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src/docs/markdown/extending-caddy/placeholders.md
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@ -10,13 +10,11 @@ This means that if you wish for your plugin to support placeholders, you must ex
If you are not yet familiar with placeholders, start by reading [here](/docs/conventions#placeholders)! If you are not yet familiar with placeholders, start by reading [here](/docs/conventions#placeholders)!
## Placeholder Parsing Rules & Gotchas ## Placeholder Internals
If you wish to use placeholders in your Caddy plugin, you must accept placeholders strings, in format `{foo}` as valid configuration values, and parse them at runtime Internally, placeholders are simply a string in format `{foo.bar}` used as valid configuration values, which is later parsed at runtime.
Placeholders-like strings which start with a dollar sign (`{$foo}`), are evaulated at Caddyfile parse time, and do not need to be dealt with by your plugin. Placeholders-like strings which start with a dollar sign (`{$FOO}`), are evaulated at Caddyfile parse time, and do not need to be dealt with by your plugin. This is because these are not placeholders, but Caddyfile-specific [environmental variable substitution](/docs/caddyfile/concepts/#environmental-variables), they just happen to share the `{}` syntax.
This is because these are not placeholders, but Caddyfile-specific [environmental variable substitution](/docs/caddyfile/concepts/#environmental-variables), they just happen to share the `{}` syntax.
It is therefore important to understand that `{env.HOST}` is inherently different from something like `{$HOST}` It is therefore important to understand that `{env.HOST}` is inherently different from something like `{$HOST}`
@ -77,17 +75,18 @@ When you adapt this Caddyfile with `HOST=example caddy adapt` you will get
Importantly, look at the `"body"` field in both `srv0` and `srv1`. Importantly, look at the `"body"` field in both `srv0` and `srv1`.
Since `srv0` used `{$ENV}`, the special environmental variable placeholder with `$`, as it is parsed during Caddyfile parse time. Since `srv0` used `{$ENV}`, the special environmental variable replacement with `$` became `example`, as it is parsed during Caddyfile parse time.
Since `srv1` used `{env.HOST}`, a standard placeholder, it was parsed as a normal string value for "body" field of the respond directive's config. Since `srv1` used `{env.HOST}`, a normal placeholder, it was parsed as its own raw string value, `{env.HOST}`
This means that down the line, the handler the plugins within `srv0` and `srv1` will receive the raw values `example` and `{env.Host}` respectively in their configurations.
This means that down the line, the handler plugins will receive both `example` and `{env.Host}` respectively in their configurations.
## How to Placeholders in your Plugin ## How to Placeholders in your Plugin
#### Parse the raw Placeholder in your unmarshaler #### Parse the raw Placeholder in your unmarshaler
Placeholders should be parsed as their raw values when parsing caddyfiles, just like any other string value Placeholders should be parsed as their raw values when parsing the Cazddyfile, just like any other string value
```go ```go
func (g *Gizmo) UnmarshalCaddyfile(d *caddyfile.Dispenser) error { func (g *Gizmo) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {