How Can I Efficiently Convert an io.Reader to a String in Go?

Efficiently Converting io.Reader to String

Problem:

Consider an io.ReadCloser object obtained from an http.Response. How can one efficiently convert the entire stream into a string?

Solution:

Using Strings.Builder (For Go 1.10 and Later):

This is the preferred and most efficient method for Go 1.10 and above:

import "strings"

func ioReaderToString(r io.ReadCloser) (string, error) {
    buf := new(strings.Builder)
    if _, err := io.Copy(buf, r); err != nil {
        return "", err
    }

    return buf.String(), nil
}

Legacy Method (For Go <= 1.9):

[Note: This solution is outdated and not recommended in favor of Strings.Builder.]

1. Read the stream into a bytes.Buffer:

import "bytes"

buf := new(bytes.Buffer)
if _, err := buf.ReadFrom(r); err != nil {
    return "", err
}

2. Convert the buffer to a string (inefficient copy operation occurs here):

s := buf.String()

Unsafe Method (Advanced and Risky):

[Use with extreme caution]

1. Read the stream into a bytes.Buffer:

import "bytes"

buf := new(bytes.Buffer)
if _, err := buf.ReadFrom(r); err != nil {
    return "", err
}

2. Convert the buffer to a byte slice:

b := buf.Bytes()

3. Unsafely convert the byte slice to a string:

import "unsafe"

s := *(*string)(unsafe.Pointer(&b))

Caveats of Unsafe Method:

• May not work in all compilers or architectures.
• The resulting string is mutable, potentially leading to unexpected behavior.

Recommendation:

Stick with the Strings.Builder method as it is efficient, safe, and avoids the pitfalls of the unsafe method.

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