1use crate::util::*;
2use crate::{ImageResult, ImageSize};
3
4use std::io::{self, BufRead, Seek, SeekFrom};
5
6pub fn size<R: BufRead + Seek>(reader: &mut R) -> ImageResult<ImageSize> {
7 reader.seek(SeekFrom::Start(2))?;
8
9 // We try to loop until we find a line that does not start with a comment
10 // or is empty. After that, we should expect width and height back to back
11 // separated by an arbitrary amount of whitespace.
12 loop {
13 // Lines can be arbitrarily long, but 1k is a good enough cap I think.
14 // Anything higher and I blame whoever made the file.
15 let line = read_until_whitespace(reader, 1024)?;
16 let trimmed_line = line.trim();
17
18 // If it's a comment, skip until newline
19 if trimmed_line.starts_with('#') {
20 read_until_capped(reader, b'\n', 1024)?;
21 continue;
22 }
23
24 // If it's just empty skip
25 if trimmed_line.is_empty() {
26 continue;
27 }
28
29 // The first thing we read that isn't empty or a comment should be the width
30 let raw_width = line;
31
32 // Read in the next non-whitespace section as the height
33 let line = read_until_whitespace(reader, 1024)?;
34 let raw_height = line.trim();
35
36 // Try to parse the width and height
37 let width_parsed = raw_width.parse::<usize>().ok();
38 let height_parsed = raw_height.parse::<usize>().ok();
39
40 // If successful return it
41 if let (Some(width), Some(height)) = (width_parsed, height_parsed) {
42 return Ok(ImageSize { width, height });
43 }
44
45 // If no successful then assume that it cannot be read
46 // If this happens we need to gather test files for those cases
47 break;
48 }
49
50 Err(io::Error::new(io::ErrorKind::InvalidData, "PNM dimensions not found").into())
51}
52
53pub fn matches(header: &[u8]) -> bool {
54 if header[0] != b'P' {
55 return false;
56 }
57
58 // We only support P1 to P6. Currently ignoring P7, PF, PFM
59 if header[1] < b'1' || header[1] > b'6' {
60 return false;
61 }
62
63 true
64}
65