perkeep/pkg/search/handler.go

/*
Copyright 2011 Google Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package search

import (
	"bytes"
	"fmt"
	"log"
	"net/http"
	"net/url"
	"os"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"camlistore.org/pkg/blobref"
	"camlistore.org/pkg/blobserver"
	"camlistore.org/pkg/httputil"
	"camlistore.org/pkg/jsonconfig"
)

const buffered = 32      // arbitrary channel buffer size
const maxPermanodes = 50 // arbitrary limit on the number of permanodes fetched

func init() {
	blobserver.RegisterHandlerConstructor("search", newHandlerFromConfig)
}

type Handler struct {
	index Index
	owner *blobref.BlobRef
}

func NewHandler(index Index, owner *blobref.BlobRef) *Handler {
	return &Handler{index: index, owner: owner}
}

func newHandlerFromConfig(ld blobserver.Loader, conf jsonconfig.Obj) (http.Handler, error) {
	indexPrefix := conf.RequiredString("index") // TODO: add optional help tips here?
	ownerBlobStr := conf.RequiredString("owner")
	devBlockStartupPrefix := conf.OptionalString("devBlockStartupOn", "")
	if err := conf.Validate(); err != nil {
		return nil, err
	}

	if devBlockStartupPrefix != "" {
		_, err := ld.GetHandler(devBlockStartupPrefix)
		if err != nil {
			return nil, fmt.Errorf("search handler references bogus devBlockStartupOn handler %s: %v", devBlockStartupPrefix, err)
		}
	}

	indexHandler, err := ld.GetHandler(indexPrefix)
	if err != nil {
		return nil, fmt.Errorf("search config references unknown handler %q", indexPrefix)
	}
	indexer, ok := indexHandler.(Index)
	if !ok {
		return nil, fmt.Errorf("search config references invalid indexer %q (actually a %T)", indexPrefix, indexHandler)
	}
	ownerBlobRef := blobref.Parse(ownerBlobStr)
	if ownerBlobRef == nil {
		return nil, fmt.Errorf("search 'owner' has malformed blobref %q; expecting e.g. sha1-xxxxxxxxxxxx",
			ownerBlobStr)
	}
	return &Handler{
		index: indexer,
		owner: ownerBlobRef,
	}, nil
}

// TODO: figure out a plan for an owner having multiple active public keys, or public
// key rotation
func (h *Handler) Owner() *blobref.BlobRef {
	return h.owner
}

func (h *Handler) Index() Index {
	return h.index
}

func jsonMap() map[string]interface{} {
	return make(map[string]interface{})
}

func jsonMapList() []map[string]interface{} {
	return make([]map[string]interface{}, 0)
}

func (sh *Handler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
	ret := jsonMap()
	_ = req.Header.Get("X-PrefixHandler-PathBase")
	suffix := req.Header.Get("X-PrefixHandler-PathSuffix")

	if req.Method == "GET" {
		switch suffix {
		case "camli/search/recent":
			sh.serveRecentPermanodes(rw, req)
			return
		case "camli/search/permanodeattr":
			sh.servePermanodesWithAttr(rw, req)
			return
		case "camli/search/describe":
			sh.serveDescribe(rw, req)
			return
		case "camli/search/claims":
			sh.serveClaims(rw, req)
			return
		case "camli/search/files":
			sh.serveFiles(rw, req)
			return
		case "camli/search/signerattrvalue":
			sh.serveSignerAttrValue(rw, req)
			return
		case "camli/search/signerpaths":
			sh.serveSignerPaths(rw, req)
			return
		case "camli/search/edgesto":
			sh.serveEdgesTo(rw, req)
			return
		}
	}

