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+# Revision history for pgxhtml
+## -- 2018-12-30
+Initial version: XSLT templating, SQL queries, parameter substitution.
diff --git a/LICENSE b/LICENSE
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--- /dev/null
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+ Version 3, 19 November 2007
+ Copyright (C) 2007 Free Software Foundation, Inc. <>
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diff --git a/Main.hs b/Main.hs
new file mode 100644
index 0000000..41abeb1
--- /dev/null
+++ b/Main.hs
@@ -0,0 +1,203 @@
+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
+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 #-}
+import qualified Data.ByteString.Char8 as BS
+import qualified Data.HashMap.Lazy as HM
+import qualified Data.Text as T
+import qualified Data.Map.Lazy as M
+import qualified Database.PostgreSQL.Simple.Types as PT
+import Database.PostgreSQL.Simple
+import Network.Wai
+import Network.HTTP.Types as HT
+import Database.PostgreSQL.Simple.FromField
+ (FromField, fromField, returnError, typename)
+import Web.FormUrlEncoded (Form(..), urlDecodeForm)
+import Database.PostgreSQL.Simple.ToField (Action (..))
+import Database.PostgreSQL.Simple.Internal (withConnection)
+import Database.PostgreSQL.LibPQ (getCancel, cancel)
+import Text.XML.HXT.Core
+ (IOSArrow, replaceChildren, arrL, ($<), constA, runX,
+ writeDocumentToString, withOutputXHTML, withIndent, stringTrim,
+ XNode(..), mkName)
+import Text.XML.HXT.DOM.XmlNode (mkRoot)
+import Text.XML.HXT.Parser.XmlParsec (xreadDoc)
+import Text.XML.HXT.XSLT.Application (XPathParams, applyStylesheetWParams)
+import Text.XML.HXT.XSLT.XsltArrows (xsltCompileStylesheetFromURI)
+import Text.XML.HXT.XSLT.Common (XmlTree, ExName(..), Expr(..), (>>>))
+import Data.Tree.Class (mkTree)
+import Data.String (fromString)
+import Data.Maybe (mapMaybe)
+import Data.Text.Encoding (encodeUtf8)
+import Network.Wai.Middleware.HttpAuth (extractBasicAuth)
+import Network.HTTP.Types.Header (hWWWAuthenticate)
+import Network.Wai.Middleware.Timeout (timeout)
+import Network.Wai.Cli (defWaiMain)
+import Control.Monad (join)
+import Control.Arrow ((***))
+import Control.Exception (bracket, finally, handle)
+import System.FilePath (replaceExtension, takeFileName, (</>))
+import System.Envy (decodeEnv, FromEnv(..), envMaybe, (.!=))
+newtype PgXmlTree = PgXmlTree { unPgXmlTree :: XmlTree }
+instance FromField PgXmlTree where
+ fromField f Nothing = returnError UnexpectedNull f ""
+ fromField f (Just mdata) = do
+ tName <- typename f
+ if tName /= "xml"
+ then returnError ConversionFailed f $
+ "Expected xml type, got " ++ BS.unpack tName
+ else pure $ PgXmlTree $
+ mkRoot [] $ xreadDoc (stringTrim $ BS.unpack mdata)
+data EnvConfig = EnvConfig
+ { connectionTimeout :: Int
+ -- ^ HTTP connection timeout, in seconds
+ , xsltDirectory :: FilePath
+ -- ^ A directory to read XSLTs from
+ }
+instance FromEnv EnvConfig where
+ fromEnv =
+ EnvConfig <$> envMaybe "TIMEOUT" .!= 10 <*> envMaybe "XSLT_DIR" .!= ""
+formToFields :: Form -> [(T.Text, T.Text)]
+formToFields = mapMaybe toField . HM.toList . unForm
+ where toField (f, [v]) = Just (f, v)
+ toField _ = Nothing
+xsltApplyStylesheetWParamsFromURI :: XPathParams -> String
+ -> IOSArrow XmlTree XmlTree
+xsltApplyStylesheetWParamsFromURI par uri = replaceChildren
+ $ arrL . applyStylesheetWParams par
+ $< (constA uri >>> xsltCompileStylesheetFromURI)
+cancelAndClose :: Connection -> IO (Maybe BS.ByteString)
+cancelAndClose c = cancelConn `finally` close c
+ where cancelConn = withConnection c $ \conn -> do
+ cl <- getCancel conn
+ case cl of
+ Nothing -> pure $ Just "Failed to get a Cancel structure"
+ Just cl' -> either Just (const Nothing) <$> cancel cl'
+prepareQuery :: Form
+ -- ^ Form data
+ -> HT.Query
+ -- ^ URL query
+ -> BS.ByteString
