gofiber/fiber · warning

binder: suitable content not found to parse body

Error message

binder: suitable content not found to parse body

What it means

Exported sentinel from the binder package indicating that no registered binder matches the request's Content-Type (binder/binder.go:19). It is intended for callers that build their own content-type dispatch on top of binder pools; Fiber's built-in Bind.Body() returns fiber.ErrUnprocessableEntity (422) for the same condition rather than this sentinel.

Solutions

  1. Register a custom binder implementing MIMETypes() that lists the media type, then app.Config.CustomBinders = []binder.CustomBinder{...} so Bind.Body() dispatches to it.
  2. If using binder types directly, switch on Content-Type yourself and fall back to a sensible default (e.g. JSON) instead of returning the sentinel.
  3. Reject unsupported media types early in middleware with 415 Unsupported Media Type so the binder never sees them.
  4. Align the client to send only Content-Types your server understands.

Example fix

// before: unknown content-type reaches the binder
ctype := header.ContentType()
// ...falls through every case, returns ErrSuitableContentNotFound

// after: register a custom binder for the MIME
app.Config().CustomBinders = []binder.CustomBinder{&CSVBinder{}}
// where CSVBinder.MIMETypes() returns []string{"text/csv"}
Defensive patterns

Strategy: validation

Validate before calling

// Validate Content-Type before dispatching to a binder
func supportedCType(ctype string) bool {
    switch ctype {
    case fiber.MIMEApplicationJSON, fiber.MIMEApplicationXML, fiber.MIMETextXML,
        fiber.MIMEApplicationCBOR, fiber.MIMEApplicationMsgPack,
        fiber.MIMEApplicationForm, fiber.MIMEMultipartForm:
        return true
    }
    // also accept any MIME covered by a registered custom binder
    return false
}

Try / catch

if err := c.Bind().Body(&out); err != nil {
    if errors.Is(err, binder.ErrSuitableContentNotFound) || errors.Is(err, fiber.ErrUnprocessableEntity) {
        return c.Status(fiber.StatusUnsupportedMediaType).SendString("unsupported media type")
    }
    return err
}

Prevention

When it happens

Trigger: A request carries a Content-Type the binder layer does not recognize (e.g. text/csv, application/graphql) and the application calls a custom dispatcher that returns ErrSuitableContentNotFound; or you use binder package types directly without registering a custom binder for that MIME type.

Common situations: Custom content negotiation where the client sends an uncommon media type; forgetting to register app.Config.CustomBinders for a new MIME; clients that send a malformed or empty Content-Type header with a body.

Related errors

AI-assisted analysis of gofiber/fiber@a105acad6c (2026-08-11). Data as JSON: /api/errors/8639e56698593090. Report an issue: GitHub.

Appendix: source

Thrown at binder/binder.go:19

package binder

import (
	"errors"
	"sync"
)

const (
	bindingURI        = "uri"
	bindingForm       = "form"
	bindingQuery      = "query"
	bindingHeader     = "header"
	bindingRespHeader = "respHeader"
	bindingCookie     = "cookie"
)

// Binder errors
var (
	ErrSuitableContentNotFound = errors.New("binder: suitable content not found to parse body")
	ErrMapNotConvertible       = errors.New("binder: map is not convertible to map[string]string or map[string][]string")
	ErrMapNilDestination       = errors.New("binder: map destination is nil and cannot be initialized")
	ErrInvalidDestinationValue = errors.New("binder: invalid destination value")
	ErrUnmatchedBrackets       = errors.New("unmatched brackets")
)

var errPoolTypeAssertion = errors.New("failed to type-assert to T")

var HeaderBinderPool = sync.Pool{
	New: func() any {
		return &HeaderBinding{}
	},
}

var RespHeaderBinderPool = sync.Pool{
	New: func() any {
		return &RespHeaderBinding{}
	},

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