	// TODO: discovery for the endpoints & better error message with link to discovery info
	ret["error"] = "Unsupported search path or method"
	ret["errorType"] = "input"
	httputil.ReturnJSON(rw, ret)
}

func (sh *Handler) serveRecentPermanodes(rw http.ResponseWriter, req *http.Request) {
	ret := jsonMap()
	defer httputil.ReturnJSON(rw, ret)

	ch := make(chan *Result)
	errch := make(chan error)
	go func() {
		errch <- sh.index.GetRecentPermanodes(ch, sh.owner, 50)
	}()

	dr := sh.NewDescribeRequest()

	recent := jsonMapList()
	for res := range ch {
		dr.Describe(res.BlobRef, 2)
		jm := jsonMap()
		jm["blobref"] = res.BlobRef.String()
		jm["owner"] = res.Signer.String()
		t := time.Unix(res.LastModTime, 0).UTC()
		jm["modtime"] = t.Format(time.RFC3339)
		recent = append(recent, jm)
	}

	err := <-errch
	if err != nil {
		// TODO: return error status code
		ret["error"] = err.Error()
		return
	}

	ret["recent"] = recent

	thumbSize := 0
	if req.FormValue("thumbnails") != "" {
		thumbSize = 50
		if i, _ := strconv.Atoi(req.FormValue("thumbnails")); i >= 25 && i < 800 {
			thumbSize = i
		}
	}
	dr.populateJSONThumbnails(ret, thumbSize)
}

// servePermanodesWithAttr uses the indexer to search for the permanodes matching
// the request.
// The valid values for the "attr" key in the request (i.e the only attributes
// for a permanode which are actually indexed as such) are "tag" and "title".
func (sh *Handler) servePermanodesWithAttr(rw http.ResponseWriter, req *http.Request) {
	ret := jsonMap()
	defer httputil.ReturnJSON(rw, ret)
	defer setPanicError(ret)

	signer := blobref.MustParse(mustGet(req, "signer"))
	value := req.FormValue("value")
	fuzzy := req.FormValue("fuzzy") // exact match if empty
	fuzzyMatch := false
	if fuzzy != "" {
		lowered := strings.ToLower(fuzzy)
		if lowered == "true" || lowered == "t" {
			fuzzyMatch = true
		}
	}
	attr := req.FormValue("attr") // all attributes if empty
	if attr == "" {               // and force fuzzy in that case.
		fuzzyMatch = true
	}
	maxResults := maxPermanodes
	max := req.FormValue("max")
	if max != "" {
		maxR, err := strconv.Atoi(max)
		if err != nil {
			log.Printf("Invalid specified max results 'max': " + err.Error())
			return
		}
		if maxR < maxResults {
			maxResults = maxR
		}
	}

	ch := make(chan *blobref.BlobRef, buffered)
	errch := make(chan error)
	go func() {
		errch <- sh.index.SearchPermanodesWithAttr(ch,
			&PermanodeByAttrRequest{Attribute: attr,
				Query:      value,
				Signer:     signer,
				FuzzyMatch: fuzzyMatch,
				MaxResults: maxResults})
	}()

	dr := sh.NewDescribeRequest()

	withAttr := jsonMapList()
	for res := range ch {
		dr.Describe(res, 2)
		jm := jsonMap()
		jm["permanode"] = res.String()
		withAttr = append(withAttr, jm)
	}

	err := <-errch
	if err != nil {
		ret["error"] = err.Error()
		ret["errorType"] = "server"
		return
	}

	ret["withAttr"] = withAttr
	dr.PopulateJSON(ret)
}

func (sh *Handler) serveClaims(rw http.ResponseWriter, req *http.Request) {
	ret := jsonMap()

	pn := blobref.Parse(req.FormValue("permanode"))
	if pn == nil {
		http.Error(rw, "Missing or invalid 'permanode' param", 400)
		return
	}

	// TODO: rename GetOwnerClaims to GetClaims?
	claims, err := sh.index.GetOwnerClaims(pn, sh.owner)
	if err != nil {
		log.Printf("Error getting claims of %s: %v", pn.String(), err)
	} else {
		sort.Sort(claims)
		jclaims := jsonMapList()

		for _, claim := range claims {
			jclaim := jsonMap()
			jclaim["blobref"] = claim.BlobRef.String()
			jclaim["signer"] = claim.Signer.String()
			jclaim["permanode"] = claim.Permanode.String()
			jclaim["date"] = claim.Date.Format(time.RFC3339)
			jclaim["type"] = claim.Type
			if claim.Attr != "" {
				jclaim["attr"] = claim.Attr
			}
			if claim.Value != "" {
				jclaim["value"] = claim.Value
			}

			jclaims = append(jclaims, jclaim)
		}
		ret["claims"] = jclaims
	}

	httputil.ReturnJSON(rw, ret)
}

type DescribeRequest struct {
	sh *Handler

	mu   sync.Mutex // protects following:
	m    map[string]*DescribedBlob
	done map[string]bool  // blobref -> described
	errs map[string]error // blobref -> error

	wg *sync.WaitGroup // for load requests
}

type DescribedBlob struct {
	Request *DescribeRequest

	BlobRef   *blobref.BlobRef
	MimeType  string
	CamliType string
	// TODO: just int is probably fine, if we're going to be capping blobs at 32MB?
	Size int64

