Redesign the caching layer

The original caching layer in cgit has no upper bound on the number of
concurrent cache entries, so when cgit is traversed by a spider (like the
googlebot), the cache might end up filling your disk. Also, if any error
occurs in the cache layer, no content is returned to the client.

This patch redesigns the caching layer to avoid these flaws by
* giving the cache a bound number of slots
* disabling the cache for the current request when errors occur

The cache size limit is implemented by hashing the querystring (the cache
lookup key) and generating a cache filename based on this hash modulo the
cache size. In order to detect hash collisions, the full lookup key (i.e.
the querystring) is stored in the cache file (separated from its associated
content by ascii 0).

The cache filename is the reversed 8-digit hexadecimal representation of

  hash(key) % cache_size

which should make the filesystem lookup pretty fast (if directory content
is indexed/sorted); reversing the representation avoids the problem where
all keys have equal prefix.

There is a new config option, cache-size, which sets the upper bound for
the cache. Default value for this option is 0, which has the same effect
as setting nocache=1 (hence nocache is now deprecated).

Included in this patch is also a new testfile which verifies that the
new option works as intended.

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

6 files changed, 418 insertions, 210 deletions

diff --git a/cache.c b/cache.c
index 89f7ecd..e590d7b 100644
--- a/cache.c
+++ b/cache.c
@@ -1,120 +1,343 @@
 /* cache.c: cache management
  *
  * Copyright (C) 2006 Lars Hjemli
  *
  * Licensed under GNU General Public License v2
  *   (see COPYING for full license text)
+ *
+ *
+ * The cache is just a directory structure where each file is a cache slot,
+ * and each filename is based on the hash of some key (e.g. the cgit url).
+ * Each file contains the full key followed by the cached content for that
+ * key.
+ *
  */
 
 #include "cgit.h"
 #include "cache.h"
 
-const int NOLOCK = -1;
+#define CACHE_BUFSIZE (1024 * 4)
+
+struct cache_slot {
+        const char *key;
+        int keylen;
+        int ttl;
+        cache_fill_fn fn;
+        void *cbdata;
+        int cache_fd;
+        int lock_fd;
+        const char *cache_name;
+        const char *lock_name;
+        int match;
+        struct stat cache_st;
+        struct stat lock_st;
+        int bufsize;
+        char buf[CACHE_BUFSIZE];
+};
 
-char *cache_safe_filename(const char *unsafe)
+/* Open an existing cache slot and fill the cache buffer with
+ * (part of) the content of the cache file. Return 0 on success
+ * and errno otherwise.
+ */
+static int open_slot(struct cache_slot *slot)
 {
-        static char buf[4][PATH_MAX];
-        static int bufidx;
-        char *s;
-        char c;
-
-        bufidx++;
-        bufidx &= 3;
-        s = buf[bufidx];
-
-        while(unsafe && (c = *unsafe++) != 0) {
-                if (c == '/' || c == ' ' || c == '&' || c == '|' ||
-                    c == '>' || c == '<' || c == '.')
-                        c = '_';
-                *s++ = c;
-        }
-        *s = '\0';
-        return buf[bufidx];
+        char *bufz;
+        int bufkeylen = -1;
+
+        slot->cache_fd = open(slot->cache_name, O_RDONLY);
+        if (slot->cache_fd == -1)
+                return errno;
+
+        if (fstat(slot->cache_fd, &slot->cache_st))
+                return errno;
+
+        slot->bufsize = read(slot->cache_fd, slot->buf, sizeof(slot->buf));
+        if (slot->bufsize == 0)
+                return errno;
+
+        bufz = memchr(slot->buf, 0, slot->bufsize);
+        if (bufz)
+                bufkeylen = bufz - slot->buf;
+
+        slot->match = bufkeylen == slot->keylen &&
+            !memcmp(slot->key, slot->buf, bufkeylen + 1);
+
+        return 0;
 }
 
-int cache_exist(struct cacheitem *item)
+/* Close the active cache slot */
+static void close_slot(struct cache_slot *slot)
 {
-        if (stat(item->name, &item->st)) {
-                item->st.st_mtime = 0;
-                return 0;
+        if (slot->cache_fd > 0) {
+                close(slot->cache_fd);
+                slot->cache_fd = -1;
         }
-        return 1;
 }
 
-int cache_create_dirs()
+/* Print the content of the active cache slot (but skip the key). */
+static int print_slot(struct cache_slot *slot)
 {
-        char *path;
+        ssize_t i, j = 0;
+
+        i = lseek(slot->cache_fd, slot->keylen + 1, SEEK_SET);
+        if (i != slot->keylen + 1)
+                return errno;
 
-        path = fmt("%s", ctx.cfg.cache_root);
-        if (mkdir(path, S_IRWXU) && errno!=EEXIST)
+        while((i=read(slot->cache_fd, slot->buf, sizeof(slot->buf))) > 0)
+                j = write(STDOUT_FILENO, slot->buf, i);
+
+        if (j < 0)
+                return errno;
+        else
                 return 0;
+}
 
-        if (!ctx.repo)
+/* Check if the slot has expired */
+static int is_expired(struct cache_slot *slot)
+{
+        if (slot->ttl < 0)
                 return 0;
+        else
+                return slot->cache_st.st_mtime + slot->ttl*60 < time(NULL);
+}
 