+ -- ^ SQL query template
+ -> (PT.Query, [Action])
+ -- ^ SQL query template and parameters
+prepareQuery f gq q = let sub = map substWord $ BS.words q
+ in (PT.Query $ BS.unwords (map fst sub), concat $ mapMaybe snd sub)
+ where
+ fields = formToFields f
+ bsFields = map (encodeUtf8 *** encodeUtf8) fields
+ keys = map fst bsFields
+ vals = map snd bsFields
+ placeholders = BS.intercalate "," (map (const "?") fields)
+ substWord ":fields" = (placeholders, Just (map EscapeIdentifier keys))
+ substWord ":values" = (placeholders, Just (map Escape vals))
+ substWord other = case BS.splitAt 2 other of
+ -- POST (form) parameter
+ ("f:", fieldName) -> ("?", pure . Escape <$> lookup fieldName bsFields)
+ -- GET (query/link or form) parameter
+ ("q:", fieldName) -> ("?", pure . Escape <$> join (lookup fieldName gq))
+ _ -> (other, Nothing)
+makeParams :: HT.Query -> XPathParams
+makeParams = M.fromList . mapMaybe makeParam
+ where makeParam (k, Just v) = Just ( ExName (BS.unpack k) ""
+ , LiteralExpr (BS.unpack v))
+ makeParam _ = Nothing
+errorXML :: PT.Query -> [Action] -> SqlError -> XmlTree
+errorXML q p e = mkRoot []
+ [mkTree (XTag (mkName "sql_error")
+ [ mkAttr "template" (show q)
+ , mkAttr "parameters" (show p)
+ , mkAttr "state" (BS.unpack $ sqlState e)
+ , mkAttr "status" (show $ sqlExecStatus e)
+ , mkAttr "message" (BS.unpack $ sqlErrorMsg e)
+ , mkAttr "detail" (BS.unpack $ sqlErrorDetail e)
+ , mkAttr "hint" (BS.unpack $ sqlErrorHint e)
+ ])
+ []]
+ where mkAttr k v = mkTree (XAttr $ mkName k) [mkTree (XText v) []]
+serve :: EnvConfig -> IO Connection -> Application
+serve conf ioc req respond = do
+ form' <- urlDecodeForm <$> strictRequestBody req
+ case form' of
+ Left _err -> respond $ responseLBS notAcceptable406 []
+ "Failed to read form data"
+ Right form -> case lookup "q" (queryString req) of
+ Just (Just q) -> do
+ let qs = queryString req
+ (q', params) = prepareQuery form qs q
+ xsltPath = xsltDirectory conf
+ </> replaceExtension
+ (takeFileName (BS.unpack $ rawPathInfo req)) "xsl"
+ resp st xml = do
+ rc <- runX $ constA xml
+ >>> xsltApplyStylesheetWParamsFromURI (makeParams qs) xsltPath
+ >>> writeDocumentToString [withOutputXHTML, withIndent True]
+ respond $ responseLBS st
+ [(hContentType, "application/xhtml+xml")]
+ (fromString $ concat $
+ "<?xml version=\"1.0\"?>\n" : "<!DOCTYPE html>\n" : rc)
+ handle (resp badRequest400 . errorXML q' params)
+ $ bracket ioc cancelAndClose $ \c -> do
+ r <- query c q' params
+ case r of
+ [Only xmlDoc] -> resp ok200 (unPgXmlTree xmlDoc)
+ _ -> respond $ responseLBS status500 []
+ "Expected a single result, got 0 or more"
+ _ -> respond $ responseLBS imATeapot418 [] "No query is provided"
+main :: IO ()
+main = do
+ conf <- decodeEnv
+ case conf of
+ Left err -> putStrLn err
+ Right conf' -> defWaiMain
+ $ timeout (connectionTimeout conf') $ \req respond ->
+ case ("authorised" `elem` pathInfo req, extractBasicAuth
+ =<< lookup hAuthorization (requestHeaders req)) of
+ (True, Just (l, p)) ->
+ serve conf'
+ (connect $ ConnectInfo "" 0 (BS.unpack l) (BS.unpack p) "")
+ req respond
+ (True, Nothing) ->
+ respond $ responseLBS unauthorized401
+ [( hWWWAuthenticate
+ , "Basic realm=\"Protected area\", charset=\"UTF-8\"")] ""
+ _ -> serve conf' (connectPostgreSQL "") req respond
diff --git a/ b/
new file mode 100644
index 0000000..7770552
--- /dev/null
+++ b/
@@ -0,0 +1,81 @@
+# pg×html
+This is a tool to make custom web interfaces to PostgreSQL databases,
+using simple and standard technologies:
+- SQL for querying
+- XSLT for templating (translation of XML query results into XHTML)
+- HTML forms for user input
+- Optional HTTP basic authentication for PostgreSQL authentication
+URL query parameters are available for use from XSLTs. SQL query
+templates also can use those, as well as HTML form data submitted with
+the POST method.
