[api] Implement GraphQL pagination

The GraphQL query has to accept the optional `endCursor` string variable
and output `pageInfo`:

    pageInfo {
      hasNextPage
      endCursor
    }

commands/api.go

 package commands
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -189,7 +190,8 @@ func apiCommand(cmd *Command, args *Args) {
 		host = defHost.Host
 	}
 
-	if path == "graphql" && params["query"] != nil {
+	isGraphQL := path == "graphql"
+	if isGraphQL && params["query"] != nil {
 		query := params["query"].(string)
 		query = strings.Replace(query, quote("{owner}"), quote(owner), 1)
 		query = strings.Replace(query, quote("{repo}"), quote(repo), 1)
@@ -253,8 +255,15 @@ func apiCommand(cmd *Command, args *Args) {
 			fmt.Fprintf(out, "\r\n")
 		}
 
+		endCursor := ""
+		hasNextPage := false
+
 		if parseJSON && jsonType {
-			utils.JSONPath(out, response.Body, colorize)
+			hasNextPage, endCursor = utils.JSONPath(out, response.Body, colorize)
+		} else if paginate && isGraphQL {
+			bodyCopy := &bytes.Buffer{}
+			io.Copy(out, io.TeeReader(response.Body, bodyCopy))
+			hasNextPage, endCursor = utils.JSONPath(ioutil.Discard, bodyCopy, false)
 		} else {
 			io.Copy(out, response.Body)
 		}
@@ -266,7 +275,16 @@ func apiCommand(cmd *Command, args *Args) {
 
 		requestLoop = false
 		if paginate {
-			if nextLink := response.Link("next"); nextLink != "" {
+			if isGraphQL && hasNextPage && endCursor != "" {
+				if v, ok := params["variables"]; ok {
+					variables := v.(map[string]interface{})
+					variables["endCursor"] = endCursor
+				} else {
+					variables := map[string]interface{}{"endCursor": endCursor}
+					params["variables"] = variables
+				}
+				requestLoop = true
+			} else if nextLink := response.Link("next"); nextLink != "" {
 				path = nextLink
 				requestLoop = true
 			}

features/api.feature

@@ -127,6 +127,28 @@ Feature: hub api
       [{"page":3}]
       """
 
+  Scenario: Paginate GraphQL
+    Given the GitHub API server:
+      """
+      post('/graphql') {
+        variables = params[:variables] || {}
+        page = (variables["endCursor"] || 1).to_i
+        json :data => {
+          :pageInfo => {
+            :hasNextPage => page < 3,
+            :endCursor => (page+1).to_s
+          }
+        }
+      }
+      """
+    When I successfully run `hub api --paginate graphql -f query=QUERY`
+    Then the output should contain exactly:
+      """
+      {"data":{"pageInfo":{"hasNextPage":true,"endCursor":"2"}}}
+      {"data":{"pageInfo":{"hasNextPage":true,"endCursor":"3"}}}
+      {"data":{"pageInfo":{"hasNextPage":false,"endCursor":"4"}}}
+      """
+
   Scenario: Avoid leaking token to a 3rd party
     Given the GitHub API server:
       """

utils/json.go

@@ -29,10 +29,7 @@ func stateKey(s *state) string {
 	}
 }
 
-func printValue(token json.Token) {
-}
-
-func JSONPath(out io.Writer, src io.Reader, colorize bool) {
+func JSONPath(out io.Writer, src io.Reader, colorize bool) (hasNextPage bool, endCursor string) {
 	dec := json.NewDecoder(src)
 	dec.UseNumber()
 
@@ -84,12 +81,18 @@ func JSONPath(out io.Writer, src io.Reader, colorize bool) {
 				switch tt := token.(type) {
 				case string:
 					fmt.Fprintf(out, "%s\n", strings.Replace(tt, "\n", "\\n", -1))
+					if strings.HasSuffix(k, ".pageInfo.endCursor") {
+						endCursor = tt
+					}
 				case json.Number:
 					fmt.Fprintf(out, "%s\n", color("0;35", tt))
 				case nil:
 					fmt.Fprintf(out, "\n")
 				case bool:
 					fmt.Fprintf(out, "%s\n", color("1;33", fmt.Sprintf("%v", tt)))
+					if strings.HasSuffix(k, ".pageInfo.hasNextPage") {
+						hasNextPage = tt
+					}
 				default:
 					panic("unknown type")
 				}
@@ -97,4 +100,5 @@ func JSONPath(out io.Writer, src io.Reader, colorize bool) {
 			}
 		}
 	}
+	return
 }