Add cgit_diff_link()

This adds a new function used to generate links to the diff page and uses
it everywhere such links appear (expect for single files in the diffstat
displayed on the commit page: this is now a link to the tree page).

The updated diff-page now expects zero, one or two revision specifiers, in
parameters head, id and id2. Id defaults to head unless otherwise specified,
while head (as usual) defaults to repo.defbranch. If id2 isn't specified, it
defaults to the first parent of id1.

The most important change is of course that now all repo pages (summary, log,
tree, commit and diff) has support for passing on the current branch and
revision, i.e. the road is now open for a 'static' menu with links to all
of these pages.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

6 files changed, 75 insertions, 69 deletions

diff --git a/cgit.c b/cgit.c
index b936a70..3fc90bf 100644
--- a/cgit.c
+++ b/cgit.c
@@ -42,130 +42,129 @@ static int cgit_prepare_cache(struct cacheitem *item)
                         item->ttl = cgit_cache_static_ttl;
                 else
                         item->ttl = cgit_cache_repo_ttl;
         }
         return 1;
 }
 
 static void cgit_print_repo_page(struct cacheitem *item)
 {
         char *title;
         int show_search;
 
         if (!cgit_query_head)
                 cgit_query_head = cgit_repo->defbranch;
 
         if (chdir(cgit_repo->path)) {
                 title = fmt("%s - %s", cgit_root_title, "Bad request");
                 cgit_print_docstart(title, item);
                 cgit_print_pageheader(title, 0);
                 cgit_print_error(fmt("Unable to scan repository: %s",
                                      strerror(errno)));
                 cgit_print_docend();
                 return;
         }
 
         title = fmt("%s - %s", cgit_repo->name, cgit_repo->desc);
         show_search = 0;
         setenv("GIT_DIR", cgit_repo->path, 1);
 
         if ((cgit_cmd == CMD_SNAPSHOT) && cgit_repo->snapshots) {
                 cgit_print_snapshot(item, cgit_query_sha1, "zip",
                                     cgit_repo->url, cgit_query_name);
                 return;
         }
 
         if (cgit_cmd == CMD_BLOB) {
                 cgit_print_blob(item, cgit_query_sha1, cgit_query_path);
                 return;
         }
 
         show_search = (cgit_cmd == CMD_LOG);
         cgit_print_docstart(title, item);
         if (!cgit_cmd) {
                 cgit_print_pageheader("summary", show_search);
                 cgit_print_summary();
                 cgit_print_docend();
                 return;
         }
 
         cgit_print_pageheader(cgit_query_page, show_search);
 
         switch(cgit_cmd) {
         case CMD_LOG:
                 cgit_print_log(cgit_query_sha1, cgit_query_ofs,
                                cgit_max_commit_count, cgit_query_search,
                                cgit_query_path, 1);
                 break;
         case CMD_TREE:
                 cgit_print_tree(cgit_query_sha1, cgit_query_path);
                 break;
         case CMD_COMMIT:
                 cgit_print_commit(cgit_query_sha1);
                 break;
         case CMD_DIFF:
-                cgit_print_diff(cgit_query_head, cgit_query_sha1, cgit_query_sha2,
-                                cgit_query_path);
+                cgit_print_diff(cgit_query_sha1, cgit_query_sha2);
                 break;
         default:
                 cgit_print_error("Invalid request");
         }
         cgit_print_docend();
 }
 
 static void cgit_fill_cache(struct cacheitem *item, int use_cache)
 {
         static char buf[PATH_MAX];
         int stdout2;
 
         getcwd(buf, sizeof(buf));
         item->st.st_mtime = time(NULL);
 
         if (use_cache) {
                 stdout2 = chk_positive(dup(STDOUT_FILENO),
                                        "Preserving STDOUT");
                 chk_zero(close(STDOUT_FILENO), "Closing STDOUT");
                 chk_positive(dup2(item->fd, STDOUT_FILENO), "Dup2(cachefile)");
         }
 
         if (cgit_repo)
                 cgit_print_repo_page(item);
         else
                 cgit_print_repolist(item);
 
