Allow parsing off-spec PDF files with prefixes before the header (#362)

src/parser/mod.rs

@@ -8,7 +8,7 @@ use std::collections::HashSet;
 use std::str::{self, FromStr};
 
 use nom::branch::alt;
-use nom::bytes::complete::{tag, take, take_while, take_while1, take_while_m_n};
+use nom::bytes::complete::{tag, take, take_until, take_while, take_while1, take_while_m_n};
 use nom::character::complete::multispace1;
 use nom::character::complete::{digit0, digit1, one_of};
 use nom::character::complete::{space0, space1};
@@ -416,7 +416,16 @@ fn _indirect_object<'a>(
 pub fn header(input: ParserInput) -> Option<String> {
     strip_nom(map_res(
         delimited(
-            tag(b"%PDF-"),
+            tuple((
+                map_res(take_until("%PDF-"), |v: ParserInput| {
+                    if v.len() > 1024 {
+                        return Err("Header prefix too long");
+                    }
+
+                    Ok(v)
+                }),
+                tag(b"%PDF-"),
+            )),
             take_while(|c: u8| !b"\r\n".contains(&c)),
             pair(eol, many0_count(comment)),
         ),
@@ -632,6 +641,22 @@ mod tests {
         assert_eq!(real(test_span(b"10.")), Some(10.0));
     }
 
+    #[test]
+    fn parses_malformed_header_with_prefix() {
+        let stream = b"\x20\x20\x20\x20\x0A\x0A\x20\x20%PDF-1.4\n";
+
+        assert_eq!(header(test_span(stream)), Some("1.4".to_string()));
+
+        // 1025 bytes prefix
+        let stream_with_prefix_too_long = [b' '; 1025]
+            .iter()
+            .copied()
+            .chain(b"%PDF-1.4".iter().copied())
+            .collect::<Vec<u8>>();
+
+        assert_eq!(header(test_span(&stream_with_prefix_too_long)), None)
+    }
+
     #[test]
     fn parse_string() {
         let literal_string = |i| tstrip(literal_string(i));