base on Fast HTTP package for Go. Tuned for high performance. Zero memory allocations in hot paths. Up to 10x faster than net/http # fasthttp
[](https://pkg.go.dev/github.com/valyala/fasthttp) [](https://goreportcard.com/report/github.com/valyala/fasthttp)
Fast HTTP implementation for Go.
## fasthttp might not be for you!
fasthttp was designed for some high performance edge cases. **Unless** your server/client needs to handle **thousands of small to medium requests per second** and needs a consistent low millisecond response time fasthttp might not be for you. **For most cases `net/http` is much better** as it's easier to use and can handle more cases. For most cases you won't even notice the performance difference.
## General info and links
Currently fasthttp is successfully used by [VertaMedia](https://vertamedia.com/)
in a production serving up to 200K rps from more than 1.5M concurrent keep-alive
connections per physical server.
[TechEmpower Benchmark round 19 results](https://www.techempower.com/benchmarks/#section=data-r19&hw=ph&test=plaintext)
[Server Benchmarks](#http-server-performance-comparison-with-nethttp)
[Client Benchmarks](#http-client-comparison-with-nethttp)
[Install](#install)
[Documentation](https://pkg.go.dev/github.com/valyala/fasthttp)
[Examples from docs](https://pkg.go.dev/github.com/valyala/fasthttp#pkg-examples)
[Code examples](examples)
[Awesome fasthttp tools](https://github.com/fasthttp)
[Switching from net/http to fasthttp](#switching-from-nethttp-to-fasthttp)
[Fasthttp best practices](#fasthttp-best-practices)
[Tricks with byte buffers](#tricks-with-byte-buffers)
[Related projects](#related-projects)
[FAQ](#faq)
## HTTP server performance comparison with [net/http](https://pkg.go.dev/net/http)
In short, fasthttp server is up to 10 times faster than net/http.
Below are benchmark results.
*GOMAXPROCS=1*
net/http server:
```
$ GOMAXPROCS=1 go test -bench=NetHTTPServerGet -benchmem -benchtime=10s
BenchmarkNetHTTPServerGet1ReqPerConn 1000000 12052 ns/op 2297 B/op 29 allocs/op
BenchmarkNetHTTPServerGet2ReqPerConn 1000000 12278 ns/op 2327 B/op 24 allocs/op
BenchmarkNetHTTPServerGet10ReqPerConn 2000000 8903 ns/op 2112 B/op 19 allocs/op
BenchmarkNetHTTPServerGet10KReqPerConn 2000000 8451 ns/op 2058 B/op 18 allocs/op
BenchmarkNetHTTPServerGet1ReqPerConn10KClients 500000 26733 ns/op 3229 B/op 29 allocs/op
BenchmarkNetHTTPServerGet2ReqPerConn10KClients 1000000 23351 ns/op 3211 B/op 24 allocs/op
BenchmarkNetHTTPServerGet10ReqPerConn10KClients 1000000 13390 ns/op 2483 B/op 19 allocs/op
BenchmarkNetHTTPServerGet100ReqPerConn10KClients 1000000 13484 ns/op 2171 B/op 18 allocs/op
```
fasthttp server:
```
$ GOMAXPROCS=1 go test -bench=kServerGet -benchmem -benchtime=10s
BenchmarkServerGet1ReqPerConn 10000000 1559 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet2ReqPerConn 10000000 1248 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet10ReqPerConn 20000000 797 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet10KReqPerConn 20000000 716 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet1ReqPerConn10KClients 10000000 1974 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet2ReqPerConn10KClients 10000000 1352 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet10ReqPerConn10KClients 20000000 789 ns/op 2 B/op 0 allocs/op
BenchmarkServerGet100ReqPerConn10KClients 20000000 604 ns/op 0 B/op 0 allocs/op
```
*GOMAXPROCS=4*
net/http server:
```
