golang base64 转回 list

在Golang中，可以使用`encoding/base64`包来进行Base64编码和解码操作。要将Base64编码的字符串转回原始数据，可以使用`DecodeString`函数。

下面是一个示例代码：

package main

import (
	"encoding/base64"
	"fmt"
)

func main() {
	base64Str := "SGVsbG8gd29ybGQh"
	decodedBytes, err := base64.StdEncoding.DecodeString(base64Str)
	if err != nil {
		fmt.Println("Base64 decoding error:", err)
		return
	}
	decodedStr := string(decodedBytes)
	fmt.Println("Decoded string:", decodedStr)
}

运行以上代码，将会输出解码后的字符串：

Decoded string: Hello world!

相关问题

golang词法BNF

golang词法BNF如下：

SourceFile       = PackageClause ";" { ImportDecl ";" } { TopLevelDecl ";" } .
PackageClause    = "package" PackageName .
PackageName      = identifier .
ImportDecl       = "import" ( ImportSpec | "(" { ImportSpec ";" } ")" ) .
ImportSpec       = [ "." | PackageName ] ImportPath .
ImportPath       = string_lit .
TopLevelDecl     = Declaration | FunctionDecl | MethodDecl .
Declaration      = ConstDecl | TypeDecl | VarDecl .
ConstDecl        = "const" ( ConstSpec | "(" { ConstSpec ";" } ")" ) .
ConstSpec        = IdentifierList [ [ Type ] "=" ExpressionList ] .
IdentifierList   = identifier { "," identifier } .
ExpressionList   = Expression { "," Expression } .
TypeDecl         = "type" ( TypeSpec | "(" { TypeSpec ";" } ")" ) .
TypeSpec         = identifier Type .
Type             = TypeName | TypeLit | "(" Type ")" | "*" Type | ArrayType | StructType | PointerType | FunctionType | InterfaceType | SliceType | MapType | ChannelType .
TypeName         = identifier .
TypeLit          = ArrayType | StructType | PointerType | FunctionType | InterfaceType | SliceType | MapType | ChannelType .
ArrayType        = "[" ArrayLength "]" ElementType .
ArrayLength      = Expression .
ElementType      = Type .
StructType       = "struct" "{" { FieldDecl ";" } "}" .
FieldDecl        = ( IdentifierList Type | EmbeddedField ) [ Tag ] .
EmbeddedField    = [ "*" ] TypeName .
Tag              = string_lit .
PointerType      = "*" BaseType .
BaseType         = Type .
FunctionType     = "func" Signature .
Signature        = Parameters [ Result ] .
Result           = Parameters | Type .
Parameters       = "(" [ ParameterList [ "," ] ] ")" .
ParameterList    = ParameterDecl { "," ParameterDecl } .
ParameterDecl    = [ IdentifierList ] [ "..." ] Type .
InterfaceType    = "interface" "{" { MethodSpec ";" } "}" .
MethodSpec       = MethodName Signature | InterfaceTypeName .
MethodName       = identifier .
InterfaceTypeName = TypeName .
SliceType        = "[" "]" ElementType .
MapType          = "map" "[" KeyType "]" ElementType .
KeyType          = Type .
ChannelType      = ( "chan" [ "<-" ] | "<-" "chan" ) ElementType .
VarDecl          = "var" ( VarSpec | "(" { VarSpec ";" } ")" ) .
VarSpec          = IdentifierList ( Type [ "=" ExpressionList ] | "=" ExpressionList ) .
Expression       = UnaryExpr | Expression binary_op Expression .
UnaryExpr        = PrimaryExpr | unary_op UnaryExpr .
PrimaryExpr      = Operand | Conversion | "(" Expression ")" | PrimaryExpr Selector | PrimaryExpr Index | PrimaryExpr Slice | PrimaryExpr TypeAssertion | PrimaryExpr Arguments .
Operand          = Literal | OperandName | MethodExpr | "(" Expression ")" .
Literal          = BasicLit | CompositeLit | FunctionLit .
BasicLit         = int_lit | float_lit | imaginary_lit | rune_lit | string_lit .
OperandName      = identifier | QualifiedIdent.
QualifiedIdent   = PackageName "." identifier .
MethodExpr       = ReceiverType "." MethodName .
ReceiverType     = Type .
Index            = "[" Expression "]" .
Slice            = "[" [ Expression ] ":" [ Expression ] "]" | "[" [ Expression ] ":" Expression ":" Expression "]" .
Arguments        = "(" [ ( ExpressionList | Type [ "," ExpressionList ] ) [ "..." ] ] ")" .
CompositeLit     = LiteralType LiteralValue .
LiteralType      = StructType | ArrayType | "[" "..." "]" ElementType | SliceType | TypeName .
LiteralValue     = "{" [ ElementList [ "," ] ] "}" .
ElementList      = KeyedElement { "," KeyedElement } .
KeyedElement     = [ Key ":" ] Element .
Key              = FieldName | Expression | LiteralValue .
FieldName        = identifier .
Conversion       = Type "(" Expression [ "," ] ")" .

