Add RenderGraphvizDot() (#2670)

This was particularly useful when writing unit tests for #2651

db/revtree.go

@@ -18,6 +18,7 @@ import (
 	"errors"
 
 	"github.com/couchbase/sync_gateway/base"
+	"bytes"
 )
 
 type RevKey string
@@ -31,6 +32,10 @@ type RevInfo struct {
 	Channels base.Set
 }
 
+func (rev RevInfo) IsRoot() bool {
+	return rev.Parent == ""
+}
+
 //  A revision tree maps each revision ID to its RevInfo.
 type RevTree map[string]*RevInfo
 
@@ -348,6 +353,103 @@ func (tree RevTree) pruneRevisions(maxDepth uint32, keepRev string) (pruned int)
 	return
 }
 
+// Render the RevTree in Graphviz Dot format, which can then be used to generate a PNG diagram
+// like http://cbmobile-bucket.s3.amazonaws.com/diagrams/example-sync-gateway-revtrees/three_branches.png
+// using the command: dot -Tpng revtree.dot > revtree.png or an online tool such as webgraphviz.com
+func (tree RevTree) RenderGraphvizDot() string {
+
+	resultBuffer := bytes.Buffer{}
+
+	// Helper func to surround graph node w/ double quotes
+	surroundWithDoubleQuotes := func(orig string) string {
+		return fmt.Sprintf(`"%s"`, orig)
+	}
+
+	// Helper func to get the graphviz dot representation of a node
+	dotRepresentation := func(node *RevInfo) string {
+		switch node.Deleted {
+		case false:
+			return fmt.Sprintf(
+				"%s -> %s; ",
+				surroundWithDoubleQuotes(node.Parent),
+				surroundWithDoubleQuotes(node.ID),
+			)
+		default:
+			multilineResult := bytes.Buffer{}
+			multilineResult.WriteString(
+				fmt.Sprintf(
+					`%s [fontcolor=red];`,
+					surroundWithDoubleQuotes(node.ID),
+				),
+			)
+			multilineResult.WriteString(
+				fmt.Sprintf(
+					`%s -> %s [label="Tombstone", fontcolor=red];`,
+					surroundWithDoubleQuotes(node.Parent),
+					surroundWithDoubleQuotes(node.ID),
+				),
+			)
+
+			return multilineResult.String()
+		}
+
+	}
+
+	// Helper func to append node to result: parent -> child;
+	dupes := base.Set{}
+	appendNodeToResult := func(node *RevInfo) {
+		nodeAsDotText := dotRepresentation(node)
+		if dupes.Contains(nodeAsDotText) {
+			return
+		} else {
+			dupes[nodeAsDotText] = struct{}{}
+		}
+		resultBuffer.WriteString(nodeAsDotText)
+	}
+
+	// Start graphviz dot file
+	resultBuffer.WriteString("digraph graphname{")
+
+	// This function will be called back for every leaf node in tree
+	leafProcessor := func(leaf *RevInfo) {
+
+		// Append the leaf to the output
+		appendNodeToResult(leaf)
+
+		// Walk up the tree until we find a root, and append each node
+		node := leaf
+		for {
+
+			node = tree[node.Parent]
+
+			// Not sure how this can happen, but in any case .. probably nothing left to do for this branch
+			if node == nil {
+				break
+			}
+
+			// Reached a root, we're done -- there's no need
+			// to call appendNodeToResult() on the root, since
+			// the child of the root will have already added a node
+			// pointing to the root.
+			if node.IsRoot() {
+				break
+			}
+
+			appendNodeToResult(node)
+		}
+	}
+
+	// Iterate over leaves
+	tree.forEachLeaf(leafProcessor)
+
+	// Finish graphviz dot file
+	resultBuffer.WriteString("}")
+
+	return resultBuffer.String()
+
+}
+
+
 //////// ENCODED REVISION LISTS (_revisions):
 
 // Parses a CouchDB _rev or _revisions property into a list of revision IDs

rest/admin_api.go

@@ -325,6 +325,18 @@ func (h *handler) handleGetRawDoc() error {
 	return err
 }
 
+func (h *handler) handleGetRevTree() error {
+	h.assertAdminOnly()
+	docid := h.PathVar("docid")
+	doc, err := h.db.GetDoc(docid)
+
+	if doc != nil {
+		h.writeText([]byte(doc.History.RenderGraphvizDot()))
+	}
+	return err
+}
+
+
 func (h *handler) handleGetLogging() error {
 	h.writeJSON(base.GetLogKeys())
 	return nil

rest/handler.go

@@ -579,6 +579,29 @@ func (h *handler) writeJSON(value interface{}) {
 	h.writeJSONStatus(http.StatusOK, value)
 }
 
+func (h *handler) writeText(value []byte) {
+	h.writeTextStatus(http.StatusOK, value)
+}
+
+func (h *handler) writeTextStatus(status int, value []byte) {
+	if !h.requestAccepts("text/plain") {
+		base.Warn("Client won't accept text/plain, only %s", h.rq.Header.Get("Accept"))
+		h.writeStatus(http.StatusNotAcceptable, "only text/plain available")
+		return
+	}
+
+	h.setHeader("Content-Type", "text/plain charset=utf-8")
+	h.setHeader("Content-Length", fmt.Sprintf("%d", len(value)))
+	if status > 0 {
+		h.response.WriteHeader(status)
+		h.setStatus(status, "")
+	}
+	h.response.Write(value)
+
+}
+
+
+
 func (h *handler) addJSON(value interface{}) {
 	encoder := json.NewEncoder(h.response)
 	err := encoder.Encode(value)

rest/routing.go

@@ -165,6 +165,9 @@ func CreateAdminRouter(sc *ServerContext) *mux.Router {
 	dbr.Handle("/_raw/{docid:"+docRegex+"}",
 		makeHandler(sc, adminPrivs, (*handler).handleGetRawDoc)).Methods("GET", "HEAD")
 
+	dbr.Handle("/_revtree/{docid:"+docRegex+"}",
+		makeHandler(sc, adminPrivs, (*handler).handleGetRevTree)).Methods("GET")
+
 	dbr.Handle("/_user/",
 		makeHandler(sc, adminPrivs, (*handler).getUsers)).Methods("GET", "HEAD")
 	dbr.Handle("/_user/",