{-
pgxhtml, an XSLT-based PostgreSQL web interface.
Copyright (C) 2018-2019 defanor
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Affero General Public License for more details.
You should have received a copy of the GNU Affero General Public License
along with this program. If not, see .
-}
{- |
Description : XSLT-based PostgreSQL web interface
Maintainer : defanor
Stability : unstable
Portability : non-portable (uses GHC extensions)
This is a tool to make custom web (HTTP with XHTML) interfaces to
PostgreSQL databases, using XSLT for templating and SQL for querying,
HTTP basic authentication and PostgreSQL roles for authentication.
-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ForeignFunctionInterface #-}
import qualified Data.ByteString.Char8 as BS
import Database.PostgreSQL.LibPQ
(getCancel, cancel, connectdb, finish, execParams, getvalue, invalidOid,
escapeIdentifier, resultStatus, errorMessage, Connection, Format(..),
ExecStatus(..))
import Data.Maybe (mapMaybe, fromMaybe, catMaybes, fromJust)
import System.Timeout (timeout)
import Control.Exception (bracket, finally)
import System.FilePath (takeFileName, (>), (<.>))
import System.Environment (lookupEnv)
import Data.List (nubBy)
import Data.ByteString.Base64 (decodeLenient)
import Data.Char (ord, chr)
import Foreign
import Foreign.C
-- * libxml bindings and functions
-- http://xmlsoft.org/html/index.html
-- http://xmlsoft.org/XSLT/html/index.html
data XmlDoc
data XsltStylesheet
data XsltTransformContext
foreign import ccall "xmlReadMemory" xmlReadMemory ::
CString -> CInt -> CString -> CString -> CInt -> IO (Ptr XmlDoc)
foreign import ccall "xmlFreeDoc" xmlFreeDoc :: Ptr XmlDoc -> IO ()
foreign import ccall "xsltParseStylesheetFile" xsltParseStylesheetFile ::
CString -> IO (Ptr XsltStylesheet)
foreign import ccall "xsltFreeStylesheet" xsltFreeStylesheet ::
Ptr XsltStylesheet -> IO ()
foreign import ccall "xsltNewTransformContext" xsltNewTransformContext ::
Ptr XsltStylesheet -> Ptr XmlDoc -> IO (Ptr XsltTransformContext)
foreign import ccall "xsltFreeTransformContext" xsltFreeTransformContext ::
Ptr XsltTransformContext -> IO ()
foreign import ccall "xsltQuoteUserParams" xsltQuoteUserParams ::
Ptr XsltTransformContext -> Ptr CString -> IO CInt
foreign import ccall "xsltApplyStylesheetUser" xsltApplyStylesheetUser ::
Ptr XsltStylesheet -> Ptr XmlDoc -> Ptr CString -> CString -> Ptr () ->
Ptr XsltTransformContext -> IO (Ptr XmlDoc)
foreign import ccall "xsltSaveResultToString" xsltSaveResultToString ::
Ptr CString -> Ptr CInt -> Ptr XmlDoc -> Ptr XsltStylesheet -> IO CInt
foreign import ccall "exsltRegisterAll" exsltRegisterAll :: IO ()
transform :: BS.ByteString
-- ^ document
-> String
-- ^ base URI
-> FilePath
-- ^ path to stylesheet
-> [(BS.ByteString, BS.ByteString)]
-- ^ string params
-> IO BS.ByteString
transform docBS baseStr pathStr stringParams =
BS.useAsCStringLen docBS $ \(docCStr, docCStrLen) ->
withCString baseStr $ \baseCStr ->
withCString pathStr $ \pathCStr ->
alloca $ \bufPtr ->
alloca $ \lenPtr ->
bracket
(notNull $ xmlReadMemory docCStr (fromIntegral docCStrLen) baseCStr nullPtr 0)
xmlFreeDoc $ \doc ->
useAsCStrings (concatMap (\(x, y) -> [x, y]) $
nubBy (\x y -> fst x == fst y) stringParams) [] $ \params ->
withArray0 nullPtr params $ \paramsArr ->
withArray0 nullPtr [] $ \emptyArr ->
bracket (notNull $ xsltParseStylesheetFile pathCStr) xsltFreeStylesheet $
\stylesheet ->