         if (use_cache) {
                 chk_zero(close(STDOUT_FILENO), "Close redirected STDOUT");
                 chk_positive(dup2(stdout2, STDOUT_FILENO),
                              "Restoring original STDOUT");
                 chk_zero(close(stdout2), "Closing temporary STDOUT");
         }
 
         chdir(buf);
 }
 
 static void cgit_check_cache(struct cacheitem *item)
 {
         int i = 0;
 
  top:
         if (++i > cgit_max_lock_attempts) {
                 die("cgit_refresh_cache: unable to lock %s: %s",
                     item->name, strerror(errno));
         }
         if (!cache_exist(item)) {
                 if (!cache_lock(item)) {
                         sleep(1);
                         goto top;
                 }
                 if (!cache_exist(item)) {
                         cgit_fill_cache(item, 1);
                         cache_unlock(item);
                 } else {
                         cache_cancel_lock(item);
                 }
         } else if (cache_expired(item) && cache_lock(item)) {
                 if (cache_expired(item)) {
                         cgit_fill_cache(item, 1);
                         cache_unlock(item);
                 } else {
                         cache_cancel_lock(item);
                 }
diff --git a/cgit.h b/cgit.h
index c276a24..bd2dd0d 100644
--- a/cgit.h
+++ b/cgit.h
@@ -146,88 +146,89 @@ extern char *cgit_query_path;
 extern char *cgit_query_name;
 extern int   cgit_query_ofs;
 
 extern int htmlfd;
 
 extern int cgit_get_cmd_index(const char *cmd);
 extern struct repoinfo *cgit_get_repoinfo(const char *url);
 extern void cgit_global_config_cb(const char *name, const char *value);
 extern void cgit_repo_config_cb(const char *name, const char *value);
 extern void cgit_querystring_cb(const char *name, const char *value);
 
 extern int chk_zero(int result, char *msg);
 extern int chk_positive(int result, char *msg);
 
 extern int hextoint(char c);
 
 extern void *cgit_free_commitinfo(struct commitinfo *info);
 
 extern int cgit_diff_files(const unsigned char *old_sha1,
                            const unsigned char *new_sha1,
                            linediff_fn fn);
 
 extern void cgit_diff_tree(const unsigned char *old_sha1,
                            const unsigned char *new_sha1,
                            filepair_fn fn);
 
 extern void cgit_diff_commit(struct commit *commit, filepair_fn fn);
 
 extern char *fmt(const char *format,...);
 
 extern void html(const char *txt);
 extern void htmlf(const char *format,...);
 extern void html_txt(char *txt);
 extern void html_ntxt(int len, char *txt);
 extern void html_attr(char *txt);
 extern void html_hidden(char *name, char *value);
 extern void html_link_open(char *url, char *title, char *class);
 extern void html_link_close(void);
 extern void html_filemode(unsigned short mode);
 extern int html_include(const char *filename);
 
 extern int cgit_read_config(const char *filename, configfn fn);
 extern int cgit_parse_query(char *txt, configfn fn);
 extern struct commitinfo *cgit_parse_commit(struct commit *commit);
 extern struct taginfo *cgit_parse_tag(struct tag *tag);
 extern void cgit_parse_url(const char *url);
 
 extern char *cache_safe_filename(const char *unsafe);
 extern int cache_lock(struct cacheitem *item);
 extern int cache_unlock(struct cacheitem *item);
 extern int cache_cancel_lock(struct cacheitem *item);
 extern int cache_exist(struct cacheitem *item);
 extern int cache_expired(struct cacheitem *item);
 
 extern char *cgit_repourl(const char *reponame);
 extern char *cgit_pageurl(const char *reponame, const char *pagename,
                           const char *query);
 
 extern void cgit_tree_link(char *name, char *title, char *class, char *head,
                            char *rev, char *path);
 extern void cgit_log_link(char *name, char *title, char *class, char *head,
                           char *rev, char *path);
 extern void cgit_commit_link(char *name, char *title, char *class, char *head,
                              char *rev);
+extern void cgit_diff_link(char *name, char *title, char *class, char *head,
+                           char *new_rev, char *old_rev, char *path);
 
