Cloud Storage

Access S3-compatible object storage. Upload, download, list, and manage files with presigned URL support.

For storage configuration, see Cloud Storage.

Loading

local cloudstorage = require("cloudstorage")

Acquiring Storage

Get a cloud storage resource by registry ID:

local storage, err = cloudstorage.get("app.infra:files")
if err then
    return nil, err
end

storage:upload_object("data/file.txt", "content")
storage:release()

Returns: Storage, error

Uploading Objects

Upload content from string or file:

local storage = cloudstorage.get("app.infra:files")

-- Upload string content
local ok, err = storage:upload_object("reports/daily.json", json.encode({
    date = "2024-01-15",
    total = 1234
}))

-- Upload from file
local fs = require("fs")
local vol = fs.get("app:data")
local file = vol:open("/large-file.bin", "r")

storage:upload_object("backups/large-file.bin", file)
file:close()

storage:release()

Returns: boolean, error

Upload Options

Attach metadata or guard the write with an options table:

storage:upload_object("reports/daily.json", body, {
    content_type = "application/json",
    cache_control = "max-age=3600",
    metadata = { owner = "team-a", run_id = "1234" },  -- stored as x-amz-meta-*
    only_if_absent = true                              -- fail if the key already exists
})

A conditional write that fails its precondition returns a precondition_failed error.

Downloading Objects

Download an object to a file writer:

local storage = cloudstorage.get("app.infra:files")
local fs = require("fs")
local vol = fs.get("app:temp")

local file = vol:open("/downloaded.json", "w")
local ok, err = storage:download_object("reports/daily.json", file)
file:close()

-- Download partial content (first 1KB)
local partial = vol:open("/partial.bin", "w")
storage:download_object("backups/large-file.bin", partial, {
    range = "bytes=0-1023"
})
partial:close()

storage:release()

Returns: boolean, error

A failed precondition (if_match/if_none_match) returns a precondition_failed error.

Listing Objects

List objects with optional prefix filtering:

local storage = cloudstorage.get("app.infra:files")

local result, err = storage:list_objects({
    prefix = "reports/2024/",
    max_keys = 100
})

for _, obj in ipairs(result.objects) do
    print(obj.key, obj.size, obj.etag)
end

-- Paginate through large results
local token = nil
repeat
    local result = storage:list_objects({
        prefix = "logs/",
        max_keys = 1000,
        continuation_token = token
    })
    for _, obj in ipairs(result.objects) do
        process(obj)
    end
    token = result.next_continuation_token
until not result.is_truncated

storage:release()

Returns: table, error

Result contains objects, is_truncated, next_continuation_token. Each object has key, size, etag, storage_class, and optional last_modified, version_id, and owner.

Object Metadata

Fetch a single object's metadata without downloading its body:

local storage = cloudstorage.get("app.infra:files")

local meta, err = storage:head_object("reports/daily.json")
if err then
    return nil, err
end

print(meta.size, meta.etag, meta.content_type)
for k, v in pairs(meta.metadata) do
    print("meta", k, v)
end

storage:release()

Returns: table, error

Result fields:

A missing object returns a not_found error.

Deleting Objects

Remove multiple objects:

local storage = cloudstorage.get("app.infra:files")

storage:delete_objects({
    "temp/file1.txt",
    "temp/file2.txt",
    "temp/file3.txt"
})

storage:release()

Returns: boolean, error

Download URLs

Create a temporary URL that allows downloading an object without credentials. Useful for sharing files with external users or serving content through your application.

local storage, err = cloudstorage.get("app.infra:files")
if err then
    return nil, err
end

local url, err = storage:presigned_get_url("reports/quarterly.pdf", {
    expiration = 3600
})

storage:release()

if err then
    return nil, err
end

-- Return URL to client for direct download
return {download_url = url}

Returns: string, error

Upload URLs

Create a temporary URL that allows uploading an object without credentials. Enables clients to upload files directly to storage without proxying through your server.

local storage, err = cloudstorage.get("app.infra:files")
if err then
    return nil, err
end

local url, err = storage:presigned_put_url("uploads/user-123/avatar.jpg", {
    expiration = 600,
    content_type = "image/jpeg",
    content_length = 1024 * 1024
})

storage:release()

if err then
    return nil, err
end

-- Return URL to client for direct upload
return {upload_url = url}

Returns: string, error

Storage Methods

Permissions

Cloud storage operations are subject to security policy evaluation.

Errors

See Error Handling for working with errors.