open-consul/agent/uiserver/uiserver.go

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Go
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package uiserver
import (
"bytes"
"fmt"
"io/ioutil"
"net/http"
"os"
"regexp"
"strings"
"sync/atomic"
"text/template"
"github.com/hashicorp/consul/agent/config"
"github.com/hashicorp/consul/logging"
"github.com/hashicorp/go-hclog"
)
// Handler is the http.Handler that serves the Consul UI. It may serve from the
// compiled-in AssetFS or from and external dir. It provides a few important
// transformations on the index.html file and includes a proxy for metrics
// backends.
type Handler struct {
// state is a reloadableState 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.
state atomic.Value
logger hclog.Logger
}
// reloadableState encapsulates all the state that might be modified during
// ReloadConfig.
type reloadableState struct {
cfg *config.UIConfig
srv http.Handler
err 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(agentCfg *config.RuntimeConfig, logger hclog.Logger) *Handler {
h := &Handler{
logger: logger.Named(logging.UIServer),
}
// Don't return the error since this is likely the result of a
// misconfiguration and reloading config could fix it. Instead we'll capture
// it and return an error for all calls to ServeHTTP so the misconfiguration
// is visible. Sadly we can't log effectively
if err := h.ReloadConfig(agentCfg); err != nil {
h.state.Store(reloadableState{
err: err,
})
}
return h
}
// ServeHTTP implements http.Handler and serves UI HTTP requests
func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// TODO: special case for compiled metrics assets in later PR
s := h.getState()
if s == nil {
panic("nil state")
}
if s.err != nil {
http.Error(w, "UI server is misconfigured.", http.StatusInternalServerError)
h.logger.Error("Failed to configure UI server: %s", s.err)
return
}
s.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 {
newState := reloadableState{
cfg: &newCfg.UIConfig,
}
var fs http.FileSystem
if newCfg.UIConfig.Dir == "" {
// Serve from assetFS
fs = assetFS()
} else {
fs = http.Dir(newCfg.UIConfig.Dir)
}
// Render a new index.html with the new config values ready to serve.
buf, info, err := renderIndex(newCfg, fs)
if _, ok := err.(*os.PathError); ok && newCfg.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.")
} else if err != nil {
return err
}
// buf can be nil in the PathError case above. We should skip this part but
// still serve the rest of the files in that case.
if buf != nil {
// Create a new fs that serves the rendered index file or falls back to the
// underlying FS.
fs = &bufIndexFS{
fs: fs,
indexRendered: buf,
indexInfo: info,
}
// 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.
fs = &redirectFS{fs: fs}
}
newState.srv = http.FileServer(fs)
// Store the new state
h.state.Store(newState)
return nil
}
// getState is a helper to access the atomic internal state
func (h *Handler) getState() *reloadableState {
if cfg, ok := h.state.Load().(reloadableState); ok {
return &cfg
}
return nil
}
func renderIndex(cfg *config.RuntimeConfig, fs http.FileSystem) ([]byte, os.FileInfo, error) {
// Open the original index.html
f, err := fs.Open("/index.html")
if err != nil {
return nil, nil, err
}
defer f.Close()
content, err := ioutil.ReadAll(f)
if err != nil {
return nil, nil, fmt.Errorf("failed reading index.html: %s", err)
}
info, err := f.Stat()
if err != nil {
return nil, nil, fmt.Errorf("failed reading metadata for index.html: %s", err)
}
// Create template data from the current config.
tplData, err := uiTemplateDataFromConfig(cfg)
if err != nil {
return nil, nil, fmt.Errorf("failed loading UI config for template: %s", err)
}
// Sadly we can't perform all the replacements we need with Go template
// because some of them end up being rendered into an escaped json encoded
// meta tag by Ember build which messes up the Go template tags. After a few
// iterations of grossness, this seemed like the least bad for now. note we
// have to match the encoded double quotes around the JSON string value that
// is there as a placeholder so the end result is an actual JSON bool not a
// string containing "false" etc.
re := regexp.MustCompile(`%22__RUNTIME_BOOL_[A-Za-z0-9-_]+__%22`)
content = []byte(re.ReplaceAllStringFunc(string(content), func(str string) string {
// Trim the prefix and __ suffix
varName := strings.TrimSuffix(strings.TrimPrefix(str, "%22__RUNTIME_BOOL_"), "__%22")
if v, ok := tplData[varName].(bool); ok && v {
return "true"
}
return "false"
}))
tpl, err := template.New("index").Parse(string(content))
if err != nil {
return nil, nil, fmt.Errorf("failed parsing index.html template: %s", err)
}
var buf bytes.Buffer
err = tpl.Execute(&buf, tplData)
if err != nil {
return nil, nil, fmt.Errorf("failed to render index.html: %s", err)
}
return buf.Bytes(), info, nil
}