httptreemux

httptreemux

High-speed, flexible, tree-based HTTP router for Go.

This is inspired by Julien Schmidt's httprouter, in that it uses a patricia tree, but the implementation is rather different. Specifically, the routing rules are relaxed so that a single path segment may be a wildcard in one route and a static token in another. This gives a nice combination of high performance with a lot of convenience in designing the routing patterns. In benchmarks, httptreemux is close to, but slightly slower than, httprouter.

Release notes may be found using the Github releases tab. Version numbers are compatible with the Semantic Versioning 2.0.0 convention, and a new release is made after every change to the code.

Why?

There are a lot of good routers out there. But looking at the ones that were really lightweight, I couldn't quite get something that fit with the route patterns I wanted. The code itself is simple enough, so I spent an evening writing this.

Handler

The handler is a simple function with the prototype func(w http.ResponseWriter, r *http.Request, params map[string]string). The params argument contains the parameters parsed from wildcards and catch-alls in the URL, as described below. This type is aliased as httptreemux.HandlerFunc.

Using http.HandlerFunc

Due to the inclusion of the context package as of Go 1.7, httptreemux now supports handlers of type http.HandlerFunc. There are two ways to enable this support.

Adapting an Existing Router

The UsingContext method will wrap the router or group in a new group at the same path, but adapted for use with context and http.HandlerFunc.

router := httptreemux.New()

group := router.NewGroup("/api")
group.GET("/v1/:id", func(w http.ResponseWriter, r *http.Request, params map[string]string) {
    id := params["id"]
    fmt.Fprintf(w, "GET /api/v1/%s", id)
})

// UsingContext returns a version of the router or group with context support.
ctxGroup := group.UsingContext() // sibling to 'group' node in tree
ctxGroup.GET("/v2/:id", func(w http.ResponseWriter, r *http.Request) {
    params := httptreemux.ContextParams(r.Context())
    id := params["id"]
    fmt.Fprintf(w, "GET /api/v2/%s", id)
})

http.ListenAndServe(":8080", router)

New Router with Context Support

The NewContextMux function returns a router preconfigured for use with context and http.HandlerFunc.

router := httptreemux.NewContextMux()

router.GET("/:page", func(w http.ResponseWriter, r *http.Request) {
    params := httptreemux.ContextParams(r.Context())
    fmt.Fprintf(w, "GET /%s", params["page"])
})

group := tree.NewGroup("/api")
group.GET("/v1/:id", func(w http.ResponseWriter, r *http.Request) {
    params := httptreemux.ContextParams(r.Context())
    id := params["id"]
    fmt.Fprintf(w, "GET /api/v1/%s", id)
})

http.ListenAndServe(":8080", router)

Routing Rules

The syntax here is also modeled after httprouter. Each variable in a path may match on one segment only, except for an optional catch-all variable at the end of the URL.

Some examples of valid URL patterns are:

• /post/all
• /post/:postid
• /post/:postid/page/:page
• /post/:postid/:page
• /images/*path
• /favicon.ico
• /:year/:month/
• /:year/:month/:post
• /:page

Note that all of the above URL patterns may exist concurrently in the router.

Path elements starting with : indicate a wildcard in the path. A wildcard will only match on a single path segment. That is, the pattern /post/:postid will match on /post/1 or /post/1/, but not /post/1/2.

A path element starting with * is a catch-all, whose value will be a string containing all text in the URL matched by the wildcards. For example, with a pattern of /images/*path and a requested URL images/abc/def, path would contain abc/def.

