Add server mode with FastAPI

Author: bsklaroff

Diff for: aider/args.py

@@ -616,6 +616,23 @@ def get_parser(default_config_files, git_root):
         default=False,
         help="Enable automatic copy/paste of chat between aider and web UI (default: False)",
     )
+    group.add_argument(
+        "--server",
+        action="store_true",
+        help="Start aider as a FastAPI server (default: False)",
+        default=False,
+    )
+    group.add_argument(
+        "--host",
+        default="127.0.0.1",
+        help="Specify the host to bind the server to (only used with --server, default: 127.0.0.1)",
+    )
+    group.add_argument(
+        "--port",
+        type=int,
+        default=8000,
+        help="Specify the port to bind the server to (only used with --server, default: 8000)",
+    )
     group.add_argument(
         "--apply",
         metavar="FILE",

Diff for: aider/main.py

@@ -660,6 +660,15 @@ def get_io(pretty):
         analytics.event("exit", reason="GUI session ended")
         return
 
+    if args.server and not return_coder:
+        from aider.server import start_server
+
+        io.tool_output("Starting aider API server...")
+        analytics.event("server session")
+        start_server(argv, host=args.host, port=args.port)
+        analytics.event("exit", reason="Server session ended")
+        return
+
     if args.verbose:
         for fname in loaded_dotenvs:
             io.tool_output(f"Loaded {fname}")

Diff for: aider/server.py

@@ -0,0 +1,56 @@
+import asyncio
+import traceback
+
+import uvicorn
+from fastapi import FastAPI, HTTPException
+from fastapi.responses import StreamingResponse
+from pydantic import BaseModel
+
+from aider.main import main as cli_main
+
+
+class ChatRequest(BaseModel):
+    message: str
+    stream: bool = True
+
+
+class ChatResponse(BaseModel):
+    content: str
+
+
+async def process_generator(generator):
+    """Convert the synchronous generator to an async one."""
+    for chunk in generator:
+        yield chunk
+        await asyncio.sleep(0)
+
+
+def create_app(coder):
+    """Create a FastAPI application with a coder instance."""
+    app = FastAPI(title="Aider API")
+
+    @app.post("/chat")
+    async def chat(request: ChatRequest):
+        """Process a chat message and return the response from the coder."""
+        try:
+            if request.stream:
+                generator = coder.run_stream(request.message)
+                return StreamingResponse(process_generator(generator), media_type="text/plain")
+            else:
+                response = coder.run(with_message=request.message)
+                return ChatResponse(content=response)
+        except Exception as e:
+            error_detail = f"{str(e)}\n{traceback.format_exc()}"
+            raise HTTPException(status_code=500, detail=error_detail)
+
+    return app
+
+
+def start_server(argv, host="127.0.0.1", port=8000):
+    """Start the FastAPI server with the given coder."""
+    coder = cli_main(argv=argv, return_coder=True)
+    app = create_app(coder)
+    # Required to force the coder to return text from run and run_stream
+    coder.stream = True
+    coder.pretty = False
+    uvicorn.run(app, host=host, port=port)

Diff for: pyproject.toml

@@ -33,6 +33,7 @@ dev = { file = "requirements/requirements-dev.txt" }
 help = { file = "requirements/requirements-help.txt" }
 browser = { file = "requirements/requirements-browser.txt" }
 playwright = { file = "requirements/requirements-playwright.txt" }
+server = { file = "requirements/requirements-server.txt" }
 
