go语言简述

0. 简述

Go是一个开源的编程语言，它能让构造简单、可靠且高效的软件变得容易。

Go语言被设计成一门应用于搭建web服务器，存储集群或类似用途的巨型中央服务器的系统编程语言。对于高性能分布式系统领域而言，Go语言无疑比大多数其他语言有着更高的开发效率。它提供了海量并行的支持，这对于游戏服务器端的开发而言是再好不过的。

Go官网：https://golang.google.cn/或https://github.com/golang/go

标准库： https://golang.google.cn/pkg/ https://godoc.org/

package main
import "fmt"
func main() {
    fmt.Println("Hello, World!")
}

X86上编译运行：

wang@ubuntu:~/go$ go build -o hello hello.go
wang@ubuntu:~/go$ ./hello
Hello, World!

或直接运行

wang@ubuntu:~/go$ go run hello.go
Hello, World!

X86平台交叉编译ARM64平台上程序：

GOOS=linux GOARCH=arm64 go build -o hello hello.go
wang@ubuntu:~/go$ file hello
hello: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), statically linked, not stripped

godoc用法：

 godoc -http=localhost:6060 -play

godoc可提供离线的go文档，便于本地查看。

可在https://godoc.org/中搜索所有golang库的接口说明。

1. Go编译器

两种官方编译器，gc和gccgo，其中gccgo基于gcc后端。

go编译器支持8种指令集，不同建构编译质量不同：

amd64 (also known as x86-64)    
386 (x86 or x86-32)   Comparable to the amd64 port.
arm (ARM)
Supports Linux, FreeBSD, NetBSD, OpenBSD and Darwin binaries. Less widely used than the other ports.
arm64 (AArch64)
Supports Linux and Darwin binaries. New in 1.5 and not as well exercised as other ports.
ppc64, ppc64le (64-bit PowerPC big- and little-endian)
Supports Linux binaries. New in 1.5 and not as well exercised as other ports.
mips, mipsle (32-bit MIPS big- and little-endian)
Supports Linux binaries. New in 1.8 and not as well exercised as other ports.
mips64, mips64le (64-bit MIPS big- and little-endian)
Supports Linux binaries. New in 1.6 and not as well exercised as other ports.
s390x (IBM System z)
Supports Linux binaries. New in 1.7 and not as well exercised as other ports.

go编译环境可以被定制，与平台和建构相关的是$GOOS和$GOARCH，分别指定目标操作系统和目标建构。常用组合如下：（注：$GOOS是darwin for macOS 10.1及以上和iOS）

$GOOS        $GOARCH
android     arm
darwin      386
darwin      amd64
darwin      arm
darwin      arm64
linux       386
linux       amd64
linux       arm
linux       arm64
windows     386
windows     amd64

go编译器（或go环境）安装

有两种安装方式：二进制发布包和源码包，参考https://golang.google.cn/doc/install。一般情况下可直接下载二进制发布包，官方已提供了常用平台的二进制发布包。

下载二进制tar包，tar -C /usr/local -xzf go$VERSION.$OS-$ARCH.tar.gz，一般安装路径为/usr/local，go工具命令要执行需要将/usr/local/go/bin导出到PATH环境变量中（/etc/profile可长期有效）。

源码包安装方式参考：Installing Go from source

ubuntu下可直接apt安装：

sudo apt-get install golang-go

go卸载

linux下直接删除/usr/local/go目录即可（同时修改PATH环境变量，或/etc/profile）。

GO环境变量

go env可打印go环境变量。

tee -a $HOME/.bashrc <<'EOF'
# Go envs
export GOVERSION=go1.17.2 # Go 版本设置
export GO_INSTALL_DIR=$HOME/go # Go 安装目录
export GOROOT=$GO_INSTALL_DIR/$GOVERSION # GOROOT 设置
export GOPATH=$WORKSPACE/golang # GOPATH 设置
export PATH=$GOROOT/bin:$GOPATH/bin:$PATH # 将 Go 语言自带的和通过 go install 安装的二进制文件加入到 PATH 路径中
export GO111MODULE="on" # 开启 Go moudles 特性
export GOPROXY=https://goproxy.cn,direct # 安装 Go 模块时，代理服务器设置
export GOPRIVATE=
export GOSUMDB=off # 关闭校验 Go 依赖包的哈希值
EOF