	// if camliType "permanode"
	Permanode *DescribedPermanode

	// if camliType "file"
	File *FileInfo

	Stub bool // if not loaded, but referenced
}

// PermanodeFile returns the blobref path from this permanode to its
// File camliContent, else (nil, false)
func (b *DescribedBlob) PermanodeFile() (path []*blobref.BlobRef, fi *FileInfo, ok bool) {
	if b == nil || b.Permanode == nil {
		return
	}
	if contentRef := b.Permanode.Attr.Get("camliContent"); contentRef != "" {
		if cdes := b.Request.DescribedBlobStr(contentRef); cdes != nil && cdes.File != nil {
			return []*blobref.BlobRef{b.BlobRef, cdes.BlobRef}, cdes.File, true
		}
	}
	return
}

func (b *DescribedBlob) DomID() string {
	if b == nil {
		return ""
	}
	return b.BlobRef.DomID()
}

func (b *DescribedBlob) Title() string {
	if b == nil {
		return ""
	}
	if b.Permanode != nil {
		if t := b.Permanode.Attr.Get("title"); t != "" {
			return t
		}
		if contentRef := b.Permanode.Attr.Get("camliContent"); contentRef != "" {
			return b.Request.DescribedBlobStr(contentRef).Title()
		}
	}
	if b.File != nil {
		return b.File.FileName
	}
	return ""
}

func (b *DescribedBlob) Description() string {
	if b == nil {
		return ""
	}
	if b.Permanode != nil {
		return b.Permanode.Attr.Get("description")
	}
	return ""
}

func (b *DescribedBlob) Members() []*DescribedBlob {
	if b == nil {
		return nil
	}
	m := make([]*DescribedBlob, 0)
	if b.Permanode != nil {
		for _, bstr := range b.Permanode.Attr["camliMember"] {
			if br := blobref.Parse(bstr); br != nil {
				m = append(m, b.PeerBlob(br))
			}
		}
	}
	return m
}

func (b *DescribedBlob) ContentRef() (br *blobref.BlobRef, ok bool) {
	if b != nil && b.Permanode != nil {
		if cref := b.Permanode.Attr.Get("camliContent"); cref != "" {
			br = blobref.Parse(cref)
			return br, br != nil
		}
	}
	return
}

// Given a blobref string returns a Description or nil.
// dr may be nil itself.
func (dr *DescribeRequest) DescribedBlobStr(blobstr string) *DescribedBlob {
	if dr == nil {
		return nil
	}
	dr.mu.Lock()
	defer dr.mu.Unlock()
	return dr.m[blobstr]
}

// PeerBlob returns a DescribedBlob for the provided blobref.
//
// Unlike DescribedBlobStr, the returned DescribedBlob is never nil.
//
// If the blob was never loaded along with the the receiver (or if the
// receiver is nil), a stub DescribedBlob is returned with its Stub
// field set true.
func (b *DescribedBlob) PeerBlob(br *blobref.BlobRef) *DescribedBlob {
	if b.Request == nil {
		return &DescribedBlob{BlobRef: br, Stub: true}
	}
	b.Request.mu.Lock()
	defer b.Request.mu.Unlock()
	return b.peerBlob(br)
}

// version of PeerBlob when b.Request.mu is already held.
func (b *DescribedBlob) peerBlob(br *blobref.BlobRef) *DescribedBlob {
	if peer, ok := b.Request.m[br.String()]; ok {
		return peer
	}
	return &DescribedBlob{Request: b.Request, BlobRef: br, Stub: true}
}

