Using JSON schema as column headers in dataframe

Ok, as per a previous question (here) I've now managed to read a load of JSON data into R and to get the data into a data frame. here's the code:-

getCall <- GET("http://long-url.com", 
                 authenticate("myusername", "password"))


contJSON <- content(getCall)

contJSON = sub("\n\r\n", "", contJSON)

df1 <- fromJSON(sprintf("[%s]", gsub("\n", ",", contJSON)), asText=TRUE)

df <- data.frame(matrix(unlist(df1), nrow=31, byrow=T))

Which gets me a data frame that looks as follows:-

head(df[,1:8])

          X1    X2    X3   X4   X5 X6         X7         X8
1 2013-05-01 33682 11838 8023 3815 84 177.000000 177.000000
2 2013-05-02 32622 11626 7945 3681 58 210.000000 210.000000
3 2013-05-03 28467 11102 7786 3316 56 186.000000 186.000000
4 2013-05-04 20884  9031 6670 2361 51   7.000000   7.000000
5 2013-05-05 20481  8782 6390 2392 58   1.000000   1.000000
6 2013-05-06 25175 10019 7082 2937 62  24.000000  24.000000

However, there are no column names in my data frame. When I search for "names" in my JSON object R returns "NULL" so that doesn't give me anything useful.

I am wondering if there is any simple way (that might be repeatable on more general cases) to get the names for the column headers from the JSON schema.

I'm aware there are similar questions elsewhere on the site, but this one did not appear to be covered.

EDIT: As per the comment, here is the structure of the contJSON object.

