filter_lua: Add chunk mode for processing multiple records

Documentation for fluent/fluent-bit#8478

Signed-off-by: Richard Treu <richard.treu@sap.com>

pipeline/filters/lua.md

@@ -21,6 +21,7 @@ The plugin supports the following configuration parameters:
 | time\_as\_table | By default when the Lua script is invoked, the record timestamp is passed as a *floating number* which might lead to precision loss when it is converted back. If you desire timestamp precision, enabling this option will pass the timestamp as a Lua table with keys `sec` for seconds since epoch and `nsec` for nanoseconds. |
 | code | Inline LUA code instead of loading from a path via `script`. |
 | enable_flb_null| If enabled, null will be converted to flb_null in Lua. It is useful to prevent removing key/value since nil is a special value to remove key value from map in Lua. Default is false. |
+| chunk_mode | If enabled, a whole chunk will be sent to Lua script as a table of timestamps and records. It may be used for e.g. parallel execution inside Lua. Default is false. |
 
 ## Getting Started <a id="getting_started"></a>
 
@@ -348,3 +349,182 @@ Configuration to get istio logs and apply response code filter to them.
 #### Output
 
 In the output only the messages with response code 0 or greater than 399 are shown.
+
+### Chunk mode
+
+There is a `chunk_mode` for the Lua filter in Fluent Bit. This mode can be useful for cases like parallelization, particularly when utilizing Lua lanes.
+
+#### Function Signature
+
+The Lua functions associated with this mode accept only two arguments:
+
+```
+function process_records(tag, records)
+```
+
+#### Configuration
+
+The configuration for the Lua filter using chunk mode looks like this:
+
+```
+[FILTER]
+    Name          lua
+    Match         my_logs
+    script        lanes_example.lua
+    call          process_records
+    chunk_mode    On
+    time_as_table On
+```
+#### Note
+
+- This mode currently only supports `time_as_table` by default.
+- Records are always emitted; there is no return code to be set.
+
+#### Return Table Format
+
+The return table must maintain this format, i.e., a table of timestamp and record pairs.
+
+| Timestamp                | Record                                |
+|--------------------------|---------------------------------------|
+| {                        | {                                     |
+|    sec: <timestamp_sec>, |    message: "your_dummy_log_message" |
+|    nsec: <timestamp_nsec>| }                                     |
+| }                        |                                       |
+|                          |                                       |
+| {                        | {                                     |
+|    sec: <timestamp_sec>, |    message: "your_dummy_log_message" |
+|    nsec: <timestamp_nsec>| }                                     |
+| }                        |                                       |
+
+Please refer to the following examples to see how to build the return table.
+
+#### Input Table Example
+
+```
+function process_records(tag, records)
+  if records and type(records) == "table" then
+    for i, record_row in ipairs(records) do
+        local timestamp = record_row.timestamp
+        local record = record_row.record
+
+        print("Timestamp entry:", timestamp.sec, timestamp.nsec)
+        print("Record entry:", record.message)
+    end
+  else
+    print("Error: Invalid 'records' table or nil")
+  end
+  return records
+end
+```
+
+
+#### Parallelization Example
+
+Ensure that you have Lua lanes installed (e.g. `luarocks install lanes`) and to set the path appropriately (`luarocks show lanes`) in your lua script.
+To inject multiple dummy messages at once, you can adjust the `Copies` parameter of the `dummy` input.
+Keep in mind that this example will create a new thread for every record in the chunk to keep the example simple.
+
+```
+fluent-bit.conf:
+
+[SERVICE]
+    Flush        5
+    Log_Level    debug
+    Daemon       off
+    HTTP_Server  Off
+
+[INPUT]
+    Name   dummy
+    Tag    my_logs
+    Rate   1
+    Copies 2
+    Dummy {"message":"your_dummy_log_message"}
+
+[FILTER]
+    Name   lua
+    Match  my_logs
+    script lanes_example.lua
+    call   threads
+    chunk_mode On
+    time_as_table On
+
+[OUTPUT]
+    Name  stdout
+    Match my_logs
+```
+
+```lua
+lanes_example.lua:
+
+-- Specify path to Lua Lanes module
+-- Install via: 'luarocks install lanes'
+local lanes_path = "/usr/local/share/lua/5.1/lanes.lua"
+
+-- Load Lanes lib
+local lanes = assert(loadfile(lanes_path))().configure()
+
+-- Lua function that will be executed as separate threads
+local function process_log(timestamp, record)
+    -- Add your CPU intensive code here
+    print("Timestamp:", timestamp.sec, timestamp.nsec)
+    print("Record:", record.message)
+
+    record.message = "Modified"
+    return timestamp, record
+end
+
+-- Entry function
+function threads(tag, records)
+  print("LUA ")
+  local thread_handles = {}
+  local results = {}
+  if records and type(records) == "table" then
+    print("Number of incoming records:", #records)
+    for i, log_event in ipairs(records) do
+        local timestamp = log_event.timestamp
+        local record = log_event.record
+
+          -- Use lanes.gen to create a new thread
+          local thread = lanes.gen("*", process_log)(timestamp, record)
+
+          -- Store the thread handle
+          table.insert(thread_handles, thread)
+    end
+    -- Wait for all threads to finish
+    for _, thread in ipairs(thread_handles) do
+        -- Get the result returned by each thread
+        local modified_record = thread[2]
+        local modified_timestamp = thread[1]
+        local result = {timestamp = modified_timestamp, record = modified_record}
+        table.insert(results, result)
+    end
+    print("All threads returned")
+  else
+    print("Error: Invalid or nil 'records' table.")
+  end
+
+  return results
+end
+```
+
+You should get a similar output:
+```
+...
+LUA
+Number of incoming records:     2
+Timestamp:      1707308482      97855348
+Record: your_dummy_log_message
+Timestamp:      1707308482      97664060
+Record: your_dummy_log_message
+All threads returned
+...
+[0] my_logs: [[1707308479.115073794, {}], {"message"=>"Modified"}]
+[1] my_logs: [[1707308479.147705065, {}], {"message"=>"Modified"}]
+[2] my_logs: [[1707308480.097053227, {}], {"message"=>"Modified"}]
+[3] my_logs: [[1707308480.097306893, {}], {"message"=>"Modified"}]
+[4] my_logs: [[1707308481.097325851, {}], {"message"=>"Modified"}]
+[5] my_logs: [[1707308481.097515912, {}], {"message"=>"Modified"}]
+[6] my_logs: [[1707308482.097664060, {}], {"message"=>"Modified"}]
+[7] my_logs: [[1707308482.097855348, {}], {"message"=>"Modified"}]
+...
+```