 extern void cgit_print_error(char *msg);
 extern void cgit_print_date(time_t secs, char *format);
 extern void cgit_print_age(time_t t, time_t max_relative, char *format);
 extern void cgit_print_docstart(char *title, struct cacheitem *item);
 extern void cgit_print_docend();
 extern void cgit_print_pageheader(char *title, int show_search);
 extern void cgit_print_snapshot_start(const char *mimetype,
                                       const char *filename,
                                       struct cacheitem *item);
 
 extern void cgit_print_repolist(struct cacheitem *item);
 extern void cgit_print_summary();
 extern void cgit_print_log(const char *tip, int ofs, int cnt, char *grep, char *path, int pager);
 extern void cgit_print_blob(struct cacheitem *item, const char *hex, char *path);
 extern void cgit_print_tree(const char *rev, char *path);
-extern void cgit_print_commit(const char *hex);
-extern void cgit_print_diff(const char *head, const char *old_hex, const char *new_hex,
-                            char *path);
+extern void cgit_print_commit(char *hex);
+extern void cgit_print_diff(const char *new_hex, const char *old_hex);
 extern void cgit_print_snapshot(struct cacheitem *item, const char *hex,
                                 const char *format, const char *prefix,
                                 const char *filename);
 
 #endif /* CGIT_H */
diff --git a/shared.c b/shared.c
index c7cd8a5..f20fb5c 100644
--- a/shared.c
+++ b/shared.c
@@ -299,80 +299,80 @@ int filediff_cb(void *priv, mmbuffer_t *mb, int nbuf)
                         /* Incomplete line */
                         diffbuf = xrealloc(diffbuf, buflen + mb[i].size);
                         memcpy(diffbuf + buflen, mb[i].ptr, mb[i].size);
                         buflen += mb[i].size;
                         continue;
                 }
 
                 /* we have a complete line */
                 if (!diffbuf) {
                         ((linediff_fn)priv)(mb[i].ptr, mb[i].size);
                         continue;
                 }
                 diffbuf = xrealloc(diffbuf, buflen + mb[i].size);
                 memcpy(diffbuf + buflen, mb[i].ptr, mb[i].size);
                 ((linediff_fn)priv)(diffbuf, buflen + mb[i].size);
                 free(diffbuf);
                 diffbuf = NULL;
                 buflen = 0;
         }
         if (diffbuf) {
                 ((linediff_fn)priv)(diffbuf, buflen);
                 free(diffbuf);
                 diffbuf = NULL;
                 buflen = 0;
         }
         return 0;
 }
 
 int cgit_diff_files(const unsigned char *old_sha1,
                      const unsigned char *new_sha1,
                      linediff_fn fn)
 {
         mmfile_t file1, file2;
         xpparam_t diff_params;
         xdemitconf_t emit_params;
         xdemitcb_t emit_cb;
 
         if (!load_mmfile(&file1, old_sha1) || !load_mmfile(&file2, new_sha1))
                 return 1;
 
         diff_params.flags = XDF_NEED_MINIMAL;
         emit_params.ctxlen = 3;
         emit_params.flags = XDL_EMIT_FUNCNAMES;
         emit_cb.outf = filediff_cb;
         emit_cb.priv = fn;
         xdl_diff(&file1, &file2, &diff_params, &emit_params, &emit_cb);
         return 0;
 }
 
 void cgit_diff_tree(const unsigned char *old_sha1,
                     const unsigned char *new_sha1,
                     filepair_fn fn)
 {
         struct diff_options opt;
         int ret;
 
         diff_setup(&opt);
         opt.output_format = DIFF_FORMAT_CALLBACK;
         opt.detect_rename = 1;
         opt.recursive = 1;
         opt.format_callback = cgit_diff_tree_cb;
         opt.format_callback_data = fn;
         diff_setup_done(&opt);
 
-        if (old_sha1)
+        if (old_sha1 && !is_null_sha1(old_sha1))
                 ret = diff_tree_sha1(old_sha1, new_sha1, "", &opt);
         else
                 ret = diff_root_tree_sha1(new_sha1, "", &opt);
         diffcore_std(&opt);
         diff_flush(&opt);
 }
 
 void cgit_diff_commit(struct commit *commit, filepair_fn fn)
 {
         unsigned char *old_sha1 = NULL;
 
         if (commit->parents)
                 old_sha1 = commit->parents->item->object.sha1;
         cgit_diff_tree(old_sha1, commit->object.sha1, fn);
 }
diff --git a/ui-commit.c b/ui-commit.c
index d489d7c..2679b59 100644
--- a/ui-commit.c
+++ b/ui-commit.c
@@ -1,242 +1,228 @@
 /* ui-commit.c: generate commit view
  *
  * Copyright (C) 2006 Lars Hjemli
  *
  * Licensed under GNU General Public License v2
  *   (see COPYING for full license text)
  */
 
 #include "cgit.h"
 
 static int files, slots;
 static int total_adds, total_rems, max_changes;
 static int lines_added, lines_removed;
+static char *curr_rev;
 
 static struct fileinfo {
         char status;
         unsigned char old_sha1[20];
         unsigned char new_sha1[20];
         unsigned short old_mode;
         unsigned short new_mode;
         char *old_path;
         char *new_path;
         unsigned int added;
         unsigned int removed;
 } *items;
 
 
 void print_fileinfo(struct fileinfo *info)
 {
-        char *query, *query2;
         char *class;
 
         switch (info->status) {
         case DIFF_STATUS_ADDED:
                 class = "add";
                 break;
         case DIFF_STATUS_COPIED:
                 class = "cpy";
                 break;
         case DIFF_STATUS_DELETED:
                 class = "del";
                 break;
         case DIFF_STATUS_MODIFIED:
                 class = "upd";
                 break;
         case DIFF_STATUS_RENAMED:
                 class = "mov";
                 break;
         case DIFF_STATUS_TYPE_CHANGED:
                 class = "typ";
                 break;
         case DIFF_STATUS_UNKNOWN:
                 class = "unk";
                 break;
         case DIFF_STATUS_UNMERGED:
                 class = "stg";
                 break;
         default:
                 die("bug: unhandled diff status %c", info->status);
         }
 
         html("<tr>");
         htmlf("<td class='mode'>");
         if (is_null_sha1(info->new_sha1)) {
                 html_filemode(info->old_mode);
         } else {
                 html_filemode(info->new_mode);
         }
 
         if (info->old_mode != info->new_mode &&
             !is_null_sha1(info->old_sha1) &&
             !is_null_sha1(info->new_sha1)) {
                 html("<span class='modechange'>[");
                 html_filemode(info->old_mode);
                 html("]</span>");
         }
         htmlf("</td><td class='%s'>", class);
-        query = fmt("id=%s&amp;id2=%s&amp;path=%s", sha1_to_hex(info->old_sha1),
-                    sha1_to_hex(info->new_sha1), info->new_path);
-        html_link_open(cgit_pageurl(cgit_query_repo, "diff", query),
-                       NULL, NULL);
-        if (info->status == DIFF_STATUS_COPIED ||
-            info->status == DIFF_STATUS_RENAMED) {
-                html_txt(info->new_path);
-                htmlf("</a> (%s from ", info->status == DIFF_STATUS_COPIED ?
-                      "copied" : "renamed");
-                query2 = fmt("id=%s", sha1_to_hex(info->old_sha1));
-                html_link_open(cgit_pageurl(cgit_query_repo, "view", query2),
-                               NULL, NULL);
-                html_txt(info->old_path);
-                html("</a>)");
-        } else {
-                html_txt(info->new_path);
-                html("</a>");
-        }
+        cgit_tree_link(info->new_path, NULL, NULL, cgit_query_head, curr_rev,
+                       info->new_path);
+        if (info->status == DIFF_STATUS_COPIED || info->status == DIFF_STATUS_RENAMED)
+                htmlf(" (%s from %s)",
+                      info->status == DIFF_STATUS_COPIED ? "copied" : "renamed",
+                      info->old_path);
         html("</td><td class='right'>");
         htmlf("%d", info->added + info->removed);
         html("</td><td class='graph'>");
         htmlf("<table width='%d%%'><tr>", (max_changes > 100 ? 100 : max_changes));
         htmlf("<td class='add' style='width: %.1f%%;'/>",
               info->added * 100.0 / max_changes);
         htmlf("<td class='rem' style='width: %.1f%%;'/>",
               info->removed * 100.0 / max_changes);
         htmlf("<td class='none' style='width: %.1f%%;'/>",
               (max_changes - info->removed - info->added) * 100.0 / max_changes);
         html("</tr></table></td></tr>\n");
 }
 
