fix(parser): accept trailing space before EOL in xref and startxref lines

Some PDF generators emit trailing spaces on structural lines like
"xref \n" and "startxref \n". The xref subsection header already
handled this with opt(tag(" ")), but the xref keyword and startxref
keyword parsers did not, causing Xref(Start) errors on valid PDFs.

Author: abimaelmartell

src/parser/mod.rs

@@ -458,7 +458,7 @@ fn xref(input: ParserInput) -> NomResult<Xref> {
     );
 
     delimited(
-        pair(tag(&b"xref"[..]), eol),
+        pair(tag(&b"xref"[..]), preceded(opt(tag(&b" "[..])), eol)),
         fold_many1(
             xref_section,
             || -> Xref { Xref::new(0, XrefType::CrossReferenceTable) },
@@ -512,7 +512,7 @@ pub fn xref_and_trailer(input: ParserInput, reader: &Reader) -> crate::Result<(X
 
 pub fn xref_start(input: ParserInput) -> Option<i64> {
     strip_nom(delimited(
-        pair(tag(&b"startxref"[..]), eol),
+        pair(tag(&b"startxref"[..]), preceded(opt(tag(&b" "[..])), eol)),
         trim_spaces(integer),
         (eol, tag(&b"%%EOF"[..]), space),
     ).parse(input))
@@ -903,4 +903,24 @@ EI";
             b"00000z0z00zzz00z0zzz0zzzEI aazazaazzzaazazzzazzz"
         )
     }
+
+    #[test]
+    fn xref_trailing_space_after_keyword() {
+        // Some PDF generators emit "xref \n" with a trailing space.
+        let input = b"xref \n0 3\n0000000000 65535 f \n0000000017 00000 n \n0000000081 00000 n \ntrailer\n<</Size 3/Root 1 0 R>>\nstartxref\n175\n%%EOF\n";
+        match xref(test_span(input)) {
+            Ok((_, re)) => assert_eq!(re.entries.len(), 2),
+            Err(err) => panic!("xref with trailing space should parse: {:?}", err),
+        }
+    }
+
+    #[test]
+    fn startxref_trailing_space_after_keyword() {
+        // Some PDF generators emit "startxref \n" with a trailing space.
+        let input = b"startxref \n135738\n%%EOF\n";
+        match xref_start(test_span(input)) {
+            Some(num) => assert_eq!(num, 135738),
+            None => panic!("startxref with trailing space should parse"),
+        }
+    }
 }