Use Timestamp type for all time fields.

This is a breaking API change. It improves usability of time fields
by automatically parsing them into a time.Time-like type.

Pointers are used for optional fields, so that the ,omitempty option
correctly omits them when they have zero value (i.e., nil).
This can't be done with values at this time (see golang/go#11939).

Resolves #55.

accounts.go

@@ -94,7 +94,7 @@ type AccountInput struct {
 // AccountDetailInfo entity contains detailed information about an account.
 type AccountDetailInfo struct {
 	AccountInfo
-	RegisteredOn string `json:"registered_on"`
+	RegisteredOn Timestamp `json:"registered_on"`
 }
 
 // AccountNameInput entity contains information for setting a name for an account.

changes.go

@@ -25,10 +25,10 @@ type WebLinkInfo struct {
 
 // GitPersonInfo entity contains information about the author/committer of a commit.
 type GitPersonInfo struct {
-	Name  string `json:"name"`
-	Email string `json:"email"`
-	Date  string `json:"date"`
-	TZ    int    `json:"tz"`
+	Name  string    `json:"name"`
+	Email string    `json:"email"`
+	Date  Timestamp `json:"date"`
+	TZ    int       `json:"tz"`
 }
 
 // NotifyInfo entity contains detailed information about who should be
@@ -67,7 +67,7 @@ type ChangeEditMessageInput struct {
 type ChangeMessageInfo struct {
 	ID             string      `json:"id"`
 	Author         AccountInfo `json:"author,omitempty"`
-	Date           string      `json:"date"`
+	Date           Timestamp   `json:"date"`
 	Message        string      `json:"message"`
 	Tag            string      `json:"tag,omitempty"`
 	RevisionNumber int         `json:"_revision_number,omitempty"`
@@ -247,7 +247,7 @@ type CommentInput struct {
 	Line      int           `json:"line,omitempty"`
 	Range     *CommentRange `json:"range,omitempty"`
 	InReplyTo string        `json:"in_reply_to,omitempty"`
-	Updated   string        `json:"updated,omitempty"`
+	Updated   *Timestamp    `json:"updated,omitempty"`
 	Message   string        `json:"message,omitempty"`
 }
 
@@ -274,9 +274,9 @@ type ChangeInfo struct {
 	ChangeID           string                  `json:"change_id"`
 	Subject            string                  `json:"subject"`
 	Status             string                  `json:"status"`
-	Created            string                  `json:"created"`
-	Updated            string                  `json:"updated"`
-	Submitted          string                  `json:"submitted,omitempty"`
+	Created            Timestamp               `json:"created"`
+	Updated            Timestamp               `json:"updated"`
+	Submitted          *Timestamp              `json:"submitted,omitempty"`
 	Starred            bool                    `json:"starred,omitempty"`
 	Reviewed           bool                    `json:"reviewed,omitempty"`
 	Mergeable          bool                    `json:"mergeable,omitempty"`
@@ -318,7 +318,7 @@ type LabelInfo struct {
 type RevisionInfo struct {
 	Draft             bool                  `json:"draft,omitempty"`
 	Number            int                   `json:"_number"`
-	Created           string                `json:"created"`
+	Created           Timestamp             `json:"created"`
 	Uploader          AccountInfo           `json:"uploader"`
 	Ref               string                `json:"ref"`
 	Fetch             map[string]FetchInfo  `json:"fetch"`
@@ -339,7 +339,7 @@ type CommentInfo struct {
 	Range     CommentRange `json:"range,omitempty"`
 	InReplyTo string       `json:"in_reply_to,omitempty"`
 	Message   string       `json:"message,omitempty"`
-	Updated   string       `json:"updated"`
+	Updated   Timestamp    `json:"updated"`
 	Author    AccountInfo  `json:"author,omitempty"`
 }
 

groups.go

@@ -16,7 +16,7 @@ type GroupAuditEventInfo struct {
 	// TODO Member AccountInfo OR GroupInfo `json:"member"`
 	Type string      `json:"type"`
 	User AccountInfo `json:"user"`
-	Date string      `json:"date"`
+	Date Timestamp   `json:"date"`
 }
 
 // GroupInfo entity contains information about a group.
@@ -30,6 +30,7 @@ type GroupInfo struct {
 	GroupID     int              `json:"group_id,omitempty"`
 	Owner       string           `json:"owner,omitempty"`
 	OwnerID     string           `json:"owner_id,omitempty"`
+	CreatedOn   *Timestamp       `json:"created_on,omitempty"`
 	Members     []AccountInfo    `json:"members,omitempty"`
 	Includes    []GroupInfo      `json:"includes,omitempty"`
 }

projects_tag.go

@@ -12,6 +12,7 @@ type TagInfo struct {
 	Object   string        `json:"object"`
 	Message  string        `json:"message"`
 	Tagger   GitPersonInfo `json:"tagger"`
+	Created  *Timestamp    `json:"created,omitempty"`
 }
 
