add schema endpoint

This commit adds a new HTTP handler to return a list of all databases
and frames in the index:

	GET /schema

This returns JSON in the following format:

	{
	  "dbs":[
	    {
	      "name":"d0",
	      "frames":[
	        {"name":"f0"},
	        {"name":"f1"}
	      ]
	    }
	  ]
	}

Fixes #61

db.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sort"
 	"sync"
 )
 
@@ -130,6 +131,20 @@ func (db *DB) Frame(name string) *Frame {
 
 func (db *DB) frame(name string) *Frame { return db.frames[name] }
 
+// Frames returns a list of all frames in the database.
+func (db *DB) Frames() []*Frame {
+	db.mu.Lock()
+	defer db.mu.Unlock()
+
+	a := make([]*Frame, 0, len(db.frames))
+	for _, f := range db.frames {
+		a = append(a, f)
+	}
+	sort.Sort(frameSlice(a))
+
+	return a
+}
+
 // CreateFrameIfNotExists returns a frame in the database by name.
 func (db *DB) CreateFrameIfNotExists(name string) (*Frame, error) {
 	db.mu.Lock()
@@ -152,3 +167,9 @@ func (db *DB) createFrameIfNotExists(name string) (*Frame, error) {
 
 	return f, nil
 }
+
+type dbSlice []*DB
+
+func (p dbSlice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+func (p dbSlice) Len() int           { return len(p) }
+func (p dbSlice) Less(i, j int) bool { return p[i].Name() < p[j].Name() }

frame.go

@@ -186,3 +186,9 @@ func (f *Frame) createFragmentIfNotExists(slice uint64) (*Fragment, error) {
 
 	return frag, nil
 }
+
+type frameSlice []*Frame
+
+func (p frameSlice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+func (p frameSlice) Len() int           { return len(p) }
+func (p frameSlice) Less(i, j int) bool { return p[i].Name() < p[j].Name() }

handler.go

@@ -52,6 +52,13 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	t := time.Now()
 
 	switch r.URL.Path {
+	case "/schema":
+		switch r.Method {
+		case "GET":
+			h.handleGetSchema(w, r)
+		default:
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+		}
 	case "/query":
 		switch r.Method {
 		case "POST":
@@ -108,6 +115,39 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	h.logger().Printf("%s %s %.03fs", r.Method, r.URL.String(), time.Since(t).Seconds())
 }
 
+// handleGetSchema handles GET /schema requests.
+func (h *Handler) handleGetSchema(w http.ResponseWriter, r *http.Request) {
+	// Construct schema based on databases and frames.
+	var resp getSchemaResponse
+	for _, db := range h.Index.DBs() {
+		respDB := getSchemaDB{Name: db.Name()}
+		for _, frame := range db.Frames() {
+			respDB.Frames = append(respDB.Frames, getSchemaFrame{
+				Name: frame.Name(),
+			})
+		}
+		resp.DBs = append(resp.DBs, respDB)
+	}
+
+	// Write JSON to response.
+	if err := json.NewEncoder(w).Encode(resp); err != nil {
+		h.logger().Printf("write schema response error: %s", err)
+	}
+}
+
+type getSchemaResponse struct {
+	DBs []getSchemaDB `json:"dbs"`
+}
+
+type getSchemaDB struct {
+	Name   string           `json:"name"`
+	Frames []getSchemaFrame `json:"frames"`
+}
+
+type getSchemaFrame struct {
+	Name string `json:"name"`
+}
+
 // handlePostQuery handles /query requests.
 func (h *Handler) handlePostQuery(w http.ResponseWriter, r *http.Request) {
 	// Parse incoming request.

handler_test.go

@@ -26,6 +26,31 @@ func TestHandler_NotFound(t *testing.T) {
 	}
 }
 
+// Ensure the handler can return the schema.
+func TestHandler_Schema(t *testing.T) {
+	idx := MustOpenIndex()
+	defer idx.Close()
+	if _, err := idx.CreateFrameIfNotExists("d0", "f1"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := idx.CreateFrameIfNotExists("d1", "f0"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := idx.CreateFrameIfNotExists("d0", "f0"); err != nil {
+		t.Fatal(err)
+	}
+
+	h := NewHandler()
+	h.Index = idx.Index
+	w := httptest.NewRecorder()
+	h.ServeHTTP(w, MustNewHTTPRequest("GET", "/schema", nil))
+	if w.Code != http.StatusOK {
+		t.Fatalf("unexpected status code: %d", w.Code)
+	} else if body := w.Body.String(); body != `{"dbs":[{"name":"d0","frames":[{"name":"f0"},{"name":"f1"}]},{"name":"d1","frames":[{"name":"f0"}]}]}`+"\n" {
+		t.Fatalf("unexpected body: %s", body)
+	}
+}
+
 // Ensure the handler can accept URL arguments.
 func TestHandler_Query_Args_URL(t *testing.T) {
 	h := NewHandler()

index.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"sort"
 	"sync"
 )
 
@@ -95,6 +96,20 @@ func (i *Index) DB(name string) *DB {
 
 func (i *Index) db(name string) *DB { return i.dbs[name] }
 
+// DBs returns a list of all databases in the index.
+func (i *Index) DBs() []*DB {
+	i.mu.Lock()
+	defer i.mu.Unlock()
+
+	a := make([]*DB, 0, len(i.dbs))
+	for _, db := range i.dbs {
+		a = append(a, db)
+	}
+	sort.Sort(dbSlice(a))
+
+	return a
+}
+
 // CreateDBIfNotExists returns a database by name.
 // The database is created if it does not already exist.
 func (i *Index) CreateDBIfNotExists(name string) (*DB, error) {