fasthttp

Fast HTTP implementation for Go.

Currently fasthttp is successfully used in a production serving 100K rps from 1M concurrent keep-alive connections on a single server.

Documentation

Examples from docs

Code examples

Switching from net/http to fasthttp

Fasthttp best practices

Tricks with byte buffers

FAQ

HTTP server performance comparison with net/http

In short, fasthttp server is up to 10 times faster than net/http. Below are benchmark results.

GOMAXPROCS=1

net/http:

$ GOMAXPROCS=1 go test -bench=NetHTTPServerGet -benchmem -benchtime=5s
PASS
BenchmarkNetHTTPServerGet1ReqPerConn            	  300000	     21236 ns/op	    2404 B/op	      30 allocs/op
BenchmarkNetHTTPServerGet2ReqPerConn            	  500000	     14634 ns/op	    2371 B/op	      24 allocs/op
BenchmarkNetHTTPServerGet10ReqPerConn           	 1000000	      9447 ns/op	    2101 B/op	      19 allocs/op
BenchmarkNetHTTPServerGet10KReqPerConn          	 1000000	      7939 ns/op	    2033 B/op	      18 allocs/op
BenchmarkNetHTTPServerGet1ReqPerConn10KClients  	  300000	     30291 ns/op	    4589 B/op	      31 allocs/op
BenchmarkNetHTTPServerGet2ReqPerConn10KClients  	  500000	     23199 ns/op	    3581 B/op	      25 allocs/op
BenchmarkNetHTTPServerGet10ReqPerConn10KClients 	  500000	     13270 ns/op	    2621 B/op	      19 allocs/op
BenchmarkNetHTTPServerGet100ReqPerConn10KClients	  500000	     11412 ns/op	    2119 B/op	      18 allocs/op

fasthttp:

$ GOMAXPROCS=1 go test -bench=kServerGet -benchmem -benchtime=5s
PASS
BenchmarkServerGet1ReqPerConn            	 3000000	      2341 ns/op	       0 B/op	       0 allocs/op
BenchmarkServerGet2ReqPerConn            	 5000000	      1799 ns/op	       0 B/op	       0 allocs/op
BenchmarkServerGet10ReqPerConn           	 5000000	      1239 ns/op	       0 B/op	       0 allocs/op
BenchmarkServerGet10KReqPerConn          	10000000	      1090 ns/op	       0 B/op	       0 allocs/op
BenchmarkServerGet1ReqPerConn10KClients  	 3000000	      2860 ns/op	       4 B/op	       0 allocs/op
BenchmarkServerGet2ReqPerConn10KClients  	 3000000	      1992 ns/op	       1 B/op	       0 allocs/op
BenchmarkServerGet10ReqPerConn10KClients 	 5000000	      1297 ns/op	       1 B/op	       0 allocs/op
BenchmarkServerGet100ReqPerConn10KClients	10000000	      1264 ns/op	       9 B/op	       0 allocs/op

GOMAXPROCS=4

net/http:

$ GOMAXPROCS=4 go test -bench=NetHTTPServerGet -benchmem -benchtime=5s
PASS
BenchmarkNetHTTPServerGet1ReqPerConn-4            	 1000000	      5545 ns/op	    2433 B/op	      30 allocs/op
BenchmarkNetHTTPServerGet2ReqPerConn-4            	 2000000	      4147 ns/op	    2398 B/op	      24 allocs/op
BenchmarkNetHTTPServerGet10ReqPerConn-4           	 3000000	      2628 ns/op	    2118 B/op	      19 allocs/op
BenchmarkNetHTTPServerGet10KReqPerConn-4          	 3000000	      2304 ns/op	    2037 B/op	      18 allocs/op
BenchmarkNetHTTPServerGet1ReqPerConn10KClients-4  	 1000000	      7327 ns/op	    3561 B/op	      30 allocs/op
BenchmarkNetHTTPServerGet2ReqPerConn10KClients-4  	 1000000	      5952 ns/op	    3073 B/op	      24 allocs/op
BenchmarkNetHTTPServerGet10ReqPerConn10KClients-4 	 2000000	      4345 ns/op	    2530 B/op	      19 allocs/op
BenchmarkNetHTTPServerGet100ReqPerConn10KClients-4	 2000000	      3866 ns/op	    2132 B/op	      18 allocs/op

fasthttp:

