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Form Data with Fiber

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This example demonstrates how to parse application/x-www-form-urlencoded request bodies into Go structs, slices and maps using Fiber v3's Bind().Body().

Description​

This project shows four ways a urlencoded form body can be parsed: a flat struct, a repeated field into a []string, a nested struct plus a slice of structs, and dynamic keys into a map via net/url.ParseQuery.

Requirements​

Project Structure​

  • main.go: The main application entry point.
  • go.mod: The Go module file.

Setup​

  1. Clone the repository:

    git clone https://github.com/gofiber/recipes.git
    cd recipes/form-data

  2. Install the dependencies:

    go mod download

  3. Run the application:

    go run main.go

The application should now be running on http://localhost:3000.

Example Usage​

  1. Send a POST request to http://localhost:3000/struct with a flat form:

    curl -X POST http://localhost:3000/struct -d "[email protected]&age=30"
    {"name":"Jane","email":"[email protected]","age":30}

  2. Send a POST request to http://localhost:3000/slice with a repeated field:

    curl -X POST http://localhost:3000/slice -d "tags=go&tags=web"
    {"tags":["go","web"]}

  3. Send a POST request to http://localhost:3000/nested with a nested struct and a slice of structs:

    curl -X POST http://localhost:3000/nested -d "customer=Jane&address.street=Main+St&address.city=Springfield&items.0.name=Widget&items.0.qty=2&items.1.name=Gadget&items.1.qty=1"
    {"customer":"Jane","address":{"street":"Main St","city":"Springfield"},"items":[{"name":"Widget","qty":2},{"name":"Gadget","qty":1}]}

  4. Send a POST request to http://localhost:3000/map with keys that have no matching struct field:

    curl -X POST http://localhost:3000/map -d "color=blue&size=M&size=L"
    {"color":["blue"],"size":["M","L"]}

  5. A field that cannot convert to its declared Go type returns a 400 with the bind error:

    curl -X POST http://localhost:3000/struct -d "[email protected]&age=notanumber"
    {"error":"bind \"age\" from body: schema: error converting value for \"age\""}

Code Overview​

main.go​

The main Go file sets up the Fiber application and four routes, each binding a urlencoded form body into a different Go shape:

  • POST /struct binds a flat form into a struct with Bind().Body().
  • POST /slice binds a repeated field (tags=go&tags=web) into a []string.
  • POST /nested binds a dotted key path (address.street) into a nested struct, and a dotted, indexed key path (items.0.qty) into a slice of structs.
  • POST /map parses the raw body into a map[string][]string using net/url.ParseQuery as a standard-library alternative (Fiber's Bind().Body() also natively supports binding form bodies into maps).

Conclusion​

This example provides a minimal reference for binding application/x-www-form-urlencoded bodies in a Go Fiber application, covering scalar fields, repeated fields, nested structs, slices of structs, and dynamic keys.

References​