rongshu/.agents/skills/lark-im/references/lark-im-messages-resources-download.md

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; defaults to file_key as the file name). File extension is automatically added based on 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
• Automatically detects and appends correct file extension from Content-Type
• 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