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
@@ -193,32 +193,33 @@ static void prepare_context(struct cgit_context *ctx)
         ctx->cfg.max_stats = 0;
         ctx->cfg.module_link = "./?repo=%s&page=commit&id=%s";
         ctx->cfg.renamelimit = -1;
         ctx->cfg.robots = "index, nofollow";
         ctx->cfg.root_title = "Git repository browser";
         ctx->cfg.root_desc = "a fast webinterface for the git dscm";
         ctx->cfg.script_name = CGIT_SCRIPT_NAME;
         ctx->cfg.summary_branches = 10;
         ctx->cfg.summary_log = 10;
         ctx->cfg.summary_tags = 10;
         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;
 };
 
 int find_current_ref(const char *refname, const unsigned char *sha1,
                      int flags, void *cb_data)
 {
         struct refmatch *info;
 
         info = (struct refmatch *)cb_data;
         if (!strcmp(refname, info->req_ref))
                 info->match = 1;
diff --git a/cgit.h b/cgit.h
index 5f7af51..2bfbe7b 100644
--- a/cgit.h
+++ b/cgit.h
@@ -167,32 +167,33 @@ struct cgit_config {
         int max_stats;
         int nocache;
         int renamelimit;
         int snapshots;
         int summary_branches;
         int summary_log;
         int summary_tags;
 };
 
 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;
         struct cgit_repo *repo;
         struct cgit_page page;
 };
 
 struct cgit_snapshot_format {
         const char *suffix;
         const char *mimetype;
         write_archive_fn_t write_func;
         int bit;
 };
diff --git a/ui-plain.c b/ui-plain.c
index 5addd9e..f73cd14 100644
--- a/ui-plain.c
+++ b/ui-plain.c
@@ -21,32 +21,33 @@ static void print_object(const unsigned char *sha1, const char *path)
         unsigned long size;
 
         type = sha1_object_info(sha1, &size);
         if (type == OBJ_BAD) {
                 html_status(404, "Not found", 0);
                 return;
         }
 
         buf = read_sha1_file(sha1, &type, &size);
         if (!buf) {
                 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,
                      const char *pathname, unsigned mode, int stage,
                      void *cbdata)
 {
         if (S_ISDIR(mode))
                 return READ_TREE_RECURSIVE;
 
         if (S_ISREG(mode))
                 print_object(sha1, pathname);
 
         return 0;
diff --git a/ui-shared.c b/ui-shared.c
index de77bbf..86a7d29 100644
--- a/ui-shared.c
+++ b/ui-shared.c
@@ -455,32 +455,34 @@ void cgit_print_age(time_t t, time_t max_relative, char *format)
 }
 
 void cgit_print_http_headers(struct cgit_context *ctx)
 {
         if (ctx->page.mimetype && ctx->page.charset)
                 htmlf("Content-Type: %s; charset=%s\n", ctx->page.mimetype,
                       ctx->page.charset);
         else if (ctx->page.mimetype)
                 htmlf("Content-Type: %s\n", ctx->page.mimetype);
         if (ctx->page.size)
                 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();
         html(cgit_doctype);
         html("<html xmlns='http://www.w3.org/1999/xhtml' xml:lang='en' lang='en'>\n");
         html("<head>\n");
         html("<title>");
         html_txt(ctx->page.title);
         html("</title>\n");
         htmlf("<meta name='generator' content='cgit %s'/>\n", cgit_version);
         if (ctx->cfg.robots && *ctx->cfg.robots)
                 htmlf("<meta name='robots' content='%s'/>\n", ctx->cfg.robots);
         html("<link rel='stylesheet' type='text/css' href='");