rage-mount: Add support for mounting an encrypted file

This behaves similarly to `mount --bind source_file target_file`, except
that `source_file` is transparently decrypted, and `target_file` is
created as a symbolic link instead of a bind-mount.

Part of #188.

rage/Cargo.toml

@@ -57,9 +57,12 @@ rust-embed = "5"
 secrecy = "0.7"
 
 # rage-mount dependencies
+ctrlc = { version = "3.1.7", optional = true }
 fuse_mt = { version = "0.5.1", optional = true }
 libc = { version = "0.2", optional = true }
+nix = { version = "0.18", optional = true }
 tar = { version = "0.4", optional = true }
+tempfile = { version = "3.2", optional = true }
 time = { version = "0.1", optional = true }
 zip = { version = "0.5.9", optional = true }
 
@@ -71,7 +74,7 @@ man = "0.3"
 
 [features]
 default = ["ssh"]
-mount = ["fuse_mt", "libc", "tar", "time", "zip"]
+mount = ["ctrlc", "fuse_mt", "libc", "nix", "tar", "tempfile", "time", "zip"]
 ssh = ["age/ssh"]
 unstable = ["age/unstable"]
 

rage/examples/generate-docs.rs

@@ -176,7 +176,7 @@ fn rage_mount_page() {
             Flag::new()
                 .short("-t")
                 .long("--types")
-                .help("The type of the filesystem (one of \"tar\", \"zip\")."),
+                .help("The type of the filesystem (one of \"file\", \"tar\", \"zip\")."),
         )
         .option(
             Opt::new("IDENTITY")
@@ -186,6 +186,11 @@ fn rage_mount_page() {
         )
         .arg(Arg::new("filename"))
         .arg(Arg::new("mountpoint"))
+        .example(
+            Example::new()
+                .text("Mounting an encrypted file to a recipient")
+                .command("rage-mount -t file -i key.txt encrypted.txt.age decrypted.txt"),
+        )
         .example(
             Example::new()
                 .text("Mounting an archive encrypted to a recipient")

rage/i18n/en-US/rage.ftl

@@ -134,6 +134,7 @@ info-mounting-as-fuse = Mounting as FUSE filesystem
 err-mnt-missing-filename = Missing filename.
 err-mnt-missing-mountpoint = Missing mountpoint.
 err-mnt-missing-types = Missing {-flag-mnt-types}.
+err-mnt-must-be-file = Mountpoint must be a file.
 err-mnt-unknown-type = Unknown filesystem type "{$fs_type}"
 
 ## Unstable features