git: Add call-with-file-in-git utility.

* tissue/git.scm (call-with-file-in-git): New public function.

1 files changed, 10 insertions, 0 deletions

diff --git a/tissue/git.scm b/tissue/git.scm
index c7b1fcc..d557984 100644
--- a/tissue/git.scm
+++ b/tissue/git.scm
@@ -33,6 +33,7 @@
             current-git-repository
             commit-date
             git-tracked-files
+            call-with-file-in-git
             file-modification-table))
 
 ;; We bind additional functions from libgit2 that are not already
@@ -79,6 +80,15 @@ returned paths are relative to the top-level directory of REPOSITORY
 and do not have a leading slash."
   (tree-list (head-tree repository)))
 
+(define (call-with-file-in-git repository path proc)
+  "Call PROC on an input port reading contents of PATH in REPOSITORY."
+  (let* ((path-tree-entry (tree-entry-bypath (head-tree repository)
+                                             path))
+         (path-object (tree-entry->object repository path-tree-entry))
+         (blob (blob-lookup repository (object-id path-object))))
+    (call-with-port (open-bytevector-input-port (blob-content blob))
+      proc)))
+
 (define (commit-deltas repository commit)
   "Return the list of <diff-delta> objects created by COMMIT with
 respect to its first parent in REPOSITORY."