misc/dashboard/app/build/build.go - go - Git at Google

 // Copyright 2011 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package build

 import (
 	"appengine"
 	"appengine/datastore"
 	"bytes"
 	"compress/gzip"
 	"crypto/sha1"
 	"fmt"
 	"http"
 	"io"
 	"json"
 	"os"
 	"strings"
 )

 const commitsPerPage = 20

 // A Package describes a package that is listed on the dashboard.
 type Package struct {
 	Name    string
 	Path    string // (empty for the main Go tree)
 	NextNum int    // Num of the next head Commit
 }

 func (p *Package) Key(c appengine.Context) *datastore.Key {
 	key := p.Path
 	if key == "" {
 		key = "go"
 	}
 	return datastore.NewKey(c, "Package", key, 0, nil)
 }

 func GetPackage(c appengine.Context, path string) (*Package, os.Error) {
 	p := &Package{Path: path}
 	err := datastore.Get(c, p.Key(c), p)
 	if err == datastore.ErrNoSuchEntity {
 		return nil, fmt.Errorf("package %q not found", path)
 	}
 	return p, err
 }

 // A Commit describes an individual commit in a package.
 //
 // Each Commit entity is a descendant of its associated Package entity.
 // In other words, all Commits with the same PackagePath belong to the same
 // datastore entity group.
 type Commit struct {
 	PackagePath string // (empty for Go commits)
 	Hash        string
 	ParentHash  string
 	Num         int // Internal monotonic counter unique to this package.

 	User string
 	Desc string `datastore:",noindex"`
 	Time datastore.Time

 	// Result is the Data string of each build Result for this Commit.
 	// For non-Go commits, only the Results for the current Go tip, weekly,
 	// and release Tags are stored here. This is purely de-normalized data.
 	// The complete data set is stored in Result entities.
 	Result []string `datastore:",noindex"`
 }

 func (com *Commit) Key(c appengine.Context) *datastore.Key {
 	if com.Hash == "" {
 		panic("tried Key on Commit with empty Hash")
 	}
 	p := Package{Path: com.PackagePath}
 	key := com.PackagePath + "|" + com.Hash
 	return datastore.NewKey(c, "Commit", key, 0, p.Key(c))
 }

 func (c *Commit) Valid() os.Error {
 	if !validHash(c.Hash) {
 		return os.NewError("invalid Hash")
 	}
 	if c.ParentHash != "" && !validHash(c.ParentHash) { // empty is OK
 		return os.NewError("invalid ParentHash")
 	}
 	return nil
 }

 // AddResult adds the denormalized Reuslt data to the Commit's Result field.
 // It must be called from inside a datastore transaction.
 func (com *Commit) AddResult(c appengine.Context, r *Result) os.Error {
 	if err := datastore.Get(c, com.Key(c), com); err != nil {
 		return err
 	}
 	com.Result = append(com.Result, r.Data())
 	_, err := datastore.Put(c, com.Key(c), com)
 	return err
 }

 func (com *Commit) HasResult(builder string) bool {
 	for _, r := range com.Result {
 		if strings.SplitN(r, "|", 2)[0] == builder {
 			return true
 		}
 	}
 	return false
 }

 func (com *Commit) HasGoHashResult(builder, goHash string) bool {
 	for _, r := range com.Result {
 		p := strings.SplitN(r, "|", 4)
 		if len(p) == 4 && p[0] == builder && p[3] == goHash {
 			return true
 		}
 	}
 	return false
 }

 // A Result describes a build result for a Commit on an OS/architecture.
 //
 // Each Result entity is a descendant of its associated Commit entity.
 type Result struct {
 	Builder     string // "arch-os[-note]"
 	Hash        string
 	PackagePath string // (empty for Go commits)

