add current difficulty to /consensus response

Fixes NebulousLabs#1396

Author: lukechampine

api/consensus.go

@@ -16,6 +16,7 @@ type ConsensusGET struct {
 	Height       types.BlockHeight `json:"height"`
 	CurrentBlock types.BlockID     `json:"currentblock"`
 	Target       types.Target      `json:"target"`
+	Difficulty   types.Currency    `json:"difficulty"`
 }
 
 // consensusHandler handles the API calls to /consensus.
@@ -27,6 +28,7 @@ func (api *API) consensusHandler(w http.ResponseWriter, req *http.Request, _ htt
 		Height:       api.cs.Height(),
 		CurrentBlock: cbid,
 		Target:       currentTarget,
+		Difficulty:   currentTarget.Difficulty(),
 	})
 }
 

doc/API.md

@@ -173,7 +173,8 @@ returns information about the consensus set, such as the current block height.
   "synced":       true,
   "height":       62248,
   "currentblock": "00000000000008a84884ba827bdc868a17ba9c14011de33ff763bd95779a9cf1",
-  "target":       [0,0,0,0,0,0,11,48,125,79,116,89,136,74,42,27,5,14,10,31,23,53,226,238,202,219,5,204,38,32,59,165]
+  "target":       [0,0,0,0,0,0,11,48,125,79,116,89,136,74,42,27,5,14,10,31,23,53,226,238,202,219,5,204,38,32,59,165],
+  "difficulty":   "1234"
 }
 ```
 

doc/api/Consensus.md

@@ -43,7 +43,10 @@ returns information about the consensus set, such as the current block height.
 
   // An immediate child block of this block must have a hash less than this
   // target for it to be valid.
-  "target": [0,0,0,0,0,0,11,48,125,79,116,89,136,74,42,27,5,14,10,31,23,53,226,238,202,219,5,204,38,32,59,165]
+  "target": [0,0,0,0,0,0,11,48,125,79,116,89,136,74,42,27,5,14,10,31,23,53,226,238,202,219,5,204,38,32,59,165],
+
+  // The difficulty of the current block target.
+  "difficulty": "1234" // arbitrary-precision integer
 }
 ```
 

siac/consensuscmd.go

@@ -29,10 +29,11 @@ func consensuscmd() {
 	}
 	if cg.Synced {
 		fmt.Printf(`Synced: %v
-Block:  %v
-Height: %v
-Target: %v
-`, yesNo(cg.Synced), cg.CurrentBlock, cg.Height, cg.Target)
+Block:      %v
+Height:     %v
+Target:     %v
+Difficulty: %v
+`, yesNo(cg.Synced), cg.CurrentBlock, cg.Height, cg.Target, cg.Difficulty)
 	} else {
 		estimatedHeight := estimatedHeightAt(time.Now())
 		estimatedProgress := float64(cg.Height) / float64(estimatedHeight) * 100