fix: align effective rate calculation

Author: strahe

costs/calculate.go

@@ -10,7 +10,7 @@ import (
 // CalculateEffectiveRate computes the storage rate for the given total data size.
 // Integer division is used to match on-chain Solidity truncation.
 // If epochsPerMonth is zero or negative, chain.EpochsPerMonth is used as a safe default.
-// Nil pricePerTiBPerMonth or minMonthlyRate are treated as zero.
+// Nil sizeBytes, pricePerTiBPerMonth, or minMonthlyRate are treated as zero.
 func CalculateEffectiveRate(
 	sizeBytes *big.Int,
 	pricePerTiBPerMonth *big.Int,
@@ -22,6 +22,9 @@ func CalculateEffectiveRate(
 	}
 	epm := big.NewInt(epochsPerMonth)
 
+	if sizeBytes == nil {
+		sizeBytes = new(big.Int)
+	}
 	if pricePerTiBPerMonth == nil {
 		pricePerTiBPerMonth = new(big.Int)
 	}
@@ -31,15 +34,13 @@ func CalculateEffectiveRate(
 
 	ratePerMonth := new(big.Int).Mul(pricePerTiBPerMonth, sizeBytes)
 	ratePerMonth.Div(ratePerMonth, bigTiB)
-	hitMin := ratePerMonth.Cmp(minMonthlyRate) < 0
-	if hitMin {
+	if ratePerMonth.Cmp(minMonthlyRate) < 0 {
 		ratePerMonth.Set(minMonthlyRate)
 	}
 
-	// ratePerEpoch is computed independently to avoid accumulating two division errors.
 	ratePerEpoch := new(big.Int).Mul(pricePerTiBPerMonth, sizeBytes)
-	ratePerEpoch.Div(ratePerEpoch, bigTiB)
-	ratePerEpoch.Div(ratePerEpoch, epm)
+	divisor := new(big.Int).Mul(bigTiB, epm)
+	ratePerEpoch.Div(ratePerEpoch, divisor)
 
 	minEpochRate := new(big.Int).Div(minMonthlyRate, epm)
 	if minEpochRate.Cmp(bigOne) < 0 {
@@ -49,14 +50,6 @@ func CalculateEffectiveRate(
 		ratePerEpoch.Set(minEpochRate)
 	}
 
-	// At the minimum floor, align ratePerMonth with the epoch-aligned rate so that
-	// ratePerEpoch × epm == ratePerMonth exactly.  Above the floor the two fields
-	// are intentionally computed independently to avoid accumulating two division
-	// truncation errors in the more-common non-minimum case.
-	if hitMin {
-		ratePerMonth.Mul(ratePerEpoch, epm)
-	}
-
 	return EffectiveRate{
 		RatePerEpoch: ratePerEpoch,
 		RatePerMonth: ratePerMonth,

costs/calculate_test.go

@@ -60,13 +60,9 @@ func TestCalculateEffectiveRate_SubTiB_HitsMinimum(t *testing.T) {
 		chain.EpochsPerMonth,
 	)
 
-	// At the minimum floor, ratePerMonth is derived from ratePerEpoch × epm so the
-	// two fields are consistent.  ratePerMonth is therefore slightly less than
-	// MinimumPricePerMonth by at most (epm-1) attoUSDFC due to integer truncation.
-	wantMonthly := new(big.Int).Mul(rate.RatePerEpoch, big.NewInt(chain.EpochsPerMonth))
-	if rate.RatePerMonth.Cmp(wantMonthly) != 0 {
-		t.Errorf("ratePerMonth should equal ratePerEpoch*epm at minimum: got %s, want %s",
-			rate.RatePerMonth, wantMonthly)
+	if rate.RatePerMonth.Cmp(pricing.MinimumPricePerMonth) != 0 {
+		t.Errorf("ratePerMonth should equal MinimumPricePerMonth: got %s, want %s",
+			rate.RatePerMonth, pricing.MinimumPricePerMonth)
 	}
 	if rate.RatePerEpoch.Cmp(bi(1)) < 0 {
 		t.Errorf("ratePerEpoch should be at least 1: got %s", rate.RatePerEpoch)
@@ -99,11 +95,9 @@ func TestCalculateEffectiveRate_ZeroSize(t *testing.T) {
 		chain.EpochsPerMonth,
 	)
 
