Merge pull request #87 from emielbeinema/85-read-only-header-for-check

Check header of file before loading it into memory

src/png.rs

@@ -11,7 +11,7 @@ use itertools::Itertools;
 use reduction::*;
 use std::collections::{HashMap, HashSet};
 use std::fs::File;
-use std::io::Read;
+use std::io::{Read, Seek, SeekFrom};
 use std::iter::Iterator;
 use std::path::Path;
 
@@ -195,8 +195,19 @@ impl PngData {
             Ok(f) => f,
             Err(_) => return Err(PngError::new("Failed to open file for reading")),
         };
-        let mut byte_data: Vec<u8> = Vec::new();
+        // Check file for PNG header
+        let mut header =  [0; 8];
+        if file.read_exact(&mut header).is_err() {
+            return Err(PngError::new("Not a PNG file: too small"));
+        }
+        if !file_header_is_valid(&header) {
+            return Err(PngError::new("Invalid PNG header detected"));
+        }
+        if file.seek(SeekFrom::Start(0)).is_err() {
+            return Err(PngError::new("Failed to read from file"));
+        }
         // Read raw png data into memory
+        let mut byte_data: Vec<u8> = Vec::new();
         match file.read_to_end(&mut byte_data) {
             Ok(_) => (),
             Err(_) => return Err(PngError::new("Failed to read from file")),