maraiah: rewrite machdr.rs to use Read/Seek

maraiah/file.rs

@@ -2,6 +2,7 @@
 
 use crate::err::*;
 use std::fs;
+use std::io::{SeekFrom, prelude::*};
 
 /// Confirms that the path `p` is a folder.
 pub fn validate_folder_path(p: &str) -> ResultS<()>
@@ -14,4 +15,40 @@ pub fn validate_folder_path(p: &str) -> ResultS<()>
    }
 }
 
+impl<T> Drop for SeekBackToStart<T>
+   where T: Seek
+{
+   fn drop(&mut self) {if self.fl {let _ = self.seek(SeekFrom::Start(0));}}
+}
+
+impl<T> std::ops::Deref for SeekBackToStart<T>
+   where T: Seek
+{
+   type Target = T;
+
+   fn deref(&self) -> &Self::Target {&self.sc}
+}
+
+impl<T> std::ops::DerefMut for SeekBackToStart<T>
+   where T: Seek
+{
+   fn deref_mut(&mut self) -> &mut Self::Target {&mut self.sc}
+}
+
+impl<T> SeekBackToStart<T>
+   where T: Seek
+{
+   pub fn new(sc: T) -> Self {SeekBackToStart{sc, fl: true}}
+
+   pub fn set_seek(&mut self, fl: bool) {self.fl = fl;}
+   pub fn get_seek(&self) -> bool       {self.fl}
+}
+
+/// Seeks back to the starting position of the inner object when losing scope,
+/// unless a flag is set.
+pub struct SeekBackToStart<T: Seek> {
+   sc: T,
+   fl: bool,
+}
+
 // EOF

maraiah/machdr.rs

@@ -1,50 +1,77 @@
 //! Macintosh archived format header utilities.
 
-use crate::bin::*;
+use crate::file::SeekBackToStart;
+use std::io::{SeekFrom, prelude::*};
 
-/// Checks for an `AppleSingle` header. Returns offset to the resource fork.
-pub fn check_apple_single(b: &[u8]) -> Option<usize>
+/// Checks for an Apple Single header. Returns offset to the resource fork.
+pub fn check_apple_single<R>(fp: &mut R) -> bool
+   where R: Read + Seek
 {
+   let mut fp = SeekBackToStart::new(fp);
+
+   let mut magic = [0; 8];
+   let     magic = if fp.read(&mut magic).is_ok() {magic} else {return false;};
+
    // check magic numbers
-   if b.len() < 26 || *b.get(0..8)? != [0, 5, 22, 0, 0, 2, 0, 0] {
-      return None;
+   if magic != [0, 5, 22, 0, 0, 2, 0, 0] {
+      return false;
    }
 
-   let num = usize::from(u16b(&b[24..]));
+   let mut num = [0; 2];
+   let     num = if fp.read(&mut num).is_ok() {num} else {return false;};
+   let     num = u64::from(u16::from_be_bytes(num));
 
-   if b.len() < 26 + 12 * num {
-      return None;
+   if fp.seek(SeekFrom::Start(26 + 12 * num)).is_err() |
+      fp.seek(SeekFrom::Start(26)).is_err() {
+      return false;
    }
 
    // get the resource fork (entity 1)
-   for i in 0..num {
-      let p   = 26 + 12 * i;
-      let ent = u32b(&b[p..]);
-      let ofs = usize_from_u32(u32b(&b[p + 4..]));
-      let len = usize_from_u32(u32b(&b[p + 8..]));
+   for _ in 0..num {
+      let mut ent = [0; 4];
+      let mut ofs = [0; 4];
+      let mut len = [0; 4];
+      let     ent = if fp.read(&mut ent).is_ok() {ent} else {return false;};
+      let     ofs = if fp.read(&mut ofs).is_ok() {ofs} else {return false;};
+      let     len = if fp.read(&mut len).is_ok() {len} else {return false;};
+      let     ent = u32::from_be_bytes(ent);
+      let     ofs = u64::from(u32::from_be_bytes(ofs));
+      let     len = u64::from(u32::from_be_bytes(len));
 
       if ent == 1 {
-         return if ofs + len > b.len() {None} else {Some(ofs)};
+         if fp.seek(SeekFrom::Start(ofs + len)).is_ok() &
+            fp.seek(SeekFrom::Start(ofs)).is_ok() {
+            fp.set_seek(false);
+            return true;
+         } else {
+            return false;
+         }
       }
    }
 
