Cache Lua Reference Documentation
chilkat.Cache
Current Version: 11.7.0
Markdown version of this page for AI tools (v 11.7.0) · all AI docs
Chilkat.Cache
Store and retrieve cached items by unique key, without the application
needing to manage the underlying cache filenames directly.
Cache strings, byte data, files, or Chilkat buffer objects depending on
the data form used by the application.
Associate cached items with expiration times, update expiration metadata,
and check whether cached content is still usable.
Store and retrieve ETag values for workflows that need HTTP-style cache
validation or conditional re-fetch logic.
Choose the cache root directory and use an optional multi-level directory
structure to avoid too many files in a single folder.
Delete a single cached item, remove expired items, remove older items, or
clear the entire cache when needed.
For an extended overview, see
Cache Class Overview.
Store, retrieve, expire, and clean up cached text or binary data on disk.
Chilkat.Cache is a disk-based cache class for storing and
retrieving text or binary items by unique key. It provides configurable cache
roots, optional multi-level directory layout, expiration metadata, ETag
metadata, cache lookup, fetch-status properties, expiration updates, and
cleanup methods for deleting individual items, expired items, older items, or
the entire cache.
Key-based storage
Text and binary data
Expiration control
ETag metadata
Configurable layout
Cleanup operations
Object Creation
local chilkat = require("chilkat")
local cache = chilkat.Cache.new()Creates the object (chilkat.Cache() does the same). Lua's garbage collector frees it when it is no longer referenced; cache:dispose() frees it at once, and in Lua 5.4 and later local cache <close> = chilkat.Cache.new() frees it when the block ends. Calling a method of a disposed object raises an error.
Errors
A method that fails returns nil followed by the error text, as io.open does: local body, err = cache:method(...), where err is the object's last_error_text. Wrap the call in assert() to raise an error with that text instead. Methods that answer a question return true or false, numbers are returned as they are (check last_method_success where the description says a value means failure), and property reads and writes never fail for Chilkat reasons.
Misuse raises a Lua error: a wrong argument type or a missing argument (bad argument #1 to ...), an unknown property name, a write to a read-only property, an out-of-range integer, or an object of the wrong class.
Names are Chilkat's in snake_case: QuickGetStr is quick_get_str, LastErrorText is last_error_text. Properties are fields (cache.verbose_logging = true) and methods use the colon (cache:method(...)). Strings are UTF-8; binary data is a Lua string of bytes. Indexes are 0-based, as in every Chilkat API. Unlocking: call chilkat.unlock_bundle("...") once at startup.
Properties
DebugLogFilePath
local strVal = cache.debug_log_file_path
cache.debug_log_file_path = strVal
If set to a file path, this property logs the LastErrorText of each Chilkat method or property call to the specified file. This logging helps identify the context and history of Chilkat calls leading up to any crash or hang, aiding in debugging.
Enabling the VerboseLogging property provides more detailed information. This property is mainly used for debugging rare instances where a Chilkat method call causes a hang or crash, which should generally not happen.
Possible causes of hangs include:
- A timeout property set to 0, indicating an infinite timeout.
- A hang occurring within an event callback in the application code.
- An internal bug in the Chilkat code causing the hang.
LastErrorHtml
local strVal = cache.last_error_html
Provides HTML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
topLastErrorText
local strVal = cache.last_error_text
Provides plain text information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
LastErrorXml
local strVal = cache.last_error_xml
Provides XML-formatted information about the last called method or property. If a method call fails or behaves unexpectedly, check this property for details. Note that information is available regardless of the method call's success.
topLastEtagFetched
local strVal = cache.last_etag_fetched
Returns the ETag metadata associated with the most recently fetched cache item. An empty string means that the fetched item has no stored ETag.
FetchBd, FetchSb, or FetchText.If-None-Match.LastExpirationFetchedStr
local strVal = cache.last_expiration_fetched_str
Returns the expiration date and time stored for the most recently fetched cache item, formatted as an RFC 822-style Internet date. An empty string represents an item with no expiration date.
LastHitExpired after the fetch to determine whether the returned entry is stale.LastHitExpired
local boolVal = cache.last_hit_expired
Returns true when the expiration time of the most recently fetched item is earlier than the current system date and time; otherwise returns false.