-        path = fmt("%s/%s", ctx.cfg.cache_root,
-                   cache_safe_filename(ctx.repo->url));
+/* Check if the slot has been modified since we opened it.
+ * NB: If stat() fails, we pretend the file is modified.
+ */
+static int is_modified(struct cache_slot *slot)
+{
+        struct stat st;
 
-        if (mkdir(path, S_IRWXU) && errno!=EEXIST)
-                return 0;
+        if (stat(slot->cache_name, &st))
+                return 1;
+        return (st.st_ino != slot->cache_st.st_ino ||
+                st.st_mtime != slot->cache_st.st_mtime ||
+                st.st_size != slot->cache_st.st_size);
+}
 
-        if (ctx.qry.page) {
-                path = fmt("%s/%s/%s", ctx.cfg.cache_root,
-                           cache_safe_filename(ctx.repo->url),
-                           ctx.qry.page);
-                if (mkdir(path, S_IRWXU) && errno!=EEXIST)
-                        return 0;
+/* Close an open lockfile */
+static void close_lock(struct cache_slot *slot)
+{
+        if (slot->lock_fd > 0) {
+                close(slot->lock_fd);
+                slot->lock_fd = -1;
         }
-        return 1;
 }
 
-int cache_refill_overdue(const char *lockfile)
+/* Create a lockfile used to store the generated content for a cache
+ * slot, and write the slot key + \0 into it.
+ * Returns 0 on success and errno otherwise.
+ */
+static int lock_slot(struct cache_slot *slot)
 {
-        struct stat st;
+        slot->lock_fd = open(slot->lock_name, O_RDWR|O_CREAT|O_EXCL,
+                             S_IRUSR|S_IWUSR);
+        if (slot->lock_fd == -1)
+                return errno;
+        write(slot->lock_fd, slot->key, slot->keylen + 1);
+        return 0;
+}
 
-        if (stat(lockfile, &st))
-                return 0;
+/* Release the current lockfile. If `replace_old_slot` is set the
+ * lockfile replaces the old cache slot, otherwise the lockfile is
+ * just deleted.
+ */
+static int unlock_slot(struct cache_slot *slot, int replace_old_slot)
+{
+        int err;
+
+        if (replace_old_slot)
+                err = rename(slot->lock_name, slot->cache_name);
         else
-                return (time(NULL) - st.st_mtime > ctx.cfg.cache_max_create_time);
+                err = unlink(slot->lock_name);
+        return err;
 }
 
-int cache_lock(struct cacheitem *item)
+/* Generate the content for the current cache slot by redirecting
+ * stdout to the lock-fd and invoking the callback function
+ */
+static int fill_slot(struct cache_slot *slot)
 {
-        int i = 0;
-        char *lockfile = xstrdup(fmt("%s.lock", item->name));
+        int tmp;
 
- top:
-        if (++i > ctx.cfg.max_lock_attempts)
-                die("cache_lock: unable to lock %s: %s",
-                    item->name, strerror(errno));
+        /* Preserve stdout */
+        tmp = dup(STDOUT_FILENO);
+        if (tmp == -1)
+                return errno;
 
-               item->fd = open(lockfile, O_WRONLY|O_CREAT|O_EXCL, S_IRUSR|S_IWUSR);
+        /* Redirect stdout to lockfile */
+        if (dup2(slot->lock_fd, STDOUT_FILENO) == -1)
+                return errno;
 
-        if (item->fd == NOLOCK && errno == ENOENT && cache_create_dirs())
-                goto top;
+        /* Generate cache content */
+        slot->fn(slot->cbdata);
 
-        if (item->fd == NOLOCK && errno == EEXIST &&
-            cache_refill_overdue(lockfile) && !unlink(lockfile))
-                        goto top;
+        /* Restore stdout */
+        if (dup2(tmp, STDOUT_FILENO) == -1)
+                return errno;
 
-        free(lockfile);
-        return (item->fd > 0);
+        /* Close the temporary filedescriptor */
+        close(tmp);
+        return 0;
 }
 
-int cache_unlock(struct cacheitem *item)
+/* Crude implementation of 32-bit FNV-1 hash algorithm,
+ * see http://www.isthe.com/chongo/tech/comp/fnv/ for details
+ * about the magic numbers.
+ */
+#define FNV_OFFSET 0x811c9dc5
+#define FNV_PRIME  0x01000193
+
+unsigned long hash_str(const char *str)
 {
-        close(item->fd);
-        return (rename(fmt("%s.lock", item->name), item->name) == 0);
+        unsigned long h = FNV_OFFSET;
+        unsigned char *s = (unsigned char *)str;
+
+        if (!s)
+                return h;
+
+        while(*s) {
+                h *= FNV_PRIME;
+                h ^= *s++;
+        }
+        return h;
 }
 
