Split code into modules

This is a massive commit that restructures the code into modules:

db/
    All functions related to modifying the Database

types/
    All type definitions and methods that can be exclusivly used on
    these types without dependencies

policy/
    All Policy related code, now without dependencies on the Database.

policy/matcher/
    Dedicated code to match machines in a list of FilterRules

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/util/dns_test.go

@@ -0,0 +1,143 @@
+package util
+
+import "testing"
+
+func TestNormalizeToFQDNRules(t *testing.T) {
+	type args struct {
+		name             string
+		stripEmailDomain bool
+	}
+	tests := []struct {
+		name    string
+		args    args
+		want    string
+		wantErr bool
+	}{
+		{
+			name: "normalize simple name",
+			args: args{
+				name:             "normalize-simple.name",
+				stripEmailDomain: false,
+			},
+			want:    "normalize-simple.name",
+			wantErr: false,
+		},
+		{
+			name: "normalize an email",
+			args: args{
+				name:             "foo.bar@example.com",
+				stripEmailDomain: false,
+			},
+			want:    "foo.bar.example.com",
+			wantErr: false,
+		},
+		{
+			name: "normalize an email domain should be removed",
+			args: args{
+				name:             "foo.bar@example.com",
+				stripEmailDomain: true,
+			},
+			want:    "foo.bar",
+			wantErr: false,
+		},
+		{
+			name: "strip enabled no email passed as argument",
+			args: args{
+				name:             "not-email-and-strip-enabled",
+				stripEmailDomain: true,
+			},
+			want:    "not-email-and-strip-enabled",
+			wantErr: false,
+		},
+		{
+			name: "normalize complex email",
+			args: args{
+				name:             "foo.bar+complex-email@example.com",
+				stripEmailDomain: false,
+			},
+			want:    "foo.bar-complex-email.example.com",
+			wantErr: false,
+		},
+		{
+			name: "user name with space",
+			args: args{
+				name:             "name space",
+				stripEmailDomain: false,
+			},
+			want:    "name-space",
+			wantErr: false,
+		},
+		{
+			name: "user with quote",
+			args: args{
+				name:             "Jamie's iPhone 5",
+				stripEmailDomain: false,
+			},
+			want:    "jamies-iphone-5",
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := NormalizeToFQDNRules(tt.args.name, tt.args.stripEmailDomain)
+			if (err != nil) != tt.wantErr {
+				t.Errorf(
+					"NormalizeToFQDNRules() error = %v, wantErr %v",
+					err,
+					tt.wantErr,
+				)
+
+				return
+			}
+			if got != tt.want {
+				t.Errorf("NormalizeToFQDNRules() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestCheckForFQDNRules(t *testing.T) {
+	type args struct {
+		name string
+	}
+	tests := []struct {
+		name    string
+		args    args
+		wantErr bool
+	}{
+		{
+			name:    "valid: user",
+			args:    args{name: "valid-user"},
+			wantErr: false,
+		},
+		{
+			name:    "invalid: capitalized user",
+			args:    args{name: "Invalid-CapItaLIzed-user"},
+			wantErr: true,
+		},
+		{
+			name:    "invalid: email as user",
+			args:    args{name: "foo.bar@example.com"},
+			wantErr: true,
+		},
+		{
+			name:    "invalid: chars in user name",
+			args:    args{name: "super-user+name"},
+			wantErr: true,
+		},
+		{
+			name: "invalid: too long name for user",
+			args: args{
+				name: "super-long-useruseruser-name-that-should-be-a-little-more-than-63-chars",
+			},
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := CheckForFQDNRules(tt.args.name); (err != nil) != tt.wantErr {
+				t.Errorf("CheckForFQDNRules() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}