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To: Bob Weinand <bobwei9@hotmail.com>
CC: "internals@lists.php.net" <internals@lists.php.net>
Thread-Topic: [PHP-DEV] [VOTE] Dump results of expressions in `php -a`
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Date: Tue, 2 Feb 2021 02:35:32 +0000
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Subject: Re: [PHP-DEV] [VOTE] Dump results of expressions in `php -a`
From: tysonandre775@hotmail.com (tyson andre)

Hi Bob Weinand,=0A=
=0A=
> > Am 20.01.2021 um 01:55 schrieb tyson andre <tysonandre775@hotmail.com>:=
=0A=
> > =0A=
> > Hi internals,=0A=
> > =0A=
> > Voting has started on https://wiki.php.net/rfc/readline_interactive_she=
ll_result_function=0A=
> > on 2021-01-19, and ends on 2021-02-02.=0A=
> > =0A=
> > This RFC proposes to dump the results of non-null expressions using var=
_dump/var_export() by default in `php -a` (the interactive shell).=0A=
> > Additionally, this adds a new function `readline_interactive_shell_resu=
lt_function` to the readline PHP module.=0A=
> > This function only affects interactive shells - it can optionally be us=
ed to set or clear a closure when `extension_loaded('readline') =3D=3D=3D t=
rue`,=0A=
> > but that closure would only be called in interactive shells (i.e. php -=
a).=0A=
> > (That closure would be called instead of the native implementation with=
 the snippet of code that was evaluated and the expression's result,=0A=
> > if a php statement contained a single expression such as `2+2;` or `$x =
=3D [1,2];` (that could be used as the expression of a return statement)=0A=
> > - Dumping of expression results can be disabled using an ini setting or=
 at runtime =0A=
> > =0A=
> > Thanks,=0A=
> > - Tyson=0A=
> =0A=
> Hey Tyson,=0A=
> =0A=
> My main concern in this iteration of the RFC is: what happens with big/de=
eply nested objects?=0A=
> They tend to spew tons of lines if var_dump()'ed. Do we have reasonable d=
epth/output limitations in default dumping mode?=0A=
> =0A=
> I'm often enough using php -a to do some quick ad-hoc processing (example=
, read a big json file, and then access a value; instantiating a mediawiki =
bot framework and calling replace on it; ...).=0A=
> =0A=
> It's really cool to have any interactive feedback at all, but please, at =
least by default, limit the output. (An example is the JS REPL in browser c=
onsole - it shows you a minimal preview of the object, and then you can exp=
and with your mouse. Obviously with a pure cli application, this needs diff=
erent - intuitive - navigation.)=0A=
> =0A=
> As it currently stands, this makes php -a unusable in any but the simples=
t cases, without just disabling the whole feature.=0A=
> =0A=
> I like the whole feature, but the missing output limitation (I have yet e=
nough nightmares from var_dump()'ing the wrong object filling my shell with=
 tons of irrelevant information=85 I don't need that potentially happening =
on every single evaluated expression)=0A=
> =0A=
> Thus I'm voting no, for now.=0A=
=0A=
As-is, the entire object or string would be dumped with var_export/var_dump=
 to stdout.=0A=
=0A=
Thoughts on the adding following output truncation mechanism =0A=
(for the default C result dumper implementation)=0A=
before printing the results of the returned expression =0A=
(the user output continues to be untruncated, and the existence of cli.page=
r =0A=
would not affect this mechanism in case the binary is not actually a pager)=
?=0A=
For arrays/objects used with var_dump - the equivalent of =0A=
`ob_start(); var_dump($result); $result =3D ob_get_clean();` =0A=
would have to be used first from C since var_dump still writes to the outpu=
t buffer (php_printf(), etc.)=0A=
=0A=
I'd omitted output truncation from the RFC because I wasn't sure how many p=
eople =0A=