$ GOMAXPROCS=4 go test -bench=NetHTTPServerGet -benchmem -benchtime=10s
BenchmarkNetHTTPServerGet1ReqPerConn-4 3000000 4529 ns/op 2389 B/op 29 allocs/op
BenchmarkNetHTTPServerGet2ReqPerConn-4 5000000 3896 ns/op 2418 B/op 24 allocs/op
BenchmarkNetHTTPServerGet10ReqPerConn-4 5000000 3145 ns/op 2160 B/op 19 allocs/op
BenchmarkNetHTTPServerGet10KReqPerConn-4 5000000 3054 ns/op 2065 B/op 18 allocs/op
BenchmarkNetHTTPServerGet1ReqPerConn10KClients-4 1000000 10321 ns/op 3710 B/op 30 allocs/op
BenchmarkNetHTTPServerGet2ReqPerConn10KClients-4 2000000 7556 ns/op 3296 B/op 24 allocs/op
BenchmarkNetHTTPServerGet10ReqPerConn10KClients-4 5000000 3905 ns/op 2349 B/op 19 allocs/op
BenchmarkNetHTTPServerGet100ReqPerConn10KClients-4 5000000 3435 ns/op 2130 B/op 18 allocs/op
```
fasthttp server:
```
$ GOMAXPROCS=4 go test -bench=kServerGet -benchmem -benchtime=10s
BenchmarkServerGet1ReqPerConn-4 10000000 1141 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet2ReqPerConn-4 20000000 707 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet10ReqPerConn-4 30000000 341 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet10KReqPerConn-4 50000000 310 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet1ReqPerConn10KClients-4 10000000 1119 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet2ReqPerConn10KClients-4 20000000 644 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet10ReqPerConn10KClients-4 30000000 346 ns/op 0 B/op 0 allocs/op
BenchmarkServerGet100ReqPerConn10KClients-4 50000000 282 ns/op 0 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 client:
```
$ GOMAXPROCS=1 go test -bench='HTTPClient(Do|GetEndToEnd)' -benchmem -benchtime=10s
BenchmarkNetHTTPClientDoFastServer 1000000 12567 ns/op 2616 B/op 35 allocs/op
BenchmarkNetHTTPClientGetEndToEnd1TCP 200000 67030 ns/op 5028 B/op 56 allocs/op
BenchmarkNetHTTPClientGetEndToEnd10TCP 300000 51098 ns/op 5031 B/op 56 allocs/op
BenchmarkNetHTTPClientGetEndToEnd100TCP 300000 45096 ns/op 5026 B/op 55 allocs/op
BenchmarkNetHTTPClientGetEndToEnd1Inmemory 500000 24779 ns/op 5035 B/op 57 allocs/op
BenchmarkNetHTTPClientGetEndToEnd10Inmemory 1000000 26425 ns/op 5035 B/op 57 allocs/op
BenchmarkNetHTTPClientGetEndToEnd100Inmemory 500000 28515 ns/op 5045 B/op 57 allocs/op
BenchmarkNetHTTPClientGetEndToEnd1000Inmemory 500000 39511 ns/op 5096 B/op 56 allocs/op
```
fasthttp client:
```
$ GOMAXPROCS=1 go test -bench='kClient(Do|GetEndToEnd)' -benchmem -benchtime=10s
BenchmarkClientDoFastServer 20000000 865 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd1TCP 1000000 18711 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd10TCP 1000000 14664 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd100TCP 1000000 14043 ns/op 1 B/op 0 allocs/op
BenchmarkClientGetEndToEnd1Inmemory 5000000 3965 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd10Inmemory 3000000 4060 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd100Inmemory 5000000 3396 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd1000Inmemory 5000000 3306 ns/op 2 B/op 0 allocs/op
```
*GOMAXPROCS=4*
net/http client:
```
$ GOMAXPROCS=4 go test -bench='HTTPClient(Do|GetEndToEnd)' -benchmem -benchtime=10s
BenchmarkNetHTTPClientDoFastServer-4 2000000 8774 ns/op 2619 B/op 35 allocs/op
BenchmarkNetHTTPClientGetEndToEnd1TCP-4 500000 22951 ns/op 5047 B/op 56 allocs/op
BenchmarkNetHTTPClientGetEndToEnd10TCP-4 1000000 19182 ns/op 5037 B/op 55 allocs/op
