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/*
Package multipartstreamer helps you encode large files in MIME multipart format
without reading the entire content into memory. It uses io.MultiReader to
combine an inner multipart.Reader with a file handle.
*/
package multipartstreamer
import (
"bytes"
"fmt"
"io"
"io/ioutil"
"mime/multipart"
"net/http"
"os"
"path/filepath"
)
type MultipartStreamer struct {
ContentType string
bodyBuffer *bytes.Buffer
bodyWriter *multipart.Writer
closeBuffer *bytes.Buffer
reader io.Reader
contentLength int64
}
// New initializes a new MultipartStreamer.
func New() (m *MultipartStreamer) {
m = &MultipartStreamer{bodyBuffer: new(bytes.Buffer)}
m.bodyWriter = multipart.NewWriter(m.bodyBuffer)
boundary := m.bodyWriter.Boundary()
m.ContentType = "multipart/form-data; boundary=" + boundary
closeBoundary := fmt.Sprintf("\r\n--%s--\r\n", boundary)
m.closeBuffer = bytes.NewBufferString(closeBoundary)
return
}
// WriteFields writes multiple form fields to the multipart.Writer.
func (m *MultipartStreamer) WriteFields(fields map[string]string) error {
var err error
for key, value := range fields {
err = m.bodyWriter.WriteField(key, value)
if err != nil {
return err
}
}
return nil
}
// WriteReader adds an io.Reader to get the content of a file. The reader is
// not accessed until the multipart.Reader is copied to some output writer.
func (m *MultipartStreamer) WriteReader(key, filename string, size int64, reader io.Reader) (err error) {
m.reader = reader
m.contentLength = size
_, err = m.bodyWriter.CreateFormFile(key, filename)
return
}
// WriteFile is a shortcut for adding a local file as an io.Reader.
func (m *MultipartStreamer) WriteFile(key, filename string) error {
fh, err := os.Open(filename)
if err != nil {
return err
}
stat, err := fh.Stat()
if err != nil {
return err
}
return m.WriteReader(key, filepath.Base(filename), stat.Size(), fh)
}
// SetupRequest sets up the http.Request body, and some crucial HTTP headers.
func (m *MultipartStreamer) SetupRequest(req *http.Request) {
req.Body = m.GetReader()
req.Header.Add("Content-Type", m.ContentType)
req.ContentLength = m.Len()
}
func (m *MultipartStreamer) Boundary() string {
return m.bodyWriter.Boundary()
}
// Len calculates the byte size of the multipart content.
func (m *MultipartStreamer) Len() int64 {
return m.contentLength + int64(m.bodyBuffer.Len()) + int64(m.closeBuffer.Len())
}
// GetReader gets an io.ReadCloser for passing to an http.Request.
func (m *MultipartStreamer) GetReader() io.ReadCloser {
reader := io.MultiReader(m.bodyBuffer, m.reader, m.closeBuffer)
return ioutil.NopCloser(reader)
}
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