diff --git a/docs/src/blog/a-site-server-with-live-reload.org b/docs/src/blog/a-site-server-with-live-reload.org index 6804faa..c7d4793 100644 --- a/docs/src/blog/a-site-server-with-live-reload.org +++ b/docs/src/blog/a-site-server-with-live-reload.org @@ -9,20 +9,27 @@ draft: true #+OPTIONS: toc:nil num:1 #+LANGUAGE: en -The core of my static site generator is the ~build~ command: take some input files, process them ---render templates, convert other markup formats into HTML--- and write the output for serving to the web. This is where I started with ~jorge~, not only because it was core functionality but because I needed to see the org-mode output as early as possible, to learn if I could expect this project to ultimately replace my Jekyll setup. +The core of my static site generator is the ~build~ command: take some input files, process them ---render templates, convert other markup formats into HTML, minify--- and write the output for serving to the web. This is where I started for ~jorge~, not only because it was core functionality but because I needed to see the org-mode output as early as possible, to learn if I could expect this project to ultimately replace my Jekyll setup. -You could say that I had a working static site generator as soon as the ~build~ command was done, but for it to be minimally useful I needed some facility to preview a site while working on it: the ~serve~ command. It could be as simple as running a local file server of the ~build~ output, but ideally it would also watch for changes in the source files and live-reload the browser tabs looking at them. +I technically had a working static site generator as soon as the ~build~ command was done, but for it to be minimally useful I needed to be able to preview a site while working on it: a ~serve~ command. It could be as simple as running a local file server of the ~build~ target directory, but ideally it would also watch for changes in the source files and live-reload the browser tabs looking at them. -I was aiming for more than the basics here because ~serve~ was the only non-trivial command of the project: the one with the most Go learning potential ---and the most fun. For similar reasons, I wanted to tackle it as early as possible: since it wasn't immediately obvious how I would implement it, it was here where unknown-unknowns and blockers were most likely to come up. -Once ~build~ and ~serve~ were out of the way, I'd be almost done with the project, the rest being nice-to-have features and UX improvements. +I was aiming for more than just the basics here because ~serve~ was the only non-trivial command of the project: the one with the most Go learning potential ---and the most fun. For similar reasons, I wanted to tackle it early on: since it wasn't immediately obvious how I would implement it, it was here where unknown-unknowns and blockers were most likely to come up. +Once ~build~ and ~serve~ were out of the way, I'd be almost done with the project, only nice-to-have features and UX improvements remaining. -The beauty of the ~serve~ command was that I could start with a naive implementation and iterate towards the ideal one, keeping a usable command at every step. Below is a summary of that process. +The beauty of the ~serve~ command was that I could start with a naive implementation and iterate towards the ideal one, keeping a usable command every step of the way. Below is a summary of that process. *** A basic file server -At its simplest, the ~serve~ command consisted of building the site once and serving the target directory with a local server. The standard ~net/http~ package provides [[https://pkg.go.dev/net/http#FileServer][facilities]] for local file servers: +The simplest ~serve~ implementation consisted of building the site once and serving the target directory on a local file server. The standard [[https://pkg.go.dev/net/http#FileServer][~net/http~]] package had what I needed: #+begin_src go +import ( + "net/http" + + "github.com/facundoolano/jorge/config" + "github.com/facundoolano/jorge/site" +) + func Serve(config config.Config) error { // load and build the project if err := site.Build(config); err != nil { @@ -38,7 +45,7 @@ func Serve(config config.Config) error { } #+end_src -This only required a minor change (based in [[https://stackoverflow.com/a/57281956/993769][this]] StackOverflow answer) to allow omitting the ~.html~ suffix from URLs: +I only had to make a minor change (based on [[https://stackoverflow.com/a/57281956/993769][this]] StackOverflow answer) for the server to allow omitting the ~.html~ suffix from URLs so, for instance, ~target/blog/hello.html~ was served at ~/blog/hello~: #+begin_src go type HTMLFileSystem struct { @@ -58,11 +65,11 @@ func (htmlFS