 	// The Go Commit this was built against (empty for Go commits).
 	GoHash string

 	OK      bool
 	Log     []byte `datastore:"-"`        // for JSON unmarshaling
 	LogHash string `datastore:",noindex"` // Key to the Log record.
 }

 func (r *Result) Key(c appengine.Context) *datastore.Key {
 	p := Package{Path: r.PackagePath}
 	key := r.Builder + "|" + r.PackagePath + "|" + r.Hash + "|" + r.GoHash
 	return datastore.NewKey(c, "Result", key, 0, p.Key(c))
 }

 func (r *Result) Data() string {
 	return fmt.Sprintf("%v|%v|%v|%v", r.Builder, r.OK, r.LogHash, r.GoHash)
 }

 func (r *Result) Valid() os.Error {
 	if !validHash(r.Hash) {
 		return os.NewError("invalid Hash")
 	}
 	if r.PackagePath != "" && !validHash(r.GoHash) {
 		return os.NewError("invalid GoHash")
 	}
 	return nil
 }

 // A Log is a gzip-compressed log file stored under the SHA1 hash of the
 // uncompressed log text.
 type Log struct {
 	CompressedLog []byte
 }

 func PutLog(c appengine.Context, text []byte) (hash string, err os.Error) {
 	h := sha1.New()
 	h.Write(text)
 	b := new(bytes.Buffer)
 	z, _ := gzip.NewWriterLevel(b, gzip.BestCompression)
 	z.Write(text)
 	z.Close()
 	hash = fmt.Sprintf("%x", h.Sum())
 	key := datastore.NewKey(c, "Log", hash, 0, nil)
 	_, err = datastore.Put(c, key, &Log{b.Bytes()})
 	return
 }

 // A Tag is used to keep track of the most recent Go weekly and release tags.
 // Typically there will be one Tag entity for each kind of hg tag.
 type Tag struct {
 	Kind string // "weekly", "release", or "tip"
 	Name string // the tag itself (for example: "release.r60")
 	Hash string
 }

 func (t *Tag) Key(c appengine.Context) *datastore.Key {
 	p := &Package{Path: ""}
 	return datastore.NewKey(c, "Tag", t.Kind, 0, p.Key(c))
 }

 func (t *Tag) Valid() os.Error {
 	if t.Kind != "weekly" || t.Kind != "release" || t.Kind != "tip" {
 		return os.NewError("invalid Kind")
 	}
 	if !validHash(t.Hash) {
 		return os.NewError("invalid Hash")
 	}
 	return nil
 }

 // commitHandler retrieves commit data or records a new commit.
 //
 // For GET requests it returns a Commit value for the specified
 // packagePath and hash.
 //
 // For POST requests it reads a JSON-encoded Commit value from the request
 // body and creates a new Commit entity. It also updates the "tip" Tag for
 // each new commit at tip.
 //
 // This handler is used by a gobuilder process in -commit mode.
 func commitHandler(r *http.Request) (interface{}, os.Error) {
 	c := appengine.NewContext(r)
 	com := new(Commit)

 	if r.Method == "GET" {
 		com.PackagePath = r.FormValue("packagePath")
 		com.Hash = r.FormValue("hash")
 		if err := datastore.Get(c, com.Key(c), com); err != nil {
 			return nil, err
 		}
 		return com, nil
 	}
 	if r.Method != "POST" {
 		return nil, errBadMethod(r.Method)
 	}

 	// POST request
 	defer r.Body.Close()
 	if err := json.NewDecoder(r.Body).Decode(com); err != nil {
 		return nil, err
 	}
 	if err := com.Valid(); err != nil {
 		return nil, err
 	}
 	tx := func(c appengine.Context) os.Error {
 		return addCommit(c, com)
 	}
 	return nil, datastore.RunInTransaction(c, tx, nil)
 }

