diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+[0.9.0](https://github.com/guillaume-nargeot/hpc-coveralls/issues?q=milestone:v0.9.0+is:closed)
+-----
+* Fix instructions and target hpc data directory for Cabal 1.22 / GHC 7.10 (issue #38)
+* Print hpc coverage data directory tree when failing to read tix file (issue #39)
+* Improve handling of coveralls response reading/parsing (issue #41)
+* Send "source digest" instead of "source" (issue #43)
+* Add --curl-verbose flag to enable curl verbose mode and replace --print-response (issue #42)
+
 [0.8.3](https://github.com/guillaume-nargeot/hpc-coveralls/issues?q=milestone:v0.8.3+is:closed)
 -----
 * Send git repository info when using other CI services than Travis (issue #37)
@@ -21,7 +29,7 @@
 
 [0.6.1](https://github.com/guillaume-nargeot/hpc-coveralls/issues?milestone=8&state=closed)
 -----
-* Safer implementation of the result coverage value retrieval from coveralls.io (issue 25)
+* Safer implementation of the result coverage value retrieval from coveralls.io (issue #25)
 * Set the delay before retrieving the result to 10 seconds (issue #26)
 
 [0.6.0](https://github.com/guillaume-nargeot/hpc-coveralls/issues?milestone=7&state=closed)
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -24,7 +24,9 @@
   - hpc-coveralls [options] [test-suite-names]
 ```
 
-If your build fails during the test phase with an error message starting by "hpc:", just replace the `cabal test` command by `run-cabal-test`, as in the following example:
+When building with Cabal 1.22 or a newer version, use the `--enable-coverage` flag instead of `--enable-library-coverage`.
+
+If the build fails during the test phase with an error message starting by "hpc:", just replace the `cabal test` command by `run-cabal-test`, as in the following example:
 ```yaml
 before_install:
   - cabal install hpc-coveralls
@@ -67,7 +69,7 @@
 The `--cabal-name` option can be used to specify a custom executable name instead of the default `cabal` when calling `cabal test`.<br/>
 Below is an example which can be useful for projects with a Travis configuration based on [multi-ghc-travis](https://github.com/hvr/multi-ghc-travis):
 
-```yaml
+```bash
 run-cabal-test --cabal-name=cabal-1.20
 ```
 
@@ -77,7 +79,7 @@
 Multiple test suites can be specified, in which case the coverage report will be made of the merged coverage data generated by the specified test suites.<br/>
 For example, if your test suite are named `test1` and `test2`, use the command as follows:
 
-```yaml
+```bash
 hpc-coveralls test1 test2
 ```
 
@@ -88,13 +90,13 @@
 The `--exclude-dir` option allows to exclude source files located under a given directory from the coverage report.<br/>
 You can exclude source files located under the `test/` directory by using this option as in the following example:
 
-```yaml
+```bash
 hpc-coveralls --exclude-dir=test [test-suite-names]
 ```
 
 You can specify multiple excluded folders by using the following example syntax:
 
-```yaml
+```bash
 hpc-coveralls --exclude-dir=test1 --exclude-dir=test2 [test-suite-names]
 ```
 
@@ -131,9 +133,9 @@
 This option can be used together with `--display-report` for testing purpose.<br/>
 For example, you can try various combinations of the other options and confirm the difference in the resulting report outputs.
 
-#### --print-response
+#### --curl-verbose
 
-This boolean option prints the raw json response received after posting the coverage report to coveralls.io.
+This boolean option enables curl verbose mode and prints the raw json response received after posting the coverage report to coveralls.io.
 
