slideshow-api/internal/api/stream.go

package api

import (
	"errors"
	"io"
	"net/http"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"time"

	"git.velvettear.de/velvettear/loggo"
	"git.velvettear.de/velvettear/slideshow-api/internal"
	"git.velvettear.de/velvettear/slideshow-api/internal/config"
	color_thief "github.com/kennykarnama/color-thief"
)

// central streaming method for images
func streamImage(writer http.ResponseWriter, image string, resolution string) {
	if config.ConvertAvailable && config.IsValidResolution(resolution) {
		streamScaledImage(writer, image, resolution)
		return
	}
	streamUnscaledImage(writer, image)
}

// stream a color palette
func streamColorPalette(writer http.ResponseWriter, image string, amount int, algorithm string) {
	timestamp := time.Now().UnixMilli()
	var response response
	algo := 1
	algorithm = strings.ToLower(algorithm)
	if algorithm == "wu" {
		algo = 0
	}
	colors, error := color_thief.GetPaletteFromFile(image, amount, algo)
	if error != nil {
		loggo.Error("encountered an error getting the color palette from image '"+image+"'", error.Error())
		response.error = error
		response.send(writer)
		return
	}
	var palette string
	for index, color := range colors {
		if index > 0 {
			palette += "\n"
		}
		tmp := strconv.Itoa(index)
		if len(tmp) < 2 {
			tmp = "0" + tmp
		}
		tmp = "SLIDESHOW_COLOR" + tmp
		palette += tmp + "=\"" + internal.RgbToHex(color) + "\""
	}
	data := []byte(palette)
	writer.Write(data)
	loggo.InfoTimed("successfully streamed color palette for image '"+image+"'", timestamp, "size: "+internal.FormatBytes(int64(len(data))), "colors: "+strconv.Itoa(amount), "algorithm: "+algorithm)
}

// stream an unscaled image
func streamUnscaledImage(writer http.ResponseWriter, image string) {
	timestamp := time.Now().UnixMilli()
	var response response
	file, error := os.Open(image)
	if error != nil {
		loggo.Error("encountered an error opening image '"+image+"' for streaming", error.Error())
		response.error = error
		response.send(writer)
		return
	}
	defer file.Close()
	written, error := io.Copy(writer, file)
	if error != nil {
		loggo.Error("encountered an error piping image '"+image+"' to stream", error.Error())
		response.error = error
		response.send(writer)
		return
	}
	loggo.InfoTimed("successfully streamed image '"+image+"'", timestamp, "size: "+internal.FormatBytes(written))
}

// scale and stream an image
func streamScaledImage(writer http.ResponseWriter, image string, resolution string) {
	timestamp := time.Now().UnixMilli()
	var response response
	cmd := exec.Command("convert", image, "-resize", resolution+"^", "-gravity", "center", "-extent", resolution, "-")
	stdout, stdoutError := cmd.StdoutPipe()
	stderr, stderrError := cmd.StderrPipe()
	cmd.Start()
	if stdoutError != nil {
		loggo.Error("enountered an error opening imagemagicks's stdout pipe", stdoutError.Error())
		response.error = stdoutError
		response.send(writer)
		return
	}
	if stderrError != nil {
		loggo.Error("enountered an error opening imagemagicks's stderr pipe", stderrError.Error())
		response.error = stderrError
		response.send(writer)
		return
	}
	written, copyError := io.Copy(writer, stdout)
	if copyError != nil {
		loggo.Error("enountered an error piping imagemagicks's output to the stream", copyError.Error())
		response.error = copyError
		response.send(writer)
		return
	}
	if written == 0 {
		errorBytes, stderrError := io.ReadAll(stderr)
		if stderrError != nil {
			loggo.Error("enountered an error reading imagemagicks's stderr", stderrError.Error())
			response.error = stderrError
			response.send(writer)
			return
		}
		if len(errorBytes) > 0 {
			error := errors.New(strings.TrimSpace(string(errorBytes)))
			loggo.Error("enountered an error executing imagemagick", error.Error())
			response.error = error
			response.send(writer)
			return
		}
	}
	cmd.Wait()
	loggo.InfoTimed("successfully streamed scaled image '"+image+"'", timestamp, "size: "+internal.FormatBytes(written), "resolution: "+resolution)
}