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AndrewStone
2020-11-04 13:23:02 -05:00
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protocol/network/messages/inv.md
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"related":["/protocol","/protocol/network/messages/getdata.md","/protocol/network/messages/filterload.md","/protocol/network/messages/filterclear.md"]
}</div>
# Announcement: Inventory ("inv")
*Notifies peers about the existence of some information (block or transaction)*
Based on selected services in the [VERSION](/protocol/network/messages/version.md) message, INV messages may not be sent.
Notifies peers about the existence of some information (block or transaction).
If a bloom filter has been sent to this node via [FILTERLOAD](/protocol/network/messages/filterload.md), transaction INVs will only be sent if they match the bloom filter.
Based on selected services in the [version](/protocol/network/messages/version) message, inventory messages may not be sent.
| compact int | 4 bytes | 32 bytes |... | 4 bytes | 32 bytes |
|----------|---------|----------|---|---------|----------|
|[vector](/protocol/p2p/vector.md) size N of| type 1 | hash 1 | | type N | hash N
If a bloom filter has been sent to this node via [filterload](/protocol/network/messages/filterload), a transaction inventory will only be sent for transactions that match the bloom filter.
NOTE: Since a block header is a relatively small data structure, and block propagation speed is an important network metric, a peer may send HEADER messages in place of INV messages when a block arrives.
## Message Format
| Field | Length | Format | Description |
|--|--|--|--|
| inventory count | variable | [variable length integer](/protocol/formats/variable-length-integer) | The number of inventory items in this message. |
| inventory items | `inventory_count` * 36 bytes | `inventory_count` [inventory items](#inventory-item-format) | The set of inventory items being transmitted. |
NOTE: Since a block header is a relatively small data structure, and block propagation speed is an important network metric, a peer may send [headers](/protocol/network/messages/headers) messages in place of inventory messages when a block arrives. This behavior can be requested using the [sendheaders](/protocol/network/messages/sendheaders) message.
#### Inventory Item Format
| Field | Length | Format | Description |
|--|--|--|--|
| type | 4 bytes | [inventory type](#inventory-types)<sup>[(LE)](/protocol/misc/endian/little)</sup> | Indicates what the following hash represents. |
| item hash | 32 bytes | bytes<sup>[(LE)](/protocol/misc/endian/little)</sup> | The [hash](/protocol/blockchain/hash) that identifies the item. |
#### Inventory Types
##### Type
The type of the object that is available.
| Type | Value|
@@ -40,3 +27,6 @@ The type of the object that is available.
| 6 | Graphene Block (Bitcoin Unlimited)
Implementations: [C++](https://github.com/BitcoinUnlimited/BitcoinUnlimited/blob/eb264e627e231f7219e60eef41b4e37cc52d6d9d/src/protocol.h#L477)
##### Hash
The [hash identifier](/glossary/hash__identifier.md) of the available object.