    // no resource fork
-   None
+   false
 }
 
-/// Checks for a `MacBinary II` header. Returns offset to the resource fork.
-pub fn check_macbin(b: &[u8]) -> Option<usize>
+/// Checks for a Mac Binary II header. Returns offset to the resource fork.
+pub fn check_macbin<R>(fp: &mut R) -> bool
+   where R: Read + Seek
 {
-   // check legacy version, length, zero fill, and macbin2 version
-   // I swear this isn't *completely* magic
-   if b.len() < 128 || b[0] != 0 || b[1] > 63 || b[74] != 0 || b[123] > 129 {
-      return None;
+   let mut fp = SeekBackToStart::new(fp);
+
+   let mut head = [0; 128];
+   let     head = if fp.read(&mut head).is_ok() {head} else {return false;};
+
+   // check legacy version, length, zero fill, and macbin2 version. I swear,
+   // this isn't *completely* magic
+   if head[0] != 0 || head[1] > 63 || head[74] != 0 || head[123] > 129 {
+      return false;
    }
 
    let mut crc = 0;
 
    // check header crc
-   for &byte in b.iter().take(124) {
+   for &byte in head.iter().take(124) {
       for j in 8..16 {
          let d = u16::from(byte) << j;
 
@@ -57,22 +84,32 @@ pub fn check_macbin(b: &[u8]) -> Option<usize>
    }
 
    // if ok, resource fork follows
-   if crc == u16b(&b[124..]) {
-      Some(128)
+   if crc == u16::from_be_bytes([head[124], head[125]]) {
+      fp.set_seek(false);
+      true
    } else {
-      None
+      false
    }
 }
 
 /// Reads a `MacBin` or `AppleSingle` header if there is one and returns the
 /// offset from the start of the header to the resource fork (if one is found.)
-pub fn try_mac_header(b: &[u8]) -> usize
+pub fn try_mac_header<R>(fp: &mut R) -> bool
+   where R: Read + Seek
 {
-   if let Some(ofs) = check_macbin(b) {
-      ofs
-   } else {
-      check_apple_single(b).unwrap_or(0)
+   if check_macbin(fp) {
+      return true;
    }
+
+   let _ = fp.seek(SeekFrom::Start(0));
+
+   if check_apple_single(fp) {
+      return true;
+   }
+
+   let _ = fp.seek(SeekFrom::Start(0));
+
+   false
 }
 
 // EOF

tests/misc.rs

@@ -7,8 +7,10 @@ fn machdr_must_process()
 {
    const INPUT: &[u8] = include_bytes!("data/misc/macbin.in");
 
-   assert_eq!(machdr::check_macbin(INPUT), Some(128));
-   assert_eq!(machdr::try_mac_header(INPUT), 128);
+   let mut inp = std::io::Cursor::new(INPUT);
+
+   assert_eq!(machdr::check_macbin(&mut inp),   true);
+   assert_eq!(machdr::try_mac_header(&mut inp), true);
 
    // FIXME: missing test data for applesingle
 }
@@ -16,10 +18,11 @@ fn machdr_must_process()
 #[test]
 fn machdr_must_not_process()
 {
-   for inp in &RANDOM {
-      assert_eq!(machdr::check_macbin(inp), None);
-      assert_eq!(machdr::check_apple_single(inp), None);
-      assert_eq!(machdr::try_mac_header(inp), 0);
+   for rinp in &RANDOM {
+      let mut inp = std::io::Cursor::new(rinp);
+      assert_eq!(machdr::check_macbin(&mut inp), false);
+      assert_eq!(machdr::check_apple_single(&mut inp), false);
+      assert_eq!(machdr::try_mac_header(&mut inp), false);
    }
 }