v2: Module documentation; refactor LoadModule(); new caddy struct tags (#2924)

This commit goes a long way toward making automated documentation of
Caddy config and Caddy modules possible. It's a broad, sweeping change,
but mostly internal. It allows us to automatically generate docs for all
Caddy modules (including future third-party ones) and make them viewable
on a web page; it also doubles as godoc comments.

As such, this commit makes significant progress in migrating the docs
from our temporary wiki page toward our new website which is still under
construction.

With this change, all host modules will use ctx.LoadModule() and pass in
both the struct pointer and the field name as a string. This allows the
reflect package to read the struct tag from that field so that it can
get the necessary information like the module namespace and the inline
key.

This has the nice side-effect of unifying the code and documentation. It
also simplifies module loading, and handles several variations on field
types for raw module fields (i.e. variations on json.RawMessage, such as
arrays and maps).

I also renamed ModuleInfo.Name -> ModuleInfo.ID, to make it clear that
the ID is the "full name" which includes both the module namespace and
the name. This clarity is helpful when describing module hierarchy.

As of this change, Caddy modules are no longer an experimental design.
I think the architecture is good enough to go forward.

1 files changed, 34 insertions, 17 deletions

diff --git a/modules/caddytls/connpolicy.go b/modules/caddytls/connpolicy.go
index c82337d..6ce6b9e 100644
--- a/modules/caddytls/connpolicy.go
+++ b/modules/caddytls/connpolicy.go
@@ -39,23 +39,21 @@ func (cp ConnectionPolicies) TLSConfig(ctx caddy.Context) (*tls.Config, error) {
 	// set up each of the connection policies
 	for i, pol := range cp {
 		// matchers
-		for modName, rawMsg := range pol.Matchers {
-			val, err := ctx.LoadModule("tls.handshake_match."+modName, rawMsg)
-			if err != nil {
-				return nil, fmt.Errorf("loading handshake matcher module '%s': %s", modName, err)
-			}
-			cp[i].matchers = append(cp[i].matchers, val.(ConnectionMatcher))
+		mods, err := ctx.LoadModule(pol, "MatchersRaw")
+		if err != nil {
+			return nil, fmt.Errorf("loading handshake matchers: %v", err)
+		}
+		for _, modIface := range mods.(map[string]interface{}) {
+			cp[i].matchers = append(cp[i].matchers, modIface.(ConnectionMatcher))
 		}
-		cp[i].Matchers = nil // allow GC to deallocate
 
 		// certificate selector
 		if pol.CertSelection != nil {
-			val, err := ctx.LoadModuleInline("policy", "tls.certificate_selection", pol.CertSelection)
+			val, err := ctx.LoadModule(pol, "CertSelection")
 			if err != nil {
 				return nil, fmt.Errorf("loading certificate selection module: %s", err)
 			}
 			cp[i].certSelector = val.(certmagic.CertificateSelector)
-			cp[i].CertSelection = nil // allow GC to deallocate
 		}
 	}
 
@@ -109,14 +107,33 @@ func (cp ConnectionPolicies) TLSConfig(ctx caddy.Context) (*tls.Config, error) {
 
 // ConnectionPolicy specifies the logic for handling a TLS handshake.
 type ConnectionPolicy struct {
-	Matchers      map[string]json.RawMessage `json:"match,omitempty"`
-	CertSelection json.RawMessage            `json:"certificate_selection,omitempty"`
-
-	CipherSuites         []string              `json:"cipher_suites,omitempty"`
-	Curves               []string              `json:"curves,omitempty"`
-	ALPN                 []string              `json:"alpn,omitempty"`
-	ProtocolMin          string                `json:"protocol_min,omitempty"`
-	ProtocolMax          string                `json:"protocol_max,omitempty"`
+	// How to match this policy with a TLS ClientHello. If
+	// this policy is the first to match, it will be used.
+	MatchersRaw caddy.ModuleMap `json:"match,omitempty" caddy:"namespace=tls.handshake_match"`
+
+	// How to choose a certificate if more than one matched
+	// the given ServerName (SNI) value.
+	CertSelection json.RawMessage `json:"certificate_selection,omitempty" caddy:"namespace=tls.certificate_selection inline_key=policy"`
+
+	// The list of cipher suites to support. Caddy's
+	// defaults are modern and secure.
+	CipherSuites []string `json:"cipher_suites,omitempty"`
+
+	// The list of elliptic curves to support. Caddy's
+	// defaults are modern and secure.
+	Curves []string `json:"curves,omitempty"`
+
+	// Protocols to use for Application-Layer Protocol
+	// Negotiation (ALPN) during the handshake.
+	ALPN []string `json:"alpn,omitempty"`
+
+	// Minimum TLS protocol version to allow. Default: `tls1.2`
+	ProtocolMin string `json:"protocol_min,omitempty"`
+
+	// Maximum TLS protocol version to allow. Default: `tls1.3`
+	ProtocolMax string `json:"protocol_max,omitempty"`
+
+	// Enables and configures TLS client authentication.
 	ClientAuthentication *ClientAuthentication `json:"client_authentication,omitempty"`
 
 	matchers     []ConnectionMatcher