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LEARN GRAFANA IN C

Learn Grafana’s Principles by Building a Clone in C

Goal: To deeply understand how a data visualization tool like Grafana works by building a simplified, command-line version from scratch in C. This project will teach you how to query time-series databases, process data, and render it into a visual format.

Why Build a Grafana Clone?

Grafana is a brilliant tool for visualizing data, but it does so much that its core principles can seem like magic. By building your own version, “C-fana,” you will demystify the entire process. You aren’t just learning an application; you are learning the fundamental pipeline of all data visualization: Query -> Process -> Render.

This project will force you to learn:

  • API Integration in C: How to make HTTP requests from a C program to query a modern database like Prometheus.
  • Data Parsing: How to process and understand JSON data structures in a low-level language.
  • Data Normalization & Scaling: The logic required to fit any dataset onto a fixed-size display.
  • Graphics Rendering: The fundamental algorithms for drawing a graph, either with simple text characters (ASCII) or by generating a vector image file (SVG).

Core Concept Analysis: The Grafana Pipeline

Grafana’s core job is to transform a query into a picture. Our C clone will follow a simplified version of the same pipeline.

┌──────────────────┐
│   Dashboard      │
│  Definition File │
│ (dashboard.json) │
└────────┬─────────┘
         │ 1. Read & Parse Config
         ▼
┌──────────────────┐
│   "C-fana"       │   2. Construct & Send Query
│  (Our C Program) │──────────────────────────────▶┌──────────────────┐
└────────┬─────────┘                                │  Data Source     │
         │ 5. Render Graph                          │ (e.g., Prometheus│
         │    to Console/SVG                        │      via HTTP)   │
         ▼                                          └────────┬─────────┘
┌──────────────────┐                                         │ 3. Send Back
│   Visual Graph   │◀─────────────────────────────────────────┘   JSON Data
│ (ASCII or SVG)   │         4. Parse & Normalize
└──────────────────┘              JSON into C structs
  1. Define: A user creates a simple file defining what to draw.
  2. Query: Our C program makes an HTTP request to a data source (Prometheus) with the query from the definition file.
  3. Receive: The data source sends back time-series data formatted as JSON.
  4. Process: Our C program parses the JSON into structs and calculates how to scale the data to fit on a “canvas”.
  5. Render: Our program draws the final graph, either as text to the console or as an SVG file.

Environment Setup (Project 0)

This is a mandatory first step. You cannot visualize data without a data source.

  • OS: Linux is recommended.
  • Compiler & Tools: gcc (or clang) and make.
  • Data Source: We will use Prometheus (a time-series database) and Node Exporter (which provides sample metrics about your system). The easiest way to run these is with Docker.

To set up your data source:

  1. Install Docker.
  2. Create a folder named monitoring. Inside it, create a docker-compose.yml file and a prometheus.yml file as described in the official Prometheus documentation or numerous online guides.
  3. Run docker compose up -d in that folder.
  4. Verify that Prometheus is running by visiting http://localhost:9090 in your browser. You should be able to run queries like up in the query bar.

A Note on the “No Libraries” Constraint in C: For this project, “from scratch” means avoiding high-level libraries for the core logic. However, parsing complex formats like JSON from absolute scratch is a separate, massive project. Therefore, we will allow one single-header utility library (cJSON) for JSON parsing. This lets us focus on the Grafana-specific logic. We will build the HTTP client from scratch using sockets.

Project List

Project 1: The Prometheus HTTP Client

  • File: LEARN_GRAFANA_IN_C.md
  • Main Programming Language: C
  • Alternative Programming Languages: N/A
  • Coolness Level: Level 4: Hardcore Tech Flex
  • Business Potential: 1. The “Resume Gold”
  • Difficulty: Level 3: Advanced
  • Knowledge Area: Network Programming / Sockets
  • Software or Tool: C Sockets API
  • Main Book: “Beej’s Guide to Network Programming”.

What you’ll build: A C program that connects to your local Prometheus server (from Project 0) over a TCP socket, sends a raw HTTP GET request for a specific PromQL query, and prints the raw JSON response from the server to the console.

Why it teaches API integration: This project is a masterclass in how web clients work at a low level. You are not using a library like curl or requests; you are manually opening sockets, formatting an HTTP 1.0 request as a string, sending it, and reading the response.

Core challenges you’ll face:

  • TCP Client Socket Programming → maps to the socket(), getaddrinfo(), connect(), send(), and recv() system call flow.
  • Formatting an HTTP GET Request → maps to manually creating the string for the request line, headers (Host), and the final \r\n\r\n.
  • Reading a variable-length response → maps to looping on the recv() call until the server closes the connection, and storing the response in a dynamically growing buffer.