-int cache_cancel_lock(struct cacheitem *item)
+static int process_slot(struct cache_slot *slot)
 {
-        return (unlink(fmt("%s.lock", item->name)) == 0);
+        int err;
+
+        err = open_slot(slot);
+        if (!err && slot->match) {
+                if (is_expired(slot)) {
+                        if (!lock_slot(slot)) {
+                                /* If the cachefile has been replaced between
+                                 * `open_slot` and `lock_slot`, we'll just
+                                 * serve the stale content from the original
+                                 * cachefile. This way we avoid pruning the
+                                 * newly generated slot. The same code-path
+                                 * is chosen if fill_slot() fails for some
+                                 * reason.
+                                 *
+                                 * TODO? check if the new slot contains the
+                                 * same key as the old one, since we would
+                                 * prefer to serve the newest content.
+                                 * This will require us to open yet another
+                                 * file-descriptor and read and compare the
+                                 * key from the new file, so for now we're
+                                 * lazy and just ignore the new file.
+                                 */
+                                if (is_modified(slot) || fill_slot(slot)) {
+                                        unlock_slot(slot, 0);
+                                        close_lock(slot);
+                                } else {
+                                        close_slot(slot);
+                                        unlock_slot(slot, 1);
+                                        slot->cache_fd = slot->lock_fd;
+                                }
+                        }
+                }
+                print_slot(slot);
+                close_slot(slot);
+                return 0;
+        }
+
+        /* If the cache slot does not exist (or its key doesn't match the
+         * current key), lets try to create a new cache slot for this
+         * request. If this fails (for whatever reason), lets just generate
+         * the content without caching it and fool the caller to belive
+         * everything worked out (but print a warning on stdout).
+         */
+
+        close_slot(slot);
+        if ((err = lock_slot(slot)) != 0) {
+                cache_log("[cgit] Unable to lock slot %s: %s (%d)\n",
+                          slot->lock_name, strerror(err), err);
+                slot->fn(slot->cbdata);
+                return 0;
+        }
+
+        if ((err = fill_slot(slot)) != 0) {
+                cache_log("[cgit] Unable to fill slot %s: %s (%d)\n",
+                          slot->lock_name, strerror(err), err);
+                unlock_slot(slot, 0);
+                close_lock(slot);
+                slot->fn(slot->cbdata);
+                return 0;
+        }
+        // We've got a valid cache slot in the lock file, which
+        // is about to replace the old cache slot. But if we
+        // release the lockfile and then try to open the new cache
+        // slot, we might get a race condition with a concurrent
+        // writer for the same cache slot (with a different key).
+        // Lets avoid such a race by just printing the content of
+        // the lock file.
+        slot->cache_fd = slot->lock_fd;
+        unlock_slot(slot, 1);
+        err = print_slot(slot);
+        close_slot(slot);
+        return err;
 }
 
-int cache_expired(struct cacheitem *item)
+/* Print cached content to stdout, generate the content if necessary. */
+int cache_process(int size, const char *path, const char *key, int ttl,
+                  cache_fill_fn fn, void *cbdata)
 {
-        if (item->ttl < 0)
+        unsigned long hash;
+        int len, i;
+        char filename[1024];
+        char lockname[1024 + 5];  /* 5 = ".lock" */
+        struct cache_slot slot;
+
+        /* If the cache is disabled, just generate the content */
+        if (size <= 0) {
+                fn(cbdata);
                 return 0;
-        return item->st.st_mtime + item->ttl * 60 < time(NULL);
+        }
+
+        /* Verify input, calculate filenames */
+        if (!path) {
+                cache_log("[cgit] Cache path not specified, caching is disabled\n");
+                fn(cbdata);
+                return 0;
+        }
+        len = strlen(path);
+        if (len > sizeof(filename) - 10) { /* 10 = "/01234567\0" */
+                cache_log("[cgit] Cache path too long, caching is disabled: %s\n",
+                          path);
+                fn(cbdata);
+                return 0;
+        }
+        if (!key)
+                key = "";
+        hash = hash_str(key) % size;
+        strcpy(filename, path);
+        if (filename[len - 1] != '/')
+                filename[len++] = '/';
+        for(i = 0; i < 8; i++) {
+                sprintf(filename + len++, "%x",
+                        (unsigned char)(hash & 0xf));
+                hash >>= 4;
+        }
+        filename[len] = '\0';
+        strcpy(lockname, filename);
+        strcpy(lockname + len, ".lock");
+        slot.fn = fn;
+        slot.cbdata = cbdata;
+        slot.ttl = ttl;
+        slot.cache_name = filename;
+        slot.lock_name = lockname;
+        slot.key = key;
+        slot.keylen = strlen(key);
+        return process_slot(&slot);
 }
+
+/* Print a message to stdout */
+void cache_log(const char *format, ...)
+{
+        va_list args;
+        va_start(args, format);
+        vfprintf(stderr, format, args);
+        va_end(args);
+}
+
diff --git a/cache.h b/cache.h
index 4dcbea3..5f2178d 100644
--- a/cache.h
+++ b/cache.h
@@ -1,23 +1,32 @@
 /*
  * Since git has it's own cache.h which we include,
  * lets test on CGIT_CACHE_H to avoid confusion
  */
 
 #ifndef CGIT_CACHE_H
 #define CGIT_CACHE_H
 
-struct cacheitem {
-        char *name;
-        struct stat st;
-        int ttl;
-        int fd;
-};
+typedef void (*cache_fill_fn)(void *cbdata);
 