-	// Zero size hits the minimum floor; ratePerMonth must equal ratePerEpoch × epm.
-	wantMonthly := new(big.Int).Mul(rate.RatePerEpoch, big.NewInt(chain.EpochsPerMonth))
-	if rate.RatePerMonth.Cmp(wantMonthly) != 0 {
-		t.Errorf("ratePerMonth should be epoch-aligned for zero size: got %s, want %s",
-			rate.RatePerMonth, wantMonthly)
+	if rate.RatePerMonth.Cmp(pricing.MinimumPricePerMonth) != 0 {
+		t.Errorf("ratePerMonth should equal MinimumPricePerMonth for zero size: got %s, want %s",
+			rate.RatePerMonth, pricing.MinimumPricePerMonth)
 	}
 }
 
@@ -673,11 +667,11 @@ func TestDepositNeeded_ZeroTotalLockup(t *testing.T) {
 // --- CalculateEffectiveRate edge cases ---
 
 func TestCalculateEffectiveRate_NilInputs(t *testing.T) {
-	rate := CalculateEffectiveRate(bi(chain.TiB), nil, nil, 0)
+	rate := CalculateEffectiveRate(nil, nil, nil, 0)
 	if rate.RatePerEpoch == nil || rate.RatePerMonth == nil {
 		t.Fatal("nil rate fields returned")
 	}
-	// nil price and nil minRate both treated as 0; ratePerEpoch is clamped to bigOne=1
+	// nil size, price, and minRate are treated as 0; ratePerEpoch is clamped to bigOne=1.
 	if rate.RatePerEpoch.Cmp(big.NewInt(1)) != 0 {
 		t.Errorf("RatePerEpoch = %s, want 1", rate.RatePerEpoch)
 	}

costs/doc.go

@@ -18,9 +18,9 @@
 //
 // Epoch — Filecoin block interval (30 seconds on mainnet and calibration).
 // All on-chain rates and durations are denominated in epochs; 120 epochs
-// equal one hour, ~86 400 equal one month. Monthly figures in this
-// package are derived by multiplying per-epoch rates by
-// [github.com/strahe/synapse-go/chain.EpochsPerMonth].
+// equal one hour, ~86 400 equal one month. On-chain lockup rates are
+// per-epoch; effective monthly rates preserve monthly pricing precision for
+// display and comparison.
 //
 // Basis points (bps) — one hundredth of one percent (1 bps = 0.01 %).
 // Commission rates returned by warmstorage are expressed in basis points

costs/multi_cost.go

@@ -40,7 +40,7 @@ type MultiContextRef struct {
 type MultiContextCosts struct {
 	// RatePerEpoch is the sum of per-context effective rates (post-upload).
 	RatePerEpoch *big.Int
-	// RatePerMonth is RatePerEpoch * EpochsPerMonth.
+	// RatePerMonth is the sum of per-context monthly effective rates.
 	RatePerMonth *big.Int
 	// DepositNeeded is the single USDFC deposit covering all contexts.
 	DepositNeeded *big.Int

costs/types.go

@@ -4,6 +4,7 @@ import "math/big"
 
 // EffectiveRate is the per-epoch and per-month storage rate for a given data size.
 // RatePerEpoch uses integer division to match on-chain Solidity truncation.
+// RatePerMonth preserves monthly pricing precision for display and comparison.
 type EffectiveRate struct {
 	RatePerEpoch *big.Int
 	RatePerMonth *big.Int

spregistry/service.go

@@ -6,7 +6,7 @@ import (
 	"fmt"
 	"log/slog"
 	"math/big"
-	"sort"
+	"slices"
 	"strings"
 	"time"
 
@@ -553,8 +553,8 @@ func (s *Service) SelectActivePDPProviders(ctx context.Context, f ProviderFilter
 		offset += pageSize
 	}
 
-	sort.Slice(all, func(i, j int) bool {
-		return all[i].Info.ID.Cmp(all[j].Info.ID) < 0
+	slices.SortFunc(all, func(a, b PDPProvider) int {
+		return a.Info.ID.Cmp(b.Info.ID)
 	})
 	return all, nil
 }

storage/types.go

@@ -240,7 +240,8 @@ func (r *UploadResult) PartialSuccess() bool {
 // direct StoreOptions, PullRequest, or CommitRequest hooks.
 type UploadOptions struct {
 	// Copies is the number of provider copies to store. Zero means the resolver
-	// default: len(DataSetIDs) or len(ProviderIDs) when those are set, otherwise 2.
+	// default: the number of unique DataSetIDs or ProviderIDs when those are set,
+	// otherwise 2.
 	Copies int
 	// PieceMetadata is stored with each piece on-chain.
 	PieceMetadata map[string]string