Add support for ETag in 'plain' view

When downloading a blob identified by its path, the client might want
to know if the blob has been modified since a previous download of the
same path. To this end, an ETag containing the blob SHA1 seems to be
ideal.

Todo: add support for HEAD requests...

Suggested-by: Owen Taylor <otaylor@redhat.com>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

4 files changed, 5 insertions, 0 deletions

diff --git a/cgit.c b/cgit.c
index 64d95f9..411e421 100644
--- a/cgit.c
+++ b/cgit.c
@@ -207,4 +207,5 @@ static void prepare_context(struct cgit_context *ctx)
 	ctx->page.modified = time(NULL);
 	ctx->page.expires = ctx->page.modified;
+	ctx->page.etag = NULL;
 }
 
diff --git a/cgit.h b/cgit.h
index 5f7af51..2bfbe7b 100644
--- a/cgit.h
+++ b/cgit.h
@@ -181,4 +181,5 @@ struct cgit_page {
 	char *charset;
 	char *filename;
+	char *etag;
 	char *title;
 };
diff --git a/ui-plain.c b/ui-plain.c
index 5addd9e..f73cd14 100644
--- a/ui-plain.c
+++ b/ui-plain.c
@@ -35,4 +35,5 @@ static void print_object(const unsigned char *sha1, const char *path)
 	ctx.page.filename = fmt("%s", path);
 	ctx.page.size = size;
+	ctx.page.etag = sha1_to_hex(sha1);
 	cgit_print_http_headers(&ctx);
 	html_raw(buf, size);
diff --git a/ui-shared.c b/ui-shared.c
index de77bbf..86a7d29 100644
--- a/ui-shared.c
+++ b/ui-shared.c
@@ -469,4 +469,6 @@ void cgit_print_http_headers(struct cgit_context *ctx)
 	htmlf("Last-Modified: %s\n", http_date(ctx->page.modified));
 	htmlf("Expires: %s\n", http_date(ctx->page.expires));
+	if (ctx->page.etag)
+		htmlf("ETag: \"%s\"\n", ctx->page.etag);
 	html("\n");
 }