-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);
+
+/* Print cached content to stdout, generate the content if necessary.
+ *
+ * Parameters
+ *   size    max number of cache files
+ *   path    directory used to store cache files
+ *   key     the key used to lookup cache files
+ *   ttl     max cache time in seconds for this key
+ *   fn      content generator function for this key
+ *   cbdata  user-supplied data to the content generator function
+ *
+ * Return value
+ *   0 indicates success, everyting else is an error
+ */
+extern int cache_process(int size, const char *path, const char *key, int ttl,
+                         cache_fill_fn fn, void *cbdata);
+
+
+/* Print a message to stdout */
+extern void cache_log(const char *format, ...);
 
 #endif /* CGIT_CACHE_H */
diff --git a/cgit.c b/cgit.c
index 38b0ba5..4dc8eec 100644
--- a/cgit.c
+++ b/cgit.c
@@ -1,95 +1,97 @@
 /* cgit.c: cgi for the git scm
  *
  * Copyright (C) 2006 Lars Hjemli
  *
  * Licensed under GNU General Public License v2
  *   (see COPYING for full license text)
  */
 
 #include "cgit.h"
 #include "cache.h"
 #include "cmd.h"
 #include "configfile.h"
 #include "html.h"
 #include "ui-shared.h"
 
 const char *cgit_version = CGIT_VERSION;
 
 void config_cb(const char *name, const char *value)
 {
         if (!strcmp(name, "root-title"))
                 ctx.cfg.root_title = xstrdup(value);
         else if (!strcmp(name, "css"))
                 ctx.cfg.css = xstrdup(value);
         else if (!strcmp(name, "logo"))
                 ctx.cfg.logo = xstrdup(value);
         else if (!strcmp(name, "index-header"))
                 ctx.cfg.index_header = xstrdup(value);
         else if (!strcmp(name, "index-info"))
                 ctx.cfg.index_info = xstrdup(value);
         else if (!strcmp(name, "logo-link"))
                 ctx.cfg.logo_link = xstrdup(value);
         else if (!strcmp(name, "module-link"))
                 ctx.cfg.module_link = xstrdup(value);
         else if (!strcmp(name, "virtual-root")) {
                 ctx.cfg.virtual_root = trim_end(value, '/');
                 if (!ctx.cfg.virtual_root && (!strcmp(value, "/")))
                         ctx.cfg.virtual_root = "";
         } else if (!strcmp(name, "nocache"))
                 ctx.cfg.nocache = atoi(value);
         else if (!strcmp(name, "snapshots"))
                 ctx.cfg.snapshots = cgit_parse_snapshots_mask(value);
         else if (!strcmp(name, "enable-index-links"))
                 ctx.cfg.enable_index_links = atoi(value);
         else if (!strcmp(name, "enable-log-filecount"))
                 ctx.cfg.enable_log_filecount = atoi(value);
         else if (!strcmp(name, "enable-log-linecount"))
                 ctx.cfg.enable_log_linecount = atoi(value);
+        else if (!strcmp(name, "cache-size"))
+                ctx.cfg.cache_size = atoi(value);
         else if (!strcmp(name, "cache-root"))
                 ctx.cfg.cache_root = xstrdup(value);
         else if (!strcmp(name, "cache-root-ttl"))
                 ctx.cfg.cache_root_ttl = atoi(value);
         else if (!strcmp(name, "cache-repo-ttl"))
                 ctx.cfg.cache_repo_ttl = atoi(value);
         else if (!strcmp(name, "cache-static-ttl"))
                 ctx.cfg.cache_static_ttl = atoi(value);
         else if (!strcmp(name, "cache-dynamic-ttl"))
                 ctx.cfg.cache_dynamic_ttl = atoi(value);
         else if (!strcmp(name, "max-message-length"))
                 ctx.cfg.max_msg_len = atoi(value);
         else if (!strcmp(name, "max-repodesc-length"))
                 ctx.cfg.max_repodesc_len = atoi(value);
         else if (!strcmp(name, "max-commit-count"))
                 ctx.cfg.max_commit_count = atoi(value);
         else if (!strcmp(name, "summary-log"))
                 ctx.cfg.summary_log = atoi(value);
         else if (!strcmp(name, "summary-branches"))
                 ctx.cfg.summary_branches = atoi(value);
         else if (!strcmp(name, "summary-tags"))
                 ctx.cfg.summary_tags = atoi(value);
         else if (!strcmp(name, "agefile"))
                 ctx.cfg.agefile = xstrdup(value);
         else if (!strcmp(name, "renamelimit"))
                 ctx.cfg.renamelimit = atoi(value);
         else if (!strcmp(name, "robots"))
                 ctx.cfg.robots = xstrdup(value);
         else if (!strcmp(name, "clone-prefix"))
                 ctx.cfg.clone_prefix = xstrdup(value);
         else if (!strcmp(name, "repo.group"))
                 ctx.cfg.repo_group = xstrdup(value);
         else if (!strcmp(name, "repo.url"))
                 ctx.repo = cgit_add_repo(value);
         else if (!strcmp(name, "repo.name"))
                 ctx.repo->name = xstrdup(value);
         else if (ctx.repo && !strcmp(name, "repo.path"))
                 ctx.repo->path = trim_end(value, '/');
         else if (ctx.repo && !strcmp(name, "repo.clone-url"))
                 ctx.repo->clone_url = xstrdup(value);
         else if (ctx.repo && !strcmp(name, "repo.desc"))
                 ctx.repo->desc = xstrdup(value);
         else if (ctx.repo && !strcmp(name, "repo.owner"))
                 ctx.repo->owner = xstrdup(value);
         else if (ctx.repo && !strcmp(name, "repo.defbranch"))
                 ctx.repo->defbranch = xstrdup(value);
         else if (ctx.repo && !strcmp(name, "repo.snapshots"))
                 ctx.repo->snapshots = ctx.cfg.snapshots & cgit_parse_snapshots_mask(value); /* XXX: &? */
@@ -98,364 +100,270 @@ void config_cb(const char *name, const char *value)
         else if (ctx.repo && !strcmp(name, "repo.enable-log-linecount"))
                 ctx.repo->enable_log_linecount = ctx.cfg.enable_log_linecount * atoi(value);
         else if (ctx.repo && !strcmp(name, "repo.module-link"))
                 ctx.repo->module_link= xstrdup(value);
         else if (ctx.repo && !strcmp(name, "repo.readme") && value != NULL) {
                 if (*value == '/')
                         ctx.repo->readme = xstrdup(value);
                 else
                         ctx.repo->readme = xstrdup(fmt("%s/%s", ctx.repo->path, value));
         } else if (!strcmp(name, "include"))
                 parse_configfile(value, config_cb);
 }
 