$ GOMAXPROCS=4 go test -bench=kServerGet -benchmem -benchtime=5s
PASS
BenchmarkServerGet1ReqPerConn-4            	10000000	      1053 ns/op	       0 B/op	       0 allocs/op
BenchmarkServerGet2ReqPerConn-4            	10000000	       685 ns/op	       0 B/op	       0 allocs/op
BenchmarkServerGet10ReqPerConn-4           	20000000	       393 ns/op	       0 B/op	       0 allocs/op
BenchmarkServerGet10KReqPerConn-4          	20000000	       338 ns/op	       0 B/op	       0 allocs/op
BenchmarkServerGet1ReqPerConn10KClients-4  	10000000	      1033 ns/op	       0 B/op	       0 allocs/op
BenchmarkServerGet2ReqPerConn10KClients-4  	10000000	       668 ns/op	       0 B/op	       0 allocs/op
BenchmarkServerGet10ReqPerConn10KClients-4 	20000000	       393 ns/op	       0 B/op	       0 allocs/op
BenchmarkServerGet100ReqPerConn10KClients-4	20000000	       384 ns/op	       4 B/op	       0 allocs/op

HTTP client comparison with net/http

In short, fasthttp client is up to 10 times faster than net/http. Below are benchmark results.

GOMAXPROCS=1

net/http:

$ GOMAXPROCS=1 go test -bench='HTTPClient(Do|GetEndToEnd)' -benchmem -benchtime=5s
PASS
BenchmarkNetHTTPClientDoFastServer	  500000	     17535 ns/op	    2624 B/op	      38 allocs/op
BenchmarkNetHTTPClientGetEndToEnd 	  200000	     56593 ns/op	    5012 B/op	      59 allocs/op

fasthttp:

$ GOMAXPROCS=1 go test -bench='kClient(Do|GetEndToEnd)' -benchmem -benchtime=5s
PASS
BenchmarkClientDoFastServer	 5000000	      1420 ns/op	       0 B/op	       0 allocs/op
BenchmarkClientGetEndToEnd 	  500000	     17912 ns/op	       0 B/op	       0 allocs/op

GOMAXPROCS=4

net/http:

$ GOMAXPROCS=4 go test -bench='HTTPClient(Do|GetEndToEnd)' -benchmem -benchtime=5s
PASS
BenchmarkNetHTTPClientDoFastServer-4	 1000000	      5795 ns/op	    2626 B/op	      38 allocs/op
BenchmarkNetHTTPClientGetEndToEnd-4 	  500000	     19304 ns/op	    5953 B/op	      62 allocs/op

fasthttp:

$ GOMAXPROCS=4 go test -bench='kClient(Do|GetEndToEnd)' -benchmem -benchtime=5s
PASS
BenchmarkClientDoFastServer-4	20000000	       443 ns/op	       0 B/op	       0 allocs/op
BenchmarkClientGetEndToEnd-4 	 1000000	      5954 ns/op	       0 B/op	       0 allocs/op

Switching from net/http to fasthttp

Unfortunately, fasthttp doesn't provide API identical to net/http. See the FAQ for details. There is net/http -> fasthttp handler converter, but it is advisable writing fasthttp request handlers by hands for gaining all the fasthttp advantages (especially high performance :) ).

Important points:

• Fasthttp works with RequestHandler functions instead of objects implementing Handler interface. Fortunately, it is easy to pass bound struct methods to fasthttp:

type MyHandler struct {
	foobar string
}

// request handler in net/http style, i.e. method bound to MyHandler struct.
func (h *MyHandler) HandleFastHTTP(ctx *fasthttp.RequestCtx) {
	// notice that we may access MyHandler properties here - see h.foobar.
	fmt.Fprintf(ctx, "Hello, world! Requested path is %q. Foobar is %q",
		ctx.Path(), h.foobar)
}

// request handler in fasthttp style, i.e. just plain function.
func fastHTTPHandler(ctx *fasthttp.RequestCtx) {
	fmt.Fprintf(ctx, "Hi there! RequestURI is %q", ctx.RequestURI())
}

// pass bound struct method to fasthttp
myHandler := &MyHandler{
	foobar: "foobar",
}
fasthttp.ListenAndServe(":8080", myHandler.HandleFastHTTP)

// pass plain function to fasthttp
fasthttp.ListenAndServe(":8081", fastHTTPHandler)

• The RequestHandler accepts only one argument - RequestCtx. It contains all the functionality required for http request processing and response writing. Below is an example of a simple request handler conversion from net/http to fasthttp.

