How to add regex constraints to Gin framework's router? - regex

Question

Use Rails' routing, for a URL like https://www.amazon.com/posts/1, can use this way to do
get 'posts/:url', to: 'posts#search', constraints: { url: /.*/ }
Use go's gin framework, didn't find a regex constraints method for such a routing
r.GET("posts/search/:url", post.Search)
In the post controller
func Search(c *gin.Context) {
fmt.Println(c.Param("url"))
}
When call http://localhost:8080/posts/search/https://www.amazon.com/posts/1, it returned 404 code.
Like https://play.golang.org/p/dsB-hv8Ugtn
➜ ~ curl http://localhost:8080/site/www.google.com
Hello www.google.com%
➜ ~ curl http://localhost:8080/site/http://www.google.com/post/1
404 page not found%
➜ ~ curl http://localhost:8080/site/https%3A%2F%2Fwww.google.com%2Fpost%2F1
404 page not found%
➜ ~ curl http://localhost:8080/site/http:\/\/www.google.com\/post\/1
404 page not found%

Answer 1

Gin does not support regular expressions in the router. This is probably because it builds a tree of paths in order to not have to allocate memory while traversing and results in excellent performance.
The parameter support for paths is also not very powerful but you can work around the issue by using an optional parameter like
c.GET("/posts/search/*url", ...)
Now c.Param("url") could contain slashes. There are two unsolved problems though:
Gin's router decodes percent encoded characters (%2F) so if the original URL had such encoded parts, it would wrongly end up decoded and not match the original url that you wanted to extract. See the corresponding Github issue: https://github.com/gin-gonic/gin/issues/2047
You would only get the scheme+host+path part of URLs in your parameter, the querystring would still be separate unless you also encode that. E.g. /posts/search/http://google.com/post/1?foo=bar would give you a "url" param of "/http://google.com/posts/1"
As seen in the example above, optional parameters in Gin also (wrongly) always contain a slash at the beginning of the string.
I would recommend you pass the URL as an encoded querystring instead. This will result in a lot less headache. Otherwise I'd recommend looking for a different router or framework that is less restrictive because I don't think Gin will resolve these issues anytime soon - they have been open for years.