BenchmarkNetHTTPClientGetEndToEnd100TCP-4 1000000 16535 ns/op 5031 B/op 55 allocs/op
BenchmarkNetHTTPClientGetEndToEnd1Inmemory-4 1000000 14495 ns/op 5038 B/op 56 allocs/op
BenchmarkNetHTTPClientGetEndToEnd10Inmemory-4 1000000 10237 ns/op 5034 B/op 56 allocs/op
BenchmarkNetHTTPClientGetEndToEnd100Inmemory-4 1000000 10125 ns/op 5045 B/op 56 allocs/op
BenchmarkNetHTTPClientGetEndToEnd1000Inmemory-4 1000000 11132 ns/op 5136 B/op 56 allocs/op
```
fasthttp client:
```
$ GOMAXPROCS=4 go test -bench='kClient(Do|GetEndToEnd)' -benchmem -benchtime=10s
BenchmarkClientDoFastServer-4 50000000 397 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd1TCP-4 2000000 7388 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd10TCP-4 2000000 6689 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd100TCP-4 3000000 4927 ns/op 1 B/op 0 allocs/op
BenchmarkClientGetEndToEnd1Inmemory-4 10000000 1604 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd10Inmemory-4 10000000 1458 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd100Inmemory-4 10000000 1329 ns/op 0 B/op 0 allocs/op
BenchmarkClientGetEndToEnd1000Inmemory-4 10000000 1316 ns/op 5 B/op 0 allocs/op
```
## Install
```
go get -u github.com/valyala/fasthttp
```
## Switching from net/http to fasthttp
Unfortunately, fasthttp doesn't provide API identical to net/http.
See the [FAQ](#faq) for details.
There is [net/http -> fasthttp handler converter](https://pkg.go.dev/github.com/valyala/fasthttp/fasthttpadaptor),
but it is better to write fasthttp request handlers by hand in order to use
all of the fasthttp advantages (especially high performance :) ).
Important points:
* Fasthttp works with [RequestHandler functions](https://pkg.go.dev/github.com/valyala/fasthttp#RequestHandler)
instead of objects implementing [Handler interface](https://pkg.go.dev/net/http#Handler).
Fortunately, it is easy to pass bound struct methods to fasthttp:
```go
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](https://pkg.go.dev/github.com/valyala/fasthttp#RequestHandler)
accepts only one argument - [RequestCtx](https://pkg.go.dev/github.com/valyala/fasthttp#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.
```go
// 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)
}
}
```
```go
// 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 an arbitrary order. There is no 'headers first, then body' restriction
like in net/http. The following code is valid for fasthttp:
```go
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](https://pkg.go.dev/net/http#ServeMux),
but there are more powerful third-party routers and web frameworks
with fasthttp support:
* [fasthttp-routing](https://github.com/qiangxue/fasthttp-routing)
* [router](https://github.com/fasthttp/router)
* [lu](https://github.com/vincentLiuxiang/lu)
* [atreugo](https://github.com/savsgio/atreugo)
* [Fiber](https://github.com/gofiber/fiber)
* [Gearbox](https://github.com/gogearbox/gearbox)
Net/http code with simple ServeMux is trivially converted to fasthttp code:
```go
// net/http code
m := &http.ServeMux{}
m.HandleFunc("/foo", fooHandlerFunc)
m.HandleFunc("/bar", barHandlerFunc)
m.Handle("/baz", bazHandler)
http.ListenAndServe(":80", m)
```
```go
// 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)
}
}
fasthttp.ListenAndServe(":80", m)
```
* Because creating a new channel for every request is just too expensive, so the channel returned by RequestCtx.Done() is only closed when the server is shutting down.