// HasSecureLinkTo returns true if there's a valid link from this blob
// to the other blob. This is used in access control (hence the
// somewhat redundant "Secure" in the name) and should be paranoid
// against e.g. random user/attacker-control attributes making links
// to other blobs.
//
// TODO: don't linear scan here.  rewrite this in terms of ResolvePrefixHop,
// passing down some policy perhaps?  or maybe that's enough.
func (b *DescribedBlob) HasSecureLinkTo(other *blobref.BlobRef) bool {
	if b == nil || other == nil {
		return false
	}
	ostr := other.String()
	if b.Permanode != nil {
		if b.Permanode.Attr.Get("camliContent") == ostr {
			return true
		}
		for _, mstr := range b.Permanode.Attr["camliMember"] {
			if mstr == ostr {
				return true
			}
		}
	}
	return false
}

func (b *DescribedBlob) isPermanode() bool {
	return b.Permanode != nil
}

// returns a path relative to the UI handler.
//
// Locking: requires that DescribedRequest is done loading or that
// Request.mu is held (as it is from populateJSONThumbnails)
func (b *DescribedBlob) thumbnail(thumbSize int) (path string, width, height int, ok bool) {
	if thumbSize <= 0 || !b.isPermanode() {
		return
	}
	if b.Stub {
		return "node.png", thumbSize, thumbSize, true
	}
	pnAttr := b.Permanode.Attr

	if members := pnAttr["camliMember"]; len(members) > 0 {
		return "folder.png", thumbSize, thumbSize, true
	}

	if content, ok := b.ContentRef(); ok {
		peer := b.peerBlob(content)
		if peer.File != nil {
			if peer.File.IsImage() {
				image := fmt.Sprintf("thumbnail/%s/%s?mw=%d&mh=%d", peer.BlobRef,
					url.QueryEscape(peer.File.FileName), thumbSize, thumbSize)
				// TODO: return the correct thumbSizes here,
				// once we know from the indexer the
				// dimensions (after correction for exif
				// orientation).  For now the thumbnails will
				// all be stretched fat squares.
				return image, thumbSize, thumbSize, true
			}

			// TODO: different thumbnails based on peer.File.MimeType.
			return "file.png", thumbSize, thumbSize, true
		}
	}

	return "node.png", thumbSize, thumbSize, true
}

func (b *DescribedBlob) jsonMap() map[string]interface{} {
	m := jsonMap()
	m["blobRef"] = b.BlobRef.String()
	if b.MimeType != "" {
		m["mimeType"] = b.MimeType
	}
	if b.CamliType != "" {
		m["camliType"] = b.CamliType
	}
	m["size"] = b.Size
	if b.Permanode != nil {
		m["permanode"] = b.Permanode.jsonMap()
	}
	if b.File != nil {
		m["file"] = b.File
	}
	return m
}

type DescribedPermanode struct {
	Attr url.Values // a map[string][]string
}

func (dp *DescribedPermanode) jsonMap() map[string]interface{} {
	m := jsonMap()

	am := jsonMap()
	m["attr"] = am
	for k, vv := range dp.Attr {
		if len(vv) > 0 {
			vl := make([]string, len(vv))
			copy(vl[:], vv[:])
			am[k] = vl
		}
	}
	return m
}

// NewDescribeRequest returns a new DescribeRequest holding the state
// of blobs and their summarized descriptions.  Use DescribeBlob
// one or more times before calling PopulateJSON or Result.
func (sh *Handler) NewDescribeRequest() *DescribeRequest {
	return &DescribeRequest{
		sh:   sh,
		m:    make(map[string]*DescribedBlob),
		errs: make(map[string]error),
		wg:   new(sync.WaitGroup),
	}
}