 void cgit_count_diff_lines(char *line, int len)
 {
         if (line && (len > 0)) {
                 if (line[0] == '+')
                         lines_added++;
                 else if (line[0] == '-')
                         lines_removed++;
         }
 }
 
 void inspect_filepair(struct diff_filepair *pair)
 {
         files++;
         lines_added = 0;
         lines_removed = 0;
         cgit_diff_files(pair->one->sha1, pair->two->sha1, cgit_count_diff_lines);
         if (files >= slots) {
                 if (slots == 0)
                         slots = 4;
                 else
                         slots = slots * 2;
                 items = xrealloc(items, slots * sizeof(struct fileinfo));
         }
         items[files-1].status = pair->status;
         hashcpy(items[files-1].old_sha1, pair->one->sha1);
         hashcpy(items[files-1].new_sha1, pair->two->sha1);
         items[files-1].old_mode = pair->one->mode;
         items[files-1].new_mode = pair->two->mode;
         items[files-1].old_path = xstrdup(pair->one->path);
         items[files-1].new_path = xstrdup(pair->two->path);
         items[files-1].added = lines_added;
         items[files-1].removed = lines_removed;
         if (lines_added + lines_removed > max_changes)
                 max_changes = lines_added + lines_removed;
         total_adds += lines_added;
         total_rems += lines_removed;
 }
 
 
-void cgit_print_commit(const char *hex)
+void cgit_print_commit(char *hex)
 {
         struct commit *commit, *parent;
         struct commitinfo *info;
         struct commit_list *p;
         unsigned char sha1[20];
-        char *query;
         char *filename;
         char *tmp;
         int i;
 
         if (!hex)
                 hex = cgit_query_head;
+        curr_rev = hex;
 
         if (get_sha1(hex, sha1)) {
                 cgit_print_error(fmt("Bad object id: %s", hex));
                 return;
         }
         commit = lookup_commit_reference(sha1);
         if (!commit) {
                 cgit_print_error(fmt("Bad commit reference: %s", hex));
                 return;
         }
         info = cgit_parse_commit(commit);
 