DeleteAllExpired or DeleteFromCache.LastKeyFetched
local strVal = cache.last_key_fetched
Returns the application-defined key associated with the most recently fetched cache item.
LastMethodSuccess
local boolVal = cache.last_method_success
cache.last_method_success = boolVal
Indicates the success or failure of the most recent method call: true means success, false means failure. This property remains unchanged by property setters or getters. This method is present to address challenges in checking for null or Nothing returns in certain programming languages. Note: This property does not apply to methods that return integer values or to boolean-returning methods where the boolean does not indicate success or failure.
Level
local intVal = cache.level
cache.level = intVal
Gets or sets the number of directory levels used beneath each cache root. Valid values are 0, 1, and 2.
| Value | Directory layout |
|---|---|
0 | All cache files are stored directly in the cache root. |
1 | Files are distributed among 256 first-level directories named 0 through 255. |
2 | Files are distributed through two levels of 256 directories, allowing as many as 65,536 leaf directories per root. |
NumRoots
local intVal = cache.num_roots
Returns the number of cache-root directories that have been registered by calling AddRoot.
VerboseLogging
local boolVal = cache.verbose_logging
cache.verbose_logging = boolVal
If set to true, then the contents of LastErrorText (or LastErrorXml, or LastErrorHtml) may contain more verbose information. The default value is false. Verbose logging should only be used for debugging. The potentially large quantity of logged information may adversely affect peformance.
Version
local strVal = cache.version
Methods
AddRoot
cache:add_root(path)
Adds path as a root directory for the disk cache. Call this method once for each root that should participate in the cache.
For example, a cache distributed across D:\cacheRoot, E:\cacheRoot, and F:\cacheRoot is configured by calling this method three times.
Level setting before accessing a cache created by an earlier process or application run.DeleteAll
local n = cache:delete_all()
Deletes every cache item from all configured roots and returns the number of cache files removed. Multi-level subdirectories are retained.
DeleteAllExpired
local n = cache:delete_all_expired()
Deletes all cache items whose stored expiration time is earlier than the current system time and returns the number of files removed.
DeleteFromCache
-- ok is true, or nil and err on failure
local ok, err = cache:delete_from_cache(key)
Deletes the cache item identified by key.
| Return value | Meaning |
|---|---|
true | The item was deleted, or no item existed for the key. |
false | The item exists but could not be deleted, for example because of a filesystem permission or sharing error. |
Returns true on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
DeleteOlderDt
Deletes cache items older than the cutoff date and time supplied in dt.
Returns the number of cache files deleted, or -1 if an error occurs.
DeleteAllExpired when the decision should be based specifically on each item's expiration metadata.DeleteOlderStr
-- n is an integer
local n = cache:delete_older_str(date_time_str)
Deletes cache items older than the cutoff date and time supplied in date_time_str as an RFC 822-style Internet date string.
Returns the number of cache files deleted, or -1 if an error occurs.
Mon, 03 Aug 2026 12:00:00 GMT. Use DeleteOlderDt when the cutoff is already available as a CkDateTime.FetchBd
-- bd is a chilkat.BinData
-- ok is true, or nil and err on failure
local ok, err = cache:fetch_bd(key, bd)
Retrieves the binary item identified by key and loads its bytes into the BinData object supplied in bd.
The key is application-defined, may contain any characters, and must uniquely identify the intended item.
true. A failed lookup or filesystem error returns false.LastHitExpired immediately afterward when stale data must not be used.Returns true on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
FetchSb
-- sb is a chilkat.StringBuilder
-- ok is true, or nil and err on failure
local ok, err = cache:fetch_sb(key, sb)
Retrieves the text item identified by key and loads its content into the StringBuilder supplied in sb.
The key is application-defined, may contain any characters, and must uniquely identify the intended item.
true. A failed lookup or filesystem error returns false.LastHitExpired immediately afterward when stale data must not be used.Returns true on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
FetchText
-- str is a string, or nil and err on failure
local str, err = cache:fetch_text(key)
Retrieves the text item identified by key and returns its string content.
The key is application-defined, may contain any characters, and must uniquely identify the intended item.
LastHitExpired immediately afterward when the application requires only fresh data.Returns the string, or nil, err on failure (or when nothing is found). The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
GetEtag
-- str is a string, or nil and err on failure
local str, err = cache:get_etag(key)
Returns the ETag metadata stored with the cache item identified by key.