 static void querystring_cb(const char *name, const char *value)
 {
         if (!strcmp(name,"r")) {
                 ctx.qry.repo = xstrdup(value);
                 ctx.repo = cgit_get_repoinfo(value);
         } else if (!strcmp(name, "p")) {
                 ctx.qry.page = xstrdup(value);
         } else if (!strcmp(name, "url")) {
                 cgit_parse_url(value);
         } else if (!strcmp(name, "qt")) {
                 ctx.qry.grep = xstrdup(value);
         } else if (!strcmp(name, "q")) {
                 ctx.qry.search = xstrdup(value);
         } else if (!strcmp(name, "h")) {
                 ctx.qry.head = xstrdup(value);
                 ctx.qry.has_symref = 1;
         } else if (!strcmp(name, "id")) {
                 ctx.qry.sha1 = xstrdup(value);
                 ctx.qry.has_sha1 = 1;
         } else if (!strcmp(name, "id2")) {
                 ctx.qry.sha2 = xstrdup(value);
                 ctx.qry.has_sha1 = 1;
         } else if (!strcmp(name, "ofs")) {
                 ctx.qry.ofs = atoi(value);
         } else if (!strcmp(name, "path")) {
                 ctx.qry.path = trim_end(value, '/');
         } else if (!strcmp(name, "name")) {
                 ctx.qry.name = xstrdup(value);
         }
 }
 
 static void prepare_context(struct cgit_context *ctx)
 {
         memset(ctx, 0, sizeof(ctx));
         ctx->cfg.agefile = "info/web/last-modified";
+        ctx->cfg.nocache = 0;
+        ctx->cfg.cache_size = 0;
         ctx->cfg.cache_dynamic_ttl = 5;
         ctx->cfg.cache_max_create_time = 5;
         ctx->cfg.cache_repo_ttl = 5;
         ctx->cfg.cache_root = CGIT_CACHE_ROOT;
         ctx->cfg.cache_root_ttl = 5;
         ctx->cfg.cache_static_ttl = -1;
         ctx->cfg.css = "/cgit.css";
         ctx->cfg.logo = "/git-logo.png";
         ctx->cfg.max_commit_count = 50;
         ctx->cfg.max_lock_attempts = 5;
         ctx->cfg.max_msg_len = 60;
         ctx->cfg.max_repodesc_len = 60;
         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.script_name = CGIT_SCRIPT_NAME;
         ctx->page.mimetype = "text/html";
         ctx->page.charset = PAGE_ENCODING;
         ctx->page.filename = NULL;
-}
-
-static int cgit_prepare_cache(struct cacheitem *item)
-{
-        if (!ctx.repo && ctx.qry.repo) {
-                ctx.page.title = fmt("%s - %s", ctx.cfg.root_title,
-                                      "Bad request");
-                cgit_print_http_headers(&ctx);
-                cgit_print_docstart(&ctx);
-                cgit_print_pageheader(&ctx);
-                cgit_print_error(fmt("Unknown repo: %s", ctx.qry.repo));
-                cgit_print_docend();
-                return 0;
-        }
-
-        if (!ctx.repo) {
-                item->name = xstrdup(fmt("%s/index.%s.html",
-                                         ctx.cfg.cache_root,
-                                         cache_safe_filename(ctx.qry.raw)));
-                item->ttl = ctx.cfg.cache_root_ttl;
-                return 1;
-        }
-
-        if (!ctx.qry.page) {
-                item->name = xstrdup(fmt("%s/%s/index.%s.html", ctx.cfg.cache_root,
-                                         cache_safe_filename(ctx.repo->url),
-                                         cache_safe_filename(ctx.qry.raw)));
-                item->ttl = ctx.cfg.cache_repo_ttl;
-        } else {
-                item->name = xstrdup(fmt("%s/%s/%s/%s.html", ctx.cfg.cache_root,
-                                         cache_safe_filename(ctx.repo->url),
-                                         ctx.qry.page,
-                                         cache_safe_filename(ctx.qry.raw)));
-                if (ctx.qry.has_symref)
-                        item->ttl = ctx.cfg.cache_dynamic_ttl;
-                else if (ctx.qry.has_sha1)
-                        item->ttl = ctx.cfg.cache_static_ttl;
-                else
-                        item->ttl = ctx.cfg.cache_repo_ttl;
-        }
-        return 1;
+        ctx->page.modified = time(NULL);
+        ctx->page.expires = ctx->page.modified;
 }
 
