open-consul/agent/uiserver/uiserver.go

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// Copyright (c) HashiCorp, Inc.
// SPDX-License-Identifier: MPL-2.0
package uiserver
import (
"bytes"
"embed"
"encoding/json"
"fmt"
"io"
"io/fs"
"net/http"
"os"
"path"
"strings"
"sync/atomic"
"text/template"
"github.com/hashicorp/go-hclog"
"github.com/hashicorp/consul/agent/config"
"github.com/hashicorp/consul/logging"
)
const (
compiledProviderJSPath = "assets/compiled-metrics-providers.js"
)
//go:embed dist
var dist embed.FS
// Handler is the http.Handler that serves the Consul UI. It may serve from the
// embedded fs.FS or from an external directory. It provides a few important
// transformations on the index.html file and includes a proxy for metrics
// backends.
type Handler struct {
// runtimeConfig is a struct accessed through an atomic value to make
// it safe to reload at run time. Each call to ServeHTTP will see the latest
// version of the state without internal locking needed.
runtimeConfig atomic.Value
logger hclog.Logger
transform UIDataTransform
}
// UIDataTransform is an optional dependency that allows the agent to add
// additional data into the UI index as needed. For example we use this to
// inject enterprise-only feature flags into the template without making this
// package inherently dependent on Enterprise-only code.
//
// It is passed the current RuntimeConfig being applied and a map containing the
// current data that will be passed to the template. It should be modified
// directly to inject additional context.
type UIDataTransform func(data map[string]interface{}) error
// NewHandler returns a Handler that can be used to serve UI http requests. It
// accepts a full agent config since properties like ACLs being enabled affect
// the UI so we need more than just UIConfig parts.
func NewHandler(runtimeCfg *config.RuntimeConfig, logger hclog.Logger, transform UIDataTransform) *Handler {
h := &Handler{
logger: logger.Named(logging.UIServer),
transform: transform,
}
h.runtimeConfig.Store(runtimeCfg)
return h
}
// ServeHTTP implements http.Handler and serves UI HTTP requests
func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// We need to support the path being trimmed by http.StripTags just like the
// file servers do since http.StripPrefix will remove the leading slash in our
// current config. Everything else works fine that way so we should to.
pathTrimmed := strings.TrimLeft(r.URL.Path, "/")
if pathTrimmed == compiledProviderJSPath {
h.serveUIMetricsProviders(w)
return
}
srv, err := h.handleIndex()
if err != nil {
http.Error(w, "UI server is misconfigured.", http.StatusInternalServerError)
h.logger.Error("Failed to configure UI server: %s", err)
return
}
srv.ServeHTTP(w, r)
}
// ReloadConfig is called by the agent when the configuration is reloaded and
// updates the UIConfig values the handler uses to serve requests.
func (h *Handler) ReloadConfig(newCfg *config.RuntimeConfig) error {
h.runtimeConfig.Store(newCfg)
return nil
}
func (h *Handler) handleIndex() (http.Handler, error) {
cfg := h.getRuntimeConfig()
var fsys fs.FS
if cfg.UIConfig.Dir == "" {
// strip the dist/ prefix
sub, err := fs.Sub(dist, "dist")
if err != nil {
return nil, err
}
fsys = sub
} else {
fsys = os.DirFS(cfg.UIConfig.Dir)
}
// Render a new index.html with the new config values ready to serve.
buf, err := h.renderIndexFile(cfg, fsys)
if _, ok := err.(*os.PathError); ok && cfg.UIConfig.Dir != "" {
// A Path error indicates that there is no index.html. This could happen if
// the user configured their own UI dir and is serving something that is not
// our usual UI. This won't work perfectly because our uiserver will still
// redirect everything to the UI but we shouldn't fail the entire UI server
// with a 500 in this case. Partly that's just bad UX and partly it's a
// breaking change although quite an edge case. Instead, continue but just
// return a 404 response for the index.html and log a warning.
h.logger.Warn("ui_config.dir does not contain an index.html. Index templating and redirects to index.html are disabled.")