Returns the string, or nil, err on failure (or when nothing is found). The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
GetExpirationStr
-- str is a string, or nil and err on failure
local str, err = cache:get_expiration_str(url)
Returns the expiration date and time stored for the item identified by url, formatted as an RFC 822-style Internet date string.
url url for historical reasons. It is the cache key and does not need to be a URL.Returns the string, or nil, err on failure (or when nothing is found). The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
GetFilename
-- str is a string, or nil and err on failure
local str, err = cache:get_filename(key)
Returns the absolute filesystem path of the cache file associated with key.
Cache API rather than modifying cache files directly.Returns the string, or nil, err on failure (or when nothing is found). The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
GetRoot
-- str is a string, or nil and err on failure
local str, err = cache:get_root(index)
Returns the directory path of the cache root at zero-based index. Valid indexes range from 0 through NumRoots - 1.
Returns the string, or nil, err on failure (or when nothing is found). The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
IsCached
-- flag is true or false
local flag = cache:is_cached(key)
Returns true if an item exists for key, or false if the key is not present.
LastHitExpired, or read its expiration metadata, when freshness matters.Returns true or false: an answer, not a success flag.
SaveBd
-- expiration is a string
-- etag is a string
-- bd is a chilkat.BinData
-- ok is true, or nil and err on failure
local ok, err = cache:save_bd(key, expiration, etag, bd)
Stores the contents of bd as binary cache data under key. If the key already exists, its data and metadata are replaced.
| Argument | Purpose |
|---|---|
key | The unique application-defined cache key. |
expiration | Expiration as an RFC 822-style Internet date string. Pass an empty string for no expiration. |
etag | Optional ETag or application metadata. Pass an empty string when unused. |
bd | The BinData containing the bytes to save. |
Returns true on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
SaveTextDt
-- expire_date_time is a chilkat.DateTime
-- e_tag is a string
-- item_text_data is a string
-- ok is true, or nil and err on failure
local ok, err = cache:save_text_dt(key, expire_date_time, e_tag, item_text_data)
Stores item_text_data as a text cache item under key, with the expiration date and time supplied in expire_date_time. If the key already exists, its data and metadata are replaced.
e_tag is optional ETag or application metadata and may be an empty string. The key may contain any characters and may be any length, but it must uniquely identify the item.
LastHitExpired to detect staleness and a deletion method to remove it.Returns true on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
SaveTextNoExpire
-- e_tag is a string
-- item_text_data is a string
-- ok is true, or nil and err on failure
local ok, err = cache:save_text_no_expire(key, e_tag, item_text_data)
Stores item_text_data as a non-expiring text cache item under key. If the key already exists, its data and metadata are replaced.
e_tag is optional ETag or application metadata and may be an empty string.
Returns true on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
SaveTextStr
-- expire_date_time is a string
-- e_tag is a string
-- item_text_data is a string
-- ok is true, or nil and err on failure
local ok, err = cache:save_text_str(key, expire_date_time, e_tag, item_text_data)
Stores item_text_data as a text cache item under key, with expire_date_time providing the expiration time as an RFC 822-style Internet date string. If the key already exists, its data and metadata are replaced.
e_tag is optional ETag or application metadata and may be empty.
SaveTextDt when the expiration is available as a CkDateTime, or SaveTextNoExpire for an entry without expiration.Returns true on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
UpdateExpirationDt
-- expire_date_time is a chilkat.DateTime
-- ok is true, or nil and err on failure
local ok, err = cache:update_expiration_dt(key, expire_date_time)
Replaces the expiration date and time of the cache item identified by key with the CkDateTime value supplied in expire_date_time. The cached data and ETag are unchanged.
Returns true on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.
UpdateExpirationStr
-- expire_date_time is a string
-- ok is true, or nil and err on failure
local ok, err = cache:update_expiration_str(key, expire_date_time)
Replaces the expiration date and time of the cache item identified by key with the RFC 822-style Internet date string supplied in expire_date_time. The cached data and ETag are unchanged.
key url; it is the cache key and does not need to be a URL. Use UpdateExpirationDt for a CkDateTime value.Returns true on success, nil, err on failure. The second return value, err, is the object's last_error_text; wrap the call in assert() to raise an error instead.