Merge #10707: Better API for estimatesmartfee RPC

06bcdb8da Convert named argument from nblocks to conf_target (Alex Morcos)
439c4e8ad Improve api to estimatesmartfee (Alex Morcos)

Pull request description:

  Through 0.14 branch, the estimatesmartfee API was tagged "WARNING: This interface is unstable and may disappear or change!" and this warning is removed for 0.15, so any wanted API updates should happen now.

  The changes here are to make the additional parameter for conservative estimates a more general estimate_mode string , to omit the feerate and include an error string instead of returning -1 on error, and to do better parameter checking initially.

  ~It is only the last 2 commits, but it's built on #10706 and #10543~.

  See https://github.com/bitcoin/bitcoin/pull/10707#issuecomment-314869251 for renaming of nblocks argument to conf_target.  Will need to be included before string freeze.

  PR description edited for clarity

Tree-SHA512: 6d8ebee8bb410e2950ffd59663eebfed8d1611d995dc935bb91e430d9da7e2f306796f45631458376027d26341c660f09e825e61748103d2f2736ec6dc3df3ae

1 files changed, 8 insertions, 11 deletions

diff --git a/src/policy/fees.cpp b/src/policy/fees.cpp
index 0f186fa845..73cc0b4a5e 100644
--- a/src/policy/fees.cpp
+++ b/src/policy/fees.cpp
@@ -839,20 +839,20 @@ CFeeRate CBlockPolicyEstimator::estimateSmartFee(int confTarget, FeeCalculation
     EstimationResult tempResult;
 
     // Return failure if trying to analyze a target we're not tracking
-    if (confTarget <= 0 || (unsigned int)confTarget > longStats->GetMaxConfirms())
-        return CFeeRate(0);
+    if (confTarget <= 0 || (unsigned int)confTarget > longStats->GetMaxConfirms()) {
+        return CFeeRate(0);  // error conditon
+    }
 
     // It's not possible to get reasonable estimates for confTarget of 1
-    if (confTarget == 1)
-        confTarget = 2;
+    if (confTarget == 1) confTarget = 2;
 
     unsigned int maxUsableEstimate = MaxUsableEstimate();
-    if (maxUsableEstimate <= 1)
-        return CFeeRate(0);
-
     if ((unsigned int)confTarget > maxUsableEstimate) {
         confTarget = maxUsableEstimate;
     }
+    if (feeCalc) feeCalc->returnedTarget = confTarget;
+
+    if (confTarget <= 1) return CFeeRate(0); // error conditon
 
     assert(confTarget > 0); //estimateCombinedFee and estimateConservativeFee take unsigned ints
     /** true is passed to estimateCombined fee for target/2 and target so
@@ -899,10 +899,7 @@ CFeeRate CBlockPolicyEstimator::estimateSmartFee(int confTarget, FeeCalculation
         }
     }
 
-    if (feeCalc) feeCalc->returnedTarget = confTarget;
-
-    if (median < 0)
-        return CFeeRate(0);
+    if (median < 0) return CFeeRate(0); // error conditon
 
     return CFeeRate(median);
 }