Added support for git-remote-gcrypt's rsync URIs

Which access a remote using rsync over ssh, and which git pushes to much
more efficiently than ssh urls.

There was some old partial support for rsync URIs from 2013, but it seemed
incomplete, and did not use rsync over ssh. Weird.

I'm not sure if there's any remaining benefit to using the non-rsync url
forms with gcrypt, now that this is implemented? Updated docs to encourage
using the rsync urls.

This commit was sponsored by Svenne Krap on Patreon.

doc/bugs/gcrypt_remote__58___every_sync_uploads_huge_manifest.mdwn

@@ -28,3 +28,5 @@ is running. The upload of the actual changeset starts after this, the processes
 git-annex is great and revolutionized my file organization and backup structure (if they were even existing before)
 
 [[!meta title="gcrypt special remotes should support rsync:// and perhaps also sftp://"]]
+
+> [[done]] --[[Joey]]

doc/bugs/gcrypt_remote__58___every_sync_uploads_huge_manifest/comment_10_83ea673f86450a856889b8fbb894bb4b._comment

@@ -0,0 +1,24 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 10"""
+ date="2021-03-09T18:10:38Z"
+ content="""
+Actually, it supports rsync urls already. But git-annex treats the url as
+literally the rsync protocol, so it will run rsync with an url like
+rsync://localhost/foo. Which will mostly fail unless there's actually a
+rsync server running.
+git-remote-gcrypt treats the same url as rsync over ssh.
+
+See [[!commit 3e079cdcd1ac4f52ceb1c3ad483917d7c6133d0b]] for when that was
+added in 2013. Although I'm doubtful if it actually worked; it seems like
+initremote supported it, but it was never implemented the rest of
+the way.
+
+If anyone has been using that, it seems git-annex and git-remote-gcrypt
+would be accessing the server in different ways, so the same server must
+support rsync over ssh too, or git pushes to the remote would fail. So, it
+seems all that's needed is for git-annex to treat that url as rsync over
+ssh, and finish the incomplete implementation of rsync urls.
+
+Ok, done!
+"""]]

doc/special_remotes/gcrypt.mdwn

@@ -26,10 +26,21 @@ gcrypt:
   repository itself. May be repeated when multiple participants
   should have access to the repository.
 
-* `gitrepo` - Required. The path or url to the git repository
+* `gitrepo` - Required. The location of the git repository
   for gcrypt to use. This repository should be either an unpopulated
   bare git repo, or an existing gcrypt repository.
 
+  To use a local git repository, use: `gitrepo=/path/to/repo`
+
+  For a git repository accessed using rsync over ssh, use:
+  `gitrepo=rsync://user@host/path/to/repo`
+
+  For a git repository accessed over ssh, and using git-annex-shell
+  to transfer data, use:
+  `gitrepo=ssh://user@host/path/to/repo` or `host:path`  
+  Note that each `git push` has to re-send the whole content of the git
+  repository when using this option.
+
 * `chunk` - Enables [[chunking]] when storing large files.
 
 * `shellescape` - See [[rsync]] for the details of this option.
@@ -37,9 +48,7 @@ gcrypt:
 ## notes
 
 For git-annex to store files in a repository on a remote server, you need
-shell access, and `rsync` must be installed. Those are the minimum
-requirements, but it's also recommended to install git-annex on the remote
-server, so that [[git-annex-shell]] can be used.
+shell access, and it needs to be able to run `rsync` or `git-annex-shell`.
 
 If you can't run `rsync` or `git-annex-shell` on the remote server,
 you can't use this special remote. Other options are the [[git-lfs]]

doc/tips/fully_encrypted_git_repositories_with_gcrypt.mdwn

@@ -66,9 +66,9 @@ the gpg key used to encrypt it, and then:
 
 ## encrypted git-annex repository on a ssh server
 
-If you have a ssh server that has git-annex or rsync installed on it, you
-can set up an encrypted repository there. Works just like the encrypted
-drive except without the cable.
+If you have a server that has ssh and rsync installed on it, you can set up an
+encrypted repository there. Works just like the encrypted drive except
+without the cable.
 
 First, on the server, run:
 
@@ -76,14 +76,14 @@ First, on the server, run:
 
 Now, in your existing git-annex repository, set up the encrypted remote:
 
-	git annex initremote encryptedrepo type=gcrypt gitrepo=ssh://my.server/home/me/encryptedrepo keyid=$mykey
+	git annex initremote encryptedrepo type=gcrypt gitrepo=rsync://my.server/home/me/encryptedrepo keyid=$mykey
 	git annex sync encryptedrepo
 
 (Remember to replace "$mykey" with the keyid of your gpg key.)
 
 This uses the [[gcrypt special remote|special_remotes/gcrypt]] to encrypt
 pushes to the git remote, and git-annex will also encrypt the files it
-stores there.
+stores there. Data is transferred using rsync over ssh.
 
 If you're going to be sharing this repository with others, be sure to also
 include their keyids, by specifying keyid= repeatedly.
@@ -98,9 +98,9 @@ the git repository changes to it as well.
 Anyone who has access to the repo it and has one of the keys
 used to encrypt it can check it out:
 
-	git clone gcrypt::ssh://my.server/home/me/encryptedrepo myrepo
+	git clone gcrypt::rsync://my.server/home/me/encryptedrepo myrepo
 	cd myrepo
-	git annex enableremote encryptedrepo gitrepo=ssh://my.server/home/me/encryptedrepo
+	git annex enableremote encryptedrepo gitrepo=rsync://my.server/home/me/encryptedrepo
 	git annex get --from encryptedrepo
 
 ## private encrypted git remote on a git-lfs hosting site