 # Limitations
 
diff --git a/hpc-coveralls.cabal b/hpc-coveralls.cabal
--- a/hpc-coveralls.cabal
+++ b/hpc-coveralls.cabal
@@ -1,5 +1,5 @@
 name:           hpc-coveralls
-version:        0.8.3
+version:        0.9.0
 synopsis:       Coveralls.io support for Haskell.
 description:
   This utility converts and sends Haskell projects hpc code coverage to
@@ -55,13 +55,16 @@
     Trace.Hpc.Coveralls.Paths
   build-depends:
     aeson,
-    base >=4 && < 5,
+    base >= 4 && < 5,
     bytestring >= 0.10,
     containers >= 0.5,
     cmdargs >= 0.10,
     curl >= 1.3.8,
+    directory >= 1.2,
+    directory-tree >= 0.12,
     hpc >= 0.6,
     process >= 1.1.0.1,
+    pureMD5 >= 2.1,
     retry >= 0.5,
     safe >= 0.3,
     split
@@ -76,8 +79,11 @@
     containers >= 0.5,
     cmdargs >= 0.10,
     curl >= 1.3.8,
+    directory >= 1.2,
+    directory-tree >= 0.12,
     hpc >= 0.6,
     process >= 1.1.0.1,
+    pureMD5 >= 2.1,
     retry >= 0.5,
     safe >= 0.3,
     split
diff --git a/src/HpcCoverallsCmdLine.hs b/src/HpcCoverallsCmdLine.hs
--- a/src/HpcCoverallsCmdLine.hs
+++ b/src/HpcCoverallsCmdLine.hs
@@ -9,24 +9,24 @@
 import Trace.Hpc.Coveralls.Types
 
 data HpcCoverallsArgs = CmdMain
-    { excludeDirs   :: [String]
-    , testSuites    :: [String]
-    , repoToken     :: Maybe String
-    , displayReport :: Bool
-    , printResponse :: Bool
-    , dontSend      :: Bool
-    , coverageMode  :: CoverageMode
+    { optExcludeDirs   :: [String]
+    , argTestSuites    :: [String]
+    , optRepoToken     :: Maybe String
+    , optDisplayReport :: Bool
+    , optCurlVerbose   :: Bool
+    , optDontSend      :: Bool
+    , optCoverageMode  :: CoverageMode
     } deriving (Data, Show, Typeable)
 
 hpcCoverallsArgs :: HpcCoverallsArgs
 hpcCoverallsArgs = CmdMain
-    { excludeDirs   = []                &= explicit &= typDir      &= name "exclude-dir"    &= help "Exclude sources files under the matching directory from the coverage report"
-    , displayReport = False             &= explicit                &= name "display-report" &= help "Display the json code coverage report that will be sent to coveralls.io"
-    , printResponse = False             &= explicit                &= name "print-response" &= help "Prints the json reponse received from coveralls.io"
-    , dontSend      = False             &= explicit                &= name "dont-send"      &= help "Do not send the report to coveralls.io"
-    , coverageMode  = AllowPartialLines &= explicit &= typ "MODE"  &= name "coverage-mode"  &= help "Coverage conversion mode: AllowPartialLines (default), StrictlyFullLines"
-    , repoToken     = Nothing           &= explicit &= typ "TOKEN" &= name "repo-token"     &= help "Coveralls repo token"
-    , testSuites    = []                &= typ "TEST-SUITES" &= args
+    { optExcludeDirs   = []                &= explicit &= typDir      &= name "exclude-dir"    &= help "Exclude sources files under the matching directory from the coverage report"
+    , optDisplayReport = False             &= explicit                &= name "display-report" &= help "Display the json code coverage report that will be sent to coveralls.io"
+    , optCurlVerbose   = False             &= explicit                &= name "curl-verbose"   &= help "Enable curl verbose mode and prints the json response received from coveralls.io"
+    , optDontSend      = False             &= explicit                &= name "dont-send"      &= help "Do not send the report to coveralls.io"
+    , optCoverageMode  = AllowPartialLines &= explicit &= typ "MODE"  &= name "coverage-mode"  &= help "Coverage conversion mode: AllowPartialLines (default), StrictlyFullLines"
+    , optRepoToken     = Nothing           &= explicit &= typ "TOKEN" &= name "repo-token"     &= help "Coveralls repo token"
+    , argTestSuites    = []                &= typ "TEST-SUITES" &= args
     } &= summary ("hpc-coveralls-" ++ versionString version ++ ", (C) Guillaume Nargeot 2014-2015")
       &= program "hpc-coveralls"
     where versionString = intercalate "." . map show . versionBranch
diff --git a/src/HpcCoverallsMain.hs b/src/HpcCoverallsMain.hs
--- a/src/HpcCoverallsMain.hs
+++ b/src/HpcCoverallsMain.hs
@@ -10,7 +10,7 @@
 import           HpcCoverallsCmdLine
 import           System.Console.CmdArgs
 import           System.Environment (getEnv, getEnvironment)
-import           System.Exit (exitFailure, exitSuccess)
+import           System.Exit (exitFailure)
 import           Trace.Hpc.Coveralls
 import           Trace.Hpc.Coveralls.Config (Config(Config))
 import           Trace.Hpc.Coveralls.Curl
@@ -39,29 +39,33 @@
 writeJson filePath = BSL.writeFile filePath . encode
 