```go
func main() {
fasthttp.ListenAndServe(":8080", fasthttp.TimeoutHandler(func(ctx *fasthttp.RequestCtx) {
select {
case <-ctx.Done():
// ctx.Done() is only closed when the server is shutting down.
log.Println("context cancelled")
return
case <-time.After(10 * time.Second):
log.Println("process finished ok")
}
}, time.Second*2, "timeout"))
}
```
* net/http -> fasthttp conversion table:
* All the pseudocode below assumes w, r and ctx have these types:
```go
var (
w http.ResponseWriter
r *http.Request
ctx *fasthttp.RequestCtx
)
```
* r.Body -> [ctx.PostBody()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.PostBody)
* r.URL.Path -> [ctx.Path()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.Path)
* r.URL -> [ctx.URI()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.URI)
* r.Method -> [ctx.Method()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.Method)
* r.Header -> [ctx.Request.Header](https://pkg.go.dev/github.com/valyala/fasthttp#RequestHeader)
* r.Header.Get() -> [ctx.Request.Header.Peek()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestHeader.Peek)
* r.Host -> [ctx.Host()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.Host)
* r.Form -> [ctx.QueryArgs()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.QueryArgs) +
[ctx.PostArgs()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.PostArgs)
* r.PostForm -> [ctx.PostArgs()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.PostArgs)
* r.FormValue() -> [ctx.FormValue()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.FormValue)
* r.FormFile() -> [ctx.FormFile()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.FormFile)
* r.MultipartForm -> [ctx.MultipartForm()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.MultipartForm)
* r.RemoteAddr -> [ctx.RemoteAddr()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.RemoteAddr)
* r.RequestURI -> [ctx.RequestURI()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.RequestURI)
* r.TLS -> [ctx.IsTLS()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.IsTLS)
* r.Cookie() -> [ctx.Request.Header.Cookie()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestHeader.Cookie)
* r.Referer() -> [ctx.Referer()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.Referer)
* r.UserAgent() -> [ctx.UserAgent()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.UserAgent)
* w.Header() -> [ctx.Response.Header](https://pkg.go.dev/github.com/valyala/fasthttp#ResponseHeader)
* w.Header().Set() -> [ctx.Response.Header.Set()](https://pkg.go.dev/github.com/valyala/fasthttp#ResponseHeader.Set)
* w.Header().Set("Content-Type") -> [ctx.SetContentType()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.SetContentType)
* w.Header().Set("Set-Cookie") -> [ctx.Response.Header.SetCookie()](https://pkg.go.dev/github.com/valyala/fasthttp#ResponseHeader.SetCookie)
* w.Write() -> [ctx.Write()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.Write),
[ctx.SetBody()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.SetBody),
[ctx.SetBodyStream()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.SetBodyStream),
[ctx.SetBodyStreamWriter()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.SetBodyStreamWriter)
* w.WriteHeader() -> [ctx.SetStatusCode()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.SetStatusCode)
* w.(http.Hijacker).Hijack() -> [ctx.Hijack()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.Hijack)
* http.Error() -> [ctx.Error()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.Error)
* http.FileServer() -> [fasthttp.FSHandler()](https://pkg.go.dev/github.com/valyala/fasthttp#FSHandler),
[fasthttp.FS](https://pkg.go.dev/github.com/valyala/fasthttp#FS)
* http.ServeFile() -> [fasthttp.ServeFile()](https://pkg.go.dev/github.com/valyala/fasthttp#ServeFile)
* http.Redirect() -> [ctx.Redirect()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.Redirect)
* http.NotFound() -> [ctx.NotFound()](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.NotFound)
* http.StripPrefix() -> [fasthttp.PathRewriteFunc](https://pkg.go.dev/github.com/valyala/fasthttp#PathRewriteFunc)
* *VERY IMPORTANT!* Fasthttp disallows holding references
to [RequestCtx](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx) or to its'
members after returning from [RequestHandler](https://pkg.go.dev/github.com/valyala/fasthttp#RequestHandler).
Otherwise [data races](http://go.dev/blog/race-detector) 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](https://pkg.go.dev/github.com/valyala/fasthttp#TimeoutHandler).
* Call [TimeoutError](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.TimeoutError)
before returning from RequestHandler if there are references to RequestCtx or to its' members.
