rest: Add "/broadcast" endpoint

This commit adds a REST endpoint to allow broadcasting a transaction:
`POST /rest/broadcast.hex`

The transaction hex must be passed in the body of the request;
on success, the txid of the broadcasted transaction will be returned.

Fixes bitcoin#31017

doc/REST-interface.md

@@ -36,6 +36,12 @@ Responds with 404 if the transaction doesn't exist.
 By default, this endpoint will only search the mempool.
 To query for a confirmed transaction, enable the transaction index via "txindex=1" command line / configuration option.
 
+`POST /rest/broadcast.hex`
+
+Broadcasts a transaction.
+The transaction hex must be passed in the body of the request.
+Returns the txid if the transaction was broadcasted correctly, responds with 400 if the transaction hex can't be parsed or if broadcasting failed.
+
 #### Blocks
 - `GET /rest/block/<BLOCK-HASH>.<bin|hex|json>`
 - `GET /rest/block/notxdetails/<BLOCK-HASH>.<bin|hex|json>`

src/node/transaction.cpp

@@ -33,9 +33,9 @@ static TransactionError HandleATMPError(const TxValidationState& state, std::str
 
 TransactionError BroadcastTransaction(NodeContext& node, const CTransactionRef tx, std::string& err_string, const CAmount& max_tx_fee, bool relay, bool wait_callback)
 {
-    // BroadcastTransaction can be called by RPC or by the wallet.
-    // chainman, mempool and peerman are initialized before the RPC server and wallet are started
-    // and reset after the RPC sever and wallet are stopped.
+    // BroadcastTransaction can be called by RPC, REST, or by the wallet.
+    // chainman, mempool and peerman are initialized before the RPC/REST servers and wallet are started
+    // and reset after the RPC/REST servers and wallet are stopped.
     assert(node.chainman);
     assert(node.mempool);
     assert(node.peerman);

src/rest.cpp

@@ -17,6 +17,7 @@
 #include <index/txindex.h>
 #include <node/blockstorage.h>
 #include <node/context.h>
+#include <node/types.h>
 #include <primitives/block.h>
 #include <primitives/transaction.h>
 #include <rpc/blockchain.h>
@@ -1006,6 +1007,45 @@ static bool rest_blockhash_by_height(const std::any& context, HTTPRequest* req,
     }
 }
 
+static bool rest_broadcast(const std::any& context, HTTPRequest* req, const std::string& str_uri_part)
+{
+    if (!CheckWarmup(req))
+        return false;
+    const std::string body = req->ReadBody();
+    std::string params;
+    const RESTResponseFormat rf = ParseDataFormat(params, str_uri_part);
+    if (params != "") {
+        return RESTERR(req, HTTP_BAD_REQUEST, "Invalid URI format. Expected /rest/broadcast.hex");
+    }
+
+    CMutableTransaction mtx;
+    if (!DecodeHexTx(mtx, body)) {
+        return RESTERR(req, HTTP_BAD_REQUEST, "TX decode failed");
+    }
+
+    switch (rf) {
+    case RESTResponseFormat::HEX: {
+        const CTransactionRef tx(MakeTransactionRef(std::move(mtx)));
+        std::string err_string;
+        NodeContext* node = GetNodeContext(context, req);
+        if (!node) return false;
+
+        const node::TransactionError error = node::BroadcastTransaction(*node, tx, err_string, /*max_tx_fee=*/0, /*relay=*/true, /*wait_callback=*/true);
+        if (node::TransactionError::OK != error) {
+            return RESTERR(req, HTTP_BAD_REQUEST, "Error while broadcasting: " + err_string);
+        }
+
+        req->WriteHeader("Content-Type", "text/plain");
+        req->WriteReply(HTTP_OK, tx->GetHash().GetHex() + "\n");
+        return true;
+    }
+
+    default: {
+        return RESTERR(req, HTTP_NOT_FOUND, "output format not found (available: hex)");
+    }
+    }
+}
+
 static const struct {
     const char* prefix;
     bool (*handler)(const std::any& context, HTTPRequest* req, const std::string& strReq);
@@ -1022,6 +1062,7 @@ static const struct {
       {"/rest/deploymentinfo/", rest_deploymentinfo},
       {"/rest/deploymentinfo", rest_deploymentinfo},
       {"/rest/blockhashbyheight/", rest_blockhash_by_height},
+      {"/rest/broadcast", rest_broadcast},
 };
 
 void StartREST(const std::any& context)

test/functional/interface_rest.py

@@ -440,5 +440,20 @@ def run_test(self):
         resp = self.test_rest_request(f"/deploymentinfo/{INVALID_PARAM}", ret_type=RetType.OBJ, status=400)
         assert_equal(resp.read().decode('utf-8').rstrip(), f"Invalid hash: {INVALID_PARAM}")
 
+        self.log.info("Test the /broadcast URI")
+        tx = self.wallet.create_self_transfer()
+        resp_hex = self.test_rest_request("/broadcast", http_method='POST', req_type=ReqType.HEX, body=tx["hex"], ret_type=RetType.OBJ)
+        assert_equal(resp_hex.read().decode('utf-8').rstrip(), tx["txid"])
+        self.sync_all()
+        assert tx["txid"] in self.nodes[1].getrawmempool()
+
+        # Check invalid requests
+        resp = self.test_rest_request("/broadcast/123", http_method='POST', req_type=ReqType.HEX, body=tx["hex"], status=400, ret_type=RetType.OBJ)
+        assert_equal(resp.read().decode('utf-8').rstrip(), f"Invalid URI format. Expected /rest/broadcast.hex")
+        resp = self.test_rest_request("/broadcast", http_method="POST", req_type=ReqType.HEX, body="0000", status=400, ret_type=RetType.OBJ)
+        assert_equal(resp.read().decode('utf-8').rstrip(), f"TX decode failed")
+        resp = self.test_rest_request("/broadcast", http_method="POST", req_type=ReqType.JSON, body=tx["hex"], status=404, ret_type=RetType.OBJ)
+        assert_equal(resp.read().decode('utf-8').rstrip(), f"output format not found (available: hex)")
+
 if __name__ == '__main__':
     RESTTest(__file__).main()