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finish serve post draft
This commit is contained in:
facundoolano
parent
28b2d32406
commit
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1 changed files with 68 additions and 52 deletions
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@ -9,20 +9,27 @@ draft: true
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#+OPTIONS: toc:nil num:1
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#+LANGUAGE: en
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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*** A basic file server
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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:
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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:
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#+begin_src go
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import (
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"net/http"
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"github.com/facundoolano/jorge/config"
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"github.com/facundoolano/jorge/site"
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)
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func Serve(config config.Config) error {
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// load and build the project
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if err := site.Build(config); err != nil {
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@ -38,7 +45,7 @@ func Serve(config config.Config) error {
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}
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#+end_src
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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:
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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~:
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#+begin_src go
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type HTMLFileSystem struct {
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@ -58,11 +65,11 @@ func (htmlFS HTMLFileSystem) Open(name string) (http.File, error) {
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}
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#+end_src
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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:
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The server setup thus changed to:
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#+begin_src diff
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- fs := http.FileServer(HTMLFileSystem{http.Dir(config.TargetDir)})
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+ fs := http.FileServer(http.Dir(config.TargetDir))
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- fs := http.FileServer(http.Dir(config.TargetDir))
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+ fs := http.FileServer(HTMLFileSystem{http.Dir(config.TargetDir)})
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http.Handle("/", fs)
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fmt.Println("server listening at http://localhost:4001/")
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@ -70,7 +77,7 @@ The ~HTMLFileSystem~ above wraps the standard ~http.Dir~ to look for a ~.html~ f
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#+end_src
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*** Watching for changes
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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.
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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.
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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:
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@ -92,13 +99,12 @@ func runWatcher(config *config.Config) {
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}
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#+end_src
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Then made the watcher look at changes in the project ~src~ directory:
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Then made this watcher look for changes in the project ~src/~ directory:
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#+begin_src go
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func watchProjectFiles(watcher *fsnotify.Watcher, config *config.Config) {
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// fsnotify watches all files within a dir, but non-recursively
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// this walks through the source dir
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// adding watches for each found subdir
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// fsnotify watches all files within a dir, but non-recursively.
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// This walks through the src dir adding watches for each subdir
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filepath.WalkDir(config.SrcDir, func(path string, entry fs.DirEntry, err error) error {
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if entry.IsDir() {
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watcher.Add(path)
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@ -109,15 +115,18 @@ func watchProjectFiles(watcher *fsnotify.Watcher, config *config.Config) {
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#+end_src
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*** Build optimizations
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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.
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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.
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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.
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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.
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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:
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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:
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#+begin_src go
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type site struct {
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config config.Config
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// ...
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}
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func (site *site) build() error {
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// clear previous target contents
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os.RemoveAll(site.Config.TargetDir)
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@ -132,19 +141,18 @@ func (site *site) build() error {
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return os.MkdirAll(targetPath, FILE_RW_MODE)
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}
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// if it's a file render or copy it at the target
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// if it's a file render or copy it to the target
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return site.buildFile(path, targetPath)
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})
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}
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#+end_src
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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:
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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:
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#+begin_src go
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// Runs a pool of workers to build files. Returns a channel
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// to send the paths of files to be built and a WaitGroup
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// to wait them to finish processing.
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Create a channel to send paths to build and a worker pool to handle them concurrently
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// Runs a pool of workers to build files.
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// Returns a channel to send the paths of files to be built
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// and a WaitGroup to wait for them to finish processing.
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func spawnBuildWorkers(site *site) (*sync.WaitGroup, chan string) {
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var wg sync.WaitGroup
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files := make(chan string, 20)
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}
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#+end_src
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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.
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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.
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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:
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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:
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#+begin_src diff
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func (site *site) build() error {
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@ -195,20 +203,15 @@ func (site *site) build() error {
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}
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#+end_src
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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.
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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.
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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.
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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.
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*** Live reload
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- intro sse (vs ws)
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- sse boilerplate
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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.
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#+begin_src diff
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fs := http.FileServer(HTMLFileSystem{http.Dir(config.TargetDir)})
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http.Handle("/", fs)
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+ http.Handle("/_events/", ServerEventsHandler)
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#+end_src
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Some googling revealed the boilerplate I needed to send events from my Go http server:
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#+begin_src go
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func ServerEventsHandler (res http.ResponseWriter, req *http.Request) {
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select {
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case <-time.After(5 * time.Second):
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// send an event to the connected client.