"{\"metricDate\":\"2013-05-01\",\"pageCountTotal\":\"33682\",\"landCountTotal\":\"11838\",\"newLandCountTotal\":\"8023\",\"returnLandCountTotal\":\"3815\",\"spiderCountTotal\":\"84\",\"goalCountTotal\":\"177.000000\",\"callGoalCountTotal\":\"177.000000\",\"callCountTotal\":\"237.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.50\",\"callConversionPerc\":\"74.68\"}\n{\"metricDate\":\"2013-05-02\",\"pageCountTotal\":\"32622\",\"landCountTotal\":\"11626\",\"newLandCountTotal\":\"7945\",\"returnLandCountTotal\":\"3681\",\"spiderCountTotal\":\"58\",\"goalCountTotal\":\"210.000000\",\"callGoalCountTotal\":\"210.000000\",\"callCountTotal\":\"297.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.81\",\"callConversionPerc\":\"70.71\"}\n{\"metricDate\":\"2013-05-03\",\"pageCountTotal\":\"28467\",\"landCountTotal\":\"11102\",\"newLandCountTotal\":\"7786\",\"returnLandCountTotal\":\"3316\",\"spiderCountTotal\":\"56\",\"goalCountTotal\":\"186.000000\",\"callGoalCountTotal\":\"186.000000\",\"callCountTotal\":\"261.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.68\",\"callConversionPerc\":\"71.26\"}\n{\"metricDate\":\"2013-05-04\",\"pageCountTotal\":\"20884\",\"landCountTotal\":\"9031\",\"newLandCountTotal\":\"6670\",\"returnLandCountTotal\":\"2361\",\"spiderCountTotal\":\"51\",\"goalCountTotal\":\"7.000000\",\"callGoalCountTotal\":\"7.000000\",\"callCountTotal\":\"44.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"0.08\",\"callConversionPerc\":\"15.91\"}\n{\"metricDate\":\"2013-05-05\",\"pageCountTotal\":\"20481\",\"landCountTotal\":\"8782\",\"newLandCountTotal\":\"6390\",\"returnLandCountTotal\":\"2392\",\"spiderCountTotal\":\"58\",\"goalCountTotal\":\"1.000000\",\"callGoalCountTotal\":\"1.000000\",\"callCountTotal\":\"8.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"0.01\",\"callConversionPerc\":\"12.50\"}\n{\"metricDate\":\"2013-05-06\",\"pageCountTotal\":\"25175\",\"landCountTotal\":\"10019\",\"newLandCountTotal\":\"7082\",\"returnLandCountTotal\":\"2937\",\"spiderCountTotal\":\"62\",\"goalCountTotal\":\"24.000000\",\"callGoalCountTotal\":\"24.000000\",\"callCountTotal\":\"47.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"0.24\",\"callConversionPerc\":\"51.06\"}\n{\"metricDate\":\"2013-05-07\",\"pageCountTotal\":\"35892\",\"landCountTotal\":\"12615\",\"newLandCountTotal\":\"8391\",\"returnLandCountTotal\":\"4224\",\"spiderCountTotal\":\"62\",\"goalCountTotal\":\"239.000000\",\"callGoalCountTotal\":\"239.000000\",\"callCountTotal\":\"321.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.89\",\"callConversionPerc\":\"74.45\"}\n{\"metricDate\":\"2013-05-08\",\"pageCountTotal\":\"34106\",\"landCountTotal\":\"12391\",\"newLandCountTotal\":\"8389\",\"returnLandCountTotal\":\"4002\",\"spiderCountTotal\":\"90\",\"goalCountTotal\":\"221.000000\",\"callGoalCountTotal\":\"221.000000\",\"callCountTotal\":\"295.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.78\",\"callConversionPerc\":\"74.92\"}\n{\"metricDate\":\"2013-05-09\",\"pageCountTotal\":\"32721\",\"landCountTotal\":\"12447\",\"newLandCountTotal\":\"8541\",\"returnLandCountTotal\":\"3906\",\"spiderCountTotal\":\"54\",\"goalCountTotal\":\"207.000000\",\"callGoalCountTotal\":\"207.000000\",\"callCountTotal\":\"280.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.66\",\"callConversionPerc\":\"73.93\"}\n{\"metricDate\":\"2013-05-10\",\"pageCountTotal\":\"29724\",\"landCountTotal\":\"11616\",\"newLandCountTotal\":\"8063\",\"returnLandCountTotal\":\"3553\",\"spiderCountTotal\":\"139\",\"goalCountTotal\":\"207.000000\",\"callGoalCountTotal\":\"207.000000\",\"callCountTotal\":\"301.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.78\",\"callConversionPerc\":\"68.77\"}\n{\"metricDate\":\"2013-05-11\",\"pageCountTotal\":\"22061\",\"landCountTotal\":\"9660\",\"newLandCountTotal\":\"6971\",\"returnLandCountTotal\":\"2689\",\"spiderCountTotal\":\"52\",\"goalCountTotal\":\"3.000000\",\"callGoalCountTotal\":\"3.000000\",\"callCountTotal\":\"40.