Problem: We are unable to get the required tokens or flow for an inst…

…ance or program VM.

Solution: Create a price API to request it just passing the message item hash.

src/aleph/services/cost.py

@@ -12,6 +12,10 @@
 from aleph.types.files import FileTag
 
 
+HOUR = 60 * 60
+MINUTE = 60
+
+
 def _get_file_from_ref(
     session: DbSession, ref: str, use_latest: bool
 ) -> Optional[StoredFileDb]:
@@ -103,3 +107,37 @@ def compute_cost(session: DbSession, content: ExecutableContent) -> Decimal:
     )
     price = compute_unit_price + get_additional_storage_price(content, session)
     return Decimal(price)
+
+
+def compute_flow_cost(session: DbSession, content: ExecutableContent) -> Decimal:
+    # TODO: Use PAYMENT_PRICING_AGGREGATE when possible
+    compute_unit_cost_hour = 0.11 if content.on.persistent else 0.011
+    compute_unit_cost_second = compute_unit_cost_hour / HOUR
+
+    compute_units_required = _get_nb_compute_units(content)
+    compute_unit_multiplier = _get_compute_unit_multiplier(content)
+
+    compute_unit_price = (
+            Decimal(compute_units_required) * Decimal(compute_unit_multiplier) * Decimal(compute_unit_cost_second)
+    )
+
+    additional_storage_flow_price = get_additional_storage_flow_price(content, session)
+    price = compute_unit_price + additional_storage_flow_price
+    return Decimal(price)
+
+
+def get_additional_storage_flow_price(
+        content: ExecutableContent, session: DbSession
+) -> Decimal:
+    # TODO: Use PAYMENT_PRICING_AGGREGATE when possible
+    additional_storage_hour_price = 0.000000977
+    additional_storage_second_price = Decimal(additional_storage_hour_price) / Decimal(HOUR)
+    nb_compute_units = _get_nb_compute_units(content)
+    free_storage_per_compute_unit = 2 * GiB if not content.on.persistent else 20 * GiB
+
+    total_volume_size = get_volume_size(session, content)
+    additional_storage = max(
+        Decimal(total_volume_size) - (Decimal(free_storage_per_compute_unit) * Decimal(nb_compute_units)), Decimal(0)
+    )
+    price = additional_storage / additional_storage_second_price / Decimal(MiB)
+    return price

src/aleph/web/controllers/prices.py

@@ -0,0 +1,54 @@
+import logging
+from decimal import Decimal
+from typing import Optional
+
+from aiohttp import web
+from dataclasses import dataclass
+from dataclasses_json import DataClassJsonMixin
+
+from aleph_message.models import ItemHash, MessageType
+from aleph.db.accessors.messages import (
+    get_message_status, get_message_by_item_hash,
+)
+from aleph.services.cost import compute_cost, compute_flow_cost
+from aleph.types.db_session import DbSessionFactory
+
+LOGGER = logging.getLogger(__name__)
+
+
+@dataclass
+class MessagePrice(DataClassJsonMixin):
+    """Dataclass used to expose message required tokens."""
+    required_tokens: Optional[Decimal] = None
+
+
+async def message_price(request: web.Request):
+    item_hash_str = request.match_info.get("item_hash")
+    try:
+        item_hash = ItemHash(item_hash_str)
+    except ValueError:
+        raise web.HTTPUnprocessableEntity(body=f"Invalid message hash: {item_hash_str}")
+
+    session_factory: DbSessionFactory = request.app["session_factory"]
+    with session_factory() as session:
+        message_status_db = get_message_status(session=session, item_hash=item_hash)
+        if message_status_db is None:
+            raise web.HTTPNotFound()
+        message = get_message_by_item_hash(session, item_hash)
+
+        if not message or message.type == (not MessageType.instance or not MessageType.program):
+            raise web.HTTPUnprocessableEntity(
+                body=f"Invalid message hash: {item_hash_str}"
+            )
+
+        content = message.parsed_content
+
+        if content.payment and content.payment.is_stream:
+            required_tokens = compute_flow_cost(session=session, content=content)
+        else:
+            required_tokens = compute_cost(session=session, content=content)
+
+    return web.Response(
+        text=MessagePrice(required_tokens=required_tokens).to_json(),
+        content_type="application/json",
+    )

src/aleph/web/controllers/routes.py

@@ -11,6 +11,7 @@
     messages,
     p2p,
     posts,
+    prices,
     storage,
     version,
 )
@@ -57,6 +58,8 @@ def register_routes(app: web.Application):
     app.router.add_get("/api/v1/posts.json", posts.view_posts_list_v1)
     app.router.add_get("/api/v1/posts/page/{page}.json", posts.view_posts_list_v1)
 
+    app.router.add_get("/api/v0/price/{item_hash}", prices.message_price)
+
     app.router.add_get("/api/v0/addresses/stats.json", accounts.addresses_stats_view)
     app.router.add_get(
         "/api/v0/addresses/{address}/balance", accounts.get_account_balance