Debugging Go http server with VS Code

Like the title said, in this article we will do debugging go application with VS Code and Go extension.

Setup simple application

We will create a simple http server that says hello

// main.go
package main

import (
    "fmt"
    "net/http"
)

func main() {
    http.HandleFunc("/", helloServer)
    http.ListenAndServe(":8080", nil)
}

func helloServer(w http.ResponseWriter, r *http.Request) {
    name := r.URL.Path[1:]
    fmt.Fprintf(w, "Hello, %s!", name)
}

Debugging

For example, you may want to debug the value of the name variable from the application above then we have two options here to debug our http server.

Option 1: Debugging with test

Step 1: Let’s write our test

// main_test.go
package main

import (
    "net/http"
    "net/http/httptest"
    "testing"
)

func Test_helloServer(t *testing.T) {
    request, _ := http.NewRequest(http.MethodGet, "/Foo", nil)
    response := httptest.NewRecorder()

    helloServer(response, request)

    got := response.Body.String()
    want := "Hello, Foo!"
    if got != want {
        t.Errorf("got %q, want %q", got, want)
    }
}

Step 2: Add breakpoint

Now we have our test for helloServer, next step we need to add a breakpoint right after this line name := r.URL.Path[1:] by click on the left of expect line number or move the pointer to the expect line number and press F9 to toggle a breakpoint.

Step 3: Debug test

Finally, click on debug test to see the result:

Here, we can see the value of the name variable is Foo in the left panel or hover mouse on the name variable

Option 2: Debug with http request using dlv

Step 1: Install dlv

Open the Command Palette (Ctrl+Shift+P or Command+Shift+P), select Go: Install/Update Tools, and select dlv

Step 2: Add launch configuration

Create .vscode/launch.json in your root project folder and put this content into it

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Launch",
            "type": "go",
            "request": "launch",
            "mode": "auto",
            "program": "${fileDirname}",
            "env": {},
            "args": []
        }
    ]
}

Note: If your main.go file inside sub folder like cmd/api/main.go, you may want add this config to launch.json file to set current working directory to root project folder: "cwd": "${workspaceRoot}"

Step 3: Add breakpoint

This step is the same as add breakpoint like Option 1

Step 4: Run and Debug

Open the main.go file and press F5 and you ready to “Go” :)
Next, open your favorite terminal and enter curl localhost:8080/Baz for example. Now you can see the debug result:

Source code

You can find source code for this article at GitHub.

Conclusion

Above are two debug options for Go using VS Code which is very useful. For me, I prefer to cover as many tests as possible (Option 1), but when I need to debug a full flow of a request then Option 2 will be the best choice. And you? Which method do you use for debugging Go code?