 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;
         if (!info->first_ref)
                 info->first_ref = xstrdup(refname);
         return info->match;
 }
 
 char *find_default_branch(struct cgit_repo *repo)
 {
         struct refmatch info;
 
         info.req_ref = repo->defbranch;
         info.first_ref = NULL;
         info.match = 0;
         for_each_branch_ref(find_current_ref, &info);
         if (info.match)
                 return info.req_ref;
         else
                 return info.first_ref;
 }
 
 static int prepare_repo_cmd(struct cgit_context *ctx)
 {
         char *tmp;
         unsigned char sha1[20];
         int nongit = 0;
 
         setenv("GIT_DIR", ctx->repo->path, 1);
         setup_git_directory_gently(&nongit);
         if (nongit) {
                 ctx->page.title = fmt("%s - %s", ctx->cfg.root_title,
                                       "config error");
                 tmp = fmt("Not a git repository: '%s'", ctx->repo->path);
                 ctx->repo = NULL;
                 cgit_print_http_headers(ctx);
                 cgit_print_docstart(ctx);
                 cgit_print_pageheader(ctx);
                 cgit_print_error(tmp);
                 cgit_print_docend();
                 return 1;
         }
         ctx->page.title = fmt("%s - %s", ctx->repo->name, ctx->repo->desc);
 
         if (!ctx->qry.head) {
                 ctx->qry.head = xstrdup(find_default_branch(ctx->repo));
                 ctx->repo->defbranch = ctx->qry.head;
         }
 
         if (!ctx->qry.head) {
                 cgit_print_http_headers(ctx);
                 cgit_print_docstart(ctx);
                 cgit_print_pageheader(ctx);
                 cgit_print_error("Repository seems to be empty");
                 cgit_print_docend();
                 return 1;
         }
 
         if (get_sha1(ctx->qry.head, sha1)) {
                 tmp = xstrdup(ctx->qry.head);
                 ctx->qry.head = ctx->repo->defbranch;
                 cgit_print_http_headers(ctx);
                 cgit_print_docstart(ctx);
                 cgit_print_pageheader(ctx);
                 cgit_print_error(fmt("Invalid branch: %s", tmp));
                 cgit_print_docend();
                 return 1;
         }
         return 0;
 }
 
-static void process_request(struct cgit_context *ctx)
+static void process_request(void *cbdata)
 {
+        struct cgit_context *ctx = cbdata;
         struct cgit_cmd *cmd;
 
         cmd = cgit_get_cmd(ctx);
         if (!cmd) {
                 ctx->page.title = "cgit error";
                 ctx->repo = NULL;
                 cgit_print_http_headers(ctx);
                 cgit_print_docstart(ctx);
                 cgit_print_pageheader(ctx);
                 cgit_print_error("Invalid request");
                 cgit_print_docend();
                 return;
         }
 
         if (cmd->want_repo && prepare_repo_cmd(ctx))
                 return;
 
         if (cmd->want_layout) {
                 cgit_print_http_headers(ctx);
                 cgit_print_docstart(ctx);
                 cgit_print_pageheader(ctx);
         }
 
         cmd->fn(ctx);
 
         if (cmd->want_layout)
                 cgit_print_docend();
 }
 
-static long ttl_seconds(long ttl)
-{
-        if (ttl<0)
-                return 60 * 60 * 24 * 365;
-        else
-                return ttl * 60;
-}
-
-static void cgit_fill_cache(struct cacheitem *item, int use_cache)
-{
-        int stdout2;
-
-        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)");
-        }
-
-        ctx.page.modified = time(NULL);
-        ctx.page.expires = ctx.page.modified + ttl_seconds(item->ttl);
-        process_request(&ctx);
-
-        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");
-        }
-}
-
-static void cgit_check_cache(struct cacheitem *item)
-{
-        int i = 0;
-
- top:
-        if (++i > ctx.cfg.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);
-                }
-        }
-}
-
-static void cgit_print_cache(struct cacheitem *item)
-{
-        static char buf[4096];
-        ssize_t i;
-
-        int fd = open(item->name, O_RDONLY);
-        if (fd<0)
-                die("Unable to open cached file %s", item->name);
-
-        while((i=read(fd, buf, sizeof(buf))) > 0)
-                write(STDOUT_FILENO, buf, i);
-
-        close(fd);
-}
-
 static void cgit_parse_args(int argc, const char **argv)
 {
         int i;
 