Key Concepts:

  • HTTP/1.0 Protocol: The basic structure of an HTTP request.
  • TCP Sockets: Beej’s Guide, Section 5 & 6 (Client/Server example).
  • Prometheus HTTP API: Prometheus Docs - Querying API.

Difficulty: Advanced Time estimate: 1-2 weeks Prerequisites: Project 0, strong C skills.

Real world outcome: You will run ./prometheus_client and it will print the full, unformatted JSON response from the Prometheus API for a query like node_cpu_seconds_total.

Implementation Hints:

  • Your HTTP request string will look something like this: "GET /api/v1/query?query=up HTTP/1.0\r\nHost: localhost:9090\r\n\r\n"
  • You must send() this exact string over the socket.
  • The server’s response will include HTTP headers followed by a blank line, then the JSON body. Your code will need to read everything, but for now, just printing it all is fine.
  • Use realloc to grow your response buffer as you receive more data from recv().

Learning milestones:

  1. You successfully connect to the Prometheus server → Your socket and connection logic is correct.
  2. You send a valid HTTP request and get a 200 OK response → Your HTTP formatting is correct.
  3. You can read and print the entire JSON body → Your response handling loop is working.

Project 2: The JSON Data Parser

  • File: LEARN_GRAFANA_IN_C.md
  • Main Programming Language: C
  • Alternative Programming Languages: N/A
  • Coolness Level: Level 3: Genuinely Clever
  • Business Potential: 1. The “Resume Gold”
  • Difficulty: Level 3: Advanced
  • Knowledge Area: Data Structures / Parsing
  • Software or Tool: C, cJSON (recommended)
  • Main Book: The cJSON documentation on GitHub.

What you’ll build: You will extend Project 1. After receiving the JSON response, you will use a parser to navigate the JSON structure and extract only the time-series data points—the [timestamp, value] pairs—into an array of C structs.

Why it teaches data processing: Raw data is useless. This project teaches you how to take a common, semi-structured data format (JSON) and turn it into a strongly-typed, easy-to-use data structure in C, which is the necessary next step for any kind of processing or rendering.

Core challenges you’ll face:

  • Integrating a single-header library → maps to learning how to include and use a small, third-party utility like cJSON.h.
  • Navigating a nested JSON object → maps to using the library’s functions (cJSON_GetObjectItemCaseSensitive, cJSON_GetArrayItem, etc.) to traverse the path to the data you need (e.g., data.result[0].values).
  • Creating a dynamic array of structs → maps to allocating memory for your time-series data (struct DataPoint { double timestamp; double value; }) and growing it as you parse.

Key Concepts:

  • JSON Data Structure: json.org.
  • Tree Traversal: The logic of navigating the parsed JSON object is a form of tree traversal.

Difficulty: Advanced Time estimate: 1 week Prerequisites: Project 1.

Real world outcome: Your program will now output a clean list of timestamp-value pairs, ready for visualization:

Timestamp: 1698400000, Value: 543.21
Timestamp: 1698400015, Value: 544.98
...

Implementation Hints:

  • Download cJSON.c and cJSON.h and add them to your project.
  • First, parse the entire response body with cJSON_Parse().
  • Then, navigate down. A typical Prometheus response is { "status": "success", "data": { "resultType": "matrix", "result": [ { "metric": {...}, "values": [ [ts, val], [ts, val], ... ] } ] } }.
  • Loop through the values array, extracting each timestamp and value and storing them in your own struct.

Learning milestones:

  1. You can parse the response string into a cJSON object without errors → The data is valid JSON.
  2. You can extract a specific field, like "status" → You understand basic object traversal.
  3. You can iterate through the values array → You can handle JSON arrays.
  4. You have a clean DataPoint struct array populated with all the time-series data → Your data is now fully processed and ready for the next stage.

Project 3: The ASCII Graph Renderer

  • File: LEARN_GRAFANA_IN_C.md
  • Main Programming Language: C
  • Alternative Programming Languages: N/A
  • Coolness Level: Level 4: Hardcore Tech Flex
  • Business Potential: 1. The “Resume Gold”
  • Difficulty: Level 2: Intermediate
  • Knowledge Area: Computer Graphics / Algorithms
  • Software or Tool: C
  • Main Book: N/A (Online articles on basic plotting algorithms).

What you’ll build: A C function that takes an array of DataPoint structs (from Project 2), a width, and a height, and prints a time-series graph to the console using only ASCII characters.

Why it teaches rendering logic: This is the core of visualization. It forces you to think about mapping a data space to a view space. You will implement the fundamental logic of scaling, normalization, and coordinate calculation that every graphics engine, from Grafana to a video game, performs.