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"0.03\",\"callConversionPerc\":\"7.50\"}\n{\"metricDate\":\"2013-05-12\",\"pageCountTotal\":\"23341\",\"landCountTotal\":\"9935\",\"newLandCountTotal\":\"6960\",\"returnLandCountTotal\":\"2975\",\"spiderCountTotal\":\"45\",\"goalCountTotal\":\"0.000000\",\"callGoalCountTotal\":\"0.000000\",\"callCountTotal\":\"12.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"0.00\",\"callConversionPerc\":\"0.00\"}\n{\"metricDate\":\"2013-05-13\",\"pageCountTotal\":\"36565\",\"landCountTotal\":\"13583\",\"newLandCountTotal\":\"9277\",\"returnLandCountTotal\":\"4306\",\"spiderCountTotal\":\"69\",\"goalCountTotal\":\"246.000000\",\"callGoalCountTotal\":\"246.000000\",\"callCountTotal\":\"324.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.81\",\"callConversionPerc\":\"75.93\"}\n{\"metricDate\":\"2013-05-14\",\"pageCountTotal\":\"35260\",\"landCountTotal\":\"13797\",\"newLandCountTotal\":\"9375\",\"returnLandCountTotal\":\"4422\",\"spiderCountTotal\":\"59\",\"goalCountTotal\":\"212.000000\",\"callGoalCountTotal\":\"212.000000\",\"callCountTotal\":\"283.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.54\",\"callConversionPerc\":\"74.91\"}\n{\"metricDate\":\"2013-05-15\",\"pageCountTotal\":\"35836\",\"landCountTotal\":\"13792\",\"newLandCountTotal\":\"9532\",\"returnLandCountTotal\":\"4260\",\"spiderCountTotal\":\"94\",\"goalCountTotal\":\"187.000000\",\"callGoalCountTotal\":\"187.000000\",\"callCountTotal\":\"258.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.36\",\"callConversionPerc\":\"72.48\"}\n{\"metricDate\":\"2013-05-16\",\"pageCountTotal\":\"33136\",\"landCountTotal\":\"12821\",\"newLandCountTotal\":\"8755\",\"returnLandCountTotal\":\"4066\",\"spiderCountTotal\":\"65\",\"goalCountTotal\":\"192.000000\",\"callGoalCountTotal\":\"192.000000\",\"callCountTotal\":\"260.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.50\",\"callConversionPerc\":\"73.85\"}\n{\"metricDate\":\"2013-05-17\",\"pageCountTotal\":\"29564\",\"landCountTotal\":\"11721\",\"newLandCountTotal\":\"8191\",\"returnLandCountTotal\":\"3530\",\"spiderCountTotal\":\"213\",\"goalCountTotal\":\"166.000000\",\"callGoalCountTotal\":\"166.000000\",\"callCountTotal\":\"222.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.42\",\"callConversionPerc\":\"74.77\"}\n{\"metricDate\":\"2013-05-18\",\"pageCountTotal\":\"23686\",\"landCountTotal\":\"9916\",\"newLandCountTotal\":\"7335\",\"returnLandCountTotal\":\"2581\",\"spiderCountTotal\":\"56\",\"goalCountTotal\":\"5.000000\",\"callGoalCountTotal\":\"5.000000\",\"callCountTotal\":\"34.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"0.05\",\"callConversionPerc\":\"14.71\"}\n{\"metricDate\":\"2013-05-19\",\"pageCountTotal\":\"23528\",\"landCountTotal\":\"9952\",\"newLandCountTotal\":\"7184\",\"returnLandCountTotal\":\"2768\",\"spiderCountTotal\":\"57\",\"goalCountTotal\":\"1.000000\",\"callGoalCountTotal\":\"1.000000\",\"callCountTotal\":\"14.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"0.01\",\"callConversionPerc\":\"7.14\"}\n{\"metricDate\":\"2013-05-20\",\"pageCountTotal\":\"37391\",\"landCountTotal\":\"13488\",\"newLandCountTotal\":\"9024\",\"returnLandCountTotal\":\"4464\",\"spiderCountTotal\":\"69\",\"goalCountTotal\":\"227.000000\",\"callGoalCountTotal\":\"227.000000\",\"callCountTotal\":\"291.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.68\",\"callConversionPerc\":\"78.01\"}\n{\"metricDate\":\"2013-05-21\",\"pageCountTotal\":\"36299\",\"landCountTotal\":\"13174\",\"newLandCountTotal\":\"8817\",\"returnLandCountTotal\":\"4357\",\"spiderCountTotal\":\"77\",\"goalCountTotal\":\"164.000000\",\"callGoalCountTotal\":\"164.000000\",\"callCountTotal\":\"221.