// net/http request handler
requestHandler := func(w http.ResponseWriter, r *http.Request) {
	switch r.URL.Path {
	case "/foo":
		fooHandler(w, r)
	case "/bar":
		barHandler(w, r)
	default:
		http.Error(w, "Unsupported path", http.StatusNotFound)
	}
}

// the corresponding fasthttp request handler
requestHandler := func(ctx *fasthttp.RequestCtx) {
	switch string(ctx.Path()) {
	case "/foo":
		fooHandler(ctx)
	case "/bar":
		barHandler(ctx)
	default:
		ctx.Error("Unsupported path", fasthttp.StatusNotFound)
	}
}

• Fasthttp allows setting response headers and writing response body in arbitrary order. There is no 'headers first, then body' restriction like in net/http. The following code is valid for fasthttp:

requestHandler := func(ctx *fasthttp.RequestCtx) {
	// set some headers and status code first
	ctx.SetContentType("foo/bar")
	ctx.SetStatusCode(fasthttp.StatusOK)

	// then write the first part of body
	fmt.Fprintf(ctx, "this is the first part of body\n")

	// then set more headers
	ctx.Response.Header.Set("Foo-Bar", "baz")

	// then write more body
	fmt.Fprintf(ctx, "this is the second part of body\n")

	// then override already written body
	ctx.SetBody([]byte("this is completely new body contents"))

	// then update status code
	ctx.SetStatusCode(fasthttp.StatusNotFound)

	// basically, anything may be updated many times before
	// returning from RequestHandler.
	//
	// Unlike net/http fasthttp doesn't put response to the wire until
	// returning from RequestHandler.
}

• Fasthttp doesn't provide ServeMux, since I believe third-party request routers like fasthttprouter must be used instead, Net/http code with simple ServeMux is trivially converted to fasthttp code:

// net/http code

m := &http.ServeMux{}
m.HandleFunc("/foo", fooHandlerFunc)
m.HandleFunc("/bar", barHandlerFunc)
m.Handle("/baz", bazHandler)

http.ListenAndServe(":80", m)

// the corresponding fasthttp code
m := func(ctx *fasthttp.RequestCtx) {
	switch string(ctx.Path()) {
	case "/foo":
		fooHandlerFunc(ctx)
	case "/bar":
		barHandlerFunc(ctx)
	case "/baz":
		bazHandler.HandlerFunc(ctx)
	default:
		ctx.Error("not found", fasthttp.StatusNotFound)
	}
}

fastttp.ListenAndServe(":80", m)

• net/http -> fasthttp conversion table:

  • All the pseudocode below assumes w, r and ctx have these types:

    var (
    	w http.ResponseWriter
    	r *http.Request
    	ctx *fasthttp.RequestCtx
    )

  • r.Body -> ctx.PostBody()
  • r.URL.Path -> ctx.Path()
  • r.URL -> ctx.URI()
  • r.Method -> ctx.Method()
  • r.Header -> ctx.Request.Header
  • r.Header.Get() -> ctx.Request.Header.Peek()
  • r.Host -> ctx.Host()
  • r.Form -> ctx.QueryArgs() + ctx.PostArgs()
  • r.PostForm -> ctx.PostArgs()
  • r.FormValue() -> ctx.FormValue()
  • r.FormFile() -> ctx.FormFile()
  • r.MultipartForm -> ctx.MultipartForm()
  • r.RemoteAddr -> ctx.RemoteAddr()
  • r.RequestURI -> ctx.RequestURI()
  • r.TLS -> ctx.IsTLS()
  • r.Cookie() -> ctx.Request.Header.Cookie()
  • r.Referer() -> ctx.Referer()
  • r.UserAgent() -> ctx.UserAgent()
  • w.Header() -> ctx.Response.Header
  • w.Header().Set() -> ctx.Response.Header.Set()
  • w.Header().Set("Content-Type") -> ctx.SetContentType()
  • w.Header().Set("Set-Cookie") -> ctx.Response.Header.SetCookie()
  • w.Write() -> ctx.Write(), ctx.SetBody(), ctx.SetBodyStream(), ctx.SetBodyStreamWriter()
  • w.WriteHeader() -> ctx.SetStatusCode()
  • w.(http.Hijacker).Hijack() -> ctx.Hijack()
  • http.Error() -> ctx.Error()
  • http.FileServer() -> fasthttp.FSHandler(), fasthttp.FS
  • http.ServeFile() -> ctx.ServeFile()
  • http.Redirect() -> ctx.Redirect()
  • http.NotFound() -> ctx.NotFound()
  • http.StripPrefix() -> fasthttp.PathRewriteFunc

• VERY IMPORTANT! Fasthttp disallows holding references to RequestCtx or to its' members after returning from RequestHandler. Otherwise data races are inevitable. Carefully inspect all the net/http request handlers converted to fasthttp whether they retain references to RequestCtx or to its' members after returning. RequestCtx provides the following band aids for this case:

  • Wrap RequestHandler into TimeoutHandler.
  • Call TimeoutError before returning from RequestHandler if there are references to RequestCtx or to its' members. See the example for more details.