         for (i = 1; i < argc; i++) {
                 if (!strncmp(argv[i], "--cache=", 8)) {
                         ctx.cfg.cache_root = xstrdup(argv[i]+8);
                 }
                 if (!strcmp(argv[i], "--nocache")) {
                         ctx.cfg.nocache = 1;
                 }
                 if (!strncmp(argv[i], "--query=", 8)) {
                         ctx.qry.raw = xstrdup(argv[i]+8);
                 }
                 if (!strncmp(argv[i], "--repo=", 7)) {
                         ctx.qry.repo = xstrdup(argv[i]+7);
                 }
                 if (!strncmp(argv[i], "--page=", 7)) {
                         ctx.qry.page = xstrdup(argv[i]+7);
                 }
                 if (!strncmp(argv[i], "--head=", 7)) {
                         ctx.qry.head = xstrdup(argv[i]+7);
                         ctx.qry.has_symref = 1;
                 }
                 if (!strncmp(argv[i], "--sha1=", 7)) {
                         ctx.qry.sha1 = xstrdup(argv[i]+7);
                         ctx.qry.has_sha1 = 1;
                 }
                 if (!strncmp(argv[i], "--ofs=", 6)) {
                         ctx.qry.ofs = atoi(argv[i]+6);
                 }
         }
 }
 
+static int calc_ttl()
+{
+        if (!ctx.repo)
+                return ctx.cfg.cache_root_ttl;
+
+        if (!ctx.qry.page)
+                return ctx.cfg.cache_repo_ttl;
+
+        if (ctx.qry.has_symref)
+                return ctx.cfg.cache_dynamic_ttl;
+
+        if (ctx.qry.has_sha1)
+                return ctx.cfg.cache_static_ttl;
+
+        return ctx.cfg.cache_repo_ttl;
+}
+
 int main(int argc, const char **argv)
 {
-        struct cacheitem item;
         const char *cgit_config_env = getenv("CGIT_CONFIG");
+        int err, ttl;
 
         prepare_context(&ctx);
-        item.st.st_mtime = time(NULL);
         cgit_repolist.length = 0;
         cgit_repolist.count = 0;
         cgit_repolist.repos = NULL;
 
         parse_configfile(cgit_config_env ? cgit_config_env : CGIT_CONFIG,
                          config_cb);
         ctx.repo = NULL;
         if (getenv("SCRIPT_NAME"))
                 ctx.cfg.script_name = xstrdup(getenv("SCRIPT_NAME"));
         if (getenv("QUERY_STRING"))
                 ctx.qry.raw = xstrdup(getenv("QUERY_STRING"));
         cgit_parse_args(argc, argv);
         http_parse_querystring(ctx.qry.raw, querystring_cb);
-        if (!cgit_prepare_cache(&item))
-                return 0;
-        if (ctx.cfg.nocache) {
-                cgit_fill_cache(&item, 0);
-        } else {
-                cgit_check_cache(&item);
-                cgit_print_cache(&item);
-        }
-        return 0;
+
+        ttl = calc_ttl();
+        ctx.page.expires += ttl*60;
+        if (ctx.cfg.nocache)
+                ctx.cfg.cache_size = 0;
+        err = cache_process(ctx.cfg.cache_size, ctx.cfg.cache_root,
+                            ctx.qry.raw, ttl, process_request, &ctx);
+        if (err)
+                cache_log("[cgit] error %d - %s\n",
+                          err, strerror(err));
+        return err;
 }
diff --git a/cgit.h b/cgit.h
index a3b6535..f04d227 100644
--- a/cgit.h
+++ b/cgit.h
@@ -89,96 +89,97 @@ struct taginfo {
 };
 
 struct refinfo {
         const char *refname;
         struct object *object;
         union {
                 struct taginfo *tag;
                 struct commitinfo *commit;
         };
 };
 
 struct reflist {
         struct refinfo **refs;
         int alloc;
         int count;
 };
 
 struct cgit_query {
         int has_symref;
         int has_sha1;
         char *raw;
         char *repo;
         char *page;
         char *search;
         char *grep;
         char *head;
         char *sha1;
         char *sha2;
         char *path;
         char *name;
         int   ofs;
 };
 
 struct cgit_config {
         char *agefile;
         char *cache_root;
         char *clone_prefix;
         char *css;
         char *index_header;
         char *index_info;
         char *logo;
         char *logo_link;
         char *module_link;
         char *repo_group;
         char *robots;
         char *root_title;
         char *script_name;
         char *virtual_root;
+        int cache_size;
         int cache_dynamic_ttl;
         int cache_max_create_time;
         int cache_repo_ttl;
         int cache_root_ttl;
         int cache_static_ttl;
         int enable_index_links;
         int enable_log_filecount;
         int enable_log_linecount;
         int max_commit_count;
         int max_lock_attempts;
         int max_msg_len;
         int max_repodesc_len;
         int nocache;
         int renamelimit;
         int snapshots;
         int summary_branches;
         int summary_log;
         int summary_tags;
 };
 
 struct cgit_page {
         time_t modified;
         time_t expires;
         char *mimetype;
         char *charset;
         char *filename;
         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;
 };
 
 extern const char *cgit_version;
 
 extern struct cgit_repolist cgit_repolist;
 extern struct cgit_context ctx;
 extern const struct cgit_snapshot_format cgit_snapshot_formats[];
diff --git a/tests/setup.sh b/tests/setup.sh
index 66bf406..e37306e 100755
--- a/tests/setup.sh
+++ b/tests/setup.sh
@@ -1,95 +1,95 @@
 # This file should be sourced by all test-scripts
 #
 # Main functions:
 #   prepare_tests(description) - setup for testing, i.e. create repos+config
 #   run_test(description, script) - run one test, i.e. eval script
 #
 # Helper functions
 #   cgit_query(querystring) - call cgit with the specified querystring
 #   cgit_url(url) - call cgit with the specified virtual url
 #
 # Example script:
 #
 # . setup.sh
 # prepare_tests "html validation"
 # run_test 'repo index' 'cgit_url "/" | tidy -e'
 # run_test 'repo summary' 'cgit_url "/foo" | tidy -e'
 