return http.FileServer(http.FS(fsys)), nil
}
if err != nil {
return nil, err
}
// Create a new fsys that serves the rendered index file or falls back to the
// underlying FS.
fsys = &bufIndexFS{
fs: fsys,
bufIndex: buf,
}
// Wrap the buffering FS our redirect FS. This needs to happen later so that
// redirected requests for /index.html get served the rendered version not the
// original.
return http.FileServer(http.FS(&redirectFS{fs: fsys})), nil
}
// getRuntimeConfig is a helper to atomically access the runtime config.
func (h *Handler) getRuntimeConfig() *config.RuntimeConfig {
if cfg, ok := h.runtimeConfig.Load().(*config.RuntimeConfig); ok {
return cfg
}
return nil
}
func (h *Handler) serveUIMetricsProviders(resp http.ResponseWriter) {
// Reload config in case it's changed
cfg := h.getRuntimeConfig()
if len(cfg.UIConfig.MetricsProviderFiles) < 1 {
http.Error(resp, "No provider JS files configured", http.StatusNotFound)
return
}
var buf bytes.Buffer
// Open each one and concatenate them
for _, file := range cfg.UIConfig.MetricsProviderFiles {
if err := concatFile(&buf, file); err != nil {
http.Error(resp, "Internal Server Error", http.StatusInternalServerError)
h.logger.Error("failed serving metrics provider js file", "file", file, "error", err)
return
}
}
// Done!
resp.Header()["Content-Type"] = []string{"application/javascript"}
_, err := buf.WriteTo(resp)
if err != nil {
http.Error(resp, "Internal Server Error", http.StatusInternalServerError)
h.logger.Error("failed writing ui metrics provider files: %s", err)
return
}
}
func concatFile(buf *bytes.Buffer, file string) error {
base := path.Base(file)
_, err := buf.WriteString("// " + base + "\n\n")
if err != nil {
return fmt.Errorf("failed writing provider JS files: %w", err)
}
// Attempt to open the file
f, err := os.Open(file)
if err != nil {
return fmt.Errorf("failed opening ui metrics provider JS file: %w", err)
}
defer f.Close()
_, err = buf.ReadFrom(f)
if err != nil {
return fmt.Errorf("failed reading ui metrics provider JS file: %w", err)
}
_, err = buf.WriteString("\n\n")
if err != nil {
return fmt.Errorf("failed writing provider JS files: %w", err)
}
return nil
}
func (h *Handler) renderIndexFile(cfg *config.RuntimeConfig, fsys fs.FS) (fs.File, error) {
// Open the original index.html
f, err := fsys.Open("index.html")
if err != nil {
return nil, err
}
defer f.Close()
content, err := io.ReadAll(f)
if err != nil {
return nil, fmt.Errorf("failed reading index.html: %w", err)
}
info, err := f.Stat()
if err != nil {
return nil, fmt.Errorf("failed reading metadata for index.html: %w", err)
}
// Create template data from the current config.
tplData, err := uiTemplateDataFromConfig(cfg)
if err != nil {
return nil, fmt.Errorf("failed loading UI config for template: %w", err)
}
// Allow caller to apply additional data transformations if needed.
if h.transform != nil {
if err := h.transform(tplData); err != nil {
return nil, fmt.Errorf("failed running transform: %w", err)
}
}
tpl, err := template.New("index").Funcs(template.FuncMap{
"jsonEncode": func(data map[string]interface{}) (string, error) {
bs, err := json.MarshalIndent(data, "", " ")
if err != nil {
return "", fmt.Errorf("failed jsonEncode: %w", err)
}
return string(bs), nil
},
}).Parse(string(content))
if err != nil {
return nil, fmt.Errorf("failed parsing index.html template: %w", err)
}
var buf bytes.Buffer
err = tpl.Execute(&buf, tplData)
if err != nil {
return nil, fmt.Errorf("failed to render index.html: %w", err)
}
file := newBufferedFile(&buf, info)
return file, nil
}