+Request timeouts are enforced and do cancel DB queries, but otherwise
+it relies on PostgreSQL for access permissions and security policies,
+as well as for any business logic that may be needed.
+It is based on WAI, and can be used with CGI, socket activation, Unix
+domain sockets, or as a standalone HTTP server.
+## Usage
+### Invocation
+See [wai-cli]( for CLI
+arguments. The used environment variables are:
+- `TIMEOUT`: request timeout in seconds, 10 by default.
+- `XSLT_DIR`: a directory to read XSLT files from, current working
+ directory by default.
+Regular [libpq environment
+are used for database connections.
+### Templating
+URL query parameters are made visible to XSLTs as `xsl:param`
+parameters. The documents they get applied to are either the results
+of SQL queries (which are expected to return a single XML document,
+using `query_to_xml` or similar functions), or error documents (which
+contain error details) in case of an SQL error.
+The XSLTs are taken from `XSLT_DIR`, using file name from the URL
+query, with its extension changed to `xsl`.
+### Querying
+SQL queries provided in the `q` URL query parameter get executed, with
+some substitutions to handle HTML forms:
+- `f:<name>` for POST parameters
+- `q:<name>` for GET parameters
+- `:fields` for POST parameter names
+- `:values` for POST parameter values (in the same order as the names)
+`:fields` and `:values` are unnecessary, but are provided for
+convenience of insert/upsert operations.
+SQL queries get tokenized by splitting into words and reassembled
+afterwards, hence some whitespace separation is needed.
+### Authentication
+Presence of `authorised` in the URL path requires HTTP basic
+authentication, and the provided credentials are used directly for
+PostgreSQL authentication.
+### Web server
+This is intended to be used with an HTTP server, which would take care
+of encryption, compression, static files, redirects, and so on, while
+pgxhtml only focuses on providing a web interface to a database.
+## See also
+[PostgREST](, "a standalone web server that
+turns your PostgreSQL database directly into a RESTful API".
diff --git a/example/ b/example/
new file mode 100644
index 0000000..b6cfbfa
--- /dev/null
+++ b/example/
@@ -0,0 +1,18 @@
+# pg×html usage example
+Here is an example that implements a very basic bug reporting system:
+users can just report, view, and list (search) the bugs.
+First of all, a database should be designed: `bugs.sql` contains
+definitions and comments.
+A common template, `common.xsl`, includes error handling and some
+shared HTML. One can choose to show error details to users, or to hide
+`view.xsl` is a basic template for bug viewing.
+`list.xsl` includes report and search forms, and lists the bugs.
+To quickly try it, run `pgxhtml --devlogging` in this directory,
+with database connection environment variables set if needed.
diff --git a/example/bugs.sql b/example/bugs.sql
new file mode 100644
index 0000000..033a1f7
--- /dev/null
+++ b/example/bugs.sql
@@ -0,0 +1,37 @@
+-- pgcrypto is needed for UUIDs.
+create extension pgcrypto;
+-- A table with defaults and constraints.
+create table bugs (
+ id uuid not null primary key default gen_random_uuid(),
+ reported timestamp with time zone not null default now(),
+ reporter varchar not null default current_user,
+ project varchar(256) not null check (project <> ''),
+ description varchar(10240) not null check (description <> '')
+-- No indexes, since they are irrelevant to this example (but normally
+-- they should be there).