Using : and * in routing patterns

The characters : and * can be used at the beginning of a path segment by escaping them with a backslash. A double backslash at the beginning of a segment is interpreted as a single backslash. These escapes are only checked at the very beginning of a path segment; they are not necessary or processed elsewhere in a token.

router.GET("/foo/\\*starToken", handler) // matches /foo/*starToken
router.GET("/foo/star*inTheMiddle", handler) // matches /foo/star*inTheMiddle
router.GET("/foo/starBackslash\\*", handler) // matches /foo/starBackslash\*
router.GET("/foo/\\\\*backslashWithStar") // matches /foo/\*backslashWithStar

Routing Groups

Lets you create a new group of routes with a given path prefix. Makes it easier to create clusters of paths like:

• /api/v1/foo
• /api/v1/bar

To use this you do:

router = httptreemux.New()
api := router.NewGroup("/api/v1")
api.GET("/foo", fooHandler) // becomes /api/v1/foo
api.GET("/bar", barHandler) // becomes /api/v1/bar

Routing Priority

The priority rules in the router are simple.

1. Static path segments take the highest priority. If a segment and its subtree are able to match the URL, that match is returned.
2. Wildcards take second priority. For a particular wildcard to match, that wildcard and its subtree must match the URL.
3. Finally, a catch-all rule will match when the earlier path segments have matched, and none of the static or wildcard conditions have matched. Catch-all rules must be at the end of a pattern.

So with the following patterns adapted from simpleblog, we'll see certain matches:

router = httptreemux.New()
router.GET("/:page", pageHandler)
router.GET("/:year/:month/:post", postHandler)
router.GET("/:year/:month", archiveHandler)
router.GET("/images/*path", staticHandler)
router.GET("/favicon.ico", staticHandler)

Example scenarios

• /abc will match /:page
• /2014/05 will match /:year/:month
• /2014/05/really-great-blog-post will match /:year/:month/:post
• /images/CoolImage.gif will match /images/*path
• /images/2014/05/MayImage.jpg will also match /images/*path, with all the text after /images stored in the variable path.
• /favicon.ico will match /favicon.ico

Special Method Behavior

If TreeMux.HeadCanUseGet is set to true, the router will call the GET handler for a pattern when a HEAD request is processed, if no HEAD handler has been added for that pattern. This behavior is enabled by default.

Go's http.ServeContent and related functions already handle the HEAD method correctly by sending only the header, so in most cases your handlers will not need any special cases for it.

By default TreeMux.OptionsHandler is a null handler that doesn't affect your routing. If you set the handler, it will be called on OPTIONS requests to a path already registered by another method. If you set a path specific handler by using router.OPTIONS, it will override the global Options Handler for that path.

Trailing Slashes

The router has special handling for paths with trailing slashes. If a pattern is added to the router with a trailing slash, any matches on that pattern without a trailing slash will be redirected to the version with the slash. If a pattern does not have a trailing slash, matches on that pattern with a trailing slash will be redirected to the version without.

The trailing slash flag is only stored once for a pattern. That is, if a pattern is added for a method with a trailing slash, all other methods for that pattern will also be considered to have a trailing slash, regardless of whether or not it is specified for those methods too. However this behavior can be turned off by setting TreeMux.RedirectTrailingSlash to false. By default it is set to true.

One exception to this rule is catch-all patterns. By default, trailing slash redirection is disabled on catch-all patterns, since the structure of the entire URL and the desired patterns can not be predicted. If trailing slash removal is desired on catch-all patterns, set TreeMux.RemoveCatchAllTrailingSlash to true.

router = httptreemux.New()
router.GET("/about", pageHandler)
router.GET("/posts/", postIndexHandler)
router.POST("/posts", postFormHandler)

GET /about will match normally.
GET /about/ will redirect to /about.
GET /posts will redirect to /posts/.
GET /posts/ will match normally.
POST /posts will redirect to /posts/, because the GET method used a trailing slash.

Custom Redirects

RedirectBehavior sets the behavior when the router redirects the request to the canonical version of the requested URL using RedirectTrailingSlash or RedirectClean. The default behavior is to return a 301 status, redirecting the browser to the version of the URL that matches the given pattern.

These are the values accepted for RedirectBehavior. You may also add these values to the RedirectMethodBehavior map to define custom per-method redirect behavior.

• Redirect301 - HTTP 301 Moved Permanently; this is the default.
• Redirect307 - HTTP/1.1 Temporary Redirect
• Redirect308 - RFC7538 Permanent Redirect
• UseHandler - Don't redirect to the canonical path. Just call the handler instead.