See [the example](https://pkg.go.dev/github.com/valyala/fasthttp#example-RequestCtx-TimeoutError)
for more details.
Use this brilliant tool - [race detector](http://go.dev/blog/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](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.TimeoutError)
before returning from [RequestHandler](https://pkg.go.dev/github.com/valyala/fasthttp#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](https://pkg.go.dev/github.com/valyala/fasthttp#RequestHandler).
So [profile](http://go.dev/blog/pprof) and optimize your
code after switching to fasthttp. For instance, use [quicktemplate](https://github.com/valyala/quicktemplate)
instead of [html/template](https://pkg.go.dev/html/template).
* See also [fasthttputil](https://pkg.go.dev/github.com/valyala/fasthttp/fasthttputil),
[fasthttpadaptor](https://pkg.go.dev/github.com/valyala/fasthttp/fasthttpadaptor) and
[expvarhandler](https://pkg.go.dev/github.com/valyala/fasthttp/expvarhandler).
## Performance optimization tips for multi-core systems
* Use [reuseport](https://pkg.go.dev/github.com/valyala/fasthttp/reuseport) listener.
* Run a separate server instance per CPU core with GOMAXPROCS=1.
* Pin each server instance to a separate CPU core using [taskset](http://linux.die.net/man/1/taskset).
* Ensure the interrupts of multiqueue network card are evenly distributed between CPU cores.
See [this article](https://blog.cloudflare.com/how-to-achieve-low-latency/) for details.
* Use the latest version of Go as each version contains performance improvements.
## Fasthttp best practices
* Do not allocate objects and `[]byte` buffers - just reuse them as much
as possible. Fasthttp API design encourages this.
* [sync.Pool](https://pkg.go.dev/sync#Pool) is your best friend.
* [Profile your program](http://go.dev/blog/pprof)
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](https://pkg.go.dev/testing) 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`.
There are some exceptions - see [this wiki page](https://github.com/golang/go/wiki/CompilerOptimizations#string-and-byte)
for more details.
* Verify your tests and production code under
[race detector](https://go.dev/doc/articles/race_detector.html) on a regular basis.
* Prefer [quicktemplate](https://github.com/valyala/quicktemplate) instead of
[html/template](https://pkg.go.dev/html/template) in your webserver.
## Tricks with `[]byte` buffers
The following tricks are used by fasthttp. Use them in your code too.
* Standard Go functions accept nil buffers
```go
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,
```go
srcLen := 0
if src != nil {
srcLen = len(src)
}
```
becomes
```go
srcLen := len(src)
```
* String may be appended to `[]byte` buffer with `append`
```go
dst = append(dst, "foobar"...)
```
* `[]byte` buffer may be extended to its' capacity.
```go
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
```go
statusCode, body, err := fasthttp.Get(nil, "http://google.com/")
uintBuf := fasthttp.AppendUint(nil, 1234)
```
* String and `[]byte` buffers may converted without memory allocations
```go
func b2s(b []byte) string {
return *(*string)(unsafe.Pointer(&b))
}
func s2b(s string) (b []byte) {
bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
sh := (*reflect.StringHeader)(unsafe.Pointer(&s))
bh.Data = sh.Data
bh.Cap = sh.Len
bh.Len = sh.Len
return b
}
```
### Warning:
This is an **unsafe** way, the result string and `[]byte` buffer share the same bytes.
**Please make sure not to modify the bytes in the `[]byte` buffer if the string still survives!**
## Related projects
* [fasthttp](https://github.com/fasthttp) - various useful
helpers for projects based on fasthttp.
* [fasthttp-routing](https://github.com/qiangxue/fasthttp-routing) - fast and
powerful routing package for fasthttp servers.
* [http2](https://github.com/dgrr/http2) - HTTP/2 implementation for fasthttp.
* [router](https://github.com/fasthttp/router) - a high
performance fasthttp request router that scales well.
* [fastws](https://github.com/fasthttp/fastws) - Bloatless WebSocket package made for fasthttp
to handle Read/Write operations concurrently.
