Not able to call different methods on the client for the same *os.File

[YashMeh]

Hi,
Thanks for the awesome package.
I am trying to run the following code but it only works for the first function call whether it be .Parse,.Detect or .Meta . I am wondering whether it is the limitation of the package or of golang GC itself and how could I solve it.

func ReadData(s *indexService) {
	//Open the file
	f, err := os.Open(fileDir)
	if err != nil {
		fmt.Println("[ERROR] Opening file")
	}
	defer f.Close()
	c := context.Background()
	
	//First function call works fine
	docBody, err := s.TClient.Parse(c, f)
	if err != nil {
		fmt.Println("[ERROR] Reading body")
	}
	//Returns file already closed error
	docContent, err := s.TClient.Detect(c, f)
	if err != nil {
		fmt.Println(err)
		fmt.Println("[ERROR] Reading MIMETYPE")
	}
	//Returns file already closed error
	docMeta, err := s.TClient.Meta(c, f)
	if err != nil {
		fmt.Println("[ERROR] Reading Meta-data")
	}
	
	defer func() {
		fmt.Printf("Tika Processed: %s \n", fileName)
	}()
	
}

indexService looks like this -

type indexService struct {
	TClient *tika.Client
}

[tbpg]

Reset the file between calls:

f.Seek(0, io.SeekStart))

Every time you call one of the Parse/Detect/etc. methods, it reads the file. To re-read the file, you have seek back to the beginning of the file.

See the docs for (*os.File).Read:

Read reads up to len(b) bytes from the File. It returns the number of bytes read and any error encountered. At end of file, Read returns 0, io.EOF.

You can see same the issue in this example: https://play.golang.org/p/0AbP0ZFL3Sm.

[YashMeh]

Hi @tbpg ,
Thanks for the prompt response, but .Seek(0,io.SeekStart) in between the calls is not solving the problem, I could not figure why, I will try sometings and will let you know.

[tbpg]

Sounds good. A quick and easy (though not elegant) solution would be to reopen the file.

[YashMeh]

Yes, currently I am doing that only.

[YashMeh]

Hi @tbpg ,
I think the problem was, os.Open() reads the file in form of streams and thus after the first API call we aren't able to re-utilise the stream. Now for sure opening the file again is a solution but I think the best way to handle this case will be to clone the stream using io.TeeReader so that the stream can be used again without making multiple concurrent operations on a file.
This worked for me ..

package main

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"os"

	"github.com/google/go-tika/tika"
)

func main() {
	client := tika.NewClient(nil, "http://localhost:9998")
	//Opening the file that creates a stream
	f, err := os.Open("./testdir/test.txt")
	if err != nil {
		fmt.Println("[ERROR] Opening file")
	}
	defer f.Close()

	//Cloning the stream
	var buf bytes.Buffer
	tee := io.TeeReader(f, &buf)
	c := context.Background()

	//First function call works fine
	docBody, err := client.Parse(c, tee)
	fmt.Println(docBody)
	
	//Second call also works fine
	docContent, err := client.Detect(c, tee)
	fmt.Println(docContent)
	
	//Third call also works fine
	docMeta, err := client.Meta(c, tee)
	fmt.Println(docMeta)

}

Let me know if you want me to mention this in the documentation.