

closed #17378 

Both errors from #17378 were caused by  #15175.

Problem 1 (error with added file):
`ToUTF8WithFallbackReader` creates a `MultiReader` from a `byte[2048]` and the remaining reader. `CreateReaderAndGuessDelimiter` tries to read 10000 bytes from this reader but only gets 2048 because that's the first reader in the `MultiReader`. Then the `if size < 1e4` thinks the input is at EOF and just returns that.

Problem 2 (error with changed file):
The blob reader gets defer closed. That was fine because the old version reads the whole file into memory. Now with the streaming version the close needs to defer after the method.

* Read expected buffer size.

* Changed name.

Fixes #16837 if a column is deleted.

We were clobbering the columns that were added by looping through the aline (base) and then when bline (head) was looped through, it clobbered what was in the "cells" array that is show in the diff, and then left a nil cell because nothing was shifted.

This fix properly shifts the cells, and properly puts the b cell either at its location or after, according to what the aline placed in the cells.

This includes test, adding a new test function since adding/removing cells works best with three columns, not two, which results in 4 columns of the resulting cells because it has a deleted column and an added column. If you try this locally, you can try those cases and others, such as adding a column.

There was no need to do anything special for the rows when `aline == 0 || bline == 0` so that was removed. This allows the same code to be used for removed or added lines, with the bcell text always being the RightCell, acell text being the LeftCell.

I still added the patch zeripath gave at https://github.com/go-gitea/gitea/issues/16837#issuecomment-913007382 so that just in case for some reason a cell is nil (which shouldn't happen now) it doesn't throw a 500 error, so the user can at least view the raw diff.

Also fixes in the [view.go](https://github.com/go-gitea/gitea/pull/17018/files#diff-43a7f4747c7ba8bff888c9be11affaafd595fd55d27f3333840eb19df9fad393L521) file how if a CSV file is empty (either created empty or if you edit it and remove all contents) it throws a huge 500 error when you then save it (when you view the file). Since we allow creating, saving and pushing empty files, we shouldn't throw an error on an empty CSV file, but just show its empty contents. This doesn't happen if it is a Markdown file or other type of file that is empty.
EDIT: Now handled in the markup/csv renderer code

Remove the unnecessary duplicate package import for `encoding/csv` in `modules/csv/csv.go`

Fix #16557

* Refactor renders

* Some performance optimization

* Fix comment

* Transform reader

* Fix csv test

* Fix test

* Fix tests

* Improve optimaziation

* Fix test

* Fix test

* Detect file encoding with reader

* Improve optimaziation

* reduce memory usage

* improve code

* fix build

* Fix test

* Fix for go1.15

* Fix render

* Fix comment

* Fix lint

* Fix test

* Don't use NormalEOF when unnecessary

* revert change on util.go

* Apply suggestions from code review

Co-authored-by: zeripath <art27@cantab.net>

* rename function

* Take NormalEOF back

Co-authored-by: zeripath <art27@cantab.net>

Implements request #14320 The rendering of CSV files does match the diff style.

* Moved CSV logic into base package.

* Added method to create a tabular diff.

* Added CSV compare context.

* Added CSV diff template.

* Use new table style in CSV markup.

* Added file size limit for CSV rendering.

* Display CSV parser errors in diff.

* Lazy read single file.

* Lazy read rows for full diff.

* Added unit tests for various CSV changes.