Hard Problem? Invalidating the browser cache
+Invalidating the browser cache
I had a bit of an issue with my website recently.
-I pushed some changes incorporating images for the first time (I know – very swish, very modern), and everything seemed to be working just fine, but when I loaded the production site… in Firefox, the images were not styled. Stranger still, they were styled when I loaded the same page in Chrome.
+I pushed some changes incorporating images for the first time (I know – very swish, very modern), and everything seemed to be working just fine, but when I loaded the production site in Firefox… the images were not styled. Stranger still, they were styled when I loaded the same page in Chrome.
The experienced computer touchers amongst you will be saying “this is obviously a cache problem”, and you’re right, it is obviously a cache problem. Pressing CTR + SHIFT + R (which forces Firefox to clear the cache and do a full reload) proved this thesis, and solved the immediate problem for me, on my machine. But what about other people’s machines? I needed to cache-bust.
Post-processors such as Tailwind use fancy ‘fingerprinting’ techniques for this, but I want something simpler than that for this project. Something I can code myself, without losing sight of what’s happening under the hood.
Invalidating cached HTML
-The best way to deal with the caching problem is to tell the browser not to cache our HTML in the first place. Yes, this is kind of (100%) cheating, but c’mon bro, it’s just one little HTML file — browsers only cache those because most websites these days are glorified SPAs where the HTML rarely changes.
-I can stop the HTML getting cached by by adding the following meta tag, in this case to index.html.
The best way to deal with the caching problem is to tell the browser not to cache our HTML in the first place. Yes, this is kind of cheating (ok, it’s 100% cheating), but c’mon bro, it’s just one little HTML file, and browsers only cache those because most websites these days are SPAs whose HTML rarely changes.
+I can stop HTML files from getting cached by adding the following meta tag. In this case, I’m adding it to index.html.
<meta http-equi"pragma" content="no-cache" />
Invalidating cached CSS
-That’s all well and good, but what I really need is for the browser to recognize my CSS as a new file and load it anew from the server. I could change the file name whenever I want to bust the cache, but this would get tedious very quickly. What’s more, as far as Git is concerned, I’d be deleting the CSS file and writing a new one with every deployment. Surely there’s a better way?
+That’s all well and good, but what I really need is for the browser to recognize my CSS as a new file and load it anew from the server. One way to achieve this would be to change the filename whenever I want to bust the cache, but this would get tedious very quickly. What’s more, as far as Git is concerned, I’d be deleting the CSS file and writing a new one with every deployment, which would be an intolerable mess. Surely there’s a better way?
+Of course there is.
Using a query
-Of course there is. Look at this:
+Look at this:
<link rel="stylesheet" href="css/defaults.css?2"/>
-As I’m requesting the file via http, I can append a query. Awesome. Not awesome enough though. I’m too lazy to do this every time I push a commit, and, being human, I’ll probably forget at a critical moment. This can only mean one thing. It’s time to bash (🤣) out a quick build script.
+As I’m requesting the file via http, I can append a query. Awesome. Not awesome enough though. I’m too lazy to edit this line of code every time I push a commit, and, being human, I’ll probably forget at a critical moment. This can only mean one thing: it’s time to bash (🤣) out a quick build script.
Automating query insertion
#!/usr/bin/env bash
COMMIT="$(git rev-parse HEAD)"
sed -i "s/css?=\w*/css?${COMMIT}/g" index.html
-Let’s talk real quick about what’s happening here:
+Let’s talk about what’s happening here:
COMMIT="$(git rev-parse HEAD)" gets the commit id from Git and assigns it to the variable $COMMIT.
Then, sed -i "s/css?=\w*/css?${COMMIT}/g" index.html does a find and replace on index.html. The regular expression css?=\w* matches ‘css?=’ plus any number of contiguous alphanumeric characters (everything until the next quote mark, basically) before replacing these alphanumeric characters with the commit id. The flag -i tells sed to edit the file in place. The g tells it to perform the operation on the whole file.
Then, sed -i "s/css?=\w*/css?${COMMIT}/g" index.html does a find and replace in the file index.html. The regular expression css?=\w* matches ‘css?=’ plus any number of contiguous alphanumeric characters (everything until the next quote mark) before replacing these alphanumeric characters with the commit id. The flag -i tells sed to edit the file in place. The g tells it to perform the operation on the whole file.
Now, whenever we push a new commit, any CSS imports in index.html will be changed to something like this:
<link rel="stylesheet"
-href="css/styles.css?=ab184
-410c10c1adfb8b85b03b316f72b"
+href="css/styles.css?=ab184410c10c1adfb8b85b03b316f72b"
/>
-Now I just need to add the build script to my Jenkinsfile, and the problem is solved.
+Now I just need to add the build script to my Jenkinsfile…
+ stage('build'){
+ steps{
+ sh './build.sh'
+ }
+ }
+and the problem is solved.
Pretty neat, huh?
There’s just one thing bugging me: surely I do actually want the CSS to be cached sometimes. Caching exists for a reason, and I don’t want to sacrifice performance. Maybe I can modify the build script so that it only updates the CSS imports when the CSS files have changed… Sounds like a topic for another blogpost…
diff --git a/public/posts/index.html b/public/posts/index.html index f472157..b5dc1b0 100644 --- a/public/posts/index.html +++ b/public/posts/index.html @@ -41,9 +41,9 @@Tempor est exercitation ad qui pariatur quis adipisicing aliquip nisi ea consequat ipsum occaecat. Nostrud consequat ullamco laboris fugiat esse esse adipisicing velit laborum ipsum incididunt ut enim. Dolor pariatur nulla quis fugiat dolore excepteur. Aliquip ad quis aliqua enim do consequat.
-Hard Problem? Invalidating the browser cache
+Invalidating the browser cache
I had a bit of an issue with my website recently.
-I pushed some changes incorporating images for the first time (I know – very swish, very modern), and everything seemed to be working just fine, but when I loaded the production site… in Firefox, the images were not styled. Stranger still, they were styled when I loaded the same page in Chrome.
+I pushed some changes incorporating images for the first time (I know – very swish, very modern), and everything seemed to be working just fine, but when I loaded the production site in Firefox… the images were not styled. Stranger still, they were styled when I loaded the same page in Chrome.
The experienced computer touchers amongst you will be saying “this is obviously a cache problem”, and you’re right, it is obviously a cache problem. Pressing CTR + SHIFT + R (which forces Firefox to clear the cache and do a full reload) proved this thesis, and solved the immediate problem for me, on my machine. But what about other people’s machines? I needed to cache-bust.