ripple/fossil/mount: don't serve short reads

FUSE doesn't actually respect the usual read() contract, so this
resulted in us serving truncated files.

Change-Id: I8bdb0bd7f03162fb78774f3f84daeefc5ba5e3b1

1 files changed, 21 insertions, 2 deletions

diff --git a/ripple/fossil/src/bin/mount.rs b/ripple/fossil/src/bin/mount.rs
index 3335c1f..2e6945b 100644
--- a/ripple/fossil/src/bin/mount.rs
+++ b/ripple/fossil/src/bin/mount.rs
@@ -215,8 +215,27 @@ impl fuser::Filesystem for Filesystem {
 					offset as u64
 				);
 
-				let mut buffer = vec![0; size];
-				let n = contents.read(&mut buffer).unwrap();
+				// NOTE: FUSE read() doesn't actually work like you expect.
+				// If you return a short read, it *will* simply treat that
+				// as the file being short. `contents` is an `io::Read`,
+				// which adheres to the usual contract, so we partially
+				// reimplement `read_exact` here.
+				let mut buffer = vec![0u8; size];
+				let n = {
+					let mut buffer = &mut buffer[..];
+					let mut total = 0;
+					loop {
+						match contents.read(buffer).unwrap() {
+							0 => break,
+							n => {
+								buffer = &mut buffer[n..];
+								total += n;
+							}
+						}
+					}
+					total
+				};
+
 				reply.data(&buffer[..n]);
 			}
 			_ => reply.error(EINVAL),