bufio: bufio.Write and bufio.WriteString behave differently #69068
Description
Go version
go version go1.23.0 darwin/arm64
Output of go env in your module/workspace:
GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/ccristi/Library/Caches/go-build'
GOENV='/Users/ccristi/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/ccristi/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/ccristi/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.23.0/libexec'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.23.0/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.23.0'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/ccristi/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/z2/2b0v421s24g_0d_fg2txybwm0000gn/T/go-build1898012219=/tmp/go-build -gno-record-gcc-switches -fno-common'What did you do?
Consider the following scenario:
Using WriteString
We see that the calls to the underlying io.Writer are buffered in calls with a buffer length of 3
type X struct {
i io.Writer
}
func (x *X) Write(p []byte) (n int, err error) {
fmt.Println("Writing ", len(p), "bytes to underlying writer")
fmt.Println()
n, err = x.i.Write(p)
if err != nil {
return
}
return
}
func main() {
x := X{os.Stdout}
bfw := bufio.NewWriterSize(&x, 3)
//nn, err := bfw.Write([]byte("abcdefghijklmno..."))
nn, err := bfw.WriteString("abcdefghijklmno...")
if err != nil {
fmt.Println("buffered writer tried writing ", nn)
panic(err)
}
}yields the following result:
Writing 3 bytes to underlying writer
abc
Written 3 bytes to underlying writer
Writing 3 bytes to underlying writer
def
Written 3 bytes to underlying writer
Writing 3 bytes to underlying writer
ghi
Written 3 bytes to underlying writer
Writing 3 bytes to underlying writer
jkl
Written 3 bytes to underlying writer
Writing 3 bytes to underlying writer
mno
Written 3 bytes to underlying writer
Using bufio.Write
func main() {
x := X{os.Stdout}
bfw := bufio.NewWriterSize(&x, 3)
nn, err := bfw.Write([]byte("abcdefghijklmno..."))
//nn, err := bfw.WriteString("abcdefghijklmno...")
if err != nil {
fmt.Println("buffered writer tried writing ", nn)
panic(err)
}
}We get the following output:
Writing 18 bytes to underlying writer
abcdefghijklmno...
Written 18 bytes to underlying writer
What did you see happen?
bufio.WriteString buffers calls to the underlying io.Writer in chunks of len(b.buf).
bufio.Write will not buffer calls to the underlying io.Writer but rather sends the whole buffer
What did you expect to see?
I was expecting to see bufio.Write behave in a similar way to bufio.WriteString.