         html("<table class='commit-info'>\n");
         html("<tr><th>author</th><td>");
         html_txt(info->author);
         html(" ");
         html_txt(info->author_email);
         html("</td><td class='right'>");
         cgit_print_date(info->author_date, FMT_LONGDATE);
         html("</td></tr>\n");
         html("<tr><th>committer</th><td>");
         html_txt(info->committer);
         html(" ");
         html_txt(info->committer_email);
         html("</td><td class='right'>");
         cgit_print_date(info->committer_date, FMT_LONGDATE);
         html("</td></tr>\n");
         html("<tr><th>tree</th><td colspan='2' class='sha1'>");
         tmp = xstrdup(hex);
         cgit_tree_link(sha1_to_hex(commit->tree->object.sha1), NULL, NULL,
                        cgit_query_head, tmp, NULL);
         html("</td></tr>\n");
               for (p = commit->parents; p ; p = p->next) {
                 parent = lookup_commit_reference(p->item->object.sha1);
                 if (!parent) {
                         html("<tr><td colspan='3'>");
                         cgit_print_error("Error reading parent commit");
                         html("</td></tr>");
                         continue;
                 }
                 html("<tr><th>parent</th>"
                      "<td colspan='2' class='sha1'>");
                 cgit_commit_link(sha1_to_hex(p->item->object.sha1), NULL, NULL,
                                  cgit_query_head, sha1_to_hex(p->item->object.sha1));
-                html(" (<a href='");
-                query = fmt("id=%s&amp;id2=%s", sha1_to_hex(parent->tree->object.sha1),
-                            sha1_to_hex(commit->tree->object.sha1));
-                html_attr(cgit_pageurl(cgit_query_repo, "diff", query));
-                html("'>diff</a>)</td></tr>");
+                html(" (");
+                cgit_diff_link("diff", NULL, NULL, cgit_query_head, hex,
+                               sha1_to_hex(p->item->object.sha1), NULL);
+                html(")</td></tr>");
         }
         if (cgit_repo->snapshots) {
                 htmlf("<tr><th>download</th><td colspan='2' class='sha1'><a href='");
                 filename = fmt("%s-%s.zip", cgit_query_repo, hex);
                 html_attr(cgit_pageurl(cgit_query_repo, "snapshot",
                                        fmt("id=%s&amp;name=%s", hex, filename)));
                 htmlf("'>%s</a></td></tr>", filename);
         }
         html("</table>\n");
         html("<div class='commit-subject'>");
         html_txt(info->subject);
         html("</div>");
         html("<div class='commit-msg'>");
         html_txt(info->msg);
         html("</div>");
         if (!(commit->parents && commit->parents->next && commit->parents->next->next)) {
                 html("<div class='diffstat-header'>Diffstat</div>");
                 html("<table class='diffstat'>");
                 max_changes = 0;
                 cgit_diff_commit(commit, inspect_filepair);
                 for(i = 0; i<files; i++)
                         print_fileinfo(&items[i]);
                 html("</table>");
                 html("<div class='diffstat-summary'>");
                 htmlf("%d files changed, %d insertions, %d deletions (",
                       files, total_adds, total_rems);
-                query = fmt("h=%s", hex);
-                html_link_open(cgit_pageurl(cgit_query_repo, "diff", query), NULL, NULL);
-                html("show diff</a>)");
-                html("</div>");
+                cgit_diff_link("show diff", NULL, NULL, cgit_query_head, hex,
+                               NULL, NULL);
+                html(")</div>");
         }
         cgit_free_commitinfo(info);
 }
diff --git a/ui-diff.c b/ui-diff.c
index 5c864d9..a76a234 100644
--- a/ui-diff.c
+++ b/ui-diff.c
@@ -28,115 +28,113 @@ static void print_line(char *line, int len)
         line[len-1] = '\0';
         html_txt(line);
         html("</div>");
         line[len-1] = c;
 }
 
 static void header(unsigned char *sha1, char *path1, int mode1,
                    unsigned char *sha2, char *path2, int mode2)
 {
         char *abbrev1, *abbrev2;
         int subproject;
 
         subproject = (S_ISDIRLNK(mode1) || S_ISDIRLNK(mode2));
         html("<div class='head'>");
         html("diff --git a/");
         html_txt(path1);
         html(" b/");
         html_txt(path2);
 
         if (is_null_sha1(sha1))
                 path1 = "dev/null";
         if (is_null_sha1(sha2))
                 path2 = "dev/null";
 
         if (mode1 == 0)
                 htmlf("<br/>new file mode %.6o", mode2);
 
         if (mode2 == 0)
                 htmlf("<br/>deleted file mode %.6o", mode1);
 
         if (!subproject) {
                 abbrev1 = xstrdup(find_unique_abbrev(sha1, DEFAULT_ABBREV));
                 abbrev2 = xstrdup(find_unique_abbrev(sha2, DEFAULT_ABBREV));
                 htmlf("<br/>index %s..%s", abbrev1, abbrev2);
                 free(abbrev1);
                 free(abbrev2);
                 if (mode1 != 0 && mode2 != 0) {
                         htmlf(" %.6o", mode1);
                         if (mode2 != mode1)
                                 htmlf("..%.6o", mode2);
                 }
                 html("<br/>--- a/");
                 html_txt(path1);
                 html("<br/>+++ b/");
                 html_txt(path2);
         }
         html("</div>");
 }
 
 static void filepair_cb(struct diff_filepair *pair)
 {
         header(pair->one->sha1, pair->one->path, pair->one->mode,
                pair->two->sha1, pair->two->path, pair->two->mode);
         if (S_ISDIRLNK(pair->one->mode) || S_ISDIRLNK(pair->two->mode)) {
                 if (S_ISDIRLNK(pair->one->mode))
                         print_line(fmt("-Subproject %s", sha1_to_hex(pair->one->sha1)), 52);
                 if (S_ISDIRLNK(pair->two->mode))
                         print_line(fmt("+Subproject %s", sha1_to_hex(pair->two->sha1)), 52);
                 return;
         }
         if (cgit_diff_files(pair->one->sha1, pair->two->sha1, print_line))
                 cgit_print_error("Error running diff");
 }
 