Rationale/Usage

On a POST request, most browsers that receive a 301 will submit a GET request to the redirected URL, meaning that any data will likely be lost. If you want to handle and avoid this behavior, you may use Redirect307, which causes most browsers to resubmit the request using the original method and request body.

Since 307 is supposed to be a temporary redirect, the new 308 status code has been proposed, which is treated the same, except it indicates correctly that the redirection is permanent. The big caveat here is that the RFC is relatively recent, and older or non-compliant browsers will not handle it. Therefore its use is not recommended unless you really know what you're doing.

Finally, the UseHandler value will simply call the handler function for the pattern, without redirecting to the canonical version of the URL.

RequestURI vs. URL.Path

Escaped Slashes

Go automatically processes escaped characters in a URL, converting + to a space and %XX to the corresponding character. This can present issues when the URL contains a %2f, which is unescaped to '/'. This isn't an issue for most applications, but it will prevent the router from correctly matching paths and wildcards.

For example, the pattern /post/:post would not match on /post/abc%2fdef, which is unescaped to /post/abc/def. The desired behavior is that it matches, and the post wildcard is set to abc/def.

Therefore, this router defaults to using the raw URL, stored in the Request.RequestURI variable. Matching wildcards and catch-alls are then unescaped, to give the desired behavior.

TL;DR: If a requested URL contains a %2f, this router will still do the right thing. Some Go HTTP routers may not due to Go issue 3659.

Escaped Characters

As mentioned above, characters in the URL are not unescaped when using RequestURI to determine the matched route. If this is a problem for you and you are unable to switch to URL.Path for the above reasons, you may set router.EscapeAddedRoutes to true. This option will run each added route through the URL.EscapedPath function, and add an additional route if the escaped version differs.

http Package Utility Functions

Although using RequestURI avoids the issue described above, certain utility functions such as http.StripPrefix modify URL.Path, and expect that the underlying router is using that field to make its decision. If you are using some of these functions, set the router's PathSource member to URLPath. This will give up the proper handling of escaped slashes described above, while allowing the router to work properly with these utility functions.

Concurrency

The router contains an RWMutex that arbitrates access to the tree. This allows routes to be safely added from multiple goroutines at once.

No concurrency controls are needed when only reading from the tree, so the default behavior is to not use the RWMutex when serving a request. This avoids a theoretical slowdown under high-usage scenarios from competing atomic integer operations inside the RWMutex. If your application adds routes to the router after it has begun serving requests, you should avoid potential race conditions by setting router.SafeAddRoutesWhileRunning to true to use the RWMutex when serving requests.

Error Handlers

NotFoundHandler

TreeMux.NotFoundHandler can be set to provide custom 404-error handling. The default implementation is Go's http.NotFound function.

MethodNotAllowedHandler

If a pattern matches, but the pattern does not have an associated handler for the requested method, the router calls the MethodNotAllowedHandler. The default version of this handler just writes the status code http.StatusMethodNotAllowed and sets the response header's Allowed field appropriately.

Panic Handling

TreeMux.PanicHandler can be set to provide custom panic handling. The SimplePanicHandler just writes the status code http.StatusInternalServerError. The function ShowErrorsPanicHandler, adapted from gocraft/web, will print panic errors to the browser in an easily-readable format.

Unexpected Differences from Other Routers

This router is intentionally light on features in the name of simplicity and performance. When coming from another router that does heavier processing behind the scenes, you may encounter some unexpected behavior. This list is by no means exhaustive, but covers some nonobvious cases that users have encountered.

gorilla/pat query string modifications

When matching on parameters in a route, the gorilla/pat router will modify Request.URL.RawQuery to make it appear like the parameters were in the query string. httptreemux does not do this. See Issue #26 for more details and a code snippet that can perform this transformation for you, should you want it.

Middleware

This package provides no middleware. But there are a lot of great options out there and it's pretty easy to write your own.

Acknowledgements

• Inspiration from Julien Schmidt's httprouter
• Show Errors panic handler from gocraft/web