Begin implementing error handling and re-handling

5 files changed, 279 insertions, 80 deletions

diff --git a/modules/caddyhttp/caddyhttp.go b/modules/caddyhttp/caddyhttp.go
index 179ad50..5f1587d 100644
--- a/modules/caddyhttp/caddyhttp.go
+++ b/modules/caddyhttp/caddyhttp.go
@@ -2,9 +2,9 @@ package caddyhttp
 
 import (
 	"context"
-	"encoding/json"
 	"fmt"
 	"log"
+	mathrand "math/rand"
 	"net"
 	"net/http"
 	"strconv"
@@ -22,6 +22,8 @@ func init() {
 	if err != nil {
 		log.Fatal(err)
 	}
+
+	mathrand.Seed(time.Now().UnixNano())
 }
 
 type httpModuleConfig struct {
@@ -32,36 +34,14 @@ type httpModuleConfig struct {
 
 func (hc *httpModuleConfig) Run() error {
 	// TODO: Either prevent overlapping listeners on different servers, or combine them into one
-	// TODO: A way to loop requests back through, so have them start the matching over again, but keeping any mutations
 	for _, srv := range hc.Servers {
-		// set up the routes
-		for i, route := range srv.Routes {
-			// matchers
-			for modName, rawMsg := range route.Matchers {
-				val, err := caddy2.LoadModule("http.matchers."+modName, rawMsg)
-				if err != nil {
-					return fmt.Errorf("loading matcher module '%s': %v", modName, err)
-				}
-				srv.Routes[i].matchers = append(srv.Routes[i].matchers, val.(RouteMatcher))
-			}
-
-			// middleware
-			for j, rawMsg := range route.Apply {
-				mid, err := caddy2.LoadModuleInlineName("http.middleware", rawMsg)
-				if err != nil {
-					return fmt.Errorf("loading middleware module in position %d: %v", j, err)
-				}
-				srv.Routes[i].middleware = append(srv.Routes[i].middleware, mid.(MiddlewareHandler))
-			}
-
-			// responder
-			if route.Respond != nil {
-				resp, err := caddy2.LoadModuleInlineName("http.responders", route.Respond)
-				if err != nil {
-					return fmt.Errorf("loading responder module: %v", err)
-				}
-				srv.Routes[i].responder = resp.(Handler)
-			}
+		err := srv.Routes.setup()
+		if err != nil {
+			return fmt.Errorf("setting up server routes: %v", err)
+		}
+		err = srv.Errors.Routes.setup()
+		if err != nil {
+			return fmt.Errorf("setting up server error handling routes: %v", err)
 		}
 
 		s := &http.Server{
@@ -104,65 +84,56 @@ type httpServerConfig struct {
 	ReadTimeout       caddy2.Duration `json:"read_timeout"`
 	ReadHeaderTimeout caddy2.Duration `json:"read_header_timeout"`
 	HiddenFiles       []string        `json:"hidden_files"` // TODO:... experimenting with shared/common state
-	Routes            []serverRoute   `json:"routes"`
+	Routes            routeList       `json:"routes"`
+	Errors            httpErrorConfig `json:"errors"`
 }
 
-func (s httpServerConfig) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	var mid []Middleware // TODO: see about using make() for performance reasons
-	var responder Handler
-	mrw := &middlewareResponseWriter{ResponseWriterWrapper: &ResponseWriterWrapper{w}}
+type httpErrorConfig struct {
+	Routes routeList `json:"routes"`
+	// TODO: some way to configure the logging of errors, probably? standardize the logging configuration first.
+}
 