* [gramework](https://github.com/gramework/gramework) - a web framework made by one of fasthttp maintainers
* [lu](https://github.com/vincentLiuxiang/lu) - a high performance
go middleware web framework which is based on fasthttp.
* [websocket](https://github.com/fasthttp/websocket) - Gorilla-based
websocket implementation for fasthttp.
* [websocket](https://github.com/dgrr/websocket) - Event-based high-performance WebSocket library for zero-allocation
websocket servers and clients.
* [fasthttpsession](https://github.com/phachon/fasthttpsession) - a fast and powerful session package for fasthttp servers.
* [atreugo](https://github.com/savsgio/atreugo) - High performance and extensible micro web framework with zero memory allocations in hot paths.
* [kratgo](https://github.com/savsgio/kratgo) - Simple, lightweight and ultra-fast HTTP Cache to speed up your websites.
* [kit-plugins](https://github.com/wencan/kit-plugins/tree/master/transport/fasthttp) - go-kit transport implementation for fasthttp.
* [Fiber](https://github.com/gofiber/fiber) - An Expressjs inspired web framework running on Fasthttp
* [Gearbox](https://github.com/gogearbox/gearbox) - :gear: gearbox is a web framework written in Go with a focus on high performance and memory optimization
* [http2curl](https://github.com/li-jin-gou/http2curl) - A tool to convert fasthttp requests to curl command line
## 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 a new request object per each request instead
of reusing existing objects like fasthttp does.
* 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 unnecessary memory allocations avoided by fasthttp.
* net/http client API requires creating a 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](https://pkg.go.dev/net/http#Hijacker)
to [fasthttp connection hijacking](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.Hijack).
* Compare [net/http Request.Body reading](https://pkg.go.dev/net/http#Request)
to [fasthttp request body reading](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.PostBody).
* *Why fasthttp doesn't support HTTP/2.0 and WebSockets?*
[HTTP/2.0 support](https://github.com/fasthttp/http2) is in progress. [WebSockets](https://github.com/fasthttp/websockets) has been done already.
Third parties also may use [RequestCtx.Hijack](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.Hijack)
for implementing these goodies.
* *Are there known net/http advantages comparing to fasthttp?*
Yes:
* net/http supports [HTTP/2.0 starting from go1.6](https://pkg.go.dev/golang.org/x/net/http2).
* net/http API is stable, while fasthttp API constantly evolves.
* net/http handles more HTTP corner cases.
* net/http can stream both request and response bodies
* net/http can handle bigger bodies as it doesn't read the whole body into memory
* net/http should contain less bugs, since it is used and tested by much
wider audience.
* *Why fasthttp API prefers returning `[]byte` instead of `string`?*
Because `[]byte` to `string` conversion isn't free - it requires memory
allocation and copy. Feel free wrapping returned `[]byte` result into
`string()` if you prefer working with strings instead of byte slices.
But be aware that this has non-zero overhead.
* *Which GO versions are supported by fasthttp?*
Go 1.21.x and newer. Older versions might work, but won't officially be supported.
* *Please provide real benchmark data and server information*
See [this issue](https://github.com/valyala/fasthttp/issues/4).
* *Are there plans to add request routing to fasthttp?*
There are no plans to add request routing into fasthttp.
Use third-party routers and web frameworks with fasthttp support:
* [fasthttp-routing](https://github.com/qiangxue/fasthttp-routing)
* [router](https://github.com/fasthttp/router)
* [gramework](https://github.com/gramework/gramework)
* [lu](https://github.com/vincentLiuxiang/lu)
* [atreugo](https://github.com/savsgio/atreugo)
* [Fiber](https://github.com/gofiber/fiber)
* [Gearbox](https://github.com/gogearbox/gearbox)
See also [this issue](https://github.com/valyala/fasthttp/issues/9) for more info.
* *I detected data race in fasthttp!*
Cool! [File a bug](https://github.com/valyala/fasthttp/issues/new). But before
doing this check the following in your code:
* Make sure there are no references to [RequestCtx](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx)
or to its' members after returning from [RequestHandler](https://pkg.go.dev/github.com/valyala/fasthttp#RequestHandler).
