Add http cabal flag.

This allows pandoc to be compiled without support for making
HTTP requests, which is useful when WASM is the target.

Closes #10980.

3 files changed, 36 insertions, 13 deletions

diff --git a/pandoc.cabal b/pandoc.cabal
index 393451b35..dcad3fffb 100644
--- a/pandoc.cabal
+++ b/pandoc.cabal
@@ -455,6 +455,10 @@ flag embed_data_files
   Description:   Embed data files in binary for relocatable executable.
   Default:       False
 
+flag http
+  Description:   Support for fetching resources using HTTP.
+  Default:       True
+
 common common-options
   default-language: Haskell2010
   build-depends:    base         >= 4.18 && < 5
@@ -517,7 +521,6 @@ library
                  commonmark-pandoc     >= 0.2.3    && < 0.3,
                  containers            >= 0.6.0.1  && < 0.9,
                  crypton               >= 0.30     && < 1.1,
-                 crypton-connection    >= 0.3.1    && < 0.5,
                  data-default          >= 0.4      && < 0.9,
                  deepseq               >= 1.3      && < 1.6,
                  directory             >= 1.2.3    && < 1.4,
@@ -529,14 +532,11 @@ library
                  filepath              >= 1.1      && < 1.6,
                  gridtables            >= 0.1      && < 0.2,
                  haddock-library       >= 1.10     && < 1.12,
-                 http-client           >= 0.4.30   && < 0.8,
-                 http-client-tls       >= 0.2.4    && < 0.4,
                  http-types            >= 0.8      && < 0.13,
                  ipynb                 >= 0.2      && < 0.3,
                  jira-wiki-markup      >= 1.5.1    && < 1.6,
                  mime-types            >= 0.1.1    && < 0.2,
                  mtl                   >= 2.2      && < 2.4,
-                 network               >= 2.6      && < 3.3,
                  network-uri           >= 2.6      && < 2.8,
                  pandoc-types          >= 1.23.1   && < 1.24,
                  parsec                >= 3.1      && < 3.2,
@@ -568,14 +568,21 @@ library
                  vector                >= 0.12     && < 0.14,
                  djot                  >= 0.1.2.4  && < 0.2,
                  asciidoc              >= 0.1      && < 0.2,
-                 tls                   >= 2.0.1    && < 2.2,
-                 crypton-x509-system   >= 1.6.7    && < 1.7
 
   if !os(windows)
     build-depends:  unix >= 2.4 && < 2.9
   if flag(embed_data_files)
      cpp-options:   -DEMBED_DATA_FILES
      other-modules: Text.Pandoc.Data.BakedIn
+  if flag(http)
+     cpp-options:   -DPANDOC_HTTP_SUPPORT
+     build-depends:
+                 crypton-connection    >= 0.3.1    && < 0.5,
+                 crypton-x509-system   >= 1.6.7    && < 1.7,
+                 http-client           >= 0.4.30   && < 0.8,
+                 http-client-tls       >= 0.2.4    && < 0.4,
+                 network               >= 2.6      && < 3.3,
+                 tls                   >= 2.0.1    && < 2.2
   hs-source-dirs:  src
 
   exposed-modules: Text.Pandoc,
diff --git a/src/Text/Pandoc/Class/CommonState.hs b/src/Text/Pandoc/Class/CommonState.hs
index e3c4efce9..27f9c7f16 100644
--- a/src/Text/Pandoc/Class/CommonState.hs
+++ b/src/Text/Pandoc/Class/CommonState.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {- |
 Module      : Text.Pandoc.Class.CommonState
 Copyright   : Copyright (C) 2016-2020 Jesse Rosenthal, John MacFarlane
@@ -23,7 +24,9 @@ import Text.Collate.Lang (Lang)
 import Text.Pandoc.MediaBag (MediaBag)
 import Text.Pandoc.Logging (LogMessage, Verbosity (WARNING))
 import Text.Pandoc.Translations.Types (Translations)
+#ifdef PANDOC_HTTP_SUPPORT
 import Network.HTTP.Client (Manager)
+#endif
 
 -- | 'CommonState' represents state that is used by all
 -- instances of 'PandocMonad'.  Normally users should not
@@ -51,9 +54,11 @@ data CommonState = CommonState
   , stResourcePath :: [FilePath]
     -- ^ Path to search for resources like
     -- included images
+#ifdef PANDOC_HTTP_SUPPORT
   , stManager      :: Maybe Manager
     -- ^ Manager for HTTP client; this needs to persist across many requests
     -- for efficiency.
+#endif
   , stVerbosity    :: Verbosity
     -- ^ Verbosity level
   , stTrace        :: Bool
@@ -79,7 +84,9 @@ defaultCommonState = CommonState
   , stInputFiles = []
   , stOutputFile = Nothing
   , stResourcePath = ["."]
+#ifdef PANDOC_HTTP_SUPPORT
   , stManager = Nothing
+#endif
   , stVerbosity = WARNING
   , stTrace = False
   }
diff --git a/src/Text/Pandoc/Class/IO.hs b/src/Text/Pandoc/Class/IO.hs
index 1a9dc2eae..4c0d7b1ab 100644
--- a/src/Text/Pandoc/Class/IO.hs
+++ b/src/Text/Pandoc/Class/IO.hs
@@ -38,13 +38,17 @@ module Text.Pandoc.Class.IO
 