-	for _, route := range s.Routes {
-		matched := len(route.matchers) == 0
-		for _, m := range route.matchers {
-			if m.Match(r) {
-				matched = true
-				break
+// ServeHTTP is the entry point for all HTTP requests.
+func (s httpServerConfig) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	stack := s.Routes.buildMiddlewareChain(w, r)
+	err := executeMiddlewareChain(w, r, stack)
+	if err != nil {
+		// add the error value to the request context so
+		// it can be accessed by error handlers
+		c := context.WithValue(r.Context(), ErrorCtxKey, err)
+		r = r.WithContext(c)
+
+		if len(s.Errors.Routes) == 0 {
+			// TODO: implement a default error handler?
+			log.Printf("[ERROR] %s", err)
+		} else {
+			errStack := s.Errors.Routes.buildMiddlewareChain(w, r)
+			err := executeMiddlewareChain(w, r, errStack)
+			if err != nil {
+				// TODO: what should we do if the error handler has an error?
+				log.Printf("[ERROR] handling error: %v", err)
 			}
 		}
-		if !matched {
-			continue
-		}
-		for _, m := range route.middleware {
-			mid = append(mid, func(next HandlerFunc) HandlerFunc {
-				return func(w http.ResponseWriter, r *http.Request) error {
-					return m.ServeHTTP(mrw, r, next)
-				}
-			})
-		}
-		if responder == nil {
-			responder = route.responder
-		}
 	}
+}
 
-	// build the middleware stack, with the responder at the end
-	stack := HandlerFunc(func(w http.ResponseWriter, r *http.Request) error {
-		if responder == nil {
-			return nil
+// executeMiddlewareChain executes stack with w and r. This function handles
+// the special ErrRehandle error value, which reprocesses requests through
+// the stack again. Any error value returned from this function would be an
+// actual error that needs to be handled.
+func executeMiddlewareChain(w http.ResponseWriter, r *http.Request, stack Handler) error {
+	const maxRehandles = 3
+	var err error
+	for i := 0; i < maxRehandles; i++ {
+		err = stack.ServeHTTP(w, r)
+		if err != ErrRehandle {
+			break
+		}
+		if i == maxRehandles-1 {
+			return fmt.Errorf("too many rehandles")
 		}
-		mrw.allowWrites = true
-		return responder.ServeHTTP(w, r)
-	})
-	for i := len(mid) - 1; i >= 0; i-- {
-		stack = mid[i](stack)
-	}
-
-	err := stack.ServeHTTP(w, r)
-	if err != nil {
-		// TODO: error handling
-		log.Printf("[ERROR] TODO: error handling: %v", err)
 	}
-}
-
-type serverRoute struct {
-	Matchers map[string]json.RawMessage `json:"match"`
-	Apply    []json.RawMessage          `json:"apply"`
-	Respond  json.RawMessage            `json:"respond"`
-
-	// decoded values
-	matchers   []RouteMatcher
-	middleware []MiddlewareHandler
-	responder  Handler
+	return err
 }
 
 // RouteMatcher is a type that can match to a request.
@@ -206,6 +177,10 @@ func (f HandlerFunc) ServeHTTP(w http.ResponseWriter, r *http.Request) error {
 	return f(w, r)
 }
 
+// emptyHandler is used as a no-op handler, which is
+// sometimes better than a nil Handler pointer.
+var emptyHandler HandlerFunc = func(w http.ResponseWriter, r *http.Request) error { return nil }
+
 func parseListenAddr(a string) (network string, addrs []string, err error) {
 	network = "tcp"
 	if idx := strings.Index(a, "/"); idx >= 0 {
diff --git a/modules/caddyhttp/caddylog/log.go b/modules/caddyhttp/caddylog/log.go
index f7bc9fd..dc940b3 100644
--- a/modules/caddyhttp/caddylog/log.go
+++ b/modules/caddyhttp/caddylog/log.go
@@ -13,6 +13,7 @@ func init() {
 	caddy2.RegisterModule(caddy2.Module{
 		Name: "http.middleware.log",
 		New:  func() (interface{}, error) { return new(Log), nil },
+		// TODO: Examples of OnLoad and OnUnload.
 		OnLoad: func(instances []interface{}, priorState interface{}) (interface{}, error) {
 			var counter int
 			if priorState != nil {
@@ -42,6 +43,17 @@ type Log struct {
 func (l *Log) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
 	start := time.Now()
 