 getConfig :: HpcCoverallsArgs -> Maybe Config
-getConfig hca = Config (excludeDirs hca) (coverageMode hca) (repoToken hca) <$> listToMaybe (testSuites hca)
+getConfig hca = Config (optExcludeDirs hca) (optCoverageMode hca) (optRepoToken hca) <$> listToMaybe (argTestSuites hca)
 
 main :: IO ()
 main = do
     hca <- cmdArgs hpcCoverallsArgs
     case getConfig hca of
-        Nothing -> putStrLn "Please specify a target test suite name" >> exitSuccess
+        Nothing -> putStrLn "Please specify a target test suite name"
         Just config -> do
             (serviceName, jobId) <- getServiceAndJobID
             gitInfo <- getGitInfo
             coverallsJson <- generateCoverallsFromTix serviceName jobId gitInfo config
-            when (displayReport hca) $ BSL.putStrLn $ encode coverallsJson
+            when (optDisplayReport hca) $ BSL.putStrLn $ encode coverallsJson
             let filePath = serviceName ++ "-" ++ jobId ++ ".json"
             writeJson filePath coverallsJson
-            unless (dontSend hca) $ do
-                response <- postJson filePath urlApiV1 (printResponse hca)
+            unless (optDontSend hca) $ do
+                response <- postJson filePath urlApiV1 (optCurlVerbose hca)
                 case response of
                     PostSuccess url -> do
                         putStrLn ("URL: " ++ url)
                         -- wait 10 seconds until the page is available
-                        threadDelay (10 * 1000000)
-                        coverageResult <- readCoverageResult url (printResponse hca)
+                        threadDelay (10 * 1000 * 1000)
+                        coverageResult <- readCoverageResult url (optCurlVerbose hca)
                         case coverageResult of
-                            Just totalCoverage -> putStrLn ("Coverage: " ++ totalCoverage) >> exitSuccess
-                            Nothing -> putStrLn "Failed to read total coverage" >> exitSuccess
-                    PostFailure msg -> putStrLn ("Error: " ++ msg) >> exitFailure
+                            Just totalCoverage -> putStrLn ("Coverage: " ++ totalCoverage)
+                            Nothing -> putStrLn "Failed to read total coverage"
+                    PostFailure msg -> do
+                        putStrLn ("Error: " ++ msg)
+                        putStrLn ("You can get support at " ++ gitterUrl)
+                        exitFailure
+                        where gitterUrl = "https://gitter.im/guillaume-nargeot/hpc-coveralls"
diff --git a/src/Trace/Hpc/Coveralls.hs b/src/Trace/Hpc/Coveralls.hs
--- a/src/Trace/Hpc/Coveralls.hs
+++ b/src/Trace/Hpc/Coveralls.hs
@@ -14,6 +14,8 @@
 import           Control.Applicative
 import           Data.Aeson
 import           Data.Aeson.Types ()
+import qualified Data.ByteString.Lazy.Char8 as LBS
+import           Data.Digest.Pure.MD5
 import           Data.Function
 import           Data.List
 import qualified Data.Map.Strict as M
@@ -75,7 +77,7 @@
 coverageToJson :: LixConverter -> FilePath -> ModuleCoverageData -> Value
 coverageToJson converter filePath (source, mix, tixs) = object [
     "name" .= filePath,
-    "source" .= source,
+    "source_digest" .= (show . md5 . LBS.pack) source,
     "coverage" .= coverage]
     where coverage = toSimpleCoverage converter lineCount mixEntriesTixs
           lineCount = length $ lines source
@@ -102,20 +104,21 @@
 mergeCoverageData :: [TestSuiteCoverageData] -> TestSuiteCoverageData
 mergeCoverageData = foldr1 (M.unionWith mergeModuleCoverageData)
 