+-- Additional restrictions.
+create policy bugs_select_policy on bugs for select using (true);
+create policy bugs_insert_policy on bugs for insert
+ with check (reported = now() and reporter = current_user);
+-- Update and delete policies can be added later.
+alter table bugs enable row level security;
+-- A search function for convenience.
+create or replace function bug_search (proj varchar, descr varchar, lim int, offs int)
+returns xml
+as $$
+ select query_to_xml(
+ 'select id, date_trunc(''second'', reported) as reported, reporter, '
+ || 'project, substring(description from ''[^\n\r]+'') as summary from bugs '
+ || 'where (project like ' || quote_literal('%' || proj || '%')
+ || ') and (description like ' || quote_literal('%' || descr || '%')
+ || ') order by reported desc limit ' || lim || ' offset ' || offs,
+ false, false, 'bugs')
+$$ language sql;
+-- Now users can be added with select and/or insert privileges,
+-- including a guest user for unauthenticated requests.
diff --git a/example/common.xsl b/example/common.xsl
new file mode 100644
index 0000000..1db0229
--- /dev/null
+++ b/example/common.xsl
@@ -0,0 +1,40 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet xmlns:xsl=""
+ xmlns:xhtml=""
+ xmlns=""
+ version="1.0">
+ <xsl:output method="xml" indent="yes"/>
+ <xsl:template match="/">
+ <html xmlns="">
+ <head>
+ <title>Bugs</title>
+ </head>
+ <body>
+ <xsl:apply-templates select="*" />
+ </body>
+ </html>
+ </xsl:template>
+ <xsl:template match="sql_error">
+ <h1>SQL error</h1>
+ <dl>
+ <dt>State</dt>
+ <dd><xsl:copy-of select="@state/text()" /></dd>
+ <dt>Status</dt>
+ <dd><xsl:copy-of select="@status/text()" /></dd>
+ <dt>Message</dt>
+ <dd><xsl:copy-of select="@message/text()" /></dd>
+ <dt>Detail</dt>
+ <dd><xsl:copy-of select="@detail/text()" /></dd>
+ <dt>Hint</dt>
+ <dd><xsl:copy-of select="@hint/text()" /></dd>
+ <dt>Query template</dt>
+ <dd><xsl:copy-of select="@template/text()" /></dd>
+ <dt>Query parameters</dt>
+ <dd><xsl:copy-of select="@parameters/text()" /></dd>
+ </dl>
+ </xsl:template>
diff --git a/example/list.xsl b/example/list.xsl
new file mode 100644
index 0000000..86c3150
--- /dev/null
+++ b/example/list.xsl
@@ -0,0 +1,92 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet xmlns:xsl=""
+ xmlns:xhtml=""
+ xmlns=""
+ version="1.0">
+ <xsl:output method="xml" indent="yes"/>
+ <xsl:include href="common.xsl"/>
+ <xsl:param name="project" />
+ <xsl:param name="description" />
+ <xsl:param name="limit" select="10" />
+ <xsl:param name="offset" select="0" />
+ <xsl:template match="table">
+ <!-- Report form -->
+ <h2>Report</h2>
+ <form method="post" action="view.xhtml?q=insert%20into%20bugs%20(%20:fields%20)%20values%20(%20:values%20)%20returning%20xmlelement(name%20table,xmlelement(name%20row,xmlelement(name%20id,id),xmlelement(name%20reported,reported),xmlelement(name%20reporter,reporter),xmlelement(name%20project,project),xmlelement(name%20description,description)))">
+ <dl>
+ <dt><label for="report_project">Project</label></dt>
+ <dd>
+ <input type="text" name="project" id="report_project"
+ required="required" maxlength="128"
+ placeholder="Project name or URL" />
+ </dd>
+ <dt><label for="report_description">Description</label></dt>
+ <dd>
+ <textarea name="description" required="required"
+ id="report_description" maxlength="10240"
+ placeholder="Issue description" />
+ </dd>
+ </dl>
+ <input type="submit" value="Report" />
+ </form>
+ <!-- Search form -->