 // addCommit adds the Commit entity to the datastore and updates the tip Tag.
 // It must be run inside a datastore transaction.
 func addCommit(c appengine.Context, com *Commit) os.Error {
 	// if this commit is already in the datastore, do nothing
 	var tc Commit // temp value so we don't clobber com
 	err := datastore.Get(c, com.Key(c), &tc)
 	if err != datastore.ErrNoSuchEntity {
 		return err
 	}
 	// get the next commit number
 	p, err := GetPackage(c, com.PackagePath)
 	if err != nil {
 		return err
 	}
 	com.Num = p.NextNum
 	p.NextNum++
 	if _, err := datastore.Put(c, p.Key(c), p); err != nil {
 		return err
 	}
 	// if this isn't the first Commit test the parent commit exists
 	if com.Num > 0 {
 		n, err := datastore.NewQuery("Commit").
 			Filter("Hash =", com.ParentHash).
 			Ancestor(p.Key(c)).
 			Count(c)
 		if err != nil {
 			return err
 		}
 		if n == 0 {
 			return os.NewError("parent commit not found")
 		}
 	}
 	// update the tip Tag if this is the Go repo
 	if p.Path == "" {
 		t := &Tag{Kind: "tip", Hash: com.Hash}
 		if _, err = datastore.Put(c, t.Key(c), t); err != nil {
 			return err
 		}
 	}
 	// put the Commit
 	_, err = datastore.Put(c, com.Key(c), com)
 	return err
 }

 // tagHandler records a new tag. It reads a JSON-encoded Tag value from the
 // request body and updates the Tag entity for the Kind of tag provided.
 //
 // This handler is used by a gobuilder process in -commit mode.
 func tagHandler(r *http.Request) (interface{}, os.Error) {
 	if r.Method != "POST" {
 		return nil, errBadMethod(r.Method)
 	}

 	t := new(Tag)
 	defer r.Body.Close()
 	if err := json.NewDecoder(r.Body).Decode(t); err != nil {
 		return nil, err
 	}
 	if err := t.Valid(); err != nil {
 		return nil, err
 	}
 	c := appengine.NewContext(r)
 	_, err := datastore.Put(c, t.Key(c), t)
 	return nil, err
 }

 // todoHandler returns the hash of the next Commit to be built.
 // It expects a "builder" query parameter.
 //
 // By default it scans the first 20 Go Commits in Num-descending order and
 // returns the first one it finds that doesn't have a Result for this builder.
 //
 // If provided with additional packagePath and goHash query parameters,
 // and scans the first 20 Commits in Num-descending order for the specified
 // packagePath and returns the first that doesn't have a Result for this builder
 // and goHash combination.
 func todoHandler(r *http.Request) (interface{}, os.Error) {
 	builder := r.FormValue("builder")
 	goHash := r.FormValue("goHash")

 	c := appengine.NewContext(r)
 	p, err := GetPackage(c, r.FormValue("packagePath"))
 	if err != nil {
 		return nil, err
 	}

 	t := datastore.NewQuery("Commit").
 		Ancestor(p.Key(c)).
 		Limit(commitsPerPage).
 		Order("-Num").
 		Run(c)
 	for {
 		com := new(Commit)
 		if _, err := t.Next(com); err != nil {
 			if err == datastore.Done {
 				err = nil
 			}
 			return nil, err
 		}
 		var hasResult bool
 		if goHash != "" {
 			hasResult = com.HasGoHashResult(builder, goHash)
 		} else {
 			hasResult = com.HasResult(builder)
 		}
 		if !hasResult {
 			return com.Hash, nil
 		}
 	}
 	panic("unreachable")
 }

 // packagesHandler returns a list of the non-Go Packages monitored
 // by the dashboard.
 func packagesHandler(r *http.Request) (interface{}, os.Error) {
 	c := appengine.NewContext(r)
 	var pkgs []*Package
 	for t := datastore.NewQuery("Package").Run(c); ; {
 		pkg := new(Package)
 		if _, err := t.Next(pkg); err == datastore.Done {
 			break
 		} else if err != nil {
 			return nil, err
 		}
 		if pkg.Path != "" {
 			pkgs = append(pkgs, pkg)
 		}
 	}
 	return pkgs, nil
 }