// Given a blobref and a few hex characters of the digest of the next hop, return the complete
// blobref of the prefix, if that's a valid next hop.
func (sh *Handler) ResolvePrefixHop(parent *blobref.BlobRef, prefix string) (child *blobref.BlobRef, err error) {
	// TODO: this is a linear scan right now. this should be
	// optimized to use a new database table of members so this is
	// a quick lookup.  in the meantime it should be in memcached
	// at least.
	if len(prefix) < 8 {
		return nil, fmt.Errorf("Member prefix %q too small", prefix)
	}
	dr := sh.NewDescribeRequest()
	dr.Describe(parent, 1)
	res, err := dr.Result()
	if err != nil {
		return
	}
	des, ok := res[parent.String()]
	if !ok {
		return nil, fmt.Errorf("Failed to describe member %q in parent %q", prefix, parent)
	}
	if des.Permanode != nil {
		if cr, ok := des.ContentRef(); ok && strings.HasPrefix(cr.Digest(), prefix) {
			return cr, nil
		}
		for _, member := range des.Members() {
			if strings.HasPrefix(member.BlobRef.Digest(), prefix) {
				return member.BlobRef, nil
			}
		}
	}
	return nil, fmt.Errorf("Member prefix %q not found in %q", prefix, parent)
}

type DescribeError map[string]error

func (de DescribeError) Error() string {
	var buf bytes.Buffer
	for b, err := range de {
		fmt.Fprintf(&buf, "%s: %v; ", b, err)
	}
	return fmt.Sprintf("Errors (%d) describing blobs: %s", len(de), buf.String())
}

// Result waits for all outstanding lookups to complete and
// returns the map of blobref (strings) to their described
// results. The returned error is non-nil if any errors
// occured, and will be of type DescribeError.
func (dr *DescribeRequest) Result() (desmap map[string]*DescribedBlob, err error) {
	dr.wg.Wait()
	// TODO: set "done" / locked flag, so no more DescribeBlob can
	// be called.
	if len(dr.errs) > 0 {
		return dr.m, DescribeError(dr.errs)
	}
	return dr.m, nil
}

// PopulateJSON waits for all outstanding lookups to complete and populates
// the results into the provided dest map, suitable for marshalling
// as JSON with the json package.
func (dr *DescribeRequest) PopulateJSON(dest map[string]interface{}) {
	dr.populateJSONThumbnails(dest, 0)
}

// Version of PopulateJSON with also including thumbnails.  thumbSize
// of zero means to not include them.
func (dr *DescribeRequest) populateJSONThumbnails(dest map[string]interface{}, thumbSize int) {
	dr.wg.Wait()
	dr.mu.Lock()
	defer dr.mu.Unlock()
	for k, desb := range dr.m {
		m := desb.jsonMap()
		dest[k] = m
		if src, w, h, ok := desb.thumbnail(thumbSize); ok {
			m["thumbnailSrc"] = src
			m["thumbnailWidth"] = float64(w)
			m["thumbnailHeight"] = float64(h)
		}
	}
	for k, err := range dr.errs {
		dest["error"] = "error populating " + k + ": " + err.Error()
		return // TODO: include all?
	}
}

func (dr *DescribeRequest) describedBlob(b *blobref.BlobRef) *DescribedBlob {
	dr.mu.Lock()
	defer dr.mu.Unlock()
	bs := b.String()
	if des, ok := dr.m[bs]; ok {
		return des
	}
	des := &DescribedBlob{Request: dr, BlobRef: b}
	dr.m[bs] = des
	return des
}

func (dr *DescribeRequest) DescribeSync(br *blobref.BlobRef) (*DescribedBlob, error) {
	dr.Describe(br, 1)
	res, err := dr.Result()
	if err != nil {
		return nil, err
	}
	return res[br.String()], nil
}

func (dr *DescribeRequest) Describe(br *blobref.BlobRef, depth int) {
	if depth <= 0 {
		return
	}
	dr.mu.Lock()
	defer dr.mu.Unlock()
	if dr.done == nil {
		dr.done = make(map[string]bool)
	}
	if dr.done[br.String()] {
		return
	}
	dr.done[br.String()] = true
	dr.wg.Add(1)
	go func() {
		defer dr.wg.Done()
		dr.describeReally(br, depth)
	}()
}

func (dr *DescribeRequest) addError(br *blobref.BlobRef, err error) {
	if err == nil {
		return
	}
	dr.mu.Lock()
	defer dr.mu.Unlock()
	// TODO: append? meh.
	dr.errs[br.String()] = err
}

func (dr *DescribeRequest) describeReally(br *blobref.BlobRef, depth int) {
	mime, size, err := dr.sh.index.GetBlobMimeType(br)
	if err == os.ErrNotExist {
		return
	}
	if err != nil {
		dr.addError(br, err)
		return
	}