-readMix' :: String -> TixModule -> IO Mix
-readMix' name tix = readMix [getMixPath name tix] (Right tix)
+readMix' :: String -> String -> TixModule -> IO Mix
+readMix' hpcDir name tix = readMix [getMixPath hpcDir name tix] (Right tix)
 
 -- | Create a list of coverage data from the tix input
-readCoverageData :: String                   -- ^ test suite name
+readCoverageData :: String                   -- ^ hpc data directory
                  -> [String]                 -- ^ excluded source folders
+                 -> String                   -- ^ test suite name
                  -> IO TestSuiteCoverageData -- ^ coverage data list
-readCoverageData testSuiteName excludeDirPatterns = do
-    tixPath <- getTixPath testSuiteName
-    mtix <- readTix tixPath
-    case mtix of
-        Nothing -> error ("Couldn't find the file " ++ tixPath) >> exitFailure
+readCoverageData hpcDir excludeDirPatterns testSuiteName = do
+    let tixPath = getTixPath hpcDir testSuiteName
+    mTix <- readTix tixPath
+    case mTix of
+        Nothing -> putStrLn ("Couldn't find the file " ++ tixPath) >> dumpDirectoryTree hpcDir >> ioFailure
         Just (Tix tixs) -> do
-            mixs <- mapM (readMix' testSuiteName) tixs
+            mixs <- mapM (readMix' hpcDir testSuiteName) tixs
             let files = map filePath mixs
             sources <- mapM readFile files
             let coverageDataList = zip4 files sources mixs (map tixModuleTixs tixs)
@@ -131,11 +134,20 @@
                          -> Config   -- ^ hpc-coveralls configuration
                          -> IO Value -- ^ code coverage result in json format
 generateCoverallsFromTix serviceName jobId gitInfo config = do
-    testSuitesCoverages <- mapM (`readCoverageData` excludedDirPatterns) testSuiteNames
-    return $ toCoverallsJson serviceName jobId repoTokenM gitInfo converter $ mergeCoverageData testSuitesCoverages
-    where excludedDirPatterns = excludedDirs config
-          testSuiteNames = testSuites config
-          repoTokenM = repoToken config
-          converter = case coverageMode config of
-              StrictlyFullLines -> strictConverter
-              AllowPartialLines -> looseConverter
+    mHpcDir <- firstExistingDirectory hpcDirs
+    case mHpcDir of
+        Nothing -> putStrLn "Couldn't find the hpc data directory" >> dumpDirectory distDir >> ioFailure
+        Just hpcDir -> do
+            testSuitesCoverages <- mapM (readCoverageData hpcDir excludedDirPatterns) testSuiteNames
+            let coverageData = mergeCoverageData testSuitesCoverages
+            return $ toCoverallsJson serviceName jobId repoTokenM gitInfo converter coverageData
+            where excludedDirPatterns = excludedDirs config
+                  testSuiteNames = testSuites config
+                  repoTokenM = repoToken config
+                  converter = case coverageMode config of
+                      StrictlyFullLines -> strictConverter
+                      AllowPartialLines -> looseConverter
+
+ioFailure :: IO a
+ioFailure = putStrLn ("You can get support at " ++ gitterUrl) >> exitFailure
+    where gitterUrl = "https://gitter.im/guillaume-nargeot/hpc-coveralls" :: String
diff --git a/src/Trace/Hpc/Coveralls/Curl.hs b/src/Trace/Hpc/Coveralls/Curl.hs
--- a/src/Trace/Hpc/Coveralls/Curl.hs
+++ b/src/Trace/Hpc/Coveralls/Curl.hs
@@ -1,5 +1,4 @@
 {-# LANGUAGE OverloadedStrings #-}
-{-# OPTIONS_GHC -fno-warn-unused-do-bind #-}
 