 // resultHandler records a build result.
 // It reads a JSON-encoded Result value from the request body,
 // creates a new Result entity, and updates the relevant Commit entity.
 // If the Log field is not empty, resultHandler creates a new Log entity
 // and updates the LogHash field before putting the Commit entity.
 func resultHandler(r *http.Request) (interface{}, os.Error) {
 	if r.Method != "POST" {
 		return nil, errBadMethod(r.Method)
 	}

 	c := appengine.NewContext(r)
 	res := new(Result)
 	defer r.Body.Close()
 	if err := json.NewDecoder(r.Body).Decode(res); err != nil {
 		return nil, err
 	}
 	if err := res.Valid(); err != nil {
 		return nil, err
 	}
 	// store the Log text if supplied
 	if len(res.Log) > 0 {
 		hash, err := PutLog(c, res.Log)
 		if err != nil {
 			return nil, err
 		}
 		res.LogHash = hash
 	}
 	tx := func(c appengine.Context) os.Error {
 		// check Package exists
 		if _, err := GetPackage(c, res.PackagePath); err != nil {
 			return err
 		}
 		// put Result
 		if _, err := datastore.Put(c, res.Key(c), res); err != nil {
 			return err
 		}
 		// add Result to Commit
 		com := &Commit{PackagePath: res.PackagePath, Hash: res.Hash}
 		return com.AddResult(c, res)
 	}
 	return nil, datastore.RunInTransaction(c, tx, nil)
 }

 func logHandler(w http.ResponseWriter, r *http.Request) {
 	c := appengine.NewContext(r)
 	h := r.URL.Path[len("/log/"):]
 	k := datastore.NewKey(c, "Log", h, 0, nil)
 	l := new(Log)
 	if err := datastore.Get(c, k, l); err != nil {
 		logErr(w, r, err)
 		return
 	}
 	d, err := gzip.NewReader(bytes.NewBuffer(l.CompressedLog))
 	if err != nil {
 		logErr(w, r, err)
 		return
 	}
 	if _, err := io.Copy(w, d); err != nil {
 		logErr(w, r, err)
 	}
 }

 type errBadMethod string

 func (e errBadMethod) String() string {
 	return "bad method: " + string(e)
 }

 type dashHandler func(*http.Request) (interface{}, os.Error)

 type dashResponse struct {
 	Response interface{}
 	Error    string
 }

 // AuthHandler wraps a http.HandlerFunc with a handler that validates the
 // supplied key and builder query parameters.
 func AuthHandler(h dashHandler) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		// Put the URL Query values into r.Form to avoid parsing the
 		// request body when calling r.FormValue.
 		r.Form = r.URL.Query()

 		// Validate key query parameter for POST requests only.
 		key := r.FormValue("key")
 		if r.Method == "POST" && key != secretKey {
 			h := sha1.New()
 			h.Write([]byte(r.FormValue("builder") + secretKey))
 			if key != fmt.Sprintf("%x", h.Sum()) {
 				logErr(w, r, os.NewError("invalid key"))
 				return
 			}
 		}

 		// Call the original HandlerFunc and return the response.
 		c := appengine.NewContext(r)
 		resp, err := h(r)
 		dashResp := dashResponse{Response: resp}
 		if err != nil {
 			c.Errorf("%v", err)
 			dashResp.Error = err.String()
 		}
 		w.Header().Set("Content-Type", "application/json")
 		if err = json.NewEncoder(w).Encode(dashResp); err != nil {
 			c.Criticalf("%v", err)
 		}
 	}
 }

 func initHandler(w http.ResponseWriter, r *http.Request) {
 	// TODO(adg): devise a better way of bootstrapping new packages
 	var pkgs = []*Package{
 		&Package{Name: "Go", Path: ""},
 		&Package{Name: "Test", Path: "code.google.com/p/go.test"},
 	}
 	c := appengine.NewContext(r)
 	for _, p := range pkgs {
 		_, err := datastore.Put(c, p.Key(c), p)
 		if err != nil {
 			logErr(w, r, err)
 			return
 		}
 	}
 	fmt.Fprint(w, "OK")
 }

 func init() {
 	// admin handlers
 	http.HandleFunc("/init", initHandler)

 	// authenticated handlers
 	http.HandleFunc("/commit", AuthHandler(commitHandler))
 	http.HandleFunc("/packages", AuthHandler(packagesHandler))
 	http.HandleFunc("/result", AuthHandler(resultHandler))
 	http.HandleFunc("/tag", AuthHandler(tagHandler))
 	http.HandleFunc("/todo", AuthHandler(todoHandler))

