Datadog Static Code Analysis lets you define static analysis rules as custom rules. You can share these custom rules within your organization.

Rule organization

SAST rules are organized within rulesets. A ruleset is a collection of rules. There are no constraints on how rules are organized within a ruleset. For example, some users might want to have rulesets for a specific language and others for a category.

A ruleset must have a unique name with only letters, numbers, and hyphens (-). Examples of valid ruleset names are python-security, cobra-team-checks, or my-company-security-checks.

Anatomy of a custom rule

A custom rule is composed of three main components:

• A tree-sitter query that captures what AST elements to check.
• JavaScript code that process the AST elements reports violations.
• Test code to test the rule.

Tree-sitter query

Custom rules use tree-sitter queries to query the code abstract syntax tree (AST) and retrieve elements to analyze. Elements of the AST are captured by the query using the @ operator.

All captured nodes from the tree-sitter query are injected in the JavaScript code and further processed to produce violations.

JavaScript code

The JavaScript code is defined in a visit function. This function is triggered at each match of the tree-sitter query. If a tree-sitter query captures a function call and the analyzed code contains 10 function calls, the visit function is called 10 times and each invocation has the capture of each occurrence.

The visit function has the signature visit(node, path, code):

• node is the tree-sitter context being matched.
• path is the path under analysis (convenient for filtering violation on path or filename).
• code is the code under analysis.

To get a captured node, use the captures attribute of the first argument of the visit function. For example, the code below retrieves the functionName from a tree-sitter query. Each element contains the following attributes:

• astType: the tree-sitter type of the node.
• start: start position of the node. The position contains line and col attributes.
• end: end position of the node. The position contains line and col attributes.

function visit(node, filename, code) {
  const functionNameNode = node.captures["functionName"];
  console.log("ast type");
  console.log(functionNameNode.astType);
  console.log("start line");
  console.log(functionNameNode.start.line);
}

The analyzer includes a few helper functions to help you write rules:

• getCodeForNode(node, code) captures the code for a specific node.
• buildError(startLine, startCol, endLine, endCol, message, severity, category) builds an error.
  • severity is one of the following: ERROR, WARNING, NOTICE and INFO.
  • category is one of the following: BEST_PRACTICES, CODE_STYLE, ERROR_PRONE, PERFORMANCE and SECURITY.
• addError(error) reports an error.

Rule examples

All Datadog default rules are available in Code Security. You can easily analyze and copy them to create your own custom rules.