debian: fix deb822 writer/parser asymmetries

write_paragraph emitted a bare-space continuation line for empty lines
inside a value, which parse_paragraphs treated as a paragraph separator
and silently dropped the rest of the value; blank lines are now encoded
as ' .' like dpkg does and decoded back on read. Tab-indented
continuation lines now strip exactly one tab instead of keeping it.

Clearsigned .dsc content no longer leaks armor metadata into parsed
fields: the Hash:/Comment: header and the signature trailer are
stripped before parse_paragraphs at both .dsc parse sites.

src/build/binary.rs

@@ -390,7 +390,9 @@ fn include_dsc_artifacts(
     checksums: &mut FileChecksums,
 ) -> Result<(), Box<dyn Error>> {
     let dsc_content = ctx.read_file(&upload_dir.join(dsc_name))?;
-    let para = crate::debian::control::parse_paragraphs(&dsc_content)
+    let para = crate::debian::control::parse_paragraphs(
+        crate::debian::control::strip_clearsigned_armour(&dsc_content),
+    )
     .into_iter()
     .next()
     .ok_or_else(|| format!("'{dsc_name}' is empty"))?;

src/build/mod.rs

@@ -376,7 +376,9 @@ pub fn run_source_build(
     // order the .dsc itself lists them.
     let dsc_content = std::fs::read_to_string(&ref_dsc_path)
         .map_err(|e| format!("cannot read '{}': {}", ref_dsc_path.display(), e))?;
-    let dsc_para = parse_paragraphs(&dsc_content)
+    let dsc_para = parse_paragraphs(crate::debian::control::strip_clearsigned_armour(
+        &dsc_content,
+    ))
     .into_iter()
     .next()
     .ok_or_else(|| format!("'{}' is empty", ref_dsc_path.display()))?;

src/debian/control.rs

@@ -12,7 +12,9 @@ use std::path::Path;
 ///
 /// Values are stored with continuation-line breaks as `\n` and without the
 /// leading whitespace of continuation lines. Serialization re-adds a single
-/// leading space in front of every continuation line, matching dpkg output.
+/// leading space in front of every continuation line, matching dpkg output;
+/// blank lines inside a value are encoded as ` .` (and decoded back) so they
+/// survive a write/parse round-trip.
 #[derive(Debug, Clone, Default, PartialEq)]
 pub struct Paragraph {
     fields: Vec<(String, String)>,
@@ -66,7 +68,9 @@ impl Paragraph {
 ///
 /// Comment lines (starting with `#`) are ignored. Blank lines separate
 /// paragraphs. Continuation lines must start with a space or a tab; exactly
-/// one leading space (or tab) is stripped from the stored value.
+/// one leading space (or tab) is stripped from the stored value, and a
+/// continuation whose content is a lone `.` decodes to an empty line
+/// (dpkg's encoding for blank lines inside field values).
 pub fn parse_paragraphs(input: &str) -> Vec<Paragraph> {
     let mut paragraphs = Vec::new();
     let mut current = Paragraph::new();
@@ -89,7 +93,14 @@ pub fn parse_paragraphs(input: &str) -> Vec<Paragraph> {
 
         // Continuation line
         if line.starts_with(' ') || line.starts_with('\t') {
-            let content = line.strip_prefix(' ').unwrap_or(line);
+            // Exactly one leading space or tab is stripped.
+            let content = line
+                .strip_prefix(' ')
+                .or_else(|| line.strip_prefix('\t'))
+                .unwrap_or(line);
+            // dpkg encodes a blank line inside a value as a lone `.` after
+            // the leading whitespace; mirror that on read.
+            let content = if content == "." { "" } else { content };
             if let Some(field) = &last_field
                 && let Some((_, v)) = current
                     .fields
@@ -147,14 +158,65 @@ pub fn write_paragraph(p: &Paragraph) -> String {
         }
         for line in lines {
             out.push('\n');
+            if line.is_empty() {
+                // dpkg encodes a blank line inside a value as ` .`; writing a
+                // bare continuation line would be mistaken for a paragraph
+                // separator on re-parse and silently drop the rest.
+                out.push_str(" .");
+            } else {
                 out.push(' ');
                 out.push_str(line);
             }
+        }
         out.push('\n');
     }
     out
 }
 
