feat: Add lazyCompileValidationSchemas option

Author: Karel Marek

docs/Options.md

@@ -233,3 +233,9 @@ If set, then when encountering a validation error Exegesis will return
 all errors found in the document instead of just the first error. This
 causes Exegesis to spend more time on requests with errors in them, so
 for performance reasons this is disabled by default.
+
+## lazyCompileValidationSchemas
+
+Response and request schemas are compiled by ajv to make validation faster. However compilation is slow
+and can cause compilation of API to take long time. Enabling this will cause validation schemas
+compilation to be executed when the validator is needed.

src/oas3/Schema/validators.ts

@@ -117,7 +117,7 @@ function doValidate(
     schemaPtr: string,
     parameterLocation: ParameterLocation,
     parameterRequired: boolean,
-    ajvValidate: ValidateFunction,
+    getAjvValidate: () => ValidateFunction,
     json: any
 ) {
     const value = { value: json };
@@ -142,6 +142,7 @@ function doValidate(
     }
 
     if (!errors) {
+        const ajvValidate = getAjvValidate();
         ajvValidate(value);
         if (ajvValidate.errors) {
             errors = ajvValidate.errors.map((err) => {
@@ -167,6 +168,23 @@ function doValidate(
     return { errors, value: value.value };
 }
 
+function createValidateGetter(schema: any, ajv: Ajv, lazy: boolean): () => ValidateFunction {
+    if (lazy) {
+        let validate: ValidateFunction | null = null;
+        return function () {
+            if (!validate) {
+                validate = ajv.compile(schema);
+            }
+            return validate;
+        };
+    } else {
+        const validate = ajv.compile(schema);
+        return function () {
+            return validate;
+        };
+    }
+}
+
 function generateValidator(
     schemaContext: Oas3CompileContext,
     parameterLocation: ParameterLocation,
@@ -212,10 +230,14 @@ function generateValidator(
         ajv.addFormat(key, customFormats[key]);
     }
 
-    const validate = ajv.compile(schema);
+    const getValidate = createValidateGetter(
+        schema,
+        ajv,
+        schemaContext.options.lazyCompileValidationSchemas
+    );
 
     return function (json: any) {
-        return doValidate(schemaPtr, parameterLocation, parameterRequired, validate, json);
+        return doValidate(schemaPtr, parameterLocation, parameterRequired, getValidate, json);
     };
 }
 

src/options.ts

@@ -37,6 +37,7 @@ export interface ExegesisCompiledOptions {
     allErrors: boolean;
     treatReturnedJsonAsPure: boolean;
     strictValidation: boolean;
+    lazyCompileValidationSchemas: boolean;
 }
 
 // See the OAS 3.0 specification for full details about supported formats:
@@ -134,5 +135,6 @@ export function compileOptions(options: ExegesisOptions = {}): ExegesisCompiledO
         allErrors: options.allErrors || false,
         treatReturnedJsonAsPure: options.treatReturnedJsonAsPure || false,
         strictValidation: options.strictValidation ?? false,
+        lazyCompileValidationSchemas: options.lazyCompileValidationSchemas ?? false,
     };
 }

src/types/options.ts

@@ -164,4 +164,11 @@ export interface ExegesisOptions {
      * If true, then this will put ajv into "strict mode" (see https://ajv.js.org/strict-mode.html).
      */
     strictValidation?: boolean;
+
+    /**
+     * Response and request schemas are compiled by ajv to make validation faster. However compilation is slow
+     * and can cause compilation of API to take long time. Enabling this will cause validation schemas
+     * compilation to be executed when the validator is needed.
+     */
+    lazyCompileValidationSchemas?: boolean;
 }