bracket (notNull $ xsltNewTransformContext stylesheet doc)
xsltFreeTransformContext $
\tc -> xsltQuoteUserParams tc paramsArr >>
bracket
(notNull $ xsltApplyStylesheetUser stylesheet doc emptyArr nullPtr nullPtr tc)
xmlFreeDoc
(\res ->
xsltSaveResultToString bufPtr lenPtr res stylesheet >>
bracket (peek bufPtr) free BS.packCString)
where
useAsCStrings :: [BS.ByteString] -> [CString] -> ([CString] -> IO a) -> IO a
useAsCStrings [] a f = f a
useAsCStrings (x:xs) a f = BS.useAsCString x $ \x' ->
useAsCStrings xs (a ++ [x']) f
notNull :: IO (Ptr a) -> IO (Ptr a)
notNull a = a >>= \p -> if p == nullPtr
then error "Unexpected NULL pointer"
else pure p
-- TODO: improve error handling
-- * PostgreSQL-related functions
connString :: [(BS.ByteString, BS.ByteString)] -> BS.ByteString
connString [] = BS.empty
connString ((k,v):xs) =
BS.concat [k, "='", BS.pack (val $ BS.unpack v), "' ", connString xs]
where val [] = []
val ('\\':cs) = '\\' : '\\' : val cs
val ('\'':cs) = '\\' : '\'' : val cs
val (c:cs) = c : val cs
-- https://www.postgresql.org/docs/11/libpq-exec.html
-- https://hackage.haskell.org/package/postgresql-libpq-0.9.4.2/docs/Database-PostgreSQL-LibPQ.html
prepareQuery :: Connection
-> [(BS.ByteString, BS.ByteString)]
-- ^ Form data
-> [(BS.ByteString, BS.ByteString)]
-- ^ URL query
-> BS.ByteString
-- ^ SQL query template
-> IO (BS.ByteString, [BS.ByteString])
-- ^ SQL query template and parameters
prepareQuery c f gq q = substWords [] [] $ BS.words q
where
placeholder :: Int -> BS.ByteString
placeholder n = BS.cons '$' $ BS.pack $ show $ n + 1
placeholders :: Int -> BS.ByteString
placeholders cnt = BS.intercalate " , "
[placeholder (cnt + n) | n <- [0 .. length f - 1]]
substWords :: [BS.ByteString]
-- ^ query bits
-> [BS.ByteString]
-- ^ parameters
-> [BS.ByteString]
-- ^ remaining words
-> IO (BS.ByteString, [BS.ByteString])
-- ^ query and parameters
substWords qs ps [] = pure (BS.unwords qs, ps)
substWords qs ps (":fields":rest) = do
identifiers <- BS.intercalate ", " . catMaybes
<$> mapM (escapeIdentifier c . fst) f
substWords (qs ++ [identifiers]) ps rest
substWords qs ps (":values":rest) =
substWords (qs ++ [placeholders $ length ps]) (ps ++ map snd f) rest
substWords qs ps (other:rest) = case BS.splitAt 2 other of
-- POST (form) parameter
("f:", fieldName) -> case lookup fieldName f of
Nothing -> substWords (qs ++ [other]) ps rest
Just v -> substWords (qs ++ [placeholder $ length ps]) (ps ++ [v]) rest
-- GET (query/link or form) parameter
("q:", fieldName) -> case lookup fieldName gq of
Nothing -> substWords (qs ++ [other]) ps rest
Just v -> substWords (qs ++ [placeholder $ length ps]) (ps ++ [v]) rest
_ -> substWords (qs ++ [other]) ps rest
cancelAndClose :: Connection -> IO (Maybe BS.ByteString)
cancelAndClose c = cancelConn `finally` finish c
where cancelConn = do
cl <- getCancel c
case cl of
Nothing -> pure $ Just "Failed to get a Cancel structure"
Just cl' -> either Just (const Nothing) <$> cancel cl'
-- * CGI and HTTP utilities
-- https://tools.ietf.org/html/rfc3875
-- https://tools.ietf.org/html/rfc2396
-- https://www.w3.org/TR/html5/sec-forms.html
-- https://url.spec.whatwg.org/
parseFormUrlencoded :: BS.ByteString -> [(BS.ByteString, BS.ByteString)]
parseFormUrlencoded s = mapMaybe seq2nv $ BS.split '&' s
where
seq2nv sq
| BS.null sq = Nothing
| otherwise = let (n, v') = BS.break (== '=') sq
v = if BS.null v' then v' else BS.tail v'
in Just (unescape n, unescape v)
unescape :: BS.ByteString -> BS.ByteString