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// data\n\n just means send an empty, unnamed event
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fmt.Fprint(res, "data\n\n")
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fmt.Fprint(res, "data: rebuild\n\n")
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res.(http.Flusher).Flush()
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case <-req.Context().Done():
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// client connection closed
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}
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#+end_src
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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:
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#+begin_src diff
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fs := http.FileServer(HTMLFileSystem{http.Dir(config.TargetDir)})
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http.Handle("/", fs)
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+ http.Handle("/_events/", ServerEventsHandler)
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#+end_src
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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:
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#+begin_src html
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<script type="text/javascript">
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</script>
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#+end_src
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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.
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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.
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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]]):
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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:
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#+begin_src go
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// The event broker mediates between the file watcher
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@ -290,7 +299,9 @@ func (broker *EventBroker) unsubscribe(id uint64)
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func (broker *EventBroker) publish(event string)
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#+end_src
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The events handler now needed to create a subscription on every client connection, to forward rebuild events through it:
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See [[https://github.com/facundoolano/jorge/blob/567db560f511b11492b85cf4f72b51599e8e3a3d/commands/serve.go#L175-L238][here]] for the full ~EventBroker~ implementation.
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The http handler now needed to subscribe every connected client to receive rebuild events through the broker:
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#+begin_src diff
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-func ServerEventsHandler (res http.ResponseWriter, req *http.Request) {
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@ -307,8 +318,7 @@ The events handler now needed to create a subscription on every client connectio
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- case <-time.After(5 * time.Second):
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+ case <-events:
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// send an event to the connected client.
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// data\n\n just means send an empty, unnamed event
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fmt.Fprint(res, "data\n\n")
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fmt.Fprint(res, "data: rebuild\n\n")
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res.(http.Flusher).Flush()
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case <-req.Context().Done():
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// client connection closed
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go func() {
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for event := range watcher.Events {
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fmt.Printf("file %s changed\n", event.Name)
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fmt.Printf("file %s changed\n", event.Name)
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// new src directories could be triggering this event
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// so project files need to be re-added every time
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watchProjectFiles(watcher, config)
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site.Build(*config)
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+ broker.publish("rebuild")
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// new src directories could be triggering this event
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// so project files need to be re-added every time
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watchProjectFiles(watcher, config)
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site.Build(*config)
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+ broker.publish("rebuild")
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}
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}()
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+ return broker
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*** Handling event bursts
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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 <it's mentioned in the fsnotify documentation. The solution (also suggested in the doc [LINK]) is to de-duplicate events by adding a delay between event arrival and response. <time.AfterFunc [LINK] helps here
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The code above worked, but not consistently. A file change would occasionally cause a browser-refresh to a 404 page, as if the new version of the file wasn't written to the target directory yet.
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This happened because a single file edit could result in multiple writes, and those in a burst of fsnotify events (as mentioned in the [[https://github.com/fsnotify/fsnotify/blob/v1.7.0/backend_inotify.go#L108-L115][documentation]]). The solution (also suggested by [[https://github.com/fsnotify/fsnotify/blob/c94b93b0602779989a9af8c023505e99055c8fe5/cmd/fsnotify/dedup.go][an example]] in the fsnotify repository) was to de-duplicate events by introducing a delay between event arrival and response. [[https://pkg.go.dev/time#AfterFunc][~time.AfterFunc~]] helped here:
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#+begin_src diff
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@ -379,6 +390,11 @@ func runWatcher(config *config.Config) *EventBroker {
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}
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#+end_src
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The initial build is triggered immediately on setup (~time.AfterFunc(0, ...)~) but subsequent rebuilds are delayed 100 milliseconds (~rebuildAfter.Reset(100 * time.Millisecond)~), canceling previous pending ones.
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-----
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That's approximately the current implementation of the ~jorge serve~ command, which I used to write this post. You can see the full code [[https://github.com/facundoolano/jorge/blob/28b2d32406c7f4e4f6c3084d521f0123435637c8/commands/serve.go][here]].
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** Notes
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[fn:1] I'm not sure if "broker" is semantically correct in this context, since there's a single event type and is sent to all subscribers. "Broadcaster" is probably more correct, but sounds worse.
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[fn:1] I'm not sure if "broker" is a proper name in this context, since there's a single event type and it's sent to all subscribers. "Broadcaster" is probably more accurate, but it also sounds worse.
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