+ <h2>Search</h2>
+ <form method="get" action="list.xhtml">
+ <dl>
+ <dt><label for="search_project">Project</label></dt>
+ <dd>
+ <input id="search_project" type="search" name="project"
+ value="{$project}" />
+ </dd>
+ <dt><label for="search_description">Description</label></dt>
+ <dd>
+ <input id="search_description" type="search" name="description"
+ value="{$description}" />
+ </dd>
+ <dt><label for="search_limit">Limit</label></dt>
+ <dd>
+ <input id="search_limit" type="number" name="limit" min="1"
+ value="{$limit}" />
+ </dd>
+ <dt><label for="search_offset">Offset</label></dt>
+ <dd>
+ <input id="search_offset" type="number" name="offset" min="0"
+ value="{$offset}" />
+ </dd>
+ <input type="hidden" name="q"
+ value="select bug_search( q:project , q:description , q:limit , q:offset )" />
+ </dl>
+ <input type="submit" value="Search" />
+ </form>
+ <!-- Search results -->
+ <table>
+ <tr>
+ <th>Reported</th>
+ <th>Reporter</th>
+ <th>Project</th>
+ <th>Summary</th>
+ </tr>
+ <xsl:for-each select="row">
+ <tr>
+ <td><xsl:copy-of select="reported/text()" /></td>
+ <td><xsl:copy-of select="reporter/text()" /></td>
+ <td>
+ <a href="list.xhtml?q=select%20bug_search('{project/text()}','',{$limit},{$offset})">
+ <xsl:copy-of select="project/text()" />
+ </a>
+ </td>
+ <td>
+ <a href="view.xhtml?q=select%20query_to_xml('select%20*%20from%20bugs%20where%20id=''{id}''',false,false,'foo')">
+ <xsl:copy-of select="summary/text()" />
+ </a>
+ </td>
+ </tr>
+ </xsl:for-each>
+ </table>
+ </xsl:template>
diff --git a/example/view.xsl b/example/view.xsl
new file mode 100644
index 0000000..af0e090
--- /dev/null
+++ b/example/view.xsl
@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<xsl:stylesheet xmlns:xsl=""
+ xmlns:xhtml=""
+ xmlns=""
+ version="1.0">
+ <xsl:output method="xml" indent="yes"/>
+ <xsl:include href="common.xsl"/>
+ <xsl:template match="table/row">
+ <a href="list.xhtml?q=select%20bug_search(%27%27,%20%27%27,%2010,%200)">back to listing</a>
+ <dl>
+ <dt>ID</dt>
+ <dd><xsl:copy-of select="id/text()" /></dd>
+ <dt>Reported</dt>
+ <dd><xsl:copy-of select="reported/text()" /></dd>
+ <dt>Reporter</dt>
+ <dd><xsl:copy-of select="reporter/text()" /></dd>
+ <dt>Project</dt>
+ <dd><xsl:copy-of select="project/text()" /></dd>
+ <dt>Description</dt>
+ <dd><pre><xsl:copy-of select="description/text()" /></pre></dd>
+ </dl>
+ </xsl:template>
diff --git a/pgxhtml.cabal b/pgxhtml.cabal
new file mode 100644
index 0000000..6430b31
--- /dev/null
+++ b/pgxhtml.cabal
@@ -0,0 +1,37 @@
+name: pgxhtml
+synopsis: XSLT-based PostgreSQL web interface
+description: This is a tool to make custom web interfaces to PostgreSQL
+ databases, using simple and standard technologies.
+license: AGPL-3
+license-file: LICENSE
+author: defanor
+category: Database
+build-type: Simple
+ ,
+cabal-version: >=1.10
+executable pgxhtml
+ main-is: Main.hs
+ other-extensions: OverloadedStrings
+ build-depends: base >=4.9 && <5
+ , bytestring >=0.10 && <0.11
+ , unordered-containers >=0.2 && <0.3
+ , text >=1.2 && <1.3
+ , containers >=0.5 && <0.6
+ , postgresql-simple >=0.5 && <0.6
+ , postgresql-libpq >=0.9 && <0.10
+ , http-types >=0.12 && <0.13
+ , hxt >=9.3 && <9.4
+ , hxt-xslt >=9.1 && <9.2
+ , http-api-data >=0.3 && <0.4
+ , wai >=3.2 && <3.3
+ , wai-extra >=3.0 && <3.1
+ , wai-cli >=0.1 && <0.2
+ , warp >=3.2 && <3.3
+ , filepath >=1.4 && <1.5
+ , envy >=1.5 && <1.6
+ default-language: Haskell2010
+ ghc-options: -Wall