Add input sanitization against prompt injection

main.py

@@ -1,4 +1,5 @@
 import os
+import re
 import traceback
 from fastapi import FastAPI, HTTPException
 from pydantic import BaseModel
@@ -11,6 +12,25 @@ from humanizer import humanize_text
 
 from fastapi.middleware.cors import CORSMiddleware
 
+def sanitize_input(text: str) -> str:
+    """
+    Strip prompt injection patterns from user input before
+    passing to the Groq API.
+    """
+    patterns = [
+        r'\[SYSTEM OVERRIDE.*?\]',
+        r'\[INST.*?\]',
+        r'ignore (all |your |previous |the )?instructions',
+        r'do not (rewrite|change|edit|humanize)',
+        r'bypass (rewriting|humanization|the system)',
+        r'output (the text|this text) (exactly|verbatim|as.is)',
+        r'disregard (all |your |previous |the )?instructions',
+        r'forget (all |your |previous |the )?instructions',
+    ]
+    for pattern in patterns:
+        text = re.sub(pattern, '', text, flags=re.IGNORECASE | re.DOTALL)
+    return text.strip()
+
 app = FastAPI(title="AI Humanizer API")
 
 app.add_middleware(
@@ -43,9 +63,17 @@ async def humanize(request: HumanizeRequest):
             status_code=400,
             detail="mode must be one of: simple, standard, enhanced"
         )
+    clean_text = sanitize_input(request.text)
+
+    if not clean_text:
+        raise HTTPException(
+            status_code=400,
+            detail="Input text is empty or invalid after sanitization."
+        )
+
     try:
         humanized_text = await humanize_text(
-            request.text,
+            clean_text,
             mode=request.mode,
             readability=request.readability,
             purpose=request.purpose,