first attempts to roundtrip signatures shows I parse it wrongly :D

The free space is part of the signature, not some sort of marker

Author: Byron

git-object/src/borrowed/commit.rs

@@ -51,7 +51,7 @@ pub fn parse(i: &[u8]) -> IResult<&[u8], Commit, Error> {
     let (i, encoding) =
         opt(|i| parse::header_field(i, b"encoding", is_not(NL)))(i).map_err(Error::context("encoding <encoding>"))?;
     let (i, pgp_signature) = opt(alt((
-        |i| parse::header_field_multi_line(i, b"gpgsig").map(|(i, o)| (i, Cow::Borrowed(o.as_bstr()))),
+        |i| parse::header_field_multi_line(i, b"gpgsig").map(|(i, o)| (i, Cow::Owned(o))),
         |i| parse::header_field(i, b"gpgsig", is_not(NL)).map(|(i, o)| (i, Cow::Borrowed(o.as_bstr()))),
     )))(i)
     .map_err(Error::context("gpg <signature>"))?;

git-object/src/borrowed/parse.rs

@@ -1,7 +1,8 @@
 use crate::{
     borrowed::{Error, Signature},
-    BStr, ByteSlice, Sign, Time,
+    ByteSlice, Sign, Time,
 };
+use bstr::{BStr, BString, ByteVec};
 use btoi::btoi;
 use nom::{
     branch::alt,
@@ -16,7 +17,7 @@ use nom::{
 pub(crate) const NL: &[u8] = b"\n";
 pub(crate) const SPACE: &[u8] = b" ";
 
-pub(crate) fn header_field_multi_line<'a>(i: &'a [u8], name: &'static [u8]) -> IResult<&'a [u8], &'a [u8], Error> {
+pub(crate) fn header_field_multi_line<'a>(i: &'a [u8], name: &'static [u8]) -> IResult<&'a [u8], BString, Error> {
     let (i, o) = peek(preceded(
         terminated(tag(name), tag(SPACE)),
         recognize(tuple((
@@ -28,7 +29,17 @@ pub(crate) fn header_field_multi_line<'a>(i: &'a [u8], name: &'static [u8]) -> I
     assert!(!o.is_empty());
     let end = &o[o.len() - 1] as *const u8 as usize;
     let start_input = &i[0] as *const u8 as usize;
-    Ok((&i[end - start_input + 1..], &o[..o.len() - 1]))
+
+    let bytes = o[..o.len() - 1].as_bstr();
+    let mut out = BString::from(Vec::with_capacity(bytes.len()));
+    let mut lines = bytes.lines();
+    out.push_str(lines.next().expect("first line"));
+    drop(lines.next()); // empty newline marker
+    for line in lines {
+        out.push(b'\n');
+        out.push_str(&line[1..]); // cut leading space
+    }
+    Ok((&i[end - start_input + 1..], out))
 }
 
 pub(crate) fn header_field<'a, T>(

git-object/src/owned/ser.rs

@@ -24,6 +24,7 @@ impl Into<io::Error> for Error {
 pub fn header_field_multi_line(name: &[u8], value: &[u8], mut out: impl io::Write) -> io::Result<()> {
     let mut lines = value.as_bstr().lines();
     trusted_header_field(name, lines.next().expect("non-empty value"), &mut out)?;
+    out.write_all(NL)?;
     for line in lines {
         out.write_all(SPACE)?;
         out.write_all(line)?;