 [tool.setuptools]
 include-package-data = true

Diff for: requirements/common-constraints.txt

@@ -1,5 +1,5 @@
 # This file was autogenerated by uv via the following command:
-#    uv pip compile --no-strip-extras --output-file=requirements/common-constraints.txt requirements/requirements.in requirements/requirements-browser.in requirements/requirements-dev.in requirements/requirements-help.in requirements/requirements-playwright.in
+#    uv pip compile --no-strip-extras --output-file=requirements/common-constraints.txt requirements/requirements.in requirements/requirements-browser.in requirements/requirements-dev.in requirements/requirements-help.in requirements/requirements-playwright.in requirements/requirements-server.in
 aiohappyeyeballs==2.6.1
     # via aiohttp
 aiohttp==3.11.16
@@ -17,6 +17,7 @@ anyio==4.9.0
     # via
     #   httpx
     #   openai
+    #   starlette
     #   watchfiles
 attrs==25.3.0
     # via
@@ -59,6 +60,7 @@ click==8.1.8
     #   pip-tools
     #   streamlit
     #   typer
+    #   uvicorn
 codespell==2.4.1
     # via -r requirements/requirements-dev.in
 cogapp==3.4.1
@@ -93,6 +95,8 @@ distro==1.9.0
     # via
     #   openai
     #   posthog
+fastapi==0.115.12
+    # via -r requirements/requirements-server.in
 filelock==3.18.0
     # via
     #   huggingface-hub
@@ -156,7 +160,9 @@ grpcio==1.71.0
 grpcio-status==1.71.0
     # via google-api-core
 h11==0.14.0
-    # via httpcore
+    # via
+    #   httpcore
+    #   uvicorn
 httpcore==1.0.7
     # via httpx
 httpx==0.28.1
@@ -363,6 +369,7 @@ pycparser==2.22
 pydantic==2.11.2
     # via
     #   banks
+    #   fastapi
     #   litellm
     #   llama-index-core
     #   openai
@@ -479,6 +486,8 @@ soupsieve==2.6
     # via beautifulsoup4
 sqlalchemy[asyncio]==2.0.40
     # via llama-index-core
+starlette==0.46.1
+    # via fastapi
 streamlit==1.44.1
     # via -r requirements/requirements-browser.in
 sympy==1.13.3
@@ -532,6 +541,7 @@ typing-extensions==4.13.1
     #   altair
     #   anyio
     #   beautifulsoup4
+    #   fastapi
     #   huggingface-hub
     #   llama-index-core
     #   openai
@@ -560,6 +570,8 @@ urllib3==2.3.0
     #   requests
 uv==0.6.12
     # via -r requirements/requirements-dev.in
+uvicorn==0.34.0
+    # via -r requirements/requirements-server.in
 virtualenv==20.30.0
     # via pre-commit
 watchfiles==1.0.4

Diff for: requirements/requirements-server.in

@@ -0,0 +1,2 @@
+fastapi
+uvicorn

Diff for: requirements/requirements-server.txt

@@ -0,0 +1,58 @@
+# This file was autogenerated by uv via the following command:
+#    uv pip compile --no-strip-extras --constraint=requirements/common-constraints.txt --output-file=requirements/requirements-server.txt requirements/requirements-server.in
+annotated-types==0.7.0
+    # via
+    #   -c requirements/common-constraints.txt
+    #   pydantic
+anyio==4.9.0
+    # via
+    #   -c requirements/common-constraints.txt
+    #   starlette
+click==8.1.8
+    # via
+    #   -c requirements/common-constraints.txt
+    #   uvicorn
+fastapi==0.115.12
+    # via
+    #   -c requirements/common-constraints.txt
+    #   -r requirements/requirements-server.in
+h11==0.14.0
+    # via
+    #   -c requirements/common-constraints.txt
+    #   uvicorn
+idna==3.10
+    # via
+    #   -c requirements/common-constraints.txt
+    #   anyio
+pydantic==2.11.2
+    # via
+    #   -c requirements/common-constraints.txt
+    #   fastapi
+pydantic-core==2.33.1
+    # via
+    #   -c requirements/common-constraints.txt
+    #   pydantic
+sniffio==1.3.1
+    # via
+    #   -c requirements/common-constraints.txt
+    #   anyio
+starlette==0.46.1
+    # via
+    #   -c requirements/common-constraints.txt
+    #   fastapi
+typing-extensions==4.13.1
+    # via
+    #   -c requirements/common-constraints.txt
+    #   anyio
+    #   fastapi
+    #   pydantic
+    #   pydantic-core
+    #   typing-inspection
+typing-inspection==0.4.0
+    # via
+    #   -c requirements/common-constraints.txt
+    #   pydantic
+uvicorn==0.34.0
+    # via
+    #   -c requirements/common-constraints.txt
+    #   -r requirements/requirements-server.in