 	// public handlers
 	http.HandleFunc("/log/", logHandler)
 }

 func validHash(hash string) bool {
 	// TODO(adg): correctly validate a hash
 	return hash != ""
 }

 func logErr(w http.ResponseWriter, r *http.Request, err os.Error) {
 	appengine.NewContext(r).Errorf("Error: %v", err)
 	w.WriteHeader(http.StatusInternalServerError)
 	fmt.Fprint(w, "Error: ", err)
 }
	// Copyright 2011 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package build

	import (
	"appengine"
	"appengine/datastore"
	"bytes"
	"compress/gzip"
	"crypto/sha1"
	"fmt"
	"http"
	"io"
	"json"
	"os"
	"strings"
	)

	const commitsPerPage = 20

	// A Package describes a package that is listed on the dashboard.
	type Package struct {
	Name string
	Path string // (empty for the main Go tree)
	NextNum int // Num of the next head Commit
	}

	func (p Package) Key(c appengine.Context) datastore.Key {
	key := p.Path
	if key == "" {
	key = "go"
	}
	return datastore.NewKey(c, "Package", key, 0, nil)
	}

	func GetPackage(c appengine.Context, path string) (*Package, os.Error) {
	p := &Package{Path: path}
	err := datastore.Get(c, p.Key(c), p)
	if err == datastore.ErrNoSuchEntity {
	return nil, fmt.Errorf("package %q not found", path)
	}
	return p, err
	}

	// A Commit describes an individual commit in a package.
	//
	// Each Commit entity is a descendant of its associated Package entity.
	// In other words, all Commits with the same PackagePath belong to the same
	// datastore entity group.
	type Commit struct {
	PackagePath string // (empty for Go commits)
	Hash string
	ParentHash string
	Num int // Internal monotonic counter unique to this package.

	User string
	Desc string `datastore:",noindex"`
	Time datastore.Time

	// Result is the Data string of each build Result for this Commit.
	// For non-Go commits, only the Results for the current Go tip, weekly,
	// and release Tags are stored here. This is purely de-normalized data.
	// The complete data set is stored in Result entities.
	Result []string `datastore:",noindex"`
	}

	func (com Commit) Key(c appengine.Context) datastore.Key {
	if com.Hash == "" {
	panic("tried Key on Commit with empty Hash")
	}
	p := Package{Path: com.PackagePath}
	key := com.PackagePath + "\|" + com.Hash
	return datastore.NewKey(c, "Commit", key, 0, p.Key(c))
	}

	func (c *Commit) Valid() os.Error {
	if !validHash(c.Hash) {
	return os.NewError("invalid Hash")
	}
	if c.ParentHash != "" && !validHash(c.ParentHash) { // empty is OK
	return os.NewError("invalid ParentHash")
	}
	return nil
	}

	// AddResult adds the denormalized Reuslt data to the Commit's Result field.
	// It must be called from inside a datastore transaction.
	func (com Commit) AddResult(c appengine.Context, r Result) os.Error {
	if err := datastore.Get(c, com.Key(c), com); err != nil {
	return err
	}
	com.Result = append(com.Result, r.Data())
	_, err := datastore.Put(c, com.Key(c), com)
	return err
	}

	func (com *Commit) HasResult(builder string) bool {
	for _, r := range com.Result {
	if strings.SplitN(r, "\|", 2)[0] == builder {
	return true
	}
	}
	return false
	}

	func (com *Commit) HasGoHashResult(builder, goHash string) bool {
	for _, r := range com.Result {
	p := strings.SplitN(r, "\|", 4)
	if len(p) == 4 && p[0] == builder && p[3] == goHash {
	return true
	}
	}
	return false
	}

	// A Result describes a build result for a Commit on an OS/architecture.
	//
	// Each Result entity is a descendant of its associated Commit entity.
	type Result struct {
	Builder string // "arch-os[-note]"
	Hash string
	PackagePath string // (empty for Go commits)