 -- |
 -- Module:      Trace.Hpc.Coveralls.Curl
@@ -25,13 +24,18 @@
 import           Trace.Hpc.Coveralls.Types
 
 parseResponse :: CurlResponse -> PostResult
-parseResponse r = case respCurlCode r of
-    CurlOK -> PostSuccess $ getField "url"
-    _      -> PostFailure $ getField "message"
-    where getField fieldName = fromJust $ mGetField fieldName
+parseResponse r = case mError of
+    Just True -> PostFailure $ fromMaybe ("error message not found. " ++ responseDump) mMessage
+    _         -> case respCurlCode r of
+        CurlOK      -> maybe (PostFailure $ "no url found. " ++ responseDump) PostSuccess mUrl
+        _           -> PostFailure $ "curl failure. " ++ responseDump
+    where mUrl     = mGetField "url"
+          mMessage = mGetField "message"
+          mError   = mGetField "error"
           mGetField fieldName = do
               result <- decode $ LBS.pack (respBody r)
               parseMaybe (.: fieldName) result
+          responseDump = "CurlCode: " ++ show (respCurlCode r) ++ ", Body: " ++ show (respBody r)
 
 httpPost :: String -> [HttpPost]
 httpPost path = [HttpPost "json_file" Nothing (ContentFile path) [] Nothing]
@@ -41,18 +45,19 @@
          -> URLString     -- ^ target url
          -> Bool          -- ^ print json response if true
          -> IO PostResult -- ^ POST request result
-postJson path url printResponse = do
+postJson path url curlVerbose = do
     h <- initialize
-    setopt h (CurlVerbose True)
-    setopt h (CurlURL url)
-    setopt h (CurlHttpPost $ httpPost path)
+    void $ setopt h (CurlVerbose curlVerbose)
+    void $ setopt h (CurlURL url)
+    void $ setopt h (CurlHttpPost $ httpPost path)
     r <- perform_with_response_ h
-    when printResponse $ putStrLn $ respBody r
+    when curlVerbose $ putStrLn $ respBody r
     return $ parseResponse r
 
 -- | Exponential retry policy of 10 seconds initial delay, up to 5 times
 expRetryPolicy :: RetryPolicy
-expRetryPolicy = exponentialBackoff (10 * 1000 * 1000) <> limitRetries 3
+expRetryPolicy = exponentialBackoff tenSecondsInMicroSeconds <> limitRetries 3
+    where tenSecondsInMicroSeconds = 10 * 1000 * 1000
 