+	// TODO: An example of returning errors
+	// return caddyhttp.Error(http.StatusBadRequest, fmt.Errorf("this is a basic error"))
+	// return caddyhttp.Error(http.StatusBadGateway, caddyhttp.HandlerError{
+	// 	Err:     fmt.Errorf("this is a detailed error"),
+	// 	Message: "We had trouble doing the thing.",
+	// 	Recommendations: []string{
+	// 		"Try reconnecting the gizbop.",
+	// 		"Turn off the Internet.",
+	// 	},
+	// })
+
 	if err := next.ServeHTTP(w, r); err != nil {
 		return err
 	}
diff --git a/modules/caddyhttp/errors.go b/modules/caddyhttp/errors.go
new file mode 100644
index 0000000..66cb2ca
--- /dev/null
+++ b/modules/caddyhttp/errors.go
@@ -0,0 +1,105 @@
+package caddyhttp
+
+import (
+	"fmt"
+	mathrand "math/rand"
+	"path"
+	"runtime"
+	"strings"
+
+	"bitbucket.org/lightcodelabs/caddy2"
+)
+
+// Error is a convenient way for a Handler to populate the
+// essential fields of a HandlerError. If err is itself a
+// HandlerError, then any essential fields that are not
+// set will be populated.
+func Error(statusCode int, err error) HandlerError {
+	const idLen = 9
+	if he, ok := err.(HandlerError); ok {
+		if he.ID == "" {
+			he.ID = randString(idLen, true)
+		}
+		if he.Trace == "" {
+			he.Trace = trace()
+		}
+		if he.StatusCode == 0 {
+			he.StatusCode = statusCode
+		}
+		return he
+	}
+	return HandlerError{
+		ID:         randString(idLen, true),
+		StatusCode: statusCode,
+		Err:        err,
+		Trace:      trace(),
+	}
+}
+
+// HandlerError is a serializable representation of
+// an error from within an HTTP handler.
+type HandlerError struct {
+	Err             error    // the original error value and message
+	StatusCode      int      // the HTTP status code to associate with this error
+	Message         string   // an optional message that can be shown to the user
+	Recommendations []string // an optional list of things to try to resolve the error
+
+	ID    string // generated; for identifying this error in logs
+	Trace string // produced from call stack
+}
+
+func (e HandlerError) Error() string {
+	var s string
+	if e.ID != "" {
+		s += fmt.Sprintf("{id=%s}", e.ID)
+	}
+	if e.Trace != "" {
+		s += " " + e.Trace
+	}
+	if e.StatusCode != 0 {
+		s += fmt.Sprintf(": HTTP %d", e.StatusCode)
+	}
+	if e.Err != nil {
+		s += ": " + e.Err.Error()
+	}
+	return strings.TrimSpace(s)
+}
+
+// randString returns a string of n random characters.
+// It is not even remotely secure OR a proper distribution.
+// But it's good enough for some things. It excludes certain
+// confusing characters like I, l, 1, 0, O, etc. If sameCase
+// is true, then uppercase letters are excluded.
+func randString(n int, sameCase bool) string {
+	if n <= 0 {
+		return ""
+	}
+	dict := []byte("abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRTUVWXY23456789")
+	if sameCase {
+		dict = []byte("abcdefghijkmnpqrstuvwxyz0123456789")
+	}
+	b := make([]byte, n)
+	for i := range b {
+		b[i] = dict[mathrand.Int63()%int64(len(dict))]
+	}
+	return string(b)
+}
+
+func trace() string {
+	if pc, file, line, ok := runtime.Caller(2); ok {
+		filename := path.Base(file)
+		pkgAndFuncName := path.Base(runtime.FuncForPC(pc).Name())
+		return fmt.Sprintf("%s (%s:%d)", pkgAndFuncName, filename, line)
+	}
+	return ""
+}
+
+// ErrRehandle is a special error value that Handlers should return
+// from their ServeHTTP() method if the request is to be re-processed.
+// This error value is a sentinel value that should not be wrapped or
+// modified.
+var ErrRehandle = fmt.Errorf("rehandling request")
+
+// ErrorCtxKey is the context key to use when storing
+// an error (for use with context.Context).
+const ErrorCtxKey = caddy2.CtxKey("handler_chain_error")
diff --git a/modules/caddyhttp/matchers.go b/modules/caddyhttp/matchers.go
index ab179d8..21cc19f 100644
--- a/modules/caddyhttp/matchers.go
+++ b/modules/caddyhttp/matchers.go
@@ -137,6 +137,7 @@ func (m matchHeader) Match(r *http.Request) bool {
 	return false
 }
 
