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, 24 insertions, 26 deletions

diff --git a/modules/caddyhttp/reverseproxy/reverseproxy.go b/modules/caddyhttp/reverseproxy/reverseproxy.go
index 87895e2..132f222 100644
--- a/modules/caddyhttp/reverseproxy/reverseproxy.go
+++ b/modules/caddyhttp/reverseproxy/reverseproxy.go
@@ -42,8 +42,8 @@ func init() {
 
 // Handler implements a highly configurable and production-ready reverse proxy.
 type Handler struct {
-	TransportRaw   json.RawMessage  `json:"transport,omitempty"`
-	CBRaw          json.RawMessage  `json:"circuit_breaker,omitempty"`
+	TransportRaw   json.RawMessage  `json:"transport,omitempty" caddy:"namespace=http.reverse_proxy.transport inline_key=protocol"`
+	CBRaw          json.RawMessage  `json:"circuit_breaker,omitempty" caddy:"namespace=http.reverse_proxy.circuit_breakers inline_key=type"`
 	LoadBalancing  *LoadBalancing   `json:"load_balancing,omitempty"`
 	HealthChecks   *HealthChecks    `json:"health_checks,omitempty"`
 	Upstreams      UpstreamPool     `json:"upstreams,omitempty"`
@@ -60,8 +60,8 @@ type Handler struct {
 // CaddyModule returns the Caddy module information.
 func (Handler) CaddyModule() caddy.ModuleInfo {
 	return caddy.ModuleInfo{
-		Name: "http.handlers.reverse_proxy",
-		New:  func() caddy.Module { return new(Handler) },
+		ID:  "http.handlers.reverse_proxy",
+		New: func() caddy.Module { return new(Handler) },
 	}
 }
 
@@ -71,30 +71,25 @@ func (h *Handler) Provision(ctx caddy.Context) error {
 
 	// start by loading modules
 	if h.TransportRaw != nil {
-		val, err := ctx.LoadModuleInline("protocol", "http.handlers.reverse_proxy.transport", h.TransportRaw)
+		mod, err := ctx.LoadModule(h, "TransportRaw")
 		if err != nil {
-			return fmt.Errorf("loading transport module: %s", err)
+			return fmt.Errorf("loading transport: %v", err)
 		}
-		h.Transport = val.(http.RoundTripper)
-		h.TransportRaw = nil // allow GC to deallocate
+		h.Transport = mod.(http.RoundTripper)
 	}
 	if h.LoadBalancing != nil && h.LoadBalancing.SelectionPolicyRaw != nil {
-		val, err := ctx.LoadModuleInline("policy",
-			"http.handlers.reverse_proxy.selection_policies",
-			h.LoadBalancing.SelectionPolicyRaw)
+		mod, err := ctx.LoadModule(h.LoadBalancing, "SelectionPolicyRaw")
 		if err != nil {
-			return fmt.Errorf("loading load balancing selection module: %s", err)
+			return fmt.Errorf("loading load balancing selection policy: %s", err)
 		}
-		h.LoadBalancing.SelectionPolicy = val.(Selector)
-		h.LoadBalancing.SelectionPolicyRaw = nil // allow GC to deallocate
+		h.LoadBalancing.SelectionPolicy = mod.(Selector)
 	}
 	if h.CBRaw != nil {
-		val, err := ctx.LoadModuleInline("type", "http.handlers.reverse_proxy.circuit_breakers", h.CBRaw)
+		mod, err := ctx.LoadModule(h, "CBRaw")
 		if err != nil {
-			return fmt.Errorf("loading circuit breaker module: %s", err)
+			return fmt.Errorf("loading circuit breaker: %s", err)
 		}
-		h.CB = val.(CircuitBreaker)
-		h.CBRaw = nil // allow GC to deallocate
+		h.CB = mod.(CircuitBreaker)
 	}
 
 	// set up transport
@@ -128,12 +123,14 @@ func (h *Handler) Provision(ctx caddy.Context) error {
 		// defaulting to a sane wait period between attempts
 		h.LoadBalancing.TryInterval = caddy.Duration(250 * time.Millisecond)
 	}
-	lbMatcherSets, err := h.LoadBalancing.RetryMatchRaw.Setup(ctx)
+	lbMatcherSets, err := ctx.LoadModule(h.LoadBalancing, "RetryMatchRaw")
+	if err != nil {
+		return err
+	}
+	err = h.LoadBalancing.RetryMatch.FromInterface(lbMatcherSets)
 	if err != nil {
 		return err
 	}
-	h.LoadBalancing.RetryMatch = lbMatcherSets
-	h.LoadBalancing.RetryMatchRaw = nil // allow GC to deallocate
 
 	// if active health checks are enabled, configure them and start a worker
 	if h.HealthChecks != nil &&
@@ -407,7 +404,7 @@ func (h *Handler) reverseProxy(rw http.ResponseWriter, req *http.Request, di Dia
 	// do the round-trip
 	start := time.Now()
 	res, err := h.Transport.RoundTrip(req)
-	latency := time.Since(start)
+	duration := time.Since(start)
 	if err != nil {
 		return err
 	}
@@ -415,12 +412,13 @@ func (h *Handler) reverseProxy(rw http.ResponseWriter, req *http.Request, di Dia
 	h.logger.Debug("upstream roundtrip",
 		zap.Object("request", caddyhttp.LoggableHTTPRequest{Request: req}),
 		zap.Object("headers", caddyhttp.LoggableHTTPHeader(res.Header)),
+		zap.Duration("duration", duration),
 		zap.Int("status", res.StatusCode),
 	)
 
 	// update circuit breaker on current conditions
 	if di.Upstream.cb != nil {
-		di.Upstream.cb.RecordMetric(res.StatusCode, latency)
+		di.Upstream.cb.RecordMetric(res.StatusCode, duration)
 	}
 
 	// perform passive health checks (if enabled)
@@ -434,7 +432,7 @@ func (h *Handler) reverseProxy(rw http.ResponseWriter, req *http.Request, di Dia
 
 		// strike if the roundtrip took too long
 		if h.HealthChecks.Passive.UnhealthyLatency > 0 &&
-			latency >= time.Duration(h.HealthChecks.Passive.UnhealthyLatency) {
+			duration >= time.Duration(h.HealthChecks.Passive.UnhealthyLatency) {
 			h.countFailure(di.Upstream)
 		}
 	}
@@ -651,10 +649,10 @@ func removeConnectionHeaders(h http.Header) {
 
 // LoadBalancing has parameters related to load balancing.
 type LoadBalancing struct {
-	SelectionPolicyRaw json.RawMessage          `json:"selection_policy,omitempty"`
+	SelectionPolicyRaw json.RawMessage          `json:"selection_policy,omitempty" caddy:"namespace=http.reverse_proxy.selection_policies inline_key=policy"`
 	TryDuration        caddy.Duration           `json:"try_duration,omitempty"`
 	TryInterval        caddy.Duration           `json:"try_interval,omitempty"`
-	RetryMatchRaw      caddyhttp.RawMatcherSets `json:"retry_match,omitempty"`
+	RetryMatchRaw      caddyhttp.RawMatcherSets `json:"retry_match,omitempty" caddy:"namespace=http.matchers"`
 
 	SelectionPolicy Selector              `json:"-"`
 	RetryMatch      caddyhttp.MatcherSets `json:"-"`