Golang調試工具Delve使用簡介

Delve 是一款很不錯的 Golang 調試工具，可以實現類似 Visual Studio 的斷點調試功能，也可以用來在程序 Crash 的時候生成 Coredump 文件，此外 Delve 也適合用於調試 Web Server。

Delve 項目

Github鏈接

安裝 Delve

go get -u github.com/go-delve/delve/cmd/dlv

Delve 常用命令

命令	功能
dlv attach	後面跟 pid，用來 Debug 編譯好的 Golang 程序
dlv core	用於 coredump
dlv debug	後面跟要調試的 go 文件，進入 Debug
dlv test	Debug test 函數

編寫用於 Debug 的 Golang Web Server

main.go， 寫一個 Hello World 的 Web Server

package main

import (
	"net/http"
)

const endpoint = ":8000"

type helloHandler struct{}

func (h *helloHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("Hello, world!"))
}

func main() {
	http.Handle("/", &helloHandler{})
	http.ListenAndServe(endpoint, nil)
}

進行斷點調試

➜  test dlv debug ./main.go
Type 'help' for list of commands.
(dlv) help
The following commands are available:
    args ------------------------ Print function arguments.
    break (alias: b) ------------ Sets a breakpoint.
    breakpoints (alias: bp) ----- Print out info for active breakpoints.
    call ------------------------ Resumes process, injecting a function call (EXPERIMENTAL!!!)
    clear ----------------------- Deletes breakpoint.
    clearall -------------------- Deletes multiple breakpoints.
    condition (alias: cond) ----- Set breakpoint condition.
    config ---------------------- Changes configuration parameters.
    continue (alias: c) --------- Run until breakpoint or program termination.
    deferred -------------------- Executes command in the context of a deferred call.
    disassemble (alias: disass) - Disassembler.
    down ------------------------ Move the current frame down.
    edit (alias: ed) ------------ Open where you are in $DELVE_EDITOR or $EDITOR
    exit (alias: quit | q) ------ Exit the debugger.
    frame ----------------------- Set the current frame, or execute command on a different frame.
    funcs ----------------------- Print list of functions.
    goroutine (alias: gr) ------- Shows or changes current goroutine
    goroutines (alias: grs) ----- List program goroutines.
    help (alias: h) ------------- Prints the help message.
    libraries ------------------- List loaded dynamic libraries
    list (alias: ls | l) -------- Show source code.
    locals ---------------------- Print local variables.
    next (alias: n) ------------- Step over to next source line.
    on -------------------------- Executes a command when a breakpoint is hit.
    print (alias: p) ------------ Evaluate an expression.
    regs ------------------------ Print contents of CPU registers.
    restart (alias: r) ---------- Restart process.
    set ------------------------- Changes the value of a variable.
    source ---------------------- Executes a file containing a list of delve commands
    sources --------------------- Print list of source files.
    stack (alias: bt) ----------- Print stack trace.
    step (alias: s) ------------- Single step through program.
    step-instruction (alias: si)  Single step a single cpu instruction.
    stepout (alias: so) --------- Step out of the current function.
    thread (alias: tr) ---------- Switch to the specified thread.
    threads --------------------- Print out info for every traced thread.
    trace (alias: t) ------------ Set tracepoint.
    types ----------------------- Print list of types
    up -------------------------- Move the current frame up.
    vars ------------------------ Print package variables.
    whatis ---------------------- Prints type of an expression.
Type help followed by a command for full documentation.

在這個交換環境下可以進行斷點調試，支持的命令主要有：

命令	alias	功能
break	b	設置斷點
continue	c	運行至斷點
print	p	打印變量
funcs		顯示支持的函數

查看包名/函數名包含 main 的函數

funcs main

(dlv) funcs main
crypto/x509.domainToReverseLabels
crypto/x509.matchDomainConstraint
internal/x/net/http/httpproxy.(*domainMatch).match
internal/x/net/http/httpproxy.domainMatch.match
main.(*helloHandler).ServeHTTP
main.init
main.main
net.absDomainName
net.isDomainName
net/http.(*body).bodyRemains
net/http.requestBodyRemains
runtime.main
runtime.main.func1
runtime.main.func2
type..eq.internal/x/net/http/httpproxy.domainMatch
type..hash.internal/x/net/http/httpproxy.domainMatch