HTMLFileSystem) Open(name string) (http.File, error) { } #+end_src -The ~HTMLFileSystem~ above wraps the standard ~http.Dir~ to look for a ~.html~ file when the filename requested isn't found so, for instance, ~target/blog/hello.html~ will be served when receiving a request for ~/blog/hello~. The server setup thus changed to: +The server setup thus changed to: #+begin_src diff -- fs := http.FileServer(HTMLFileSystem{http.Dir(config.TargetDir)}) -+ fs := http.FileServer(http.Dir(config.TargetDir)) +- fs := http.FileServer(http.Dir(config.TargetDir)) ++ fs := http.FileServer(HTMLFileSystem{http.Dir(config.TargetDir)}) http.Handle("/", fs) fmt.Println("server listening at http://localhost:4001/") @@ -70,7 +77,7 @@ The ~HTMLFileSystem~ above wraps the standard ~http.Dir~ to look for a ~.html~ f #+end_src *** Watching for changes -As a next step, instead of building the site once before running the server I wanted the command to watch the project source directory and trigger new builds every time a file changed. I found the [[https://github.com/fsnotify/fsnotify][fsnotify]] library for this exact purpose; the fact that both Hugo and gojekyll listed it in their dependencies suggested that it was a reasonable choice for the job. +As a next step, I needed the command to watch the project source directory and trigger new builds whenever a file changed. I found the [[https://github.com/fsnotify/fsnotify][fsnotify]] library for this exact purpose; the fact that both Hugo and gojekyll listed as a dependency suggested that it was the reasonable choice for the job. Following [[https://github.com/fsnotify/fsnotify/blob/c94b93b0602779989a9af8c023505e99055c8fe5/README.md#usage][an example]] from the fsnotify documentation, I created a watcher and a goroutine that triggered a ~site.Build~ call every time a file change event was received: @@ -92,13 +99,12 @@ func runWatcher(config *config.Config) { } #+end_src -Then made the watcher look at changes in the project ~src~ directory: +Then made this watcher look for changes in the project ~src/~ directory: #+begin_src go func watchProjectFiles(watcher *fsnotify.Watcher, config *config.Config) { - // fsnotify watches all files within a dir, but non-recursively - // this walks through the source dir - // adding watches for each found subdir + // fsnotify watches all files within a dir, but non-recursively. + // This walks through the src dir adding watches for each subdir filepath.WalkDir(config.SrcDir, func(path string, entry fs.DirEntry, err error) error { if entry.IsDir() { watcher.Add(path) @@ -109,15 +115,18 @@ func watchProjectFiles(watcher *fsnotify.Watcher, config *config.Config) { #+end_src *** Build optimizations -At this point I had a useful file server, always responding with the most recent version of the site. But the responsiveness of the ~serve~ command was less than ideal: the entire website had to be processed and copied to the target for any small edit I made on a source file. - -I wanted to attempt some performance improvements to the build process, but without introducing much complexity: instead of adding the structure to support incremental or conditional builds, I wanted to try first to keep building the entire site on every change, only faster. +At this point I had a useful file server, always responding with the most recent version of the site. But the responsiveness of the ~serve~ command wasn't ideal: it processed the entire website for every small edit I made on a source file. I wanted to attempt some performance improvements here, but without introducing much complexity: rather than supporting incremental or conditional builds ---which would have required tracking state and dependencies between files---, I wanted to keep building the entire site on every change, only faster. The first cheap optimization was obvious from looking at the command output: most of the work was copying static assets (e.g. images, static CSS files, etc.). So I changed the ~site.Build~ implementation to optionally create links instead of copying files. -The next thing I wanted to try was to process source files work concurrently. The logic for creating target directories and rendering files was handled by an internal method: +The next thing I wanted to try was to process source files concurrently. The logic for creating target directories and rendering files was handled by an internal ~site~ method: #+begin_src go +type site struct { + config config.Config + // ... +} + func (site *site) build() error { // clear previous target contents os.RemoveAll(site.Config.TargetDir) @@ -132,19 +141,18 @@ func (site *site) build() error { return os.MkdirAll(targetPath, FILE_RW_MODE) } - // if it's a file render or copy it at the target + // if it's a file