The cache API enables plugins to read, write, and remove objects in the
Traffic Server cache. All cache APIs are keyed by an object called an
TSCacheKey; cache keys are created via
are destroyed via
set the hash of the cache key.
Note that the cache APIs differentiate between HTTP data and plugin data. The cache APIs do not allow you to write HTTP docs in the cache; you can only write plugin-specific data (a specific type of data that differs from the HTTP type).
const unsigned char *key_name = "example key name"; TSCacheKey key; TSCacheKeyCreate (&key); TSCacheKeyDigestSet (key, (unsigned char *) key_name , strlen(key_name)); TSCacheKeyDestroy (key);
TSCacheRead does not really read - it is used for lookups (see the
sample Protocol plugin). Possible callback events include:
TS_EVENT_CACHE_OPEN_READ- indicates the lookup was successful. The data passed back along with this event is a cache vconnection that can be used to initiate a read on this keyed data.
TS_EVENT_CACHE_OPEN_READ_FAILED- indicates the lookup was unsuccessful. Reasons for this event could be that another continuation is writing to that cache location, or the cache key doesn’t refer to a cached resource. Data payload for this event indicates the possible reason the read failed (
TSCacheWrite to write to a cache (see the sample Protocol
callback events include:
TS_EVENT_CACHE_WRITE_READ- indicates the lookup was successful. The data passed back along with this event is a cache vconnection that can be used to initiate a cache write.
TS_EVENT_CACHE_OPEN_WRITE_FAILED- event returned when another continuation is currently writing to this location in the cache. Data payload for this event indicates the possible reason for the write failing (
TSCacheRemove to remove items from the cache. Possible callback
TS_EVENT_CACHE_REMOVE- the item was removed. There is no data payload for this event.
TS_EVENT_CACHE_REMOVE_FAILED- indicates the cache was unable to remove the item identified by the cache key.
TSCacheErrordata indicates why the remove failed.
Errors pertaining to the failure of various cache operations are
TSCacheError (enumeration). They are as follows:
TS_CACHE_ERROR_NO_DOC- the key does not match a cached resource
TS_CACHE_ERROR_DOC_BUSY- e.g, another continuation could be writing to the cache location
TS_CACHE_ERROR_NOT_READY- the cache is not ready
In the example below, suppose there is a cache hit and the cache returns
a vconnection that enables you to read the document from cache. To do
this, you need to prepare a buffer (
cache_bufp) to hold the
document; meanwhile, use
TSVConnCachedObjectSizeGet to find out the
actual size of the document (
content_length). Then, issue
TSVConnRead to read the document with the total data length required
content_length. Assume the following data:
TSIOBuffer cache_bufp = TSIOBufferCreate (); TSIOBufferReader cache_readerp = TSIOBufferReaderAlloc (out_bufp); TSVConn cache_vconnp = NULL; TSVIO cache_vio = NULL; int content_length = 0;
cache_vconnp = (TSVConn) data; TSVConnCachedObjectSizeGet (cache_vconnp, &content_length); cache_vio = TSVConnRead (cache_vconn, contp, cache_bufp, content_length);
(usual VCONN_READ_READY handler logic) int nbytes = TSVIONBytesGet (cache_vio); int ntodo = TSVIONTodoGet (cache_vio); int ndone = TSVIONDoneGet (cache_vio); (consume data in cache_bufp) TSVIOReenable (cache_vio);
Do not try to get continuations or VIOs from
TSVConn objects for
cache vconnections. Also note that the following APIs can only be used
on transformation vconnections and must not be used on cache
vconnections or net vconnections:
APIs such as
TSVConnShutdown can be used on any kind of
When you are finished: