How Can I Duplicate an io.Reader for Multiple Read Operations in Go?

Duplicating io.Reader Instances for Multiple Operations

Problem

When working with an io.ReadCloser type like request.Body, it can be problematic when wanting to perform multiple operations (e.g., write to a file and decode). Direct calls to ioutil.ReadAll() consume the entire stream, making subsequent operations impossible.

Solution: Using io.TeeReader

Unlike direct reads, io.TeeReader allows users to duplicate an io.Reader stream, enabling multiple references to the same content. This solves the problem of reading the same data twice.

Implementation

Here's an implementation using io.TeeReader:

package main

import (
    "bytes"
    "io"
    "io/ioutil"
    "log"
    "strings"
)

func main() {
    r := strings.NewReader("io.Reader contents to be read")
    var buf bytes.Buffer
    tee := io.TeeReader(r, &buf)

    // Perform the first operation using tee.
    log.Println(ioutil.ReadAll(tee))

    // Perform the second operation using the duplicated content in the buffer.
    log.Println(ioutil.ReadAll(&buf))
}

Notes

• Remember to read from the TeeReader first to fill the buffer.
• If you need to create multiple references to different parts of the stream, use io.MultiReader or io.PipeReader.

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