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/log/setup.go

@@ -0,0 +1,141 @@
+package log
+
+import (
+	"io"
+	"log"
+	"os"
+
+	"github.com/miekg/coredns/core/dnsserver"
+	"github.com/miekg/coredns/middleware"
+	"github.com/miekg/coredns/server"
+
+	"github.com/hashicorp/go-syslog"
+	"github.com/mholt/caddy"
+	"github.com/miekg/dns"
+)
+
+func init() {
+	caddy.RegisterPlugin("log", caddy.Plugin{
+		ServerType: "dns",
+		Action:     setup,
+	})
+}
+
+func setup(c *caddy.Controller) error {
+	rules, err := logParse(c)
+	if err != nil {
+		return err
+	}
+
+	// Open the log files for writing when the server starts
+	c.OnStartup(func() error {
+		for i := 0; i < len(rules); i++ {
+			var err error
+			var writer io.Writer
+
+			if rules[i].OutputFile == "stdout" {
+				writer = os.Stdout
+			} else if rules[i].OutputFile == "stderr" {
+				writer = os.Stderr
+			} else if rules[i].OutputFile == "syslog" {
+				writer, err = gsyslog.NewLogger(gsyslog.LOG_INFO, "LOCAL0", "coredns")
+				if err != nil {
+					return err
+				}
+			} else {
+				var file *os.File
+				file, err = os.OpenFile(rules[i].OutputFile, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0644)
+				if err != nil {
+					return err
+				}
+				if rules[i].Roller != nil {
+					file.Close()
+					rules[i].Roller.Filename = rules[i].OutputFile
+					writer = rules[i].Roller.GetLogWriter()
+				} else {
+					writer = file
+				}
+			}
+
+			rules[i].Log = log.New(writer, "", 0)
+		}
+
+		return nil
+	})
+
+	dnsserver.GetConfig(c).AddMiddleware(func(next dnsserver.Handler) dnsserver.Handler {
+		return Logger{Next: next, Rules: rules, ErrorFunc: server.DefaultErrorFunc}
+	})
+
+	return nil
+}
+
+func logParse(c *caddy.Controller) ([]Rule, error) {
+	var rules []Rule
+
+	for c.Next() {
+		args := c.RemainingArgs()
+
+		var logRoller *middleware.LogRoller
+		if c.NextBlock() {
+			if c.Val() == "rotate" {
+				if c.NextArg() {
+					if c.Val() == "{" {
+						var err error
+						logRoller, err = middleware.ParseRoller(c)
+						if err != nil {
+							return nil, err
+						}
+						// This part doesn't allow having something after the rotate block
+						if c.Next() {
+							if c.Val() != "}" {
+								return nil, c.ArgErr()
+							}
+						}
+					}
+				}
+			}
+		}
+		if len(args) == 0 {
+			// Nothing specified; use defaults
+			rules = append(rules, Rule{
+				NameScope:  ".",
+				OutputFile: DefaultLogFilename,
+				Format:     DefaultLogFormat,
+				Roller:     logRoller,
+			})
+		} else if len(args) == 1 {
+			// Only an output file specified
+			rules = append(rules, Rule{
+				NameScope:  ".",
+				OutputFile: args[0],
+				Format:     DefaultLogFormat,
+				Roller:     logRoller,
+			})
+		} else {
+			// Name scope, output file, and maybe a format specified
+
+			format := DefaultLogFormat
+
+			if len(args) > 2 {
+				switch args[2] {
+				case "{common}":
+					format = CommonLogFormat
+				case "{combined}":
+					format = CombinedLogFormat
+				default:
+					format = args[2]
+				}
+			}
+
+			rules = append(rules, Rule{
+				NameScope:  dns.Fqdn(args[0]),
+				OutputFile: args[1],
+				Format:     format,
+				Roller:     logRoller,
+			})
+		}
+	}
+
+	return rules, nil
+}