	// TODO: convert all this in terms of
	// DescribedBlob/DescribedPermanode/DescribedFile, not json
	// maps.  Then add JSON marhsallers to those types. Add tests.
	des := dr.describedBlob(br)
	des.setMimeType(mime)
	des.Size = size

	switch des.CamliType {
	case "permanode":
		des.Permanode = new(DescribedPermanode)
		dr.populatePermanodeFields(des.Permanode, br, dr.sh.owner, depth)
	case "file":
		var err error
		des.File, err = dr.sh.index.GetFileInfo(br)
		if err != nil {
			dr.addError(br, err)
		}
	}
}

func (sh *Handler) serveDescribe(rw http.ResponseWriter, req *http.Request) {
	ret := jsonMap()
	defer httputil.ReturnJSON(rw, ret)

	br := blobref.Parse(req.FormValue("blobref"))
	if br == nil {
		ret["error"] = "Missing or invalid 'blobref' param"
		ret["errorType"] = "input"
		return
	}

	dr := sh.NewDescribeRequest()
	dr.Describe(br, 4)
	thumbSize := 0
	if req.FormValue("thumbnails") != "" {
		thumbSize = 50
		if i, _ := strconv.Atoi(req.FormValue("thumbnails")); i >= 25 && i < 800 {
			thumbSize = i
		}
	}
	dr.populateJSONThumbnails(ret, thumbSize)
}

func (sh *Handler) serveFiles(rw http.ResponseWriter, req *http.Request) {
	ret := jsonMap()
	defer httputil.ReturnJSON(rw, ret)

	br := blobref.Parse(req.FormValue("wholedigest"))
	if br == nil {
		ret["error"] = "Missing or invalid 'wholedigest' param"
		ret["errorType"] = "input"
		return
	}

	files, err := sh.index.ExistingFileSchemas(br)
	if err != nil {
		ret["error"] = err.Error()
		ret["errorType"] = "server"
		return
	}

	strList := []string{}
	for _, br := range files {
		strList = append(strList, br.String())
	}
	ret["files"] = strList
	return
}

func (dr *DescribeRequest) populatePermanodeFields(pi *DescribedPermanode, pn, signer *blobref.BlobRef, depth int) {
	pi.Attr = make(url.Values)
	attr := pi.Attr

	claims, err := dr.sh.index.GetOwnerClaims(pn, signer)
	if err != nil {
		log.Printf("Error getting claims of %s: %v", pn.String(), err)
		dr.addError(pn, fmt.Errorf("Error getting claims of %s: %v", pn.String(), err))
		return
	}

	sort.Sort(claims)
claimLoop:
	for _, cl := range claims {
		switch cl.Type {
		case "del-attribute":
			if cl.Value == "" {
				delete(attr, cl.Attr)
			} else {
				sl := attr[cl.Attr]
				filtered := make([]string, 0, len(sl))
				for _, val := range sl {
					if val != cl.Value {
						filtered = append(filtered, val)
					}
				}
				attr[cl.Attr] = filtered
			}
		case "set-attribute":
			delete(attr, cl.Attr)
			fallthrough
		case "add-attribute":
			if cl.Value == "" {
				continue
			}
			sl, ok := attr[cl.Attr]
			if ok {
				for _, exist := range sl {
					if exist == cl.Value {
						continue claimLoop
					}
				}
			} else {
				sl = make([]string, 0, 1)
				attr[cl.Attr] = sl
			}
			attr[cl.Attr] = append(sl, cl.Value)
		}
	}

	// If the content permanode is now known, look up its type
	if content, ok := attr["camliContent"]; ok && len(content) > 0 {
		cbr := blobref.Parse(content[len(content)-1])
		dr.Describe(cbr, depth-1)
	}