render or copy it to the target return site.buildFile(path, targetPath) }) } #+end_src -This ~site.build~ method walks the source file tree, recreating directories in the target. For non-directory files, it calls another method, ~site.buildFile~, to do the actual processing (rendering templates, converting markdown and org-mode syntax to HTML, "smartifying" quotes, and writing the results to the target files). I wanted the calls to ~site.buildFile~ offloaded to a pool of workers; I found the facilities I needed in a couple of [[https://gobyexample.com/][Go by Example]] entries: +This ~site.build~ method walks the source file tree, recreating it at the target. For non-directory files, it calls another method, ~site.buildFile~, to do the actual processing (rendering templates, converting markdown and org-mode syntax to HTML, and writing the results to the target files). I wanted ~site.buildFile~ to run in a worker pool; I found the facilities I needed in a couple of [[https://gobyexample.com/][Go by Example]] entries: #+begin_src go -// Runs a pool of workers to build files. Returns a channel -// to send the paths of files to be built and a WaitGroup -// to wait them to finish processing. -Create a channel to send paths to build and a worker pool to handle them concurrently +// Runs a pool of workers to build files. +// Returns a channel to send the paths of files to be built +// and a WaitGroup to wait for them to finish processing. func spawnBuildWorkers(site *site) (*sync.WaitGroup, chan string) { var wg sync.WaitGroup files := make(chan string, 20) @@ -162,9 +170,9 @@ func spawnBuildWorkers(site *site) (*sync.WaitGroup, chan string) { } #+end_src -The function above creates a buffered channel to receive source file paths, and a worker pool with the size of the amount of CPU cores. Each worker registers itself on a ~WaitGroup~ that can be used by callers to block until all workers finish their work. +The function above creates a buffered channel to send source file paths, and a worker pool that reads from it. Each worker registers itself on a ~WaitGroup~ that can be used by callers to block until all workers finish their work. -Then I just needed to adapt the ~build~ function to spawn the workers and send them file paths through the channel, instead of processing them sequentially: +Then I just needed to adapt the ~build~ function to spawn the workers and send them file paths through the channel, instead of processing them inline: #+begin_src diff func (site *site) build() error { @@ -195,20 +203,15 @@ func (site *site) build() error { } #+end_src -the ~close(files)~ call informs the workers that no more work will be sent, and ~wg.Wait()~ blocks execution until all pending work is finished. +the ~close(files)~ call informs the workers that no more work will be sent, and ~wg.Wait()~ blocks execution until all pending work is done. -I was very satisfied to see a sequential piece of code turned into a concurrent one with minimal structural changes, without affecting callers of the function I updated. In other languages, a similar process would have required me to add ~async~ and ~await~ statements all over the place. +I was very satisfied to see a sequential piece of code turned into a concurrent one with minimal structural changes, without affecting callers of the function that contained it. In other languages, a similar operation would have required me to add ~async~ and ~await~ statements all over the place. *** Live reload -- intro sse (vs ws) -- sse boilerplate +Without having looked into their code, I presumed that the live-reloading tools I had used in the past (~jekyll serve~, [[https://github.com/shime/livedown/][livedown]]) worked by running WebSocket servers and injecting some JavaScript in the HTML files they served. I wanted to see if I could get away with implementing live reloading for ~jorge serve~ with [[https://en.wikipedia.org/wiki/Server-sent_events][Server-sent events]] instead, a slightly simpler alternative to WebSockets that didn't require a dedicated server. -#+begin_src diff - fs := http.FileServer(HTMLFileSystem{http.Dir(config.TargetDir)}) - http.Handle("/", fs) -+ http.Handle("/_events/", ServerEventsHandler) -#+end_src +Some googling revealed the boilerplate I needed to send events from my Go http server: #+begin_src go func ServerEventsHandler (res http.ResponseWriter, req *http.Request) { @@ -221,8 +224,7 @@ func ServerEventsHandler (res http.ResponseWriter, req *http.Request) { select { case <-time.After(5 * time.Second): // send an event to the connected client. - // data\n\n just means send an empty, unnamed event - fmt.Fprint(res, "data\n\n") + fmt.Fprint(res, "data: rebuild\n\n") res.