Go 默认已经不需要配置任何环境变量了——什么 GOROOT、GOPATH 等都不需要了。但是PATH和GOPROXY还需要在~/.bash_profile指定下。

export PATH=$PATH:/usr/local/go/bin
export GOPROXY=https://goproxy.cn,https://goproxy.io,direct

##############################如下环境变量可忽略！！！

$GOPATH

GOPATH指定workspace位置，默认为$home/go，go项目在本地的开发环境的项目根路径（以便项目编译，go build, go install，go get）。若工作在其他目录，需设定GOPATH。export GOPATH=$HOME/go

或直接写到/etc/profile中，然后source /etc/profile

注意GOPATH不能和go安装目录相同。

go env GOPATH

打印当前有效的GOPATH，若没有设置打印默认位置。

For convenience, add the workspace's bin subdirectory to your PATH:

$ export PATH=$PATH:$(go env GOPATH)/bin

GOPATH之下主要包含三个目录：bin，pkg，src。bin目录主要存放可执行文件；pkg目录存放编译好的库文件，主要是*.a文件；src目录下主要存放go的源文件。

$GOROOT

go的安装目录，配置后不会更改。一般为/usr/local/go或/usr/go或/usr/lib/go。

$GOROOT_FINAL

$GOOS and $GOARCH

用于不同平台的交叉编译，只需要在build之前设置这两个变量即可，这也是go语言的优势之一：可以编译生成跨平台运行的可执行文件。

注意：这个交叉编译暂不支持cgo方式，因此交叉编译时需要设置$CGO_ENABLED设置为0。

$GOHOSTOS and $GOHOSTARCH

$GOBIN

go二进制文件安装目录，默认为$GOROOT/bin。

$GO386

$GOARM

$GOMIPS

集成开发环境IDE

vscode-golang配置参考：VS code golang 开发环境搭建 VSCode 开发 Go 程序也可以和 GoLand 一样强大--polarisxu

2. cgo

Cgo lets Go packages call C code.

The basics

If a Go source file imports "C", it is using cgo. The Go file will have access to anything appearing in the comment immediately preceding the line import "C", and will be linked against all other cgo comments in other Go files, and all C files included in the build process.

Note that there must be no blank lines in between the cgo comment and the import statement.

To access a symbol originating from the C side, use the package name C. That is, if you want to call the C function printf() from Go code, you write C.printf(). Since variable argument methods like printf aren't supported yet (issue 975), we will wrap it in the C method "myprint":

package main

/*
#include <stdio.h>
#include <stdlib.h>

void myprint(char* s) {
    printf("%s", s);
}
*/
import "C"

import "unsafe"

func main() {
    cs := C.CString("Hello from stdio\n")
    C.myprint(cs)
    C.free(unsafe.Pointer(cs))
}

参考：

1. http://golang.org/doc/articles/c_go_cgo.html

2. https://github.com/golang/go/wiki/cgo

3. http://wiki.jikexueyuan.com/project/go-command-tutorial/0.13.html 极客学院go命令详解

4. https://books.studygolang.com/advanced-go-programming-book/ch2-cgo/readme.html Go语言高级编程（Advanced Go Programming）cgo编程

3. Go交叉编译

参考：Go cross compilation

If cgo is not required (common go programs, not including c/c++)

The go tool won’t require any bootstrapping if cgo is not required. That allows you to target the following program to any GOOS/GOARCH without requiring you to do any additional work. Invoke go build.

$ cat main.go
package main
import "fmt"
func main() {
    fmt.Println("hello world")
}

In order to target android/arm, run the following command.

$ GOOS=android GOARCH=arm GOARM=7 go build .

The produced binary is targeting ARMv7 processors that runs Android. All possible GOOS and GOARCH values are listed on the environment docs.

If cgo is required (including c/c++)

If you need to have cgo enabled, the go tool allows you to provide custom C and C++ compilers via CC and CXX environment variables.

$ CGO_ENABLED=1 CC=android-armeabi-gcc CXX=android-armeabi-g++ \
    GOOS=android GOARCH=arm GOARM=7 go build .

The toolchain will invoke android-armeabi-gcc and android-armeabi-g++ if it is required to compile any part of the package with a C or C++ compiler. Consider the following program with a slightly different main function. Rather than outputting “hello world” to the standard I/O, it will use Android system libraries to write “hello world” to the system log.

