im +messages-resources-download

Prerequisite: Read ../lark-shared/SKILL.md first to understand authentication, global parameters, and safety rules.

Download image or file resources from a message. Supports automatic chunked download for large files using HTTP Range requests. Resources are identified by the combination of message_id + file_key, both of which come directly from message content returned by im +chat-messages-list.

Note: read-only message commands render resource keys in message content, but they do not download binaries automatically. Use this command whenever you need to fetch the actual image/file bytes or save them to a specific path.

This skill maps to the shortcut: lark-cli im +messages-resources-download (internally calls GET /open-apis/im/v1/messages/{message_id}/resources/{file_key}).

Commands

# Download an image (save to the current directory)
lark-cli im +messages-resources-download --message-id om_xxx --file-key img_v3_xxx --type image

# Download a file
lark-cli im +messages-resources-download --message-id om_xxx --file-key file_v3_xxx --type file

# Specify the output path
lark-cli im +messages-resources-download --message-id om_xxx --file-key img_v3_xxx --type image --output ./photo.png

# Download as a bot
lark-cli im +messages-resources-download --message-id om_xxx --file-key img_v3_xxx --type image --as bot

# Preview the request without executing it
lark-cli im +messages-resources-download --message-id om_xxx --file-key img_v3_xxx --type image --dry-run

Parameters

Parameter	Required	Description
`--message-id <id>`	Yes	Message ID (`om_xxx` format)
`--file-key <key>`	Yes	Resource key (`img_xxx` or `file_xxx`)
`--type <type>`	Yes	Resource type: `image` or `file`
`--output <path>`	No	Output path (relative paths only; `..` traversal is not allowed). When omitted, the server's original filename from `Content-Disposition` is used if available; otherwise defaults to `file_key`. File extension is automatically inferred from `Content-Disposition` or `Content-Type` if not provided
`--as <identity>`	No	Identity type: `user` (default) or `bot`
`--dry-run`	No	Print the request only, do not execute it

Large File Download (Auto Chunking)

When downloading large files, the command automatically uses HTTP Range requests for reliable chunked downloading:

Behavior	Details
Probe chunk	First 128 KB to detect file size and Content-Type
Chunk size	8 MB per subsequent request
Workers	Single-threaded sequential download (ensures reliability)
Retries	Up to 2 retries for transient request failures, with exponential backoff

Benefits:

Reduces the impact of transient request failures during large downloads
Preserves the server's original filename via Content-Disposition (supports RFC 5987 UTF-8 encoding); falls back to Content-Type-based extension inference
Validates file size integrity after download completion

`file_key` Sources

Different resource markers in message content correspond to different file_key and type values:

Message Type	Marker in Content	`file_key` Format	`--type`
Image	`img_xxx`	`img_xxx`	`image`
File	`file_xxx`	`file_xxx`	`file`
Audio	`file_xxx`	`file_xxx`	`file`
Video	`file_xxx`	`file_xxx`	`file`

Usage Scenario

Scenario: Extract and download an image from a message

# Step 1: Fetch messages and find one containing an image
lark-cli im +chat-messages-list --chat-id oc_xxx
# In the response you see: { "msg_type": "image", "content": "{\"image_key\":\"img_v3_xxx\"}" }

# Step 2: Download the image
lark-cli im +messages-resources-download --message-id om_xxx --file-key img_v3_xxx --type image

Common Errors and Troubleshooting

Symptom	Root Cause	Solution
Download failed	`file_key` does not match the `message_id`	Make sure the `file_key` came from that message's content
Hit error code 234002 or 14005	No permission, not missing API scope	no access to this chat or file was deleted — do not retry, return the error to the user
Permission denied	`im:message:readonly` is not authorized	Run `auth login --scope "im:message:readonly"`
File size mismatch	Chunked download integrity check failed	Network instability during download; retry the command
Content-Range error	Server returned invalid range header	Transient API issue; retry the command

References

lark-im - all message-related commands
lark-shared - authentication and global parameters

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