unescape bs = case BS.uncons bs of
Nothing -> bs
Just ('+', rest) -> BS.cons ' ' (unescape rest)
Just ('%', rest) -> case BS.uncons rest of
Nothing -> BS.pack ['%']
Just (c1, rest') -> case BS.uncons rest' of
Nothing -> BS.pack ['%', c1]
Just (c2, rest'') -> case (parseChar c1, parseChar c2) of
(Just c1', Just c2') ->
BS.cons (chr $ c1' * 0x10 + c2') (unescape rest'')
_ -> BS.cons '%' (unescape rest)
Just (c, rest) -> BS.cons c (unescape rest)
parseChar :: Char -> Maybe Int
parseChar c
| c >= 'A' && c <= 'F' = Just $ ord c - ord 'A' + 10
| c >= '0' && c <= '9' = Just $ ord c - ord '0'
| otherwise = Nothing
-- https://tools.ietf.org/html/rfc7235
-- https://tools.ietf.org/html/rfc7617
baCredentials :: BS.ByteString -> Maybe (BS.ByteString, BS.ByteString)
baCredentials cred = do
(login, password) <-
BS.break (== ':') . decodeLenient <$> BS.stripPrefix "Basic " cred
if BS.length password > 0
then Just (login, BS.tail password)
else Nothing
respond' :: Int -> [String] -> BS.ByteString -> IO ()
respond' code headers content = do
putStrLn "Content-Type:application/xhtml+xml"
mapM_ putStrLn headers
putStrLn $ concat ["Status:", show code, " ", reason, "\n"]
BS.putStr content
where
reason = case code of
200 -> "OK"
401 -> "Unauthorized"
418 -> "I'm a teapot"
504 -> "Gateway Timeout"
_ -> ""
respond :: Int -> BS.ByteString -> IO ()
respond c = respond' c []
-- * Main routines
errorXML :: [(BS.ByteString, BS.ByteString)] -> BS.ByteString
errorXML kv = xmlElem "error" " xmlns=\"urn:x-pgxhtml\"" $
BS.concat $ map (\(k,v) -> xmlElem k "" v) kv
where
xmlElem n a s = BS.concat ["<", n, a, ">", s, "", n, ">"]
serve :: FilePath -> IO Connection -> [(BS.ByteString, BS.ByteString)] -> IO ()
serve xsltDirectory ioc ps = case lookup "q" ps of
Just q -> bracket ioc cancelAndClose $ \c -> do
formData <- parseFormUrlencoded <$> BS.getContents
(q', params) <- prepareQuery c formData ps q
r <- execParams c q'
(map (\p -> Just (invalidOid, p, Text)) params) Text
case r of
Just r' -> do
rs <- resultStatus r'
case rs of
TuplesOk -> do
-- TODO: add more checks and error messages
val <- getvalue r' 0 0
case val of
Nothing ->
respError 500 [("message", "Failed to read query result")]
Just val' -> resp 200 val'
CommandOk ->
respError 500 [("message", "The command didn't return XML")]
_ -> do
errMsg <- maybe [] (\m -> [("message", m)]) <$> errorMessage c
respError 500 $ ("exec_status", BS.pack (show rs)) : errMsg
Nothing -> respError 500 [("message", "Failed to execute the query")]
_ -> respError 418 [("message", "No query is provided")]
where
xsltPath = xsltDirectory >
takeFileName (BS.unpack $ fromMaybe "default" $ lookup "t" ps)
<.> "xsl"
resp st xml = do
doc <- transform xml "" xsltPath ps
respond st doc
respError st e = resp st (errorXML e)
main :: IO ()
main = do
exsltRegisterAll
-- It's okay to fail when not invoked properly.
ps <- parseFormUrlencoded . BS.pack . fromJust <$> lookupEnv "QUERY_STRING"
ha <- lookupEnv "HTTP_AUTHORIZATION"
xsltDir <- fromMaybe "." <$> lookupEnv "XSLT_DIR"
to <- maybe 10 read <$> lookupEnv "TIMEOUT"
maybe (respond 504 "") pure =<< timeout (to * 10 ^ (6 :: Int))
(case (lookup "auth" ps, baCredentials =<< BS.pack <$> ha) of
(Just "on", Just (l, p)) ->
serve xsltDir (connectdb (connString [("user", l), ("password", p)]))
ps
(Just "on", Nothing) ->
respond' 401
["WWW-Authenticate:Basic realm=\"Protected area\", charset=\"UTF-8\""]
""
_ -> serve xsltDir (connectdb "") ps)