 
 mkrepo() {
         name=$1
         count=$2
         dir=$PWD
         test -d $name && return
         printf "Creating testrepo %s\n" $name
         mkdir -p $name
         cd $name
         git init
         for ((n=1; n<=count; n++))
         do
                 echo $n >file-$n
                 git add file-$n
                 git commit -m "commit $n"
         done
         cd $dir
 }
 
 setup_repos()
 {
         rm -rf trash/cache
         mkdir -p trash/cache
         mkrepo trash/repos/foo 5 >/dev/null
         mkrepo trash/repos/bar 50 >/dev/null
         cat >trash/cgitrc <<EOF
 virtual-root=/
 cache-root=$PWD/trash/cache
 
-nocache=0
+cache-size=1021
 snapshots=tar.gz tar.bz zip
 enable-log-filecount=1
 enable-log-linecount=1
 summary-log=5
 summary-branches=5
 summary-tags=5
 
 repo.url=foo
 repo.path=$PWD/trash/repos/foo/.git
 # Do not specify a description for this repo, as it then will be assigned
 # the constant value "[no description]" (which actually used to cause a
 # segfault).
 
 repo.url=bar
 repo.path=$PWD/trash/repos/bar/.git
 repo.desc=the bar repo
 EOF
 }
 
 prepare_tests()
 {
         setup_repos
         rm -f test-output.log 2>/dev/null
         test_count=0
         test_failed=0
         echo "[$0]" "$@" >test-output.log
         echo "$@" "($0)"
 }
 
 tests_done()
 {
         printf "\n"
         if test $test_failed -gt 0
         then
                 printf "test: *** %s failure(s), logfile=%s\n" \
                         $test_failed "$(pwd)/test-output.log"
                 false
         fi
 }
 
 run_test()
 {
         desc=$1
         script=$2
         ((test_count++))
         printf "\ntest %d: name='%s'\n" $test_count "$desc" >>test-output.log
         printf "test %d: eval='%s'\n" $test_count "$2" >>test-output.log
         eval "$2" >>test-output.log 2>>test-output.log
diff --git a/tests/t0020-validate-cache.sh b/tests/t0020-validate-cache.sh
new file mode 100755
index 0000000..53ec2eb
--- a/dev/null
+++ b/tests/t0020-validate-cache.sh
@@ -0,0 +1,67 @@
+#!/bin/sh
+
+. ./setup.sh
+
+prepare_tests 'Validate cache'
+
+run_test 'verify cache-size=0' '
+
+        rm -f trash/cache/* &&
+        sed -i -e "s/cache-size=1021$/cache-size=0/" trash/cgitrc &&
+        cgit_url "" &&
+        cgit_url "foo" &&
+        cgit_url "foo/refs" &&
+        cgit_url "foo/tree" &&
+        cgit_url "foo/log" &&
+        cgit_url "foo/diff" &&
+        cgit_url "foo/patch" &&
+        cgit_url "bar" &&
+        cgit_url "bar/refs" &&
+        cgit_url "bar/tree" &&
+        cgit_url "bar/log" &&
+        cgit_url "bar/diff" &&
+        cgit_url "bar/patch" &&
+        test 0 -eq $(ls trash/cache | wc -l)
+'
+
+run_test 'verify cache-size=1' '
+
+        rm -f trash/cache/* &&
+        sed -i -e "s/cache-size=0$/cache-size=1/" trash/cgitrc &&
+        cgit_url "" &&
+        cgit_url "foo" &&
+        cgit_url "foo/refs" &&
+        cgit_url "foo/tree" &&
+        cgit_url "foo/log" &&
+        cgit_url "foo/diff" &&
+        cgit_url "foo/patch" &&
+        cgit_url "bar" &&
+        cgit_url "bar/refs" &&
+        cgit_url "bar/tree" &&
+        cgit_url "bar/log" &&
+        cgit_url "bar/diff" &&
+        cgit_url "bar/patch" &&
+        test 1 -eq $(ls trash/cache | wc -l)
+'
+
+run_test 'verify cache-size=1021' '
+
+        rm -f trash/cache/* &&
+        sed -i -e "s/cache-size=1$/cache-size=1021/" trash/cgitrc &&
+        cgit_url "" &&
+        cgit_url "foo" &&
+        cgit_url "foo/refs" &&
+        cgit_url "foo/tree" &&
+        cgit_url "foo/log" &&
+        cgit_url "foo/diff" &&
+        cgit_url "foo/patch" &&
+        cgit_url "bar" &&
+        cgit_url "bar/refs" &&
+        cgit_url "bar/tree" &&
+        cgit_url "bar/log" &&
+        cgit_url "bar/diff" &&
+        cgit_url "bar/patch" &&
+        test 13 -eq $(ls trash/cache | wc -l)
+'
+
+tests_done