-void cgit_print_diff(const char *head, const char *old_hex, const char *new_hex, char *path)
+void cgit_print_diff(const char *new_rev, const char *old_rev)
 {
         unsigned char sha1[20], sha2[20];
         enum object_type type;
         unsigned long size;
-        struct commit *commit;
+        struct commit *commit, *commit2;
 
-        html("<table class='diff'>");
-        html("<tr><td>");
-
-        if (head && !old_hex && !new_hex) {
-                get_sha1(head, sha1);
-                commit = lookup_commit_reference(sha1);
-                if (commit && !parse_commit(commit))
-                        cgit_diff_commit(commit, filepair_cb);
-                else
-                        cgit_print_error(fmt("Bad commit: %s", head));
-                html("</td></tr>");
-                html("</table>");
+        if (!new_rev)
+                new_rev = cgit_query_head;
+        get_sha1(new_rev, sha1);
+        type = sha1_object_info(sha1, &size);
+        if (type == OBJ_BAD) {
+                cgit_print_error(fmt("Bad object name: %s", new_rev));
+                return;
+        }
+        if (type != OBJ_COMMIT) {
+                cgit_print_error(fmt("Unhandled object type: %s",
+                                     typename(type)));
                 return;
         }
 
-        get_sha1(old_hex, sha1);
-        get_sha1(new_hex, sha2);
+        commit = lookup_commit_reference(sha1);
+        if (!commit || parse_commit(commit))
+                cgit_print_error(fmt("Bad commit: %s", sha1_to_hex(sha1)));
 
-        type = sha1_object_info(sha1, &size);
-        if (type == OBJ_BAD) {
+        if (old_rev)
+                get_sha1(old_rev, sha2);
+        else if (commit->parents && commit->parents->item)
+                hashcpy(sha2, commit->parents->item->object.sha1);
+        else
+                hashclr(sha2);
+
+        if (!is_null_sha1(sha2)) {
                 type = sha1_object_info(sha2, &size);
                 if (type == OBJ_BAD) {
-                        cgit_print_error(fmt("Bad object names: %s, %s", old_hex, new_hex));
+                        cgit_print_error(fmt("Bad object name: %s", sha1_to_hex(sha2)));
                         return;
                 }
+                commit2 = lookup_commit_reference(sha2);
+                if (!commit2 || parse_commit(commit2))
+                        cgit_print_error(fmt("Bad commit: %s", sha1_to_hex(sha2)));
         }
 
-        switch(type) {
-        case OBJ_BLOB:
-                header(sha1, path, 0644, sha2, path, 0644);
-                if (cgit_diff_files(sha1, sha2, print_line))
-                        cgit_print_error("Error running diff");
-                break;
-        case OBJ_TREE:
-                cgit_diff_tree(sha1, sha2, filepair_cb);
-                break;
-        default:
-                cgit_print_error(fmt("Unhandled object type: %s",
-                                     typename(type)));
-                break;
-        }
+        html("<table class='diff'>");
+        html("<tr><td>");
+        cgit_diff_tree(sha2, sha1, filepair_cb);
         html("</td></tr>");
         html("</table>");
 }
diff --git a/ui-shared.c b/ui-shared.c
index 71c899a..15d8254 100644
--- a/ui-shared.c
+++ b/ui-shared.c
@@ -115,128 +115,150 @@ static char *repolink(char *title, char *class, char *page, char *head,
                 html("/");
                 if (path)
                         html_attr(path);
         } else {
                 html(cgit_script_name);
                 html("?url=");
                 html_attr(cgit_repo->url);
                 if (cgit_repo->url[strlen(cgit_repo->url) - 1] != '/')
                         html("/");
                 html(page);
                 html("/");
                 if (path)
                         html_attr(path);
                 delim = "&amp;";
         }
         if (head && strcmp(head, cgit_repo->defbranch)) {
                 html(delim);
                 html("h=");
                 html_attr(head);
                 delim = "&amp;";
         }
         return fmt("%s", delim);
 }
 