 performWithRetry :: IO (Maybe a) -> IO (Maybe a)
 performWithRetry = retrying expRetryPolicy isNothingM
@@ -70,14 +75,15 @@
 readCoverageResult :: URLString         -- ^ target url
                    -> Bool              -- ^ print json response if true
                    -> IO (Maybe String) -- ^ coverage result
-readCoverageResult url printResponse =
+readCoverageResult url curlVerbose =
     performWithRetry readAction
     where readAction = do
               response <- curlGetString url curlOptions
-              when printResponse $ putStrLn $ snd response
+              when curlVerbose $ putStrLn $ snd response
               return $ case response of
                   (CurlOK, body) -> extractCoverage body
                   _ -> Nothing
               where curlOptions = [
+                        CurlVerbose curlVerbose,
                         CurlTimeout 60,
                         CurlConnectTimeout 60]
diff --git a/src/Trace/Hpc/Coveralls/Paths.hs b/src/Trace/Hpc/Coveralls/Paths.hs
--- a/src/Trace/Hpc/Coveralls/Paths.hs
+++ b/src/Trace/Hpc/Coveralls/Paths.hs
@@ -1,3 +1,5 @@
+{-# OPTIONS_GHC -fno-warn-unused-do-bind #-}
+
 -- |
 -- Module:      Trace.Hpc.Coveralls.Paths
 -- Copyright:   (c) 2014-2015 Guillaume Nargeot
@@ -9,23 +11,57 @@
 
 module Trace.Hpc.Coveralls.Paths where
 
+import Control.Monad
+-- import Data.Foldable
+import Data.Traversable (traverse)
+import System.Directory (
+    doesDirectoryExist, getDirectoryContents
+    )
+import System.Directory.Tree (
+    AnchoredDirTree(..), dirTree, readDirectoryWith
+    )
 import Trace.Hpc.Tix
 
-hpcDir :: FilePath
-hpcDir = "dist/hpc/"
+distDir :: FilePath
+distDir = "dist/"
 
-tixDir :: FilePath
-tixDir = hpcDir ++ "tix/"
+hpcDirs :: [FilePath]
+hpcDirs = map (distDir ++) ["hpc/vanilla/", "hpc/"]
 
-mixDir :: FilePath
-mixDir = hpcDir ++ "mix/"
+tixDir :: String -> FilePath
+tixDir = (++ "tix/")
 
-getMixPath :: String -> TixModule -> FilePath
-getMixPath testSuiteName tix = mixDir ++ dirName ++ "/"
+mixDir :: String -> FilePath
+mixDir = (++ "mix/")
+
+getMixPath :: String -> String -> TixModule -> FilePath
+getMixPath hpcDir testSuiteName tix = mixDir hpcDir ++ dirName ++ "/"
     where dirName = case span (/= '/') modName of
               (_, []) -> testSuiteName
               (packageId, _) -> packageId
           TixModule modName _ _ _ = tix
 
-getTixPath :: String -> IO FilePath
-getTixPath testSuiteName = return $ tixDir ++ testSuiteName ++ "/" ++ getTixFileName testSuiteName
+getTixPath :: String -> String -> FilePath
+getTixPath hpcDir testSuiteName = tixDir hpcDir ++ testSuiteName ++ "/" ++ getTixFileName testSuiteName
+
+firstExistingDirectory :: [FilePath] -> IO (Maybe FilePath)
+firstExistingDirectory = fmap msum . mapM pathIfExist
+    where pathIfExist path = do
+              pathExists <- doesDirectoryExist path
+              return $ if pathExists then Just path else Nothing
+
+dumpDirectory :: FilePath -> IO ()
+dumpDirectory path = do
+    directoryExists <- doesDirectoryExist path
+    unless directoryExists $ putStrLn ("Couldn't find the directory " ++ path)
+    putStrLn ("Dumping " ++ path ++ " directory content:")
+    contents <- getDirectoryContents path
+    traverse putStrLn contents
+    return ()
+
+dumpDirectoryTree :: FilePath -> IO ()
+dumpDirectoryTree path = do
+    putStrLn ("Dumping " ++ path ++ " directory tree:")
+    tree <- readDirectoryWith return path
+    traverse putStrLn $ dirTree tree
+    return ()