+/// Return the signed body of a clearsigned message, as a slice of `text`.
+///
+/// If `text` starts with the OpenPGP clearsigned-marker line, the armor
+/// header block (the `Hash: ...` line and any `Comment:` lines, up to and
+/// including the blank line that closes the header) is skipped, and the
+/// result is cut at the `-----BEGIN PGP SIGNATURE-----` marker so the
+/// signature trailer is dropped as well. This keeps the armor metadata from
+/// being parsed as deb822 fields (`Hash:` would otherwise land in the first
+/// stanza and `Comment:` in the last one).
+///
+/// Input that is not clearsigned is returned unchanged, so callers can apply
+/// this unconditionally before parsing.
+pub fn strip_clearsigned_armour(text: &str) -> &str {
+    const BEGIN_SIGNED: &str = "-----BEGIN PGP SIGNED MESSAGE-----";
+    const BEGIN_SIGNATURE: &str = "-----BEGIN PGP SIGNATURE-----";
+
+    if !text.starts_with(BEGIN_SIGNED) {
+        return text;
+    }
+
+    // Walk past the armor headers to the blank line that precedes the body.
+    let mut body = text;
+    loop {
+        match body.split_once('\n') {
+            Some((line, remainder)) => {
+                body = remainder;
+                // An empty line ends the armor header block (`\r` covers a
+                // CRLF-terminated blank line).
+                if line.is_empty() || line == "\r" {
+                    break;
+                }
+            }
+            // Malformed armor: no body at all.
+            None => return "",
+        }
+    }
+
+    // Cut off the signature block, if present.
+    match body.find(BEGIN_SIGNATURE) {
+        Some(i) => &body[..i],
+        None => body,
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -197,6 +259,75 @@ mod tests {
         assert_eq!(reparsed[0].get("Description"), Some(value));
     }
 
+    #[test]
+    fn blank_lines_survive_roundtrip() {
+        let mut p = Paragraph::new();
+        p.set("Description", "a\n\nb");
+        let text = write_paragraph(&p);
+        // dpkg encoding: a blank line inside a value is written as ` .`.
+        assert_eq!(text, "Description: a\n .\n b\n");
+        // parse -> write -> parse must not lose data.
+        let reparsed = parse_paragraphs(&text);
+        assert_eq!(reparsed[0].get("Description"), Some("a\n\nb"));
+        assert_eq!(
+            parse_paragraphs(&write_paragraph(&reparsed[0]))[0].get("Description"),
+            Some("a\n\nb")
+        );
+    }
+
+    #[test]
+    fn parse_lone_dot_continuation_is_blank_line() {
+        let paras = parse_paragraphs("Description:\n a\n .\n b\n");
+        assert_eq!(paras[0].get("Description"), Some("\na\n\nb"));
+    }
+
+    #[test]
+    fn tab_continuation_strips_exactly_one_tab() {
+        let paras = parse_paragraphs("Description: a\n\tb\n\t\tdeep\n");
+        assert_eq!(paras[0].get("Description"), Some("a\nb\n\tdeep"));
+    }
+
+    #[test]
+    fn strip_armour_extracts_signed_dsc_body() {
+        let signed = "\
+-----BEGIN PGP SIGNED MESSAGE-----
+Hash: SHA256
+
+Format: 3.0 (native)
+Source: hello
+Binary: hello
+Architecture: any
+Version: 1.0-1
+Checksums-Sha256:
+ abc 100 hello_1.0.tar.gz
+
+-----BEGIN PGP SIGNATURE-----
+
+iQEcBAABCgAGBQJabcdAAoJEL abc
+-----END PGP SIGNATURE-----
+";
+        let body = strip_clearsigned_armour(signed);
+        assert!(body.starts_with("Format:"));
+        assert!(!body.contains("SIGNATURE"));
+        let paras = parse_paragraphs(body);
+        assert_eq!(paras.len(), 1);
+        // The armor `Hash:` header must not land in the stanza...
+        assert!(paras[0].get("Hash").is_none());
+        assert_eq!(paras[0].get("Source"), Some("hello"));
+        // ...and the signature trailer must not contribute a `Comment:` field.
+        assert!(paras[0].get("Comment").is_none());
+        assert_eq!(
+            paras[0].get("Checksums-Sha256"),
+            Some("\nabc 100 hello_1.0.tar.gz")
+        );
+    }
+
+    #[test]
+    fn strip_armour_passes_unsigned_text_through() {
+        let plain = "Source: hello\nVersion: 1.0\n";
+        assert_eq!(strip_clearsigned_armour(plain), plain);
+    }
+
     #[test]
     fn set_replaces_case_insensitive() {
         let mut p = Paragraph::new();

src/debian/mod.rs

@@ -24,6 +24,8 @@ pub use changelog::{
     parse_previous_version_from_str,
 };
 pub use checksums::{Entry as ChecksumEntry, FileChecksums};
-pub use control::{ControlInfo, Paragraph, parse_paragraphs, write_paragraph};
+pub use control::{
+    ControlInfo, Paragraph, parse_paragraphs, strip_clearsigned_armour, write_paragraph,
+};
 pub use files::{FilesEntry, FilesList};
 pub use version::DebianVersion;