iso9660.rs: added an error check

Added an "Incomplete download of ISO image" error check to the ISO9660 parser and a following test to verify it.

docs/release-notes.md

@@ -12,6 +12,7 @@ Major changes:
 Minor changes:
 
 - Add release notes to documentation
+- Added an error check for detecting an incomplete ISO image
 
 Internal changes:
 

src/iso9660.rs

@@ -48,8 +48,20 @@ pub struct IsoFs {
 
 impl IsoFs {
     pub fn from_file(mut file: fs::File) -> Result<Self> {
+        let length = file.metadata()?.len();
         let descriptors = get_volume_descriptors(&mut file)?;
-        Ok(Self { descriptors, file })
+        let iso_fs = IsoFs {
+            descriptors: descriptors,
+            file: file,
+        };
+        let primary_volume_descriptor = iso_fs.get_primary_volume_descriptor()?;
+        if u64::from(primary_volume_descriptor.volume_space_size) * ISO9660_SECTOR_SIZE as u64
+            > length
+        {
+            bail!("Incomplete download of the ISO Image");
+        }
+
+        Ok(iso_fs)
     }
 
     pub fn as_file(&mut self) -> Result<&mut fs::File> {
@@ -181,6 +193,7 @@ struct BootVolumeDescriptor {
 struct PrimaryVolumeDescriptor {
     system_id: String,
     volume_id: String,
+    volume_space_size: u32,
     root: Directory,
 }
 
@@ -298,13 +311,16 @@ impl PrimaryVolumeDescriptor {
             parse_iso9660_string(eat(buf, 1), 32, IsoString::StrA).context("parsing system id")?;
         let volume_id = // technically should be StrD, but non-compliance is common
             parse_iso9660_string(buf, 32, IsoString::StrA).context("parsing volume id")?;
-        let root = match get_next_directory_record(eat(buf, 156 - 72), 34, true)? {
+        eat(buf, 8); // Unused field always 0x00
+        let volume_space_size = buf.get_u32_le();
+        let root = match get_next_directory_record(eat(buf, 156 - 84), 34, true)? {
             Some(DirectoryRecord::Directory(d)) => d,
             _ => bail!("failed to parse root directory record from primary descriptor"),
         };
         Ok(Self {
             system_id,
             volume_id,
+            volume_space_size,
             root,
         })
     }
@@ -554,6 +570,7 @@ fn path_components(s: &str) -> Vec<&str> {
 mod tests {
     use super::*;
 
+    use anyhow::Error;
     use std::io::copy;
 
     use tempfile::tempfile;
@@ -567,8 +584,21 @@ mod tests {
         IsoFs::from_file(iso_file).unwrap()
     }
 
+    fn open_truncated_iso() -> Result<IsoFs, Error> {
+        let iso_bytes: &[u8] = include_bytes!("../fixtures/iso/synthetic.iso.xz");
+        let mut decoder = XzDecoder::new(iso_bytes);
+        let mut iso_file = tempfile().unwrap();
+        copy(&mut decoder, &mut iso_file).unwrap();
+        let _output = iso_file.set_len(iso_file.metadata().unwrap().len() / 2);
+        IsoFs::from_file(iso_file)
+    }
+
     #[test]
     fn test_primary_volume_descriptor() {
+        assert_eq!(
+            open_truncated_iso().unwrap_err().to_string(),
+            "Incomplete download of the ISO Image"
+        );
         let iso = open_iso();
         let desc = iso.get_primary_volume_descriptor().unwrap();
         assert_eq!(desc.system_id, "system-ID-string");