Write metadata into file

cmd/convert.go

@@ -54,7 +54,7 @@ Pass "-" as the filename to read from stdin.`,
 			output = file
 		}
 
-		result, err := epd.ConvertImage(input, width, height)
+		result, err := epd.ConvertImage(&input, width, height)
 		if err != nil {
 			log.Fatalf("Could not convert image: %v", err)
 		}

cmd/serve.go

@@ -6,10 +6,11 @@ package cmd
 
 import (
 	"fmt"
+	"io"
 	"net/http"
 
-	"github.com/gin-gonic/gin"
 	"github.com/gin-contrib/gzip"
+	"github.com/gin-gonic/gin"
 	"github.com/saunaclub/inkpot-cli/epd"
 	"github.com/spf13/cobra"
 )
@@ -47,8 +48,8 @@ A webserver to convert GIFs, PNGs and JPEGs to 4-bit grayscale images.
 
 ## Routes
 
-- POST /convert can be used to convert a file on your filesystem
-- GET /convert?url=[url] can be used to convert a file publically accessible via URL
+- PUT /convert can be used to convert a file on your filesystem
+- GET /convert takes a "url" parameter that can be used to convert a file publically accessible via http
 
 Both routes accept a "width" and a "height" parameter to configure the output size.
 If you want the response to be gzip encoded, just set the Accept-Encoding header.
@@ -107,7 +108,8 @@ func getConvert(c *gin.Context) {
 	reader := response.Body
 	defer reader.Close()
 
-	converted, err := epd.ConvertImage(reader, width, height)
+	r := io.Reader(reader)
+	converted, err := epd.ConvertImage(&r, width, height)
 	if err != nil {
 		c.Error(err)
 	}
@@ -138,14 +140,13 @@ func postConvert(c *gin.Context) {
 	if err != nil {
 		c.Error(err)
 	}
-
 	reader, err := file.Open()
 	if err != nil {
 		c.Error(err)
 	}
-	defer reader.Close()
 
-	converted, err := epd.ConvertImage(reader, width, height)
+	r := io.Reader(reader)
+	converted, err := epd.ConvertImage(&r, width, height)
 	if err != nil {
 		c.Error(err)
 	}

epd/epd.go

@@ -1,6 +1,7 @@
 package epd
 
 import (
+	"fmt"
 	"image"
 	"image/color"
 	_ "image/gif"
@@ -40,8 +41,8 @@ func fitRectInto(src *image.Rectangle, dst *image.Rectangle) image.Rectangle {
 // Converts a GIF, JPEG or PNG into a 16-color grayscale image. A single pixel
 // is represented by 4 bits and each byte holds two pixels. The final 4-bits of
 // the last byte may be discarded if width * height is odd.
-func ConvertImage(input io.Reader, width int, height int) ([]byte, error) {
-	src, _, err := image.Decode(input)
+func ConvertImage(input *io.Reader, width int, height int) ([]byte, error) {
+	src, _, err := image.Decode(*input)
 	if err != nil {
 		return nil, err
 	}
@@ -53,18 +54,21 @@ func ConvertImage(input io.Reader, width int, height int) ([]byte, error) {
 	draw.Draw(dst, dst.Bounds(), &image.Uniform{color.White}, image.ZP, draw.Src)
 	draw.CatmullRom.Scale(dst, targetRect, src, src.Bounds(), draw.Over, nil)
 
+	// we prepend information that is required to decode the image correctly in a
+  // header of ascii key-value pairs, separated by a colon and a space, one per
+  // line. the header ends with two consecutive newlines.
+	headerString := fmt.Sprintf("width: %d\nheight: %d\n\n", width, height) // remember to strconv.QuoteToASCII(headerString) if necessary
+	header := []byte(headerString)
+
 	// the actual conversion works by packing two nibbles together in a byte
 	var result = make([]byte, (width*height+1)/2)
 	for i, p := range dst.Pix {
 		res := uint8((uint16(p) + 8) / 16)
 		if i%2 == 0 {
-			result[i/2] = (res << 4)
-		} else {
-			// note that integer division makes sure we're writing at the same
-			// index for odd and even indices
+			res = res << 4
+		}
 		result[i/2] |= res
 	}
-	}
 
-	return result, nil
+	return append(header, result...), nil
 }