update services doc to libs

Docs/Libs/FastAPI/13-Body-Post.md

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+# FastAPI – POST Requests with JSON Body (`Body`)
+
+This document demonstrates how to receive data from the **request body** using `Body()` in FastAPI.
+This approach is commonly used when clients send **JSON payloads**.
+
+---
+
+## Example Application
+
+Create or update `main.py` with the following content:
+
+```python
+from fastapi import FastAPI, Body, status
+from fastapi.responses import JSONResponse
+
+app = FastAPI()
+
+users_db = [
+    {"id": "1", "name": "radin", "password": "123"}
+]
+
+
+@app.post("/user/")
+def get_user_from_body(
+    target: int = Body(
+        ...,
+        embed=True,
+        gt=0,
+        alias="User ID",
+        description="Enter target unique ID",
+    )
+):
+    for item in users_db:
+        if item["id"] == str(target):
+            return JSONResponse(
+                content={"msg": f"Your target user name is {item['name']}"},
+                status_code=status.HTTP_200_OK,
+            )
+
+    return JSONResponse(
+        content={"msg": "user not found"},
+        status_code=status.HTTP_404_NOT_FOUND,
+    )
+```
+
+---
+
+## JSON Body Overview
+
+### What Is a Request Body
+
+The request body contains structured data sent by the client, most commonly as **JSON**.
+
+**Content-Type:**
+
+```
+application/json
+```
+
+---
+
+## Request Format
+
+### Example JSON Payload
+
+```json
+{
+  "User ID": 1
+}
+```
+
+* `embed=True` requires the value to be wrapped inside a JSON object
+* The key name is controlled by the `alias`
+
+---
+
+## Example Request Using `curl`
+
+```bash
+curl -X POST "http://localhost:8000/user/" \
+  -H "Content-Type: application/json" \
+  -d '{"User ID": 1}'
+```
+
+---
+
+## Response Examples
+
+### Success Response
+
+```json
+{
+  "msg": "Your target user name is radin"
+}
+```
+
+Status Code: **200 OK**
+
+---
+
+### Failure Response
+
+```json
+{
+  "msg": "user not found"
+}
+```
+
+Status Code: **404 Not Found**
+
+---
+
+## `Body()` Parameter Configuration
+
+```python
+Body(
+    ...,
+    embed=True,
+    gt=0,
+    alias="User ID",
+    description="Enter target unique ID"
+)
+```
+
+| Parameter     | Purpose                          |
+| ------------- | -------------------------------- |
+| `...`         | Field is required                |
+| `embed=True`  | Wraps the value in a JSON object |
+| `gt=0`        | Validates input value            |
+| `alias`       | Custom JSON key name             |
+| `description` | Shown in API documentation       |
+
+---
+
+## Swagger / OpenAPI Behavior
+
+* JSON schema is automatically generated
+* Validation errors are returned if rules are violated
+* Aliases and descriptions appear in Swagger UI
+* Request body is clearly documented
+
+---
+
+## Running the Application
+
+Start the service using `uvicorn`:
+
+```bash
+uvicorn main:app --reload
+```
+
+---
+
+## Best Practices
+
+* Prefer request body over query parameters for POST requests
+* Use Pydantic models instead of raw `Body()` for complex payloads
+* Keep JSON structures consistent
+* Avoid spaces in JSON keys for production APIs
+* Never send sensitive data in plain text
+* Use HTTPS for all JSON-based APIs