(http.Flusher).Flush() case <-req.Context().Done(): // client connection closed @@ -232,7 +234,14 @@ func ServerEventsHandler (res http.ResponseWriter, req *http.Request) { } #+end_src -The code above will send an empty event every 5 seconds to clients connected to the ~/_events/~ endpoint. After some trial-and-error, I arrived to the following JavaScript snippet for the client side: +#+begin_src diff + fs := http.FileServer(HTMLFileSystem{http.Dir(config.TargetDir)}) + http.Handle("/", fs) ++ http.Handle("/_events/", ServerEventsHandler) +#+end_src + + +In this test setup, clients connected to the ~/_events/~ endpoint would receive an event with the ~"rebuild"~ message every 5 seconds. After some trial-and-error, I arrived to the corresponding JavaScript: #+begin_src html #+end_src -Clients will establish an [[https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events][EventSource]] connection through the ~/_events/~ endpoint, and reload the window whenever a server-sent event arrives. I updated the ~site.buildFile~ logic to inject this script in the header of every HTML file written to the target directory. +Clients would establish an [[https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events][EventSource]] connection through the ~/_events/~ endpoint, and reload the window whenever a server-sent event arrived. I updated ~site.buildFile~ to inject this ~script~ tag in the header of every HTML file written to the target directory. -So far I had a working events handler and clients connecting to it. I just needed to update the handler to only send events after site rebuilds triggered by the fsnotify watcher. I couldn't just use a channel to connect both components since every rebuild event needed to be broadcast to all connected clients (there could be more than one open tab at any given moment). I introduced an ~EventBroker~ [fn:1]struct for that purpose, with this API (see the full implementation [[https://github.com/facundoolano/jorge/blob/567db560f511b11492b85cf4f72b51599e8e3a3d/commands/serve.go#L175-L238][here]]): +With the code above I had everything in place to send and receive events, and reload the browser accordingly. I just needed to update the http handler to only send events in response to site rebuilds triggered by source file changes. I couldn't just use a channel to connect the handler with the fsnotify watcher, since there could be multiple clients connected at a time (multiple tabs browsing the site) and each needed to receive the reload event; a single-channel message would be consumed by a single client. I needed some method to broadcast rebuild events; I introduced an ~EventBroker~[fn:1] struct for that purpose, with this interface: #+begin_src go // The event broker mediates between the file watcher @@ -290,7 +299,9 @@ func (broker *EventBroker) unsubscribe(id uint64) func (broker *EventBroker) publish(event string) #+end_src -The events handler now needed to create a subscription on every client connection, to forward rebuild events through it: +See [[https://github.com/facundoolano/jorge/blob/567db560f511b11492b85cf4f72b51599e8e3a3d/commands/serve.go#L175-L238][here]] for the full ~EventBroker~ implementation. + +The http handler now needed to subscribe every connected client to receive rebuild events through the broker: #+begin_src diff -func ServerEventsHandler (res http.ResponseWriter, req *http.Request) { @@ -307,8 +318,7 @@ The events handler now needed to create a subscription on every client connectio - case <-time.After(5 * time.Second): + case <-events: // send an event to the connected client. - // data\n\n just means send an empty, unnamed event - fmt.Fprint(res, "data\n\n") + fmt.Fprint(res, "data: rebuild\n\n") res.(http.Flusher).Flush() case <-req.Context().Done(): // client connection closed @@ -331,13 +341,13 @@ The watcher, in turn, had to publish an event after every rebuild: go func() { for event := range watcher.Events { - fmt.Printf("file %s changed\n", event.Name) + fmt.Printf("file %s changed\n", event.Name) - // new src directories could be triggering this event - // so project files need to be re-added every time - watchProjectFiles(watcher, config) - site.Build(*config) -+ broker.publish("rebuild") + // new src directories could be triggering this event + // so project files need to be re-added every time + watchProjectFiles(watcher, config) + site.Build(*config) ++ broker.publish("rebuild") } }() + return broker @@ -347,7 +357,8 @@ The watcher, in turn, had to publish an event after every rebuild: *** Handling event bursts -The code above worked, but not always. Some times, a file change would trigger a browser refresh to a 404 page, as if the new target file wasn't yet written. This was a consequence of single file changes producing many write events, and