	// Resolve children
	if members, ok := attr["camliMember"]; ok {
		for _, member := range members {
			membr := blobref.Parse(member)
			if membr != nil {
				dr.Describe(membr, depth-1)
			}
		}
	}
}

func mustGet(req *http.Request, param string) string {
	v := req.FormValue(param)
	if v == "" {
		panic(fmt.Sprintf("missing required parameter %q", param))
	}
	return v
}

func setPanicError(m map[string]interface{}) {
	p := recover()
	if p == nil {
		return
	}
	m["error"] = p.(string)
	m["errorType"] = "input"
}

func (sh *Handler) serveSignerAttrValue(rw http.ResponseWriter, req *http.Request) {
	ret := jsonMap()
	defer httputil.ReturnJSON(rw, ret)
	defer setPanicError(ret)

	signer := blobref.MustParse(mustGet(req, "signer"))
	attr := mustGet(req, "attr")
	value := mustGet(req, "value")
	pn, err := sh.index.PermanodeOfSignerAttrValue(signer, attr, value)
	if err != nil {
		ret["error"] = err.Error()
	} else {
		ret["permanode"] = pn.String()

		dr := sh.NewDescribeRequest()
		dr.Describe(pn, 2)
		dr.PopulateJSON(ret)
	}
}

// Unlike the index interface's EdgesTo method, the "edgesto" Handler
// here additionally filters out since-deleted permanode edges.
func (sh *Handler) serveEdgesTo(rw http.ResponseWriter, req *http.Request) {
	ret := jsonMap()
	defer httputil.ReturnJSON(rw, ret)
	defer setPanicError(ret)

	toRef := blobref.MustParse(mustGet(req, "blobref"))
	toRefStr := toRef.String()
	blobInfo := jsonMap()
	ret[toRefStr] = blobInfo

	jsonEdges := jsonMapList()

	edges, err := sh.index.EdgesTo(toRef, nil)
	if err != nil {
		panic(err)
	}

	type mapOrError struct {
		m   map[string]interface{} // nil if no map
		err error
	}
	resc := make(chan mapOrError)
	verify := func(edge *Edge) {
		fromStr := edge.From.String()
		db, err := sh.NewDescribeRequest().DescribeSync(edge.From)
		if err != nil {
			resc <- mapOrError{err: err}
			return
		}
		found := false
		if db.Permanode != nil {
			for attr, vv := range db.Permanode.Attr {
				if IsBlobReferenceAttribute(attr) {
					for _, v := range vv {
						if v == toRefStr {
							found = true
						}
					}
				}
			}
		}
		var em map[string]interface{}
		if found {
			em = jsonMap()
			em["from"] = fromStr
			em["fromType"] = "permanode"
		}
		resc <- mapOrError{m: em}
	}
	verifying := 0
	for _, edge := range edges {
		if edge.FromType == "permanode" {
			verifying++
			go verify(edge)
			continue
		}
		em := jsonMap()
		em["from"] = edge.From.String()
		em["fromType"] = edge.FromType
		jsonEdges = append(jsonEdges, em)
	}
	for i := 0; i < verifying; i++ {
		res := <-resc
		if res.err != nil {
			panic(res.err) // caught and put in JSON response
		}
		if res.m != nil {
			jsonEdges = append(jsonEdges, res.m)
		}
	}
	blobInfo["edgesTo"] = jsonEdges
}

func (sh *Handler) serveSignerPaths(rw http.ResponseWriter, req *http.Request) {
	ret := jsonMap()
	defer httputil.ReturnJSON(rw, ret)
	defer setPanicError(ret)

	signer := blobref.MustParse(mustGet(req, "signer"))
	target := blobref.MustParse(mustGet(req, "target"))
	paths, err := sh.index.PathsOfSignerTarget(signer, target)
	if err != nil {
		ret["error"] = err.Error()
	} else {
		jpaths := []map[string]interface{}{}
		for _, path := range paths {
			jpaths = append(jpaths, map[string]interface{}{
				"claimRef": path.Claim.String(),
				"baseRef":  path.Base.String(),
				"suffix":   path.Suffix,
			})
		}
		ret["paths"] = jpaths
		dr := sh.NewDescribeRequest()
		for _, path := range paths {
			dr.Describe(path.Base, 2)
		}
		dr.PopulateJSON(ret)
	}
}

const camliTypePrefix = "application/json; camliType="

func (d *DescribedBlob) setMimeType(mime string) {
	d.MimeType = mime
	if strings.HasPrefix(mime, camliTypePrefix) {
		d.CamliType = mime[len(camliTypePrefix):]
	}
}