* Make sure you call [TimeoutError](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx.TimeoutError)
before returning from [RequestHandler](https://pkg.go.dev/github.com/valyala/fasthttp#RequestHandler)
if there are references to [RequestCtx](https://pkg.go.dev/github.com/valyala/fasthttp#RequestCtx)
or to its' members, which may be accessed by other goroutines.
* *I didn't find an answer for my question here*
Try exploring [these questions](https://github.com/valyala/fasthttp/issues?q=label%3Aquestion).
", Assign "at most 3 tags" to the expected json: {"id":"1584","tags":[]} "only from the tags list I provide: [{"id":77,"name":"3d"},{"id":89,"name":"agent"},{"id":17,"name":"ai"},{"id":54,"name":"algorithm"},{"id":24,"name":"api"},{"id":44,"name":"authentication"},{"id":3,"name":"aws"},{"id":27,"name":"backend"},{"id":60,"name":"benchmark"},{"id":72,"name":"best-practices"},{"id":39,"name":"bitcoin"},{"id":37,"name":"blockchain"},{"id":1,"name":"blog"},{"id":45,"name":"bundler"},{"id":58,"name":"cache"},{"id":21,"name":"chat"},{"id":49,"name":"cicd"},{"id":4,"name":"cli"},{"id":64,"name":"cloud-native"},{"id":48,"name":"cms"},{"id":61,"name":"compiler"},{"id":68,"name":"containerization"},{"id":92,"name":"crm"},{"id":34,"name":"data"},{"id":47,"name":"database"},{"id":8,"name":"declarative-gui "},{"id":9,"name":"deploy-tool"},{"id":53,"name":"desktop-app"},{"id":6,"name":"dev-exp-lib"},{"id":59,"name":"dev-tool"},{"id":13,"name":"ecommerce"},{"id":26,"name":"editor"},{"id":66,"name":"emulator"},{"id":62,"name":"filesystem"},{"id":80,"name":"finance"},{"id":15,"name":"firmware"},{"id":73,"name":"for-fun"},{"id":2,"name":"framework"},{"id":11,"name":"frontend"},{"id":22,"name":"game"},{"id":81,"name":"game-engine "},{"id":23,"name":"graphql"},{"id":84,"name":"gui"},{"id":91,"name":"http"},{"id":5,"name":"http-client"},{"id":51,"name":"iac"},{"id":30,"name":"ide"},{"id":78,"name":"iot"},{"id":40,"name":"json"},{"id":83,"name":"julian"},{"id":38,"name":"k8s"},{"id":31,"name":"language"},{"id":10,"name":"learning-resource"},{"id":33,"name":"lib"},{"id":41,"name":"linter"},{"id":28,"name":"lms"},{"id":16,"name":"logging"},{"id":76,"name":"low-code"},{"id":90,"name":"message-queue"},{"id":42,"name":"mobile-app"},{"id":18,"name":"monitoring"},{"id":36,"name":"networking"},{"id":7,"name":"node-version"},{"id":55,"name":"nosql"},{"id":57,"name":"observability"},{"id":46,"name":"orm"},{"id":52,"name":"os"},{"id":14,"name":"parser"},{"id":74,"name":"react"},{"id":82,"name":"real-time"},{"id":56,"name":"robot"},{"id":65,"name":"runtime"},{"id":32,"name":"sdk"},{"id":71,"name":"search"},{"id":63,"name":"secrets"},{"id":25,"name":"security"},{"id":85,"name":"server"},{"id":86,"name":"serverless"},{"id":70,"name":"storage"},{"id":75,"name":"system-design"},{"id":79,"name":"terminal"},{"id":29,"name":"testing"},{"id":12,"name":"ui"},{"id":50,"name":"ux"},{"id":88,"name":"video"},{"id":20,"name":"web-app"},{"id":35,"name":"web-server"},{"id":43,"name":"webassembly"},{"id":69,"name":"workflow"},{"id":87,"name":"yaml"}]" returns me the "expected json"