 import Control.Monad.Except (throwError)
 import Control.Monad.IO.Class (MonadIO, liftIO)
-import Data.ByteString.Lazy (toChunks)
 import Data.Text (Text, pack, unpack)
 import Data.Time (TimeZone, UTCTime)
 import Data.Unique (hashUnique)
+#ifdef PANDOC_HTTP_SUPPORT
+import Data.ByteString.Lazy (toChunks)
+import System.Environment (getEnv)
+import Data.Default (def)
 import Network.Connection (TLSSettings(..))
 import qualified Network.TLS as TLS
 import qualified Network.TLS.Extra as TLS
+import System.X509 (getSystemCertificateStore)
 import Network.HTTP.Client
        (httpLbs, Manager, responseBody, responseHeaders,
         Request(port, host, requestHeaders), parseUrlThrow, newManager, HttpException)
@@ -52,17 +56,19 @@ import Network.HTTP.Client.Internal (addProxy)
 import Network.HTTP.Client.TLS (mkManagerSettings)
 import Network.HTTP.Types.Header ( hContentType )
 import Network.Socket (withSocketsDo)
+import Text.Pandoc.Class.CommonState (CommonState (..))
+import Text.Pandoc.Class.PandocMonad ( getsCommonState, modifyCommonState )
+import qualified Data.CaseInsensitive as CI
+#endif
 import Network.URI (URI(..), parseURI, unEscapeString)
 import System.Directory (createDirectoryIfMissing)
-import System.Environment (getEnv)
 import System.FilePath ((</>), takeDirectory, normalise)
 import qualified System.FilePath.Posix as Posix
 import System.IO (stderr)
 import System.IO.Error
 import System.Random (StdGen)
-import Text.Pandoc.Class.CommonState (CommonState (..))
 import Text.Pandoc.Class.PandocMonad
-       (PandocMonad, getsCommonState, modifyCommonState,
+       (PandocMonad,
         getMediaBag, report, extractURIData)
 import Text.Pandoc.Definition (Pandoc, Inline (Image))
 import Text.Pandoc.Error (PandocError (..))
@@ -73,7 +79,6 @@ import Text.Pandoc.Walk (walk)
 import qualified Control.Exception as E
 import qualified Data.ByteString as B
 import qualified Data.ByteString.Lazy as BL
-import qualified Data.CaseInsensitive as CI
 import qualified Data.Text as T
 import qualified Data.Time
 import qualified Data.Time.LocalTime
@@ -83,8 +88,6 @@ import qualified System.Environment as Env
 import qualified System.FilePath.Glob
 import qualified System.Random
 import qualified Text.Pandoc.UTF8 as UTF8
-import Data.Default (def)
-import System.X509 (getSystemCertificateStore)
 #ifndef EMBED_DATA_FILES
 import qualified Paths_pandoc as Paths
 #endif
@@ -125,6 +128,7 @@ newStdGen = liftIO System.Random.newStdGen
 newUniqueHash :: MonadIO m => m Int
 newUniqueHash = hashUnique <$> liftIO Data.Unique.newUnique
 
+#ifdef PANDOC_HTTP_SUPPORT
 getManager :: (PandocMonad m, MonadIO m) => m Manager
 getManager = do
   mbManager <- getsCommonState stManager
@@ -154,12 +158,14 @@ getManager = do
         newManager tlsManagerSettings
       modifyCommonState $ \st -> st{ stManager = Just manager }
       pure manager
+#endif
 
 openURL :: (PandocMonad m, MonadIO m) => Text -> m (B.ByteString, Maybe MimeType)
 openURL u
  | Just (URI{ uriScheme = "data:",
               uriPath = upath }) <- parseURI (T.unpack u)
      = pure $ extractURIData upath
+#ifdef PANDOC_HTTP_SUPPORT
  | otherwise = do
      let toReqHeader (n, v) = (CI.mk (UTF8.fromText n), UTF8.fromText v)
      customHeaders <- map toReqHeader <$> getsCommonState stRequestHeaders
@@ -181,6 +187,9 @@ openURL u
           Right r -> return r
           Left (e :: HttpException)
                   -> throwError $ PandocHttpError u (T.pack (show e))
+#else
+ | otherwise = error "Text.Pandoc.Class.IO.openURL"
+#endif
 
 -- | Read the lazy ByteString contents from a file path, raising an error on
 -- failure.