@@ -24,6 +24,8 @@ dapi-grpc = { path = "../dapi-grpc", default-features = false, features = [
 dash-context-provider = { path = "../rs-context-provider", default-features = false }
 dash-platform-macros = { path = "../rs-dash-platform-macros" }
 dpp = { path = "../rs-dpp", default-features = false, features = [
+  "dashpay-contract",
+  "dpns-contract",
   "platform-value-cbor",
   "state-transitions",
   "state-transition-validation",
 
@@ -0,0 +1,254 @@
+//! Transport-free DashPay document assembly.
+//!
+//! The Sdk-bound DashPay surface (ECDH, encryption, fetching the recipient,
+//! broadcasting) lives in `dash-sdk`; this is the pure DIP-15 document
+//! assembly it shares with embedders that hold the encrypted material
+//! themselves. Field size bounds come from the DashPay contract schema, so
+//! the builder cannot drift from what the contract accepts.
+
+use crate::dpns_usernames::new_document;
+use crate::Error;
+use dpp::data_contract::accessors::v0::DataContractV0Getters;
+use dpp::data_contract::document_type::accessors::DocumentTypeV0Getters;
+use dpp::data_contract::document_type::DocumentTypeRef;
+use dpp::data_contract::errors::DataContractError;
+use dpp::document::Document;
+use dpp::platform_value::Value;
+use dpp::prelude::{DataContract, Identifier};
+use dpp::system_data_contracts::dashpay_contract::v1::document_types::contact_request;
+use std::collections::BTreeMap;
+
+/// Inputs of a DIP-15 `contactRequest` document. The encrypted fields are
+/// supplied already encrypted (ECDH, AES-CBC with a fresh IV prepended);
+/// see `dash-sdk`'s `create_contact_request` for the encryption itself.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ContactRequestDocumentParams {
+    /// Identity sending the request; becomes the document owner.
+    pub sender_id: Identifier,
+    /// Identity receiving the request (`toUserId`).
+    pub recipient_id: Identifier,
+    /// Index of the sender's encryption key used for ECDH.
+    pub sender_key_index: u32,
+    /// Index of the recipient's key used for ECDH.
+    pub recipient_key_index: u32,
+    /// DashPay receiving-account reference.
+    pub account_reference: u32,
+    /// Encrypted DIP-15 compact extended public key (IV ‖ ciphertext).
+    pub encrypted_public_key: Vec<u8>,
+    /// Encrypted account label (IV ‖ ciphertext), if any.
+    pub encrypted_account_label: Option<Vec<u8>>,
+    /// Unencrypted auto-accept proof, if any.
+    pub auto_accept_proof: Option<Vec<u8>>,
+    /// Entropy the document id derives from; reuse it on the create
+    /// transition.
+    pub entropy: [u8; 32],
+}
+
+/// Assemble a `contactRequest` document, checking every byte-array field
+/// against the size bounds the contract schema declares for it.
+pub fn build_contact_request_document(
+    contract: &DataContract,
+    params: ContactRequestDocumentParams,
+) -> Result<Document, Error> {
+    let document_type = contract.document_type_for_name(contact_request::NAME)?;
+
+    check_byte_field(
+        document_type,
+        "encryptedPublicKey",
+        &params.encrypted_public_key,
+    )?;
+    if let Some(label) = &params.encrypted_account_label {
+        check_byte_field(document_type, "encryptedAccountLabel", label)?;
+    }
+    if let Some(proof) = &params.auto_accept_proof {
+        check_byte_field(document_type, "autoAcceptProof", proof)?;
+    }
+
+    let mut properties = BTreeMap::from([
+        (
+            contact_request::properties::TO_USER_ID.to_string(),
+            Value::Identifier(params.recipient_id.to_buffer()),
+        ),
+        (
+            "encryptedPublicKey".to_string(),
+            Value::Bytes(params.encrypted_public_key),
+        ),
+        (
+            "senderKeyIndex".to_string(),
+            Value::U32(params.sender_key_index),
+        ),
+        (
+            "recipientKeyIndex".to_string(),
+            Value::U32(params.recipient_key_index),
+        ),
+        (
+            "accountReference".to_string(),
+            Value::U32(params.account_reference),
+        ),
+    ]);
+    if let Some(label) = params.encrypted_account_label {
+        properties.insert("encryptedAccountLabel".to_string(), Value::Bytes(label));
+    }
+    if let Some(proof) = params.auto_accept_proof {
+        properties.insert("autoAcceptProof".to_string(), Value::Bytes(proof));
+    }
+
+    Ok(new_document(
+        contract,
+        document_type.name(),
+        params.sender_id,
+        params.entropy,
+        properties,
+    ))
+}
+
+/// Check `bytes` against the `minItems`/`maxItems` the contract declares for
+/// the byte-array property `field`.
+fn check_byte_field(
+    document_type: DocumentTypeRef,
+    field: &str,
+    bytes: &[u8],
+) -> Result<(), Error> {
+    let property = document_type.properties().get(field).ok_or_else(|| {
+        DataContractError::DocumentTypeFieldNotFound(format!(
+            "{} has no property {field}",
+            document_type.name()
+        ))
+    })?;
+    // Only `Array`/`VariableTypeArray` report no size, and dpp refuses those
+    // at contract creation ("only byte arrays are supported now"), so every
+    // property reachable here is sized and the defaults never apply.