	// The Go Commit this was built against (empty for Go commits).
	GoHash string

	OK bool
	Log []byte `datastore:"-"` // for JSON unmarshaling
	LogHash string `datastore:",noindex"` // Key to the Log record.
	}

	func (r Result) Key(c appengine.Context) datastore.Key {
	p := Package{Path: r.PackagePath}
	key := r.Builder + "\|" + r.PackagePath + "\|" + r.Hash + "\|" + r.GoHash
	return datastore.NewKey(c, "Result", key, 0, p.Key(c))
	}

	func (r *Result) Data() string {
	return fmt.Sprintf("%v\|%v\|%v\|%v", r.Builder, r.OK, r.LogHash, r.GoHash)
	}

	func (r *Result) Valid() os.Error {
	if !validHash(r.Hash) {
	return os.NewError("invalid Hash")
	}
	if r.PackagePath != "" && !validHash(r.GoHash) {
	return os.NewError("invalid GoHash")
	}
	return nil
	}

	// A Log is a gzip-compressed log file stored under the SHA1 hash of the
	// uncompressed log text.
	type Log struct {
	CompressedLog []byte
	}

	func PutLog(c appengine.Context, text []byte) (hash string, err os.Error) {
	h := sha1.New()
	h.Write(text)
	b := new(bytes.Buffer)
	z, _ := gzip.NewWriterLevel(b, gzip.BestCompression)
	z.Write(text)
	z.Close()
	hash = fmt.Sprintf("%x", h.Sum())
	key := datastore.NewKey(c, "Log", hash, 0, nil)
	_, err = datastore.Put(c, key, &Log{b.Bytes()})
	return
	}

	// A Tag is used to keep track of the most recent Go weekly and release tags.
	// Typically there will be one Tag entity for each kind of hg tag.
	type Tag struct {
	Kind string // "weekly", "release", or "tip"
	Name string // the tag itself (for example: "release.r60")
	Hash string
	}

	func (t Tag) Key(c appengine.Context) datastore.Key {
	p := &Package{Path: ""}
	return datastore.NewKey(c, "Tag", t.Kind, 0, p.Key(c))
	}

	func (t *Tag) Valid() os.Error {
	if t.Kind != "weekly" \|\| t.Kind != "release" \|\| t.Kind != "tip" {
	return os.NewError("invalid Kind")
	}
	if !validHash(t.Hash) {
	return os.NewError("invalid Hash")
	}
	return nil
	}

	// commitHandler retrieves commit data or records a new commit.
	//
	// For GET requests it returns a Commit value for the specified
	// packagePath and hash.
	//
	// For POST requests it reads a JSON-encoded Commit value from the request
	// body and creates a new Commit entity. It also updates the "tip" Tag for
	// each new commit at tip.
	//
	// This handler is used by a gobuilder process in -commit mode.
	func commitHandler(r *http.Request) (interface{}, os.Error) {
	c := appengine.NewContext(r)
	com := new(Commit)

	if r.Method == "GET" {
	com.PackagePath = r.FormValue("packagePath")
	com.Hash = r.FormValue("hash")
	if err := datastore.Get(c, com.Key(c), com); err != nil {
	return nil, err
	}
	return com, nil
	}
	if r.Method != "POST" {
	return nil, errBadMethod(r.Method)
	}

	// POST request
	defer r.Body.Close()
	if err := json.NewDecoder(r.Body).Decode(com); err != nil {
	return nil, err
	}
	if err := com.Valid(); err != nil {
	return nil, err
	}
	tx := func(c appengine.Context) os.Error {
	return addCommit(c, com)
	}
	return nil, datastore.RunInTransaction(c, tx, nil)
	}