 // ListTags list the tags of a project.

types.go

@@ -4,8 +4,55 @@ import (
 	"encoding/json"
 	"errors"
 	"strconv"
+	"time"
 )
 
+// Timestamp represents an instant in time with nanosecond precision, in UTC time zone.
+// It encodes to and from JSON in Gerrit's timestamp format.
+// All exported methods of time.Time can be called on Timestamp.
+//
+// Gerrit API docs: https://gerrit-review.googlesource.com/Documentation/rest-api.html#timestamp
+type Timestamp struct {
+	// Time is an instant in time. Its time zone must be UTC.
+	time.Time
+}
+
+// MarshalJSON implements the json.Marshaler interface.
+// The time is a quoted string in Gerrit's timestamp format.
+// An error is returned if t.Time time zone is not UTC.
+func (t Timestamp) MarshalJSON() ([]byte, error) {
+	if t.Location() != time.UTC {
+		return nil, errors.New("Timestamp.MarshalJSON: time zone must be UTC")
+	}
+	if y := t.Year(); y < 0 || 9999 < y {
+		// RFC 3339 is clear that years are 4 digits exactly.
+		// See golang.org/issue/4556#issuecomment-66073163 for more discussion.
+		return nil, errors.New("Timestamp.MarshalJSON: year outside of range [0,9999]")
+	}
+	b := make([]byte, 0, len(timeLayout)+2)
+	b = append(b, '"')
+	b = t.AppendFormat(b, timeLayout)
+	b = append(b, '"')
+	return b, nil
+}
+
+// UnmarshalJSON implements the json.Unmarshaler interface.
+// The time is expected to be a quoted string in Gerrit's timestamp format.
+func (t *Timestamp) UnmarshalJSON(b []byte) error {
+	// Ignore null, like in the main JSON package.
+	if string(b) == "null" {
+		return nil
+	}
+	var err error
+	t.Time, err = time.Parse(`"`+timeLayout+`"`, string(b))
+	return err
+}
+
+// Gerrit's timestamp layout is like time.RFC3339Nano, but with a space instead
+// of the "T", without a timezone (it's always in UTC), and always includes nanoseconds.
+// See https://gerrit-review.googlesource.com/Documentation/rest-api.html#timestamp.
+const timeLayout = "2006-01-02 15:04:05.000000000"
+
 // Number is a string representing a number. This type is only used in cases
 // where the API being queried may return an inconsistent result.
 type Number string

types_test.go

@@ -1,12 +1,64 @@
 package gerrit_test
 
 import (
+	"bytes"
 	"encoding/json"
+	"reflect"
 	"testing"
+	"time"
 
 	"github.com/andygrunwald/go-gerrit"
 )
 
+func TestTimestamp(t *testing.T) {
+	const jsonData = `{
+	"subject": "net/http: write status code in Redirect when Content-Type header set",
+	"created": "2018-05-04 17:24:39.000000000",
+	"updated": "0001-01-01 00:00:00.000000000",
+	"submitted": "2018-05-04 18:01:10.000000000",
+	"_number": 111517
+}
+`
+	type ChangeInfo struct {
+		Subject   string            `json:"subject"`
+		Created   gerrit.Timestamp  `json:"created"`
+		Updated   gerrit.Timestamp  `json:"updated"`
+		Submitted *gerrit.Timestamp `json:"submitted,omitempty"`
+		Omitted   *gerrit.Timestamp `json:"omitted,omitempty"`
+		Number    int               `json:"_number"`
+	}
+	ci := ChangeInfo{
+		Subject:   "net/http: write status code in Redirect when Content-Type header set",
+		Created:   gerrit.Timestamp{Time: time.Date(2018, 5, 4, 17, 24, 39, 0, time.UTC)},
+		Updated:   gerrit.Timestamp{},
+		Submitted: &gerrit.Timestamp{Time: time.Date(2018, 5, 4, 18, 1, 10, 0, time.UTC)},
+		Omitted:   nil,
+		Number:    111517,
+	}
+
+	// Try decoding JSON data into a ChangeInfo struct.
+	var v ChangeInfo
+	err := json.Unmarshal([]byte(jsonData), &v)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, want := v, ci; !reflect.DeepEqual(got, want) {
+		t.Errorf("decoding JSON data into a ChangeInfo struct:\ngot:\n%v\nwant:\n%v", got, want)
+	}
+
+	// Try encoding a ChangeInfo struct into JSON data.
+	var buf bytes.Buffer
+	e := json.NewEncoder(&buf)
+	e.SetIndent("", "\t")
+	err = e.Encode(ci)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, want := buf.String(), jsonData; got != want {
+		t.Errorf("encoding a ChangeInfo struct into JSON data:\ngot:\n%v\nwant:\n%v", got, want)
+	}
+}
+
 func TestTypesNumber_String(t *testing.T) {
 	number := gerrit.Number("7")
 	if number.String() != "7" {