$ cat main.go
// +build android

package main

// #cgo LDFLAGS: -llog
//
// #include <android/log.h>
//
// void hello() {
//   __android_log_print(
//     ANDROID_LOG_INFO, "MyProgram", "hello world");
// }
import "C"
func main() {
    C.hello()
}

If you build the program with the command above and examine the build with -x, you can observe that cgo is delegating the C compilation to arm-linux-androideabi-gcc.

$ CGO_ENABLED=1 \
CC=arm-linux-androideabi-gcc \
CXX=arm-linux-androideabi-g++ \
GOOS=android GOARCH=arm GOARM=7 go build -x .
...
CGO_LDFLAGS=”-g” “-O2” “-llog” /Users/jbd/go/pkg/tool/darwin_amd64/cgo -objdir $WORK/github.com/rakyll/hello/_obj/ -importpath github.com/rakyll/hello — -I $WORK/github.com/rakyll/hello/_obj/ main.go
arm-linux-androideabi-gcc -I . -fPIC -marm -pthread -fmessage-length=0 -print-libgcc-file-name
arm-linux-androideabi-gcc -I . -fPIC -marm -pthread -fmessage-length=0 -I $WORK/github.com/rakyll/hello/_obj/ -g -O2 -o $WORK/github.com/rakyll/hello/_obj/_cgo_main.o -c $WORK/github.com/rakyll/hello/_obj/_cgo_main.c
...

Pre-building the standard library

The go tool also provides a utility if you would like to pre-build the standard library, targeting a specific GOOS and GOARCH.

$ CGO_ENABLED=1 \
    CC=arm-linux-androideabi-gcc \
    CXX=arm-linux-androideabi-g++ \
    GOOS=android GOARCH=arm GOARM=7 go install std

The standard library targeting android/armv7 will be available at $GOROOT/pkg/android_arm.

$ ls $GOROOT/pkg/android_arm
archive    fmt.a      math       runtime.a
bufio.a    go         math.a     sort.a
bytes.a    hash       mime       strconv.a
compress   hash.a     mime.a     strings.a
container  html       net        sync
crypto     html.a     net.a      sync.a
crypto.a   image      os         syscall.a
database   image.a    os.a       testing
debug      index      path       testing.a
encoding   internal   path.a     text
encoding.a io         reflect.a  time.a
errors.a   io.a       regexp     unicode
expvar.a   log        regexp.a   unicode.a
flag.a     log.a      runtime

If you prefer not to pre-build and install the standard library to the GOROOT, required libraries will be built while building user packages. But, the standard libraries builds are not preserved for future use at this stage and they will be rebuilt each time you run go build.

4. golang代理

由于网络限制，一般要使用代理获取仓库。

golang代理使用proxy.cn，参考：https://github.com/goproxy/goproxy.cn/blob/master/README.zh-CN.md

使用方法：

$ export GOPROXY=https://goproxy.cn,https://goproxy.io,direct

或

$ export GO111MODULE=on

$ export GOPROXY=https://goproxy.cn,https://goproxy.io,direct

或直接写入：～/.bash_profile

5. go命令工具

可通过go help获取go命令，如下记录一些易忽略的go命令用法。

go help

https://github.com/golang/tools.git提供了golang内置的工具，有些会在golang二进制安装包中，如vet，godoc等，可通过如下命令安装：

包含工具unmarshal/stress/stringer/stingintconv/shadow/guru/godex/goimports/eg/cover/bundle等。

go get -u golang.org/x/tools/...

1） go build

缩小输出文件体积

go 编译出的文件，体积挺大的。一个重要原因是其中包含了调试信息，可以通过编译参数使其不包含调试信息。

# 移除 调试信息（-w） 和 符号表（-s）
go build -o main -ldflags "-w -s" main.go

上述操作使用 -ldflags 参数指定 -w 和 -s，分别表示在编译时不包含调试信息和符号表，此举可以较好地缩减二进制文件体积。

编译时写入全局变量

go 可以通过编译参数，在编译时对变量进行赋值。一般情况下，这种操作可以让程序保留编译信息等数据。
通过 -ldflags 参数，设定 -X 操作，可以为全局变量赋值（一定要加-X）。

go build -ldflags "-X 'main.BuildTime=time006'" main.go
go build -ldflags "-X 'main.BuildTime=`date`' -X 'main.GitHash=`git rev-parse HEAD`'" main.go

go build -ldflags "-X cnca.HTTP2ClientTLSCAPath=/etc/openness/certs/ngc" -o "kubectl-cnca"

参考：关于 golang build