	// addCommit adds the Commit entity to the datastore and updates the tip Tag.
	// It must be run inside a datastore transaction.
	func addCommit(c appengine.Context, com *Commit) os.Error {
	// if this commit is already in the datastore, do nothing
	var tc Commit // temp value so we don't clobber com
	err := datastore.Get(c, com.Key(c), &tc)
	if err != datastore.ErrNoSuchEntity {
	return err
	}
	// get the next commit number
	p, err := GetPackage(c, com.PackagePath)
	if err != nil {
	return err
	}
	com.Num = p.NextNum
	p.NextNum++
	if _, err := datastore.Put(c, p.Key(c), p); err != nil {
	return err
	}
	// if this isn't the first Commit test the parent commit exists
	if com.Num > 0 {
	n, err := datastore.NewQuery("Commit").
	Filter("Hash =", com.ParentHash).
	Ancestor(p.Key(c)).
	Count(c)
	if err != nil {
	return err
	}
	if n == 0 {
	return os.NewError("parent commit not found")
	}
	}
	// update the tip Tag if this is the Go repo
	if p.Path == "" {
	t := &Tag{Kind: "tip", Hash: com.Hash}
	if _, err = datastore.Put(c, t.Key(c), t); err != nil {
	return err
	}
	}
	// put the Commit
	_, err = datastore.Put(c, com.Key(c), com)
	return err
	}

	// tagHandler records a new tag. It reads a JSON-encoded Tag value from the
	// request body and updates the Tag entity for the Kind of tag provided.
	//
	// This handler is used by a gobuilder process in -commit mode.
	func tagHandler(r *http.Request) (interface{}, os.Error) {
	if r.Method != "POST" {
	return nil, errBadMethod(r.Method)
	}

	t := new(Tag)
	defer r.Body.Close()
	if err := json.NewDecoder(r.Body).Decode(t); err != nil {
	return nil, err
	}
	if err := t.Valid(); err != nil {
	return nil, err
	}
	c := appengine.NewContext(r)
	_, err := datastore.Put(c, t.Key(c), t)
	return nil, err
	}

	// todoHandler returns the hash of the next Commit to be built.
	// It expects a "builder" query parameter.
	//
	// By default it scans the first 20 Go Commits in Num-descending order and
	// returns the first one it finds that doesn't have a Result for this builder.
	//
	// If provided with additional packagePath and goHash query parameters,
	// and scans the first 20 Commits in Num-descending order for the specified
	// packagePath and returns the first that doesn't have a Result for this builder
	// and goHash combination.
	func todoHandler(r *http.Request) (interface{}, os.Error) {
	builder := r.FormValue("builder")
	goHash := r.FormValue("goHash")

	c := appengine.NewContext(r)
	p, err := GetPackage(c, r.FormValue("packagePath"))
	if err != nil {
	return nil, err
	}

	t := datastore.NewQuery("Commit").
	Ancestor(p.Key(c)).
	Limit(commitsPerPage).
	Order("-Num").
	Run(c)
	for {
	com := new(Commit)
	if _, err := t.Next(com); err != nil {
	if err == datastore.Done {
	err = nil
	}
	return nil, err
	}
	var hasResult bool
	if goHash != "" {
	hasResult = com.HasGoHashResult(builder, goHash)
	} else {
	hasResult = com.HasResult(builder)
	}
	if !hasResult {
	return com.Hash, nil
	}
	}
	panic("unreachable")
	}

	// packagesHandler returns a list of the non-Go Packages monitored
	// by the dashboard.
	func packagesHandler(r *http.Request) (interface{}, os.Error) {
	c := appengine.NewContext(r)
	var pkgs []*Package
	for t := datastore.NewQuery("Package").Run(c); ; {
	pkg := new(Package)
	if _, err := t.Next(pkg); err == datastore.Done {
	break
	} else if err != nil {
	return nil, err
	}
	if pkg.Path != "" {
	pkgs = append(pkgs, pkg)
	}
	}
	return pkgs, nil
	}

	// resultHandler records a build result.
	// It reads a JSON-encoded Result value from the request body,
	// creates a new Result entity, and updates the relevant Commit entity.
	// If the Log field is not empty, resultHandler creates a new Log entity
	// and updates the LogHash field before putting the Commit entity.
	func resultHandler(r *http.Request) (interface{}, os.Error) {
	if r.Method != "POST" {
	return nil, errBadMethod(r.Method)
	}

