What is data_file in FiveM?

files {
    'data/handling.meta',
}

data_file 'HANDLING_FILE' 'data/handling.meta'

There are two halves and both are required. The files entry adds the file to the set that clients download. The data_file line tells the game to mount that file as a particular type. The path is relative to the resource root and has to be identical in both places. Glob patterns are accepted, so one line such as data_file 'HANDLING_FILE' 'data/**/handling.meta' can register a file for every car in a pack.

The type names are the game's own. They are the same identifiers that appear as fileType in the content.xml of a single-player dlc.rpf, which makes that file a reliable checklist when converting a mod.

files {
    'data/vehiclelayouts.meta',
    'data/handling.meta',
    'data/vehicles.meta',
    'data/carcols.meta',
    'data/carvariations.meta',
}

data_file 'VEHICLE_LAYOUTS_FILE' 'data/vehiclelayouts.meta'
data_file 'HANDLING_FILE' 'data/handling.meta'
data_file 'VEHICLE_METADATA_FILE' 'data/vehicles.meta'
data_file 'CARCOLS_FILE' 'data/carcols.meta'
data_file 'VEHICLE_VARIATION_FILE' 'data/carvariations.meta'

Only include lines for files the mod actually has. Most cars have no vehiclelayouts.meta, and many have no carcols.meta. The order shown is the convention most vehicle resources follow, with each file declared after the ones it refers to.

• Car will not spawn although the files are present: the VEHICLE_METADATA_FILE line is missing or its path is wrong, so the model name was never registered. See invalid model.
• Handling changes are ignored: the handling file is listed under files but has no HANDLING_FILE line.
• Wrong type for the file: registering carvariations.meta as CARCOLS_FILE, or the reverse, makes the game parse it as the wrong structure.
• Path differs by case: Data/vehicles.meta and data/vehicles.meta are different files on a Linux server.
• Metas placed in the stream folder: the stream folder is for binary assets. Metas go in a data folder or the root, with files and data_file entries.

The FXManifest Generator writes matching files and data_file entries, and the Resource Inspector flags metas that are present in a resource but not registered.