+    let min = property.property_type.min_size().unwrap_or(0) as usize;
+    let max = property.property_type.max_size().unwrap_or(u16::MAX) as usize;
+    if bytes.len() < min || bytes.len() > max {
+        return Err(Error::Config(format!(
+            "{field} must be {min}-{max} bytes, got {}",
+            bytes.len()
+        )));
+    }
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use dpp::document::DocumentV0Getters;
+    use dpp::system_data_contracts::{load_system_data_contract, SystemDataContract};
+    use dpp::version::PlatformVersion;
+
+    fn params(encrypted_public_key: Vec<u8>) -> ContactRequestDocumentParams {
+        ContactRequestDocumentParams {
+            sender_id: Identifier::from([1u8; 32]),
+            recipient_id: Identifier::from([2u8; 32]),
+            sender_key_index: 1,
+            recipient_key_index: 2,
+            account_reference: 3,
+            encrypted_public_key,
+            encrypted_account_label: None,
+            auto_accept_proof: None,
+            entropy: [7u8; 32],
+        }
+    }
+
+    fn contract() -> DataContract {
+        load_system_data_contract(SystemDataContract::Dashpay, PlatformVersion::latest())
+            .expect("dashpay contract")
+    }
+
+    #[test]
+    fn should_derive_the_document_id_from_the_entropy() {
+        let contract = contract();
+        let document = build_contact_request_document(&contract, params(vec![0u8; 96]))
+            .expect("valid contact request");
+        assert_eq!(
+            document.id(),
+            Document::generate_document_id_v0(
+                &contract.id(),
+                &Identifier::from([1u8; 32]),
+                contact_request::NAME,
+                &[7u8; 32]
+            )
+        );
+        assert_eq!(document.owner_id(), Identifier::from([1u8; 32]));
+        assert_eq!(
+            document.get("toUserId"),
+            Some(&Value::Identifier([2u8; 32]))
+        );
+    }
+
+    #[test]
+    fn should_enforce_the_contract_byte_bounds() {
+        let contract = contract();
+        build_contact_request_document(&contract, params(vec![0u8; 95]))
+            .expect_err("encryptedPublicKey below the schema's 96 bytes");
+        let mut with_label = params(vec![0u8; 96]);
+        with_label.encrypted_account_label = Some(vec![0u8; 81]);
+        build_contact_request_document(&contract, with_label)
+            .expect_err("encryptedAccountLabel above the schema's 80 bytes");
+        let mut with_proof = params(vec![0u8; 96]);
+        with_proof.auto_accept_proof = Some(vec![0u8; 37]);
+        build_contact_request_document(&contract, with_proof)
+            .expect_err("autoAcceptProof below the schema's 38 bytes");
+    }
+
+    /// The optional fields are the ones a wire-format slip would silently
+    /// drop, so pin every property the document carries when both are set.
+    #[test]
+    fn should_carry_every_property_when_the_optional_fields_are_present() {
+        let contract = contract();
+        let mut with_optionals = params(vec![1u8; 96]);
+        with_optionals.encrypted_account_label = Some(vec![2u8; 64]);
+        with_optionals.auto_accept_proof = Some(vec![3u8; 40]);
+
+        let document = build_contact_request_document(&contract, with_optionals)
+            .expect("valid contact request");
+
+        assert_eq!(
+            document.get("toUserId"),
+            Some(&Value::Identifier([2u8; 32]))
+        );
+        assert_eq!(
+            document.get("encryptedPublicKey"),
+            Some(&Value::Bytes(vec![1u8; 96]))
+        );
+        assert_eq!(document.get("senderKeyIndex"), Some(&Value::U32(1)));
+        assert_eq!(document.get("recipientKeyIndex"), Some(&Value::U32(2)));
+        assert_eq!(document.get("accountReference"), Some(&Value::U32(3)));
+        assert_eq!(
+            document.get("encryptedAccountLabel"),
+            Some(&Value::Bytes(vec![2u8; 64]))
+        );
+        assert_eq!(
+            document.get("autoAcceptProof"),
+            Some(&Value::Bytes(vec![3u8; 40]))
+        );
+    }
+
+    /// A contract that declares no `contactRequest` surfaces dpp's
+    /// `DataContractError` through our `Error`, rather than panicking.
+    #[test]
+    fn should_refuse_a_contract_without_a_contact_request_type() {
+        let dpns = load_system_data_contract(SystemDataContract::DPNS, PlatformVersion::latest())
+            .expect("dpns contract");
+        let error = build_contact_request_document(&dpns, params(vec![0u8; 96]))
+            .expect_err("dpns declares no contactRequest document type");
+        assert!(
+            matches!(error, Error::Protocol(_)),
+            "unexpected error: {error:?}"
+        );
+    }
+
+    #[test]
+    fn should_refuse_a_field_the_document_type_does_not_declare() {
+        let contract = contract();
+        let document_type = contract
+            .document_type_for_name(contact_request::NAME)
+            .expect("contactRequest document type");
+        let error = check_byte_field(document_type, "notAProperty", &[])
+            .expect_err("contactRequest declares no such property");
+        assert!(
+            matches!(error, Error::Protocol(_)),
+            "unexpected error: {error:?}"
+        );
+    }
+}