add support for environment variables

Author: lovasoa

CHANGELOG.md

@@ -1,6 +1,7 @@
 # CHANGELOG.md
 
 ## 0.11.0 (unreleased)
+ - Support for **environment variables** ! You can now read environment variables from sql code using `sqlpage.environment_variable('VAR_NAME')`.
  - Better support for connection options in mssql.
  - New icons (see https://tabler-icons.io/changelog)
  - New version of the CSS library (see https://preview.tabler.io/changelog.html)

examples/official-site/sqlpage/migrations/08_functions.sql

@@ -235,4 +235,39 @@ Currently running from `/home/user/my_sqlpage_website`
 The current working directory is the directory from which the SQLPage server process was started.
 By default, this is also the directory from which `.sql` files are loaded and served.
 However, this can be changed by setting the `web_root` [configuration option](https://github.com/lovasoa/SQLpage/blob/main/configuration.md).
-');
+'
+    );
+INSERT INTO sqlpage_functions (
+        "name",
+        "introduced_in_version",
+        "icon",
+        "description_md"
+    )
+VALUES (
+        'enviroment_variable',
+        '0.11.0',
+        'variable',
+        'Returns the value of the given [environment variable](https://en.wikipedia.org/wiki/Environment_variable).
+
+### Example
+
+```sql
+SELECT ''text'' AS component;
+SELECT ''The value of the HOME environment variable is '' AS contents;
+SELECT sqlpage.environment_variable(''HOME'') as contents, true as code;
+```'
+    );
+INSERT INTO sqlpage_function_parameters (
+        "function",
+        "index",
+        "name",
+        "description_md",
+        "type"
+    )
+VALUES (
+        'enviroment_variable',
+        1,
+        'name',
+        'The name of the environment variable to read. Must be a literal string.',
+        'TEXT'
+    );

src/webserver/database/sql_pseudofunctions.rs

@@ -27,6 +27,7 @@ pub(super) enum StmtParam {
     HashPassword(Box<StmtParam>),
     RandomString(usize),
     CurrentWorkingDir,
+    EnvironmentVariable(String),
 }
 
 pub(super) fn func_call_to_param(func_name: &str, arguments: &mut [FunctionArg]) -> StmtParam {
@@ -43,6 +44,8 @@ pub(super) fn func_call_to_param(func_name: &str, arguments: &mut [FunctionArg])
         "random_string" => extract_integer("random_string", arguments)
             .map_or_else(StmtParam::Error, StmtParam::RandomString),
         "current_working_directory" => StmtParam::CurrentWorkingDir,
+        "environment_variable" => extract_single_quoted_string("environment_variable", arguments)
+            .map_or_else(StmtParam::Error, StmtParam::EnvironmentVariable),
         unknown_name => StmtParam::Error(format!(
             "Unknown function {unknown_name}({})",
             FormatArguments(arguments)
@@ -75,6 +78,10 @@ pub(super) fn extract_req_param<'a>(
             .map_or(Ok(None), |x| hash_password(&x).map(Cow::Owned).map(Some))?,
         StmtParam::RandomString(len) => Some(Cow::Owned(random_string(*len))),
         StmtParam::CurrentWorkingDir => cwd()?,
+        StmtParam::EnvironmentVariable(var) => std::env::var(var)
+            .map(Cow::Owned)
+            .map(Some)
+            .with_context(|| format!("Unable to read environment variable {var}"))?,
     })
 }