Reputation: 21
I have to read a PPM file with its data encrypted (metadata is not encrypted), using Go, and the file format is given to me containing:
The "P3" magic number (read as string)
Image width (read as integer)
Image height (read as integer)
Maximum color value (read as integer)
Then, I need to read the rest of the file is the encrypted bits, which I have to read as a single byte array/slice.
e.g.:
P6
480 360
255
�š��GHFHFI�GHFHFG~EG~EG~E
...
HFD{BR�Rz�y|�vxyyhlf%8&NFzx
What is a good way to read string and integers (the 4 initial metadata values) and the rest (encrypted part) as bytes from the file? It can be the most efficient, but the cleanest (less lines) is preferred.
Upvotes: 2
Views: 5289
Reputation: 38343
You can use bufio.Reader to read the first 3 lines using the ReadLine or ReadString method and reading the rest of the file using the Read method.
After you've read the first 3 lines you can use the strings package to split the second line, and then the strconv package to parse the strings containing numbers as integers.
For example:
r := bufio.NewReader(file)
line1, err := r.ReadString('\n')
if err != nil {
panic(err)
}
// repeat to read line 2 and 3
size := strings.Split(line2, " ")
width, err := strconv.Atoi(size[0])
if err != nil {
panic(err)
}
height, err := strconv.Atoi(size[1])
if err != nil {
panic(err)
}
// repeat with line 3
Update:
As mentioned in the comments by Adrian you can use bufio.Scanner together with the bufio.ScanWord SplitFunc
to scan for the metadata.
s := bufio.NewScanner(r)
s.Split(bufio.ScanWords)
var count int
for s.Scan() && count < 4 {
switch count {
case 0:
magic = s.Text()
case 1:
if width, err = strconv.Atoi(s.Text()); err != nil {
return
}
case 2:
if height, err = strconv.Atoi(s.Text()); err != nil {
return
}
case 3:
if color, err = strconv.Atoi(s.Text()); err != nil {
return
}
}
count++
}
https://play.golang.org/p/-rOJb_WlFf
Upvotes: 1