Binding

Ply binds request data into a struct with Bind, or with a specific source method when you need control.

type CreateUser struct {
	Name  string `json:"name"`
	Email string `json:"email"`
	Age   int    `json:"age"`
}

app.Post("/users", func(c *core.Context) {
	var input CreateUser
	if err := c.BindJSON(&input); err != nil {
		c.JSON(400, map[string]string{"error": err.Error()})
		return
	}
	c.JSON(201, input)
})

Automatic source selection

c.Bind(&input) chooses a source from the request content type:

Bind also runs validation. The individual bind methods do not.

var input CreateUser
if err := c.Bind(&input); err != nil {
	c.JSON(400, map[string]string{"error": err.Error()})
	return
}

Explicit methods

c.BindJSON(&input)
c.BindQuery(&input)
c.BindForm(&input)

BindForm reads multipart values first, then falls back to URL-encoded form values.

Struct tags

Field names use the first available tag in this order:

1. query
2. form
3. json

If none is present, the Go field name is used. A tag value of - skips the field.

type Search struct {
	Term  string   `query:"q" json:"q"`
	Page  int      `query:"page" json:"page"`
	Tags  []string `query:"tag" json:"tag"`
	Token string   `json:"-" query:"-"`
}

Only exported fields are bound. Embedded structs are processed recursively.

Supported field types

• strings
• booleans
• signed and unsigned integers
• floats
• pointers to supported types
• slices of strings or slices of supported scalar types

A query or form value with the same key repeated populates a slice. For other slices, each value is parsed as one element.

Errors

Binding returns an error when:

• the target is not a non-nil struct pointer,
• a value cannot be parsed, or
• a field type is unsupported.

The error includes the field name, for example field "Age": strconv.ParseInt: parsing "abc": invalid syntax.

BindJSON returns the JSON decoder error directly. It does not reject unknown fields.

Limits

Binding does not enforce a maximum request size. Configure a body limit at the server or proxy when request bodies are untrusted.