Use brilliant tool - race detector - for detecting and eliminating data races in your program. If you detected data race related to fasthttp in your program, then there is high probability you forgot calling TimeoutError before returning from RequestHandler.

• Blind switching from net/http to fasthttp won't give you performance boost. While fasthttp is optimized for speed, its' performance may be easily saturated by slow RequestHandler. So profile and optimize your code after switching to fasthttp.

Performance optimization tips for multi-core systems

• Use reuseport listener.
• Run a separate server instance per CPU core with GOMAXPROCS=1.
• Pin each server instance to a separate CPU core using taskset.
• Ensure the interrupts of multiqueue network card are evenly distributed between CPU cores. See this article for details.

Fasthttp best practices

• Do not allocate objects and []byte buffers - just reuse them as much as possible. Fasthttp API design encourages this.
• sync.Pool is your best friend.
• Profile your program in production. go tool pprof --alloc_objects your-program mem.pprof usually gives better insights for optimization opportunities than go tool pprof your-program cpu.pprof.
• Write tests and benchmarks for hot paths.
• Avoid conversion between []byte and string, since this may result in memory allocation+copy. Fasthttp API provides functions for both []byte and string - use these functions instead of converting manually between []byte and string.
• Verify your tests and production code under race detector on a regular basis.

Tricks with []byte buffers

The following tricks are used by fasthttp. Use them in your code too.

• Standard Go functions accept nil buffers

var (
	// both buffers are uninitialized
	dst []byte
	src []byte
)
dst = append(dst, src...)  // is legal if dst is nil and/or src is nil
copy(dst, src)  // is legal if dst is nil and/or src is nil
(string(src) == "")  // is true if src is nil
(len(src) == 0)  // is true if src is nil
src = src[:0]  // works like a charm with nil src

// this for loop doesn't panic if src is nil
for i, ch := range src {
	doSomething(i, ch)
}

So throw away nil checks for []byte buffers from you code. For example,

srcLen := 0
if src != nil {
	srcLen = len(src)
}

becomes

srcLen := len(src)

• String may be appended to []byte buffer with append

dst = append(dst, "foobar"...)

• []byte buffer may be extended to its' capacity.

buf := make([]byte, 100)
a := buf[:10]  // len(a) == 10, cap(a) == 100.
b := a[:100]  // is valid, since cap(a) == 100.

• All fasthttp functions accept nil []byte buffer

statusCode, body, err := fasthttp.Get(nil, "http://google.com/")
uintBuf := fasthttp.AppendUint(nil, 1234)

FAQ

• Why creating yet another http package instead of optimizing net/http?

  Because net/http API limits many optimization opportunities. For example:

  • net/http Request object lifetime isn't limited by request handler execution time. So the server must create new request object per each request instead of reusing existing objects like fasthttp do.
  • net/http headers are stored in a map[string][]string. So the server must parse all the headers, convert them from []byte to string and put them into the map before calling user-provided request handler. This all requires unnesessary memory allocations avoided by fasthttp.
  • net/http client API requires creating new response object per each request.

• Why fasthttp API is incompatible with net/http?

  Because net/http API limits many optimization opportunities. See the answer above for more details. Also certain net/http API parts are suboptimal for use:

  • Compare net/http connection hijacking to fasthttp connection hijacking.
  • Compare net/http Request.Body reading to fasthttp request body reading.

• Why fasthttp doesn't support HTTP/2.0 and WebSockets?

  There are plans for adding HTTP/2.0 and WebSockets support in the future. In the mean time, third parties may use RequestCtx.Hijack for implementing these goodies. See the first third-party websocket implementation on the top of fasthttp.

• Are there known net/http advantages comparing to fasthttp?

  Yes:

  • net/http supports HTTP/2.0 starting from go1.6.
  • net/http API is stable, while fasthttp API constantly evolves.
  • net/http handles more HTTP corner cases.
  • net/http should contain less bugs, since it is used and tested by much wider audience.
  • Many existing web frameworks and request routers are built on top of net/http.
  • net/http works on Go older than 1.5.

• Which GO versions are supported by fasthttp?

  Go1.5+. Older versions won't be supported, since their standard package miss useful functions.

• Please provide real benchmark data and sever information

  See this issue.

• Are there plans to add request routing to fasthttp?

  There are no plans to add request routing into fasthttp. I believe request routing must be implemented in a separate package(s) like httprouter. Try fasthttprouter, httprouter fork for fasthttp. See also this issue for more info.

• I detected data race in fasthttp!

  Cool! File a bug. But before doing this check the following in your code:

  • Make sure there are no references to RequestCtx or to its' members after returning from RequestHandler.
  • Make sure you call TimeoutError before returning from RequestHandler if there are references to RequestCtx or to its' members, which may be accessed by other goroutines.