Form and Multipart Handling

class FormBody private constructor() : RequestBody() {
    val size: Int
    fun encodedName(index: Int): String
    fun name(index: Int): String
    fun encodedValue(index: Int): String
    fun value(index: Int): String
    
    class Builder {
        fun add(name: String, value: String): Builder
        fun addEncoded(name: String, value: String): Builder
        fun build(): FormBody
    }
}

class MultipartBody private constructor() : RequestBody() {
    val type: MediaType
    val boundary: String
    val size: Int
    fun part(index: Int): Part
    fun parts(): List<Part>
    
    class Builder {
        constructor()
        constructor(boundary: String)
        
        fun setType(type: MediaType): Builder
        fun addPart(body: RequestBody): Builder
        fun addPart(headers: Headers?, body: RequestBody): Builder
        fun addFormDataPart(name: String, value: String): Builder
        fun addFormDataPart(name: String, filename: String?, body: RequestBody): Builder
        fun build(): MultipartBody
    }
    
    class Part private constructor() {
        val headers: Headers?
        val body: RequestBody
        
        companion object {
            fun create(body: RequestBody): Part
            fun create(headers: Headers?, body: RequestBody): Part
            fun createFormData(name: String, value: String): Part
            fun createFormData(name: String, filename: String?, body: RequestBody): Part
        }
    }
    
    companion object {
        val MIXED: MediaType
        val ALTERNATIVE: MediaType
        val DIGEST: MediaType
        val PARALLEL: MediaType
        val FORM: MediaType
    }
}

val file = File("photo.jpg")
val requestBody = file.asRequestBody("image/jpeg".toMediaType())

val multipartBody = MultipartBody.Builder()
    .setType(MultipartBody.FORM)
    .addFormDataPart("title", "My Photo")
    .addFormDataPart("photo", "photo.jpg", requestBody)
    .build()

val request = Request.Builder()
    .url("https://api.example.com/upload")
    .post(multipartBody)
    .build()