+// Interface guards
 var (
 	_ RouteMatcher = matchHost{}
 	_ RouteMatcher = matchPath{}
diff --git a/modules/caddyhttp/routes.go b/modules/caddyhttp/routes.go
new file mode 100644
index 0000000..95b6ee8
--- /dev/null
+++ b/modules/caddyhttp/routes.go
@@ -0,0 +1,106 @@
+package caddyhttp
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+
+	"bitbucket.org/lightcodelabs/caddy2"
+)
+
+type serverRoute struct {
+	Matchers map[string]json.RawMessage `json:"match"`
+	Apply    []json.RawMessage          `json:"apply"`
+	Respond  json.RawMessage            `json:"respond"`
+
+	Exclusive bool `json:"exclusive"`
+
+	// decoded values
+	matchers   []RouteMatcher
+	middleware []MiddlewareHandler
+	responder  Handler
+}
+
+type routeList []serverRoute
+
+func (routes routeList) buildMiddlewareChain(w http.ResponseWriter, r *http.Request) Handler {
+	if len(routes) == 0 {
+		return emptyHandler
+	}
+
+	var mid []Middleware
+	var responder Handler
+	mrw := &middlewareResponseWriter{ResponseWriterWrapper: &ResponseWriterWrapper{w}}
+
+	for _, route := range routes {
+		matched := len(route.matchers) == 0
+		for _, m := range route.matchers {
+			if m.Match(r) {
+				matched = true
+				break
+			}
+		}
+		if !matched {
+			continue
+		}
+		for _, m := range route.middleware {
+			mid = append(mid, func(next HandlerFunc) HandlerFunc {
+				return func(w http.ResponseWriter, r *http.Request) error {
+					return m.ServeHTTP(mrw, r, next)
+				}
+			})
+		}
+		if responder == nil {
+			responder = route.responder
+		}
+		if route.Exclusive {
+			break
+		}
+	}
+
+	// build the middleware stack, with the responder at the end
+	stack := HandlerFunc(func(w http.ResponseWriter, r *http.Request) error {
+		if responder == nil {
+			return nil
+		}
+		mrw.allowWrites = true
+		return responder.ServeHTTP(w, r)
+	})
+	for i := len(mid) - 1; i >= 0; i-- {
+		stack = mid[i](stack)
+	}
+
+	return stack
+}
+
+func (routes routeList) setup() error {
+	for i, route := range routes {
+		// matchers
+		for modName, rawMsg := range route.Matchers {
+			val, err := caddy2.LoadModule("http.matchers."+modName, rawMsg)
+			if err != nil {
+				return fmt.Errorf("loading matcher module '%s': %v", modName, err)
+			}
+			routes[i].matchers = append(routes[i].matchers, val.(RouteMatcher))
+		}
+
+		// middleware
+		for j, rawMsg := range route.Apply {
+			mid, err := caddy2.LoadModuleInlineName("http.middleware", rawMsg)
+			if err != nil {
+				return fmt.Errorf("loading middleware module in position %d: %v", j, err)
+			}
+			routes[i].middleware = append(routes[i].middleware, mid.(MiddlewareHandler))
+		}
+
+		// responder
+		if route.Respond != nil {
+			resp, err := caddy2.LoadModuleInlineName("http.responders", route.Respond)
+			if err != nil {
+				return fmt.Errorf("loading responder module: %v", err)
+			}
+			routes[i].responder = resp.(Handler)
+		}
+	}
+	return nil
+}