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.24\",\"callConversionPerc\":\"74.21\"}\n{\"metricDate\":\"2013-05-22\",\"pageCountTotal\":\"34201\",\"landCountTotal\":\"12433\",\"newLandCountTotal\":\"8388\",\"returnLandCountTotal\":\"4045\",\"spiderCountTotal\":\"76\",\"goalCountTotal\":\"195.000000\",\"callGoalCountTotal\":\"195.000000\",\"callCountTotal\":\"262.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.57\",\"callConversionPerc\":\"74.43\"}\n{\"metricDate\":\"2013-05-23\",\"pageCountTotal\":\"32951\",\"landCountTotal\":\"11611\",\"newLandCountTotal\":\"7757\",\"returnLandCountTotal\":\"3854\",\"spiderCountTotal\":\"68\",\"goalCountTotal\":\"167.000000\",\"callGoalCountTotal\":\"167.000000\",\"callCountTotal\":\"231.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.44\",\"callConversionPerc\":\"72.29\"}\n{\"metricDate\":\"2013-05-24\",\"pageCountTotal\":\"28967\",\"landCountTotal\":\"10821\",\"newLandCountTotal\":\"7396\",\"returnLandCountTotal\":\"3425\",\"spiderCountTotal\":\"106\",\"goalCountTotal\":\"167.000000\",\"callGoalCountTotal\":\"167.000000\",\"callCountTotal\":\"203.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.54\",\"callConversionPerc\":\"82.27\"}\n{\"metricDate\":\"2013-05-25\",\"pageCountTotal\":\"19741\",\"landCountTotal\":\"8393\",\"newLandCountTotal\":\"6168\",\"returnLandCountTotal\":\"2225\",\"spiderCountTotal\":\"78\",\"goalCountTotal\":\"0.000000\",\"callGoalCountTotal\":\"0.000000\",\"callCountTotal\":\"28.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"0.00\",\"callConversionPerc\":\"0.00\"}\n{\"metricDate\":\"2013-05-26\",\"pageCountTotal\":\"19770\",\"landCountTotal\":\"8237\",\"newLandCountTotal\":\"6009\",\"returnLandCountTotal\":\"2228\",\"spiderCountTotal\":\"79\",\"goalCountTotal\":\"0.000000\",\"callGoalCountTotal\":\"0.000000\",\"callCountTotal\":\"8.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"0.00\",\"callConversionPerc\":\"0.00\"}\n{\"metricDate\":\"2013-05-27\",\"pageCountTotal\":\"26208\",\"landCountTotal\":\"9755\",\"newLandCountTotal\":\"6779\",\"returnLandCountTotal\":\"2976\",\"spiderCountTotal\":\"82\",\"goalCountTotal\":\"26.000000\",\"callGoalCountTotal\":\"26.000000\",\"callCountTotal\":\"40.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"0.27\",\"callConversionPerc\":\"65.00\"}\n{\"metricDate\":\"2013-05-28\",\"pageCountTotal\":\"36980\",\"landCountTotal\":\"12463\",\"newLandCountTotal\":\"8226\",\"returnLandCountTotal\":\"4237\",\"spiderCountTotal\":\"132\",\"goalCountTotal\":\"208.000000\",\"callGoalCountTotal\":\"208.000000\",\"callCountTotal\":\"276.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.67\",\"callConversionPerc\":\"75.36\"}\n{\"metricDate\":\"2013-05-29\",\"pageCountTotal\":\"34190\",\"landCountTotal\":\"12014\",\"newLandCountTotal\":\"8279\",\"returnLandCountTotal\":\"3735\",\"spiderCountTotal\":\"90\",\"goalCountTotal\":\"179.000000\",\"callGoalCountTotal\":\"179.000000\",\"callCountTotal\":\"235.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.49\",\"callConversionPerc\":\"76.17\"}\n{\"metricDate\":\"2013-05-30\",\"pageCountTotal\":\"33867\",\"landCountTotal\":\"11965\",\"newLandCountTotal\":\"8231\",\"returnLandCountTotal\":\"3734\",\"spiderCountTotal\":\"63\",\"goalCountTotal\":\"160.000000\",\"callGoalCountTotal\":\"160.000000\",\"callCountTotal\":\"219.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.34\",\"callConversionPerc\":\"73.06\"}\n{\"metricDate\":\"2013-05-31\",\"pageCountTotal\":\"27536\",\"landCountTotal\":\"10302\",\"newLandCountTotal\":\"7333\",\"returnLandCountTotal\":\"2969\",\"spiderCountTotal\":\"108\",\"goalCountTotal\":\"173.000000\",\"callGoalCountTotal\":\"173.000000\",\"callCountTotal\":\"226.000000\",\"onlineGoalCountTotal\":\"0.000000\",\"conversionPerc\":\"1.68\",\"callConversionPerc\":\"76.55\"}\n\r\n"