Memory-mapped artifact upload into Pulp in Go and oapi-gen Go HTTP client

artifact.go

import (
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"io"
	"mime/multipart"
	"os"
	"path/filepath"

	"golang.org/x/exp/mmap"
)

// ArtifactsCreate creates an artifact from a file. It uses UNIX mmap to avoid buffering the file in memory.
func (c *PulpService) ArtifactsCreate(ctx context.Context, filename string) (*ArtifactResponse, error) {
	at, err := mmap.Open(filename)
	if err != nil {
		return nil, err
	}
	file := MmapReader{at: at}
	defer file.Close()

	hash := sha256.New()
	if _, err := io.Copy(hash, &file); err != nil {
		return nil, err
	}
	sha256h := hash.Sum(nil)
	file.Reset()

	body := &bytes.Buffer{}
	writer := multipart.NewWriter(body)

	err = writer.WriteField("size", fmt.Sprintf("%d", at.Len()))
	if err != nil {
		return nil, err
	}

	err = writer.WriteField("sha256", hex.EncodeToString(sha256h[:]))
	if err != nil {
		return nil, err
	}

	part, err := writer.CreateFormFile("file", filepath.Base(filename))
	if err != nil {
		return nil, err
	}
	_, err = io.Copy(part, &file)
	if err != nil {
		return nil, err
	}

	err = writer.Close()
	if err != nil {
		return nil, err
	}

	resp, err := c.cwr.ArtifactsCreateWithBodyWithResponse(ctx, c.dom, writer.FormDataContentType(), body, addAuthenticationHeader)

	if err != nil {
		return nil, err
	}

	if resp.JSON201 == nil {
		return nil, fmt.Errorf("unexpected response: %d, correlation id: %s, body: %s", resp.StatusCode(), resp.HTTPResponse.Header.Get("Correlation-Id"), string(resp.Body))
	}

	return resp.JSON201, nil
}

type MmapReader struct {
	at  *mmap.ReaderAt
	cur int
}

func (r *MmapReader) Read(p []byte) (n int, err error) {
	n, err = r.at.ReadAt(p, int64(r.cur))
	r.cur += n
	return
}

func (r *MmapReader) Reset() {
	r.cur = 0
}

func (r *MmapReader) Close() error {
	return r.at.Close()
}