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package mimetype_test
import (
"bytes"
"fmt"
"io"
"io/ioutil"
"github.com/gabriel-vasile/mimetype"
)
// Pure io.Readers (meaning those without a Seek method) cannot be read twice.
// This means that once DetectReader has been called on an io.Reader, that reader
// is missing the bytes representing the header of the file.
// To detect the MIME type and then reuse the input, use a buffer, io.TeeReader,
// and io.MultiReader to create a new reader containing the original, unaltered data.
//
// If the input is an io.ReadSeeker instead, call input.Seek(0, io.SeekStart)
// before reusing it.
func Example_detectReader() {
testBytes := []byte("This random text has a MIME type of text/plain; charset=utf-8.")
input := bytes.NewReader(testBytes)
mtype, recycledInput, err := recycleReader(input)
// Verify recycledInput contains the original input.
text, _ := ioutil.ReadAll(recycledInput)
fmt.Println(mtype, bytes.Equal(testBytes, text), err)
// Output: text/plain; charset=utf-8 true <nil>
}
// recycleReader returns the MIME type of input and a new reader
// containing the whole data from input.
func recycleReader(input io.Reader) (mimeType string, recycled io.Reader, err error) {
// header will store the bytes mimetype uses for detection.
header := bytes.NewBuffer(nil)
// After DetectReader, the data read from input is copied into header.
mtype, err := mimetype.DetectReader(io.TeeReader(input, header))
// Concatenate back the header to the rest of the file.
// recycled now contains the complete, original data.
recycled = io.MultiReader(header, input)
return mtype.String(), recycled, err
}
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