cache.c: fix error checking in print_slot()

The change to print_slot() in cdc6b2f8e7a8d43dcfe0475a9d3498333ea686b8 made
the function return correct errno for read errors while ignoring write errors,
which is not what was intended. This patch tries to rectify things.

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

1 files changed, 7 insertions, 4 deletions

diff --git a/cache.c b/cache.c
index aa97ae1..9f02cf5 100644
--- a/cache.c
+++ b/cache.c
@@ -1,436 +1,439 @@
 /* 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"
 
 #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];
 };
 
 /* 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)
 {
         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 = xread(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;
 }
 
 /* Close the active cache slot */
 static int close_slot(struct cache_slot *slot)
 {
         int err = 0;
         if (slot->cache_fd > 0) {
                 if (close(slot->cache_fd))
                         err = errno;
                 else
                         slot->cache_fd = -1;
         }
         return err;
 }
 
 /* Print the content of the active cache slot (but skip the key). */
 static int print_slot(struct cache_slot *slot)
 {
-        ssize_t i;
+        ssize_t i, j;
 
         i = lseek(slot->cache_fd, slot->keylen + 1, SEEK_SET);
         if (i != slot->keylen + 1)
                 return errno;
 
-        while((i = xread(slot->cache_fd, slot->buf, sizeof(slot->buf))) > 0)
-                i = xwrite(STDOUT_FILENO, slot->buf, i);
+        do {
+                i = j = xread(slot->cache_fd, slot->buf, sizeof(slot->buf));
+                if (i > 0)
+                        j = xwrite(STDOUT_FILENO, slot->buf, i);
+        } while (i > 0 && j == i);
 
-        if (i < 0)
+        if (i < 0 || j != i)
                 return errno;
         else
                 return 0;
 }
 
 /* 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);
 }
 
 /* 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 (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);
 }
 
 /* Close an open lockfile */
 static int close_lock(struct cache_slot *slot)
 {
         int err = 0;
         if (slot->lock_fd > 0) {
                 if (close(slot->lock_fd))
                         err = errno;
                 else
                         slot->lock_fd = -1;
         }
         return err;
 }
 
 /* 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)
 {
         slot->lock_fd = open(slot->lock_name, O_RDWR|O_CREAT|O_EXCL,
                              S_IRUSR|S_IWUSR);
         if (slot->lock_fd == -1)
                 return errno;
         if (xwrite(slot->lock_fd, slot->key, slot->keylen + 1) < 0)
                 return errno;
         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
                 err = unlink(slot->lock_name);
 
         if (err)
                 return errno;
 
         return 0;
 }
 
 /* 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 tmp;
 
         /* Preserve stdout */
         tmp = dup(STDOUT_FILENO);
         if (tmp == -1)
                 return errno;
 
         /* Redirect stdout to lockfile */
         if (dup2(slot->lock_fd, STDOUT_FILENO) == -1)
                 return errno;
 
         /* Generate cache content */
         slot->fn(slot->cbdata);
 
         /* Restore stdout */
         if (dup2(tmp, STDOUT_FILENO) == -1)
                 return errno;
 
         /* Close the temporary filedescriptor */
         if (close(tmp))
                 return errno;
 
         return 0;
 }
 
 /* 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)
 {
         unsigned long h = FNV_OFFSET;
         unsigned char *s = (unsigned char *)str;
 
         if (!s)
                 return h;
 
         while(*s) {
                 h *= FNV_PRIME;
                 h ^= *s++;
         }
         return h;
 }
 
 static int process_slot(struct cache_slot *slot)
 {
         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;
                                 }
                         }
                 }
                 if ((err = print_slot(slot)) != 0) {
                         cache_log("[cgit] error printing cache %s: %s (%d)\n",
                                   slot->cache_name,
                                   strerror(err),
                                   err);
                 }
                 close_slot(slot);
                 return err;
         }
 
         /* 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);
         if ((err = print_slot(slot)) != 0) {
                 cache_log("[cgit] error printing cache %s: %s (%d)\n",
                           slot->cache_name,
                           strerror(err),
                           err);
         }
         close_slot(slot);
         return err;
 }
 
 /* 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)
 {
         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;
         }
 
         /* 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);
 }
 
 /* Return a strftime formatted date/time
  * NB: the result from this function is to shared memory
  */
 char *sprintftime(const char *format, time_t time)
 {
         static char buf[64];
         struct tm *tm;
 
         if (!time)
                 return NULL;
         tm = gmtime(&time);
         strftime(buf, sizeof(buf)-1, format, tm);
         return buf;
 }
 
 int cache_ls(const char *path)
 {
         DIR *dir;
         struct dirent *ent;
         int err = 0;
         struct cache_slot slot;
         char fullname[1024];
         char *name;
 
         if (!path) {
                 cache_log("[cgit] cache path not specified\n");
                 return -1;
         }
         if (strlen(path) > 1024 - 10) {
                 cache_log("[cgit] cache path too long: %s\n",
                           path);
                 return -1;
         }
         dir = opendir(path);
         if (!dir) {
                 err = errno;
                 cache_log("[cgit] unable to open path %s: %s (%d)\n",
                           path, strerror(err), err);
                 return err;
         }
         strcpy(fullname, path);
         name = fullname + strlen(path);
         if (*(name - 1) != '/') {
                 *name++ = '/';
                 *name = '\0';
         }
         slot.cache_name = fullname;
         while((ent = readdir(dir)) != NULL) {
                 if (strlen(ent->d_name) != 8)
                         continue;
                 strcpy(name, ent->d_name);
                 if ((err = open_slot(&slot)) != 0) {
                         cache_log("[cgit] unable to open path %s: %s (%d)\n",
                                   fullname, strerror(err), err);
                         continue;
                 }
                 printf("%s %s %10lld %s\n",
                        name,
                        sprintftime("%Y-%m-%d %H:%M:%S",
                                    slot.cache_st.st_mtime),
                        slot.cache_st.st_size,
                        slot.buf);
                 close_slot(&slot);
         }
         closedir(dir);
         return 0;
 }
 
 /* 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);
 }