http: Add Starlark handler

This migrates a feature that was previously reserved for enterprise
users, according to #2786.

The Starlark integration needs to be updated since this was made before
some significant changes in the v2 code base. When functional, it makes
it possible to have very dynamic HTTP handlers. This will be a long-term
ongoing project.

Credit to Danny Navarro

1 files changed, 165 insertions, 0 deletions

diff --git a/modules/caddyhttp/starlarkmw/internal/lib/module.go b/modules/caddyhttp/starlarkmw/internal/lib/module.go
new file mode 100644
index 0000000..a7164cd
--- /dev/null
+++ b/modules/caddyhttp/starlarkmw/internal/lib/module.go
@@ -0,0 +1,165 @@
+package lib
+
+import (
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
+
+	"github.com/caddyserver/caddy/v2"
+	"go.starlark.net/starlark"
+)
+
+// ResponderModule represents a module that satisfies the caddyhttp handler.
+type ResponderModule struct {
+	Name     string
+	Cfg      json.RawMessage
+	Instance caddyhttp.Handler
+}
+
+func (r ResponderModule) Freeze()               {}
+func (r ResponderModule) Hash() (uint32, error) { return 0, fmt.Errorf("unhashable: responder module") }
+func (r ResponderModule) String() string        { return "responder module" }
+func (r ResponderModule) Type() string          { return "responder module" }
+func (r ResponderModule) Truth() starlark.Bool  { return true }
+
+// Middleware represents a module that satisfies the starlark Value interface.
+type Middleware struct {
+	Name     string
+	Cfg      json.RawMessage
+	Instance caddyhttp.MiddlewareHandler
+}
+
+func (r Middleware) Freeze()               {}
+func (r Middleware) Hash() (uint32, error) { return 0, fmt.Errorf("unhashable: middleware") }
+func (r Middleware) String() string        { return "middleware" }
+func (r Middleware) Type() string          { return "middleware" }
+func (r Middleware) Truth() starlark.Bool  { return true }
+
+// LoadMiddleware represents the method exposed to starlark to load a Caddy module.
+type LoadMiddleware struct {
+	Middleware Middleware
+	Ctx        caddy.Context
+}
+
+func (r LoadMiddleware) Freeze()               {}
+func (r LoadMiddleware) Hash() (uint32, error) { return 0, fmt.Errorf("unhashable: loadMiddleware") }
+func (r LoadMiddleware) String() string        { return "loadMiddleware" }
+func (r LoadMiddleware) Type() string          { return "function: loadMiddleware" }
+func (r LoadMiddleware) Truth() starlark.Bool  { return true }
+
+// Run is the method bound to the starlark loadMiddleware function.
+func (r *LoadMiddleware) Run(thread *starlark.Thread, fn *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
+	var name string
+	var cfg *starlark.Dict
+	err := starlark.UnpackPositionalArgs(fn.Name(), args, kwargs, 2, &name, &cfg)
+	if err != nil {
+		return starlark.None, fmt.Errorf("unpacking arguments: %v", err.Error())
+	}
+
+	js := json.RawMessage(cfg.String())
+
+	if strings.Index(name, "http.handlers.") == -1 {
+		name = fmt.Sprintf("http.handlers.%s", name)
+	}
+
+	inst, err := r.Ctx.LoadModule(name, js)
+	if err != nil {
+		return starlark.None, err
+	}
+
+	mid, ok := inst.(caddyhttp.MiddlewareHandler)
+	if !ok {
+		return starlark.None, fmt.Errorf("could not assert as middleware handler")
+	}
+
+	m := Middleware{
+		Name:     name,
+		Cfg:      js,
+		Instance: mid,
+	}
+
+	r.Middleware = m
+
+	return m, nil
+}
+
+// LoadResponder represents the method exposed to starlark to load a Caddy middleware responder.
+type LoadResponder struct {
+	Module ResponderModule
+	Ctx    caddy.Context
+}
+
+func (r LoadResponder) Freeze()               {}
+func (r LoadResponder) Hash() (uint32, error) { return 0, fmt.Errorf("unhashable: loadModule") }
+func (r LoadResponder) String() string        { return "loadModule" }
+func (r LoadResponder) Type() string          { return "function: loadModule" }
+func (r LoadResponder) Truth() starlark.Bool  { return true }
+
+// Run is the method bound to the starlark loadResponder function.
+func (r *LoadResponder) Run(thread *starlark.Thread, fn *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
+	var name string
+	var cfg *starlark.Dict
+	err := starlark.UnpackPositionalArgs(fn.Name(), args, kwargs, 2, &name, &cfg)
+	if err != nil {
+		return starlark.None, fmt.Errorf("unpacking arguments: %v", err.Error())
+	}
+
+	js := json.RawMessage(cfg.String())
+
+	if strings.Index(name, "http.handlers.") == -1 {
+		name = fmt.Sprintf("http.handlers.%s", name)
+	}
+
+	inst, err := r.Ctx.LoadModule(name, js)
+	if err != nil {
+		return starlark.None, err
+	}
+
+	res, ok := inst.(caddyhttp.Handler)
+	if !ok {
+		return starlark.None, fmt.Errorf("could not assert as responder")
+	}
+
+	m := ResponderModule{
+		Name:     name,
+		Cfg:      js,
+		Instance: res,
+	}
+
+	r.Module = m
+
+	return m, nil
+}
+
+// Execute represents the method exposed to starlark to build a middleware chain.
+type Execute struct {
+	Modules []Middleware
+}
+
+func (r Execute) Freeze()               {}
+func (r Execute) Hash() (uint32, error) { return 0, fmt.Errorf("unhashable: execute") }
+func (r Execute) String() string        { return "execute" }
+func (r Execute) Type() string          { return "function: execute" }
+func (r Execute) Truth() starlark.Bool  { return true }
+
+// Run is the method bound to the starlark execute function.
+func (r *Execute) Run(thread *starlark.Thread, fn *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
+	var mids *starlark.List
+	err := starlark.UnpackPositionalArgs(fn.Name(), args, kwargs, 1, &mids)
+	if err != nil {
+		return starlark.None, fmt.Errorf("unpacking arguments: %v", err.Error())
+	}
+
+	for i := 0; i < mids.Len(); i++ {
+		val, ok := mids.Index(i).(Middleware)
+		if !ok {
+			return starlark.None, fmt.Errorf("cannot get module from execute")
+		}
+
+		r.Modules = append(r.Modules, val)
+	}
+
+	return starlark.None, nil
+}