Changes to graph.go. All files

graph.go

new file mode 100644@@ -0,0 +1,90 @@+package main++import (+	"bytes"+	"context"+	"crypto/sha256"+	"errors"+	"html/template"+	"os"+	"os/exec"+	"strings"+	"time"+)++// graphCache keeps the SVG that dot drew for each fence, by the hash of+// its source, so a doc with diagrams renders again within the budget.+var graphCache = newCache(8 << 20)++// graphTimeout bounds one run of dot; a large graph can take seconds.+const graphTimeout = 5 * time.Second++// maxGraph bounds the SVG a fence may produce.+const maxGraph = 4 << 20++// isGraph reports whether a fence's language names Graphviz.+func isGraph(lang string) bool {+	return lang == "dot" || lang == "graphviz"+}++// drawGraph returns a fence's diagram as inline SVG, drawn by dot. dot+// reads the source as data: SERVER_NAME makes it refuse the image files a+// graph may name, so a diagram cannot show what lies outside the tree.+// Without dot, or when dot rejects the source, the error says why.+func drawGraph(src string) (template.HTML, error) {+	sum := sha256.Sum256([]byte(src))+	key := string(sum[:])+	if svg, ok := graphCache.get(key); ok {+		return svg.(template.HTML), nil+	}+	dot, err := exec.LookPath("dot")+	if err != nil {+		return "", errors.New("dot is not installed; install graphviz to draw this graph")+	}+	ctx, cancel := context.WithTimeout(context.Background(), graphTimeout)+	defer cancel()+	cmd := exec.CommandContext(ctx, dot, "-Tsvg")+	// fontconfig keeps its font cache under home; without it every run+	// scans the fonts again.+	cmd.Env = []string{"SERVER_NAME=" + progName, "GV_FILE_PATH=/nonexistent"}+	for _, k := range []string{"HOME", "XDG_CACHE_HOME", "LANG"} {+		if v, ok := os.LookupEnv(k); ok {+			cmd.Env = append(cmd.Env, k+"="+v)+		}+	}+	cmd.Stdin = strings.NewReader(src)+	var out, stderr bytes.Buffer+	cmd.Stdout, cmd.Stderr = &limited{&out, maxGraph}, &stderr+	if err := cmd.Run(); err != nil {+		msg := strings.TrimSpace(stderr.String())+		if ctx.Err() != nil {+			msg = "dot took over " + graphTimeout.String()+		}+		if msg == "" {+			msg = err.Error()+		}+		return "", errors.New(msg)+	}+	// dot writes an XML prolog and doctype before the svg element, which+	// HTML does not take.+	svg := out.String()+	if i := strings.Index(svg, "<svg"); i >= 0 {+		svg = svg[i:]+	}+	h := template.HTML(`<div class="graph">` + svg + `</div>`)+	graphCache.put(key, h, int64(len(h)))+	return h, nil+}++// limited fails a write past n bytes, which stops dot.+type limited struct {+	w *bytes.Buffer+	n int+}++func (l *limited) Write(p []byte) (int, error) {+	if l.w.Len()+len(p) > l.n {+		return 0, errors.New("graph larger than 4 MB")+	}+	return l.w.Write(p)+}