 static void reporevlink(char *page, char *name, char *title, char *class,
                         char *head, char *rev, char *path)
 {
         char *delim;
 
         delim = repolink(title, class, page, head, path);
         if (rev && strcmp(rev, cgit_query_head)) {
                 html(delim);
                 html("id=");
                 html_attr(rev);
         }
         html("'>");
         html_txt(name);
         html("</a>");
 }
 
 void cgit_tree_link(char *name, char *title, char *class, char *head,
                     char *rev, char *path)
 {
         reporevlink("tree", name, title, class, head, rev, path);
 }
 
 void cgit_log_link(char *name, char *title, char *class, char *head,
                    char *rev, char *path)
 {
         reporevlink("log", name, title, class, head, rev, path);
 }
 
 void cgit_commit_link(char *name, char *title, char *class, char *head,
                       char *rev)
 {
         if (strlen(name) > cgit_max_msg_len && cgit_max_msg_len >= 15) {
                 name[cgit_max_msg_len] = '\0';
                 name[cgit_max_msg_len - 1] = '.';
                 name[cgit_max_msg_len - 2] = '.';
                 name[cgit_max_msg_len - 3] = '.';
         }
         reporevlink("commit", name, title, class, head, rev, NULL);
 }
 
+void cgit_diff_link(char *name, char *title, char *class, char *head,
+                    char *new_rev, char *old_rev, char *path)
+{
+        char *delim;
+
+        delim = repolink(title, class, "diff", head, path);
+        if (new_rev && strcmp(new_rev, cgit_query_head)) {
+                html(delim);
+                html("id=");
+                html_attr(new_rev);
+                delim = "&amp;";
+        }
+        if (old_rev) {
+                html(delim);
+                html("id2=");
+                html_attr(old_rev);
+        }
+        html("'>");
+        html_txt(name);
+        html("</a>");
+}
+
 void cgit_print_date(time_t secs, char *format)
 {
         char buf[64];
         struct tm *time;
 
         time = gmtime(&secs);
         strftime(buf, sizeof(buf)-1, format, time);
         html_txt(buf);
 }
 
 void cgit_print_age(time_t t, time_t max_relative, char *format)
 {
         time_t now, secs;
 
         time(&now);
         secs = now - t;
 
         if (secs > max_relative && max_relative >= 0) {
                 cgit_print_date(t, format);
                 return;
         }
 
         if (secs < TM_HOUR * 2) {
                 htmlf("<span class='age-mins'>%.0f min.</span>",
                       secs * 1.0 / TM_MIN);
                 return;
         }
         if (secs < TM_DAY * 2) {
                 htmlf("<span class='age-hours'>%.0f hours</span>",
                       secs * 1.0 / TM_HOUR);
                 return;
         }
         if (secs < TM_WEEK * 2) {
                 htmlf("<span class='age-days'>%.0f days</span>",
                       secs * 1.0 / TM_DAY);
                 return;
         }
         if (secs < TM_MONTH * 2) {
                 htmlf("<span class='age-weeks'>%.0f weeks</span>",
                       secs * 1.0 / TM_WEEK);
                 return;
         }
         if (secs < TM_YEAR * 2) {
                 htmlf("<span class='age-months'>%.0f months</span>",
                       secs * 1.0 / TM_MONTH);
                 return;
         }
         htmlf("<span class='age-years'>%.0f years</span>",
               secs * 1.0 / TM_YEAR);
 }
 
 void cgit_print_docstart(char *title, struct cacheitem *item)
 {
         html("Content-Type: text/html; charset=utf-8\n");
         htmlf("Last-Modified: %s\n", http_date(item->st.st_mtime));
         htmlf("Expires: %s\n", http_date(item->st.st_mtime +
                                          ttl_seconds(item->ttl)));
         html("\n");
         html(cgit_doctype);
         html("<html>\n");
         html("<head>\n");
         html("<title>");
         html_txt(title);
         html("</title>\n");