golang 下载gmail 邮件附件

以下是使用golang下载gmail邮件附件的示例代码：

package main

import (
	"encoding/base64"
	"fmt"
	"io"
	"log"
	"net/mail"
	"net/smtp"
	"os"
	"path/filepath"
	"strings"

	"github.com/joho/godotenv"
	"golang.org/x/net/context"
	"golang.org/x/oauth2"
	"golang.org/x/oauth2/google"
	"google.golang.org/api/gmail/v1"
)

func main() {
	// 加载.env环境变量文件
	err := godotenv.Load()
	if err != nil {
		log.Fatalf("Error loading .env file: %v", err)
	}

	// 获取OAuth2访问令牌
	ctx := context.Background()
	config, err := google.ConfigFromJSON([]byte(os.Getenv("GOOGLE_CLIENT_SECRET")), gmail.GmailReadonlyScope)
	if err != nil {
		log.Fatalf("Unable to parse client secret file to config: %v", err)
	}
	token := &oauth2.Token{
		AccessToken:  os.Getenv("GOOGLE_ACCESS_TOKEN"),
		RefreshToken: os.Getenv("GOOGLE_REFRESH_TOKEN"),
		TokenType:    "Bearer",
		Expiry:       oauth2.Now(),
	}
	client := config.Client(ctx, token)

	// 创建Gmail服务
	srv, err := gmail.New(client)
	if err != nil {
		log.Fatalf("Unable to retrieve Gmail client: %v", err)
	}

	// 获取最新的10封邮件
	user := "me"
	r, err := srv.Users.Messages.List(user).MaxResults(10).Q("is:unread").Do()
	if err != nil {
		log.Fatalf("Unable to retrieve messages: %v", err)
	}

	// 下载每个邮件的附件
	for _, m := range r.Messages {
		msg, err := srv.Users.Messages.Get(user, m.Id).Do()
		if err != nil {
			log.Fatalf("Unable to retrieve message %v: %v", m.Id, err)
		}

		// 解析邮件头部
		h := msg.Payload.Headers
		var subject, from, date string
		for _, v := range h {
			switch v.Name {
			case "Subject":
				subject = v.Value
			case "From":
				from = v.Value
			case "Date":
				date = v.Value
			}
		}

		// 下载附件
		for _, p := range msg.Payload.Parts {
			if p.Filename != "" {
				part := p.Body
				data, err := base64.URLEncoding.DecodeString(part.Data)
				if err != nil {
					log.Fatalf("Unable to decode attachment %v: %v", p.Filename, err)
				}

				// 将附件保存到本地
				ext := filepath.Ext(p.Filename)
				filename := fmt.Sprintf("%s_%s%s", strings.ReplaceAll(from, "@", "_"), subject, ext)
				f, err := os.Create(filename)
				if err != nil {
					log.Fatalf("Unable to create file %v: %v", filename, err)
				}
				defer f.Close()

				_, err = io.Copy(f, strings.NewReader(string(data)))
				if err != nil {
					log.Fatalf("Unable to save file %v: %v", filename, err)
				}

				log.Printf("Attachment saved: %v", filename)
			}
		}
	}
}

在上面的代码中，首先加载.env文件，该文件包含Google应用程序凭据和OAuth2访问令牌。

然后使用OAuth2访问令牌创建Gmail客户端，并使用该客户端获取最新的10封未读邮件。

对于每个邮件，我们获取其详细信息，包括邮件头部和附件。然后，我们使用base64解码附件数据，并将其保存到本地文件中。文件名采用发送方的电子邮件地址、主题和附件扩展名的组合。

最后，我们在控制台输出“Attachment saved: filename”以指示附件已成功保存。