would consider it excessive to include a limit on var_dump output, and ther=
e was little feedback before the RFC vote started.=0A=
The simplest implementation would be to truncate to a byte limit and append=
 `...` if truncated, =0A=
but the main concern that's been brought up is the approximate number of li=
nes.=0A=
Obviously, there'd be a value in truncating the output if there were to be =
megabytes of output,=0A=
though exactly what settings make sense as a default would vary.=0A=
=0A=
C would not print anything (e.g. `=3D> `) or even call var_dump/var_export =
if the limits were set to 0.=0A=
=0A=
```=0A=
<?php=0A=
=0A=
const ASSUMED_BYTES_PER_LINE =3D 80;=0A=
const ASSUMED_TAB_WIDTH =3D 4;=0A=
=0A=
/**=0A=
 * This is a C-like php function used as an example of the proposed logic f=
or truncating strings.=0A=
 * The real implementation would be written in C instead.=0A=
 *=0A=
 * The goal is to limit both of the following:=0A=
 * 1. The **approximate** number of lines, for terminals for limited scroll=
back.=0A=
 * 2. The **approximate** number of bytes, when that is a limitation (e.g. =
poor internet connection, inefficient terminal, etc.)=0A=
 *=0A=
 * The ini settings cli.interactive_shell_result_function_byte_limit and cl=
i.interactive_shell_result_function_line_limit=0A=
 * are proposed for controlling this limitation.=0A=
 *=0A=
 * This deliberately makes no attempt at inferring tab width, terminal widt=
h, line ending of the **terminal emulator**=0A=
 * (e.g. windows sshed into linux, or a console output log that's viewed la=
ter in a web browser), or character encoding.=0A=
 */=0A=
function truncate_string(string $raw_output, int $max_lines =3D 100, int $m=
ax_bytes =3D 8000): ?string {=0A=
    $max_lines =3D min($max_bytes, $max_lines);=0A=
    if ($max_lines <=3D 0) {=0A=
        return NULL;=0A=
    }=0A=
    $strlen =3D strlen($raw_output);=0A=
    if ($strlen <=3D $max_lines) {=0A=
        return $raw_output;=0A=
    }=0A=
    $max_bytes =3D min($max_bytes, $strlen);=0A=
    $truncated =3D false;=0A=
    $original =3D $raw_output;=0A=
    $total_lines =3D 0;=0A=
    $offset =3D 0;=0A=
    for ($i =3D 0; $i < $max_bytes && $total_lines < $max_lines; $i++) {=0A=
        switch ($raw_output[$i]) {=0A=
            case "\n":=0A=
            case "\v":  // give up on obscure vertical tab character, treat=
 it like a newline=0A=
                $total_lines++;=0A=
                $offset =3D 0;=0A=
                break;=0A=
            case "\r":=0A=
                if (($raw_output[$i + 1] ?? "\0") =3D=3D=3D "\n") {=0A=
                    $i++;=0A=
                }=0A=
                $total_lines++;=0A=
                $offset =3D 0;=0A=
                break;=0A=
            case "\t";=0A=
                $offset +=3D ASSUMED_TAB_WIDTH - ($offset % ASSUMED_TAB_WID=
TH);=0A=
                if ($offset >=3D ASSUMED_BYTES_PER_LINE) {=0A=
                    $total_lines++;=0A=
                    $offset =3D ($offset - ASSUMED_BYTES_PER_LINE) % ASSUME=
D_TAB_WIDTH;=0A=
                }=0A=
                break;=0A=
            default:=0A=
                $offset++;=0A=
                if ($offset >=3D ASSUMED_BYTES_PER_LINE) {=0A=
                    $total_lines++;=0A=
                    $offset =3D 0;=0A=
                }=0A=
                break;=0A=
        }=0A=
    }=0A=
    if ($i >=3D $strlen) {=0A=
        return $raw_output;=0A=
    }=0A=
    return substr($raw_output, 0, $i) . "...";  // C appends newlines alrea=
dy if there was none=0A=
}=0A=
// unmodified=0A=
var_dump(truncate_string("test short string"));=0A=
// 5000 'A's followed by "...\n"=0A=
var_dump(truncate_string(str_repeat('A', 10000)));=0A=
// 100 lines containing "A" followed by "...\n"=0A=
var_dump(truncate_string(str_repeat("A\n", 10000)));=0A=
```=0A=
=0A=
Thanks,=0A=
- Tyson=0A=