funcs [param] 默認是返回包含 param 的func，可以看到 main package 包含3個 func

main.(*helloHandler).ServeHTTP
main.init
main.main

設置斷點

break [name] <linespec>

1. 在 main 處設置一個斷點，break 的參數可以是 funcs 查看等到的 func name

   break main.main
   

   (dlv) break main.main
   Breakpoint 1 set at 0x1331513 for main.main() ./main.go:15
   

2. 設置斷點的另外一種方式

   <filename>:<line>  
   

   (dlv) break ./main.go:15
   Breakpoint 1 set at 0x1331513 for main.main() ./main.go:15
   

3. linespec 支持的完整形式
   linespec說明

   *<address> Specifies the location of memory address address. address can be specified as a decimal, hexadecimal or octal number
   
   <filename>:<line> Specifies the line line in filename. filename can be the partial path to a file or even just the base name as long as the expression remains unambiguous.
   
   <line> Specifies the line line in the current file
   
   +<offset> Specifies the line offset lines after the current one
   
   -<offset> Specifies the line offset lines before the current one
   
   <function>[:<line>] Specifies the line line inside function. The full syntax for function is <package>.(*<receiver type>).<function name> however the only required element is the function name, everything else can be omitted as long as the expression remains unambiguous. For setting a breakpoint on an init function (ex: main.init), the <filename>:<line> syntax should be used to break in the correct init function at the correct location.
   
   /<regex>/ Specifies the location of all the functions matching regex
   

運行至斷點

continue 命令運行至斷點

continue

(dlv) continue
> main.main() ./main.go:15 (hits goroutine(1):1 total:1) (PC: 0x1331513)
    10:
    11:	func (h *helloHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    12:		w.Write([]byte("Hello, world!"))
    13:	}
    14:
=>  15:	func main() {
    16:		http.Handle("/", &helloHandler{})
    17:		http.ListenAndServe(endpoint, nil)
    18:	}

打印變量

1. 可以繼續設置斷點至 ServeHTTP 函數，並執行 continue 開啓 Web Server 服務

   (dlv) break main.(*helloHandler).ServeHTTP
   Breakpoint 2 set at 0x1331443 for main.(*helloHandler).ServeHTTP() ./main.go:11
   (dlv) c
   

2. 訪問 Web Server
   這時候 Web Server 的 Delve 需要輸入

   ➜  curl http://localhost:8000
   Hello, world!%
   

3. 在執行至斷點 ServeHTTP 時，可輸入 print 查詢變量

   • 輸入 n 回車，單步執行，
   • 輸入 args 打印出所有的方法參數信息
   • 輸入 locals 打印所有的本地變量

   (dlv) c
   > main.(*helloHandler).ServeHTTP() ./main.go:11 (hits goroutine(26):1 total:13) (PC: 0x1331443)
       6:
       7:	const endpoint = ":8000"
       8:
       9:	type helloHandler struct{}
       10:
   =>  11:	func (h *helloHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
       12:		w.Write([]byte("Hello, world!"))
       13:	}
       14:
       15:	func main() {
       16:		http.Handle("/", &helloHandler{})
   (dlv) n
   > main.(*helloHandler).ServeHTTP() ./main.go:12 (PC: 0x1331451)
       7:	const endpoint = ":8000"
       8:
       9:	type helloHandler struct{}
       10:
       11:	func (h *helloHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
   =>  12:		w.Write([]byte("Hello, world!"))
       13:	}
       14:
       15:	func main() {
       16:		http.Handle("/", &helloHandler{})
       17:		http.ListenAndServe(endpoint, nil)
   (dlv) args
   h = (*main.helloHandler)(0x16485d0)
   w = net/http.ResponseWriter(*net/http.response) 0xc00010b998
   r = ("*net/http.Request")(0xc0001c0200)
   (dlv) locals
   (no locals)
   (dlv) print r.Method
   "GET"
   (dlv)