	c := appengine.NewContext(r)
	res := new(Result)
	defer r.Body.Close()
	if err := json.NewDecoder(r.Body).Decode(res); err != nil {
	return nil, err
	}
	if err := res.Valid(); err != nil {
	return nil, err
	}
	// store the Log text if supplied
	if len(res.Log) > 0 {
	hash, err := PutLog(c, res.Log)
	if err != nil {
	return nil, err
	}
	res.LogHash = hash
	}
	tx := func(c appengine.Context) os.Error {
	// check Package exists
	if _, err := GetPackage(c, res.PackagePath); err != nil {
	return err
	}
	// put Result
	if _, err := datastore.Put(c, res.Key(c), res); err != nil {
	return err
	}
	// add Result to Commit
	com := &Commit{PackagePath: res.PackagePath, Hash: res.Hash}
	return com.AddResult(c, res)
	}
	return nil, datastore.RunInTransaction(c, tx, nil)
	}

	func logHandler(w http.ResponseWriter, r *http.Request) {
	c := appengine.NewContext(r)
	h := r.URL.Path[len("/log/"):]
	k := datastore.NewKey(c, "Log", h, 0, nil)
	l := new(Log)
	if err := datastore.Get(c, k, l); err != nil {
	logErr(w, r, err)
	return
	}
	d, err := gzip.NewReader(bytes.NewBuffer(l.CompressedLog))
	if err != nil {
	logErr(w, r, err)
	return
	}
	if _, err := io.Copy(w, d); err != nil {
	logErr(w, r, err)
	}
	}

	type errBadMethod string

	func (e errBadMethod) String() string {
	return "bad method: " + string(e)
	}

	type dashHandler func(*http.Request) (interface{}, os.Error)

	type dashResponse struct {
	Response interface{}
	Error string
	}

	// AuthHandler wraps a http.HandlerFunc with a handler that validates the
	// supplied key and builder query parameters.
	func AuthHandler(h dashHandler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
	// Put the URL Query values into r.Form to avoid parsing the
	// request body when calling r.FormValue.
	r.Form = r.URL.Query()

	// Validate key query parameter for POST requests only.
	key := r.FormValue("key")
	if r.Method == "POST" && key != secretKey {
	h := sha1.New()
	h.Write([]byte(r.FormValue("builder") + secretKey))
	if key != fmt.Sprintf("%x", h.Sum()) {
	logErr(w, r, os.NewError("invalid key"))
	return
	}
	}

	// Call the original HandlerFunc and return the response.
	c := appengine.NewContext(r)
	resp, err := h(r)
	dashResp := dashResponse{Response: resp}
	if err != nil {
	c.Errorf("%v", err)
	dashResp.Error = err.String()
	}
	w.Header().Set("Content-Type", "application/json")
	if err = json.NewEncoder(w).Encode(dashResp); err != nil {
	c.Criticalf("%v", err)
	}
	}
	}

	func initHandler(w http.ResponseWriter, r *http.Request) {
	// TODO(adg): devise a better way of bootstrapping new packages
	var pkgs = []*Package{
	&Package{Name: "Go", Path: ""},
	&Package{Name: "Test", Path: "code.google.com/p/go.test"},
	}
	c := appengine.NewContext(r)
	for _, p := range pkgs {
	_, err := datastore.Put(c, p.Key(c), p)
	if err != nil {
	logErr(w, r, err)
	return
	}
	}
	fmt.Fprint(w, "OK")
	}

	func init() {
	// admin handlers
	http.HandleFunc("/init", initHandler)

	// authenticated handlers
	http.HandleFunc("/commit", AuthHandler(commitHandler))
	http.HandleFunc("/packages", AuthHandler(packagesHandler))
	http.HandleFunc("/result", AuthHandler(resultHandler))
	http.HandleFunc("/tag", AuthHandler(tagHandler))
	http.HandleFunc("/todo", AuthHandler(todoHandler))

	// public handlers
	http.HandleFunc("/log/", logHandler)
	}

	func validHash(hash string) bool {
	// TODO(adg): correctly validate a hash
	return hash != ""
	}

	func logErr(w http.ResponseWriter, r *http.Request, err os.Error) {
	appengine.NewContext(r).Errorf("Error: %v", err)
	w.WriteHeader(http.StatusInternalServerError)
	fmt.Fprint(w, "Error: ", err)
	}