fastcgi: Add new php_fastcgi subdirectives to override shortcut behaviour

[francislavoie]

The php_fastcgi Caddyfile directive acts as a shortcut to a quite long expanded form. There are many situations where users might want to override some of the behaviour generated by the shortcut.

This change makes it possible to override some aspects of the shortcut by first reading the subdirective block once, handling any subdirectives that are relevant, and importantly, deleting the tokens as it goes. Then, it rewinds the Dispenser's cursor to the point just before so that the reverse_proxy's UnmarshalCaddyfile can read it for itself. We delete as we go, because otherwise the default: case in reverse_proxy would return d.Errf("unrecognized subdirective %s", d.Val()).

Adds the following subdirectives:

• split: passthrough to the split_path subdirective of the fastcgi transport, but also affects the path matcher for the list of PHP file extensions to support
• env: passthrough to the env subdirective of the fastcgi transport
• root: passthrough to the root subdirective of the fastcgi transport
• index: defaults to index.php, controls the file that is used as a try_files fallback. If the value is set to off, it disables the path canonicalization redirect and the try_files rewrite altogether.

Caddyfile:

:8884

php_fastcgi localhost:9000 {
        # some php_fastcgi-specific subdirectives
        split .php .phpt
        env PATH /something
        root /var/somewhere
        index off

        # passed through to reverse_proxy (directive order doesn't matter!)
        lb_policy random
}

JSON output:

{
  "apps": {
    "http": {
      "servers": {
        "srv0": {
          "listen": [
            ":8884"
          ],
          "routes": [
            {
              "match": [
                {
                  "path": [
                    "*.php",
                    "*.phpt"
                  ]
                }
              ],
              "handle": [
                {
                  "handler": "reverse_proxy",
                  "load_balancing": {
                    "selection_policy": {
                      "policy": "random"
                    }
                  },
                  "transport": {
                    "env": {
                      "PATH": "/something"
                    },
                    "protocol": "fastcgi",
                    "root": "/var/somewhere",
                    "split_path": [
                      ".php",
                      ".phpt"
                    ]
                  },
                  "upstreams": [
                    {
                      "dial": "localhost:9000"
                    }
                  ]
                }
              ]
            }
          ]
        }
      }
    }
  }
}

[francislavoie]

I was reading through the codebase some more and I realized there's a better approach than adding 2 new funcs to Dispenser to manipulate the cursor.

I'm pretty sure I can use NewFromNextSegment(), mutate that new Dispenser as I currently do, then Reset() it and pass it down to reverse_proxy's unmarshal.

I'll refactor this soon.

Edit: Done

[mholt]

@francislavoie When you get a chance, could you fix the merge conflict? Then I'll do a final review. Looking good though.

Note that I'll be relying on you for fixes to any potential bug reports that come in related to this in the future 😅 (esp. since I don't really have a PHP environment!)

Thanks!

[francislavoie]

Yep, this one will need a bit of reworking actually, because of the split_path thing we added.

[mholt]

Gotcha... no hurry. I can see the huge value in this though. Thanks!

[mholt]

Thanks for working on this! It'll be super useful.

I haven't verified that all the hidden/implicit route logic was brought over correctly, but I trust that it works.

Just a couple minor nits -- nothing showstopping though. Would be nice if a few more people with actual PHP environments could test this out first?

[mholt]

Thanks! Code looks nice, I'll assume it works. Anyone with a PHP environment could please test it out, thank you!