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
@@ -203,12 +203,13 @@ static void prepare_context(struct cgit_context *ctx)
 	ctx->page.mimetype = "text/html";
 	ctx->page.charset = PAGE_ENCODING;
 	ctx->page.filename = NULL;
 	ctx->page.size = 0;
 	ctx->page.modified = time(NULL);
 	ctx->page.expires = ctx->page.modified;
+	ctx->page.etag = NULL;
 }
 
 struct refmatch {
 	char *req_ref;
 	char *first_ref;
 	int match;
diff --git a/cgit.h b/cgit.h
index 5f7af51..2bfbe7b 100644
--- a/cgit.h
+++ b/cgit.h
@@ -177,12 +177,13 @@ struct cgit_page {
 	time_t modified;
 	time_t expires;
 	size_t size;
 	char *mimetype;
 	char *charset;
 	char *filename;
+	char *etag;
 	char *title;
 };
 
 struct cgit_context {
 	struct cgit_query qry;
 	struct cgit_config cfg;
diff --git a/ui-plain.c b/ui-plain.c
index 5addd9e..f73cd14 100644
--- a/ui-plain.c
+++ b/ui-plain.c
@@ -31,12 +31,13 @@ static void print_object(const unsigned char *sha1, const char *path)
 		html_status(404, "Not found", 0);
 		return;
 	}
 	ctx.page.mimetype = "text/plain";
 	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);
 	match = 1;
 }
 
 static int walk_tree(const unsigned char *sha1, const char *base, int baselen,
diff --git a/ui-shared.c b/ui-shared.c
index de77bbf..86a7d29 100644
--- a/ui-shared.c
+++ b/ui-shared.c
@@ -465,12 +465,14 @@ void cgit_print_http_headers(struct cgit_context *ctx)
 		htmlf("Content-Length: %ld\n", ctx->page.size);
 	if (ctx->page.filename)
 		htmlf("Content-Disposition: inline; filename=\"%s\"\n",
 		      ctx->page.filename);
 	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");
 }
 
 void cgit_print_docstart(struct cgit_context *ctx)
 {
 	char *host = cgit_hosturl();