Make CoreDNS a server type plugin for Caddy (#220)

* Make CoreDNS a server type plugin for Caddy

Remove code we don't need and port all middleware over. Fix all tests
and rework the documentation.

Also make `go generate` build a caddy binary which we then copy into
our directory. This means `go build`-builds remain working as-is.

And new etc instances in each etcd test for better isolation.
Fix more tests and rework test.Server with the newer support Caddy offers.

Fix Makefile to support new mode of operation.

middleware/errors/setup.go

@@ -0,0 +1,133 @@
+package errors
+
+import (
+	"io"
+	"log"
+	"os"
+
+	"github.com/miekg/coredns/core/dnsserver"
+	"github.com/miekg/coredns/middleware"
+
+	"github.com/hashicorp/go-syslog"
+	"github.com/mholt/caddy"
+)
+
+func init() {
+	caddy.RegisterPlugin("errors", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	handler, err := errorsParse(c)
+	if err != nil {
+		return err
+	}
+
+	var writer io.Writer
+
+	switch handler.LogFile {
+	case "visible":
+		handler.Debug = true
+	case "stdout":
+		writer = os.Stdout
+	case "stderr":
+		writer = os.Stderr
+	case "syslog":
+		writer, err = gsyslog.NewLogger(gsyslog.LOG_ERR, "LOCAL0", "coredns")
+		if err != nil {
+			return err
+		}
+	default:
+		if handler.LogFile == "" {
+			writer = os.Stderr // default
+			break
+		}
+
+		var file *os.File
+		file, err = os.OpenFile(handler.LogFile, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0644)
+		if err != nil {
+			return err
+		}
+		if handler.LogRoller != nil {
+			file.Close()
+
+			handler.LogRoller.Filename = handler.LogFile
+
+			writer = handler.LogRoller.GetLogWriter()
+		} else {
+			writer = file
+		}
+	}
+	handler.Log = log.New(writer, "", 0)
+
+	dnsserver.GetConfig(c).AddMiddleware(func(next dnsserver.Handler) dnsserver.Handler {
+		handler.Next = next
+		return handler
+	})
+
+	return nil
+}
+
+func errorsParse(c *caddy.Controller) (ErrorHandler, error) {
+	handler := ErrorHandler{}
+
+	optionalBlock := func() (bool, error) {
+		var hadBlock bool
+
+		for c.NextBlock() {
+			hadBlock = true
+
+			what := c.Val()
+			if !c.NextArg() {
+				return hadBlock, c.ArgErr()
+			}
+			where := c.Val()
+
+			if what == "log" {
+				if where == "visible" {
+					handler.Debug = true
+				} else {
+					handler.LogFile = where
+					if c.NextArg() {
+						if c.Val() == "{" {
+							c.IncrNest()
+							logRoller, err := middleware.ParseRoller(c)
+							if err != nil {
+								return hadBlock, err
+							}
+							handler.LogRoller = logRoller
+						}
+					}
+				}
+			}
+		}
+		return hadBlock, nil
+	}
+
+	for c.Next() {
+		// weird hack to avoid having the handler values overwritten.
+		if c.Val() == "}" {
+			continue
+		}
+		// Configuration may be in a block
+		hadBlock, err := optionalBlock()
+		if err != nil {
+			return handler, err
+		}
+
+		// Otherwise, the only argument would be an error log file name or 'visible'
+		if !hadBlock {
+			if c.NextArg() {
+				if c.Val() == "visible" {
+					handler.Debug = true
+				} else {
+					handler.LogFile = c.Val()
+				}
+			}
+		}
+	}
+
+	return handler, nil
+}