Core challenges you’ll face:

  • Finding data boundaries → maps to iterating through your data to find the min/max timestamp and the min/max value.
  • Scaling and mapping coordinates → maps to writing the formula to convert a timestamp into a column index (x-coordinate) and a data value into a row index (y-coordinate).
  • Drawing on a 2D grid → maps to creating a char grid[HEIGHT][WIDTH], filling it with spaces, and then placing an asterisk * at each calculated (x, y) coordinate.
  • Handling the inverted Y-axis → maps to remembering that in a 2D array, row 0 is the top, so you must flip your Y-coordinate calculation (y = HEIGHT - 1 - scaled_y).

Key Concepts:

  • Linear Interpolation (Lerp): The mathematical basis for scaling a value from one range to another.
  • 2D Array Manipulation: A core C programming skill.

Difficulty: Intermediate Time estimate: Weekend Prerequisites: Strong C array and pointer skills.

Real world outcome: Your program will produce a text-based graph on the console, giving you a recognizable shape of your data.

|                  *
|                 * *
| *************** *
|*
+--------------------------------------

Implementation Hints:

  • Create a function void render_ascii(DataPoint *data, int count, int width, int height).
  • Inside, first find min_time, max_time, min_val, max_val.
  • For each point in data:
    • x = (point.timestamp - min_time) / (max_time - min_time) * (width - 1);
    • y = (point.value - min_val) / (max_val - min_val) * (height - 1);
    • grid[height - 1 - y][x] = '*';
  • Print the grid row by row.

Learning milestones:

  1. You can correctly calculate the bounds of your dataset → The first step of scaling is complete.
  2. You can map data points to grid coordinates → Your scaling logic is correct.
  3. The final printed grid shows a recognizable shape of the data → Your rendering engine works.

Project 4: The SVG Vector Graphics Renderer

  • File: LEARN_GRAFANA_IN_C.md
  • Main Programming Language: C
  • Alternative Programming Languages: N/A
  • Coolness Level: Level 4: Hardcore Tech Flex
  • Business Potential: 2. The “Micro-SaaS / Pro Tool”
  • Difficulty: Level 3: Advanced
  • Knowledge Area: Computer Graphics / File Formats
  • Software or Tool: C
  • Main Book: MDN Web Docs for SVG.

What you’ll build: A replacement for the ASCII renderer. This new C function will take the same array of DataPoint structs but instead of printing to the console, it will write a valid .svg file to disk that represents the time-series graph.

Why it teaches advanced rendering: This moves from a conceptual text graph to a real, scalable, vector graphics format. SVG is just XML, so it can be generated as a text file from C. This teaches you how to programmatically generate a standard image format.

Core challenges you’ll face:

  • Generating XML/Text → maps to using fprintf to write the SVG header, footer, and element tags to a file.
  • Using the SVG <polyline> element → maps to learning that a polyline takes a single attribute points which is a long string of “x,y” coordinates.
  • Transforming coordinates → maps to scaling your data to fit a pixel canvas (e.g., 800x600) and remembering that the SVG coordinate system has (0,0) at the top-left.

Key Concepts:

  • SVG File Format: MDN - SVG Tutorial
  • <polyline> element: MDN - <polyline>
  • String Formatting in C: fprintf, snprintf.

Difficulty: Advanced Time estimate: Weekend Prerequisites: Project 3.

Real world outcome: Your program will generate a graph.svg file. You can open this file in any web browser, and you will see a clean, sharp, vector line graph of your data.

Implementation Hints:

  • Your C function will open a file graph.svg for writing.
  • fprintf(f, "<svg width='800' height='600' xmlns='http://www.w3.org/2000/svg'>\n");
  • Create a large character buffer. Loop through your data points, scaling them to the 800x600 coordinate space. For each point, use sprintf to append “ %d,%d”`, to the buffer.
  • fprintf(f, "<polyline points='%s' stroke='blue' fill='none' />\n", point_buffer);
  • fprintf(f, "</svg>\n");
  • Close the file.

Learning milestones:

  1. Your program generates a file that is a valid SVG → Your header/footer and basic syntax are correct.
  2. Opening the SVG file shows a line → You are correctly formatting the points attribute.
  3. The shape of the line accurately represents the data from Prometheus → Your scaling and coordinate mapping logic is correct for a graphical canvas.

Summary

Project Main Concept Core Skill Difficulty
0. Environment Setup Time-Series Database Docker, Prometheus Intermediate
1. Prometheus HTTP Client Low-Level Networking C Socket Programming Advanced
2. JSON Data Parser Data Processing Structs & Parsing Advanced
3. ASCII Graph Renderer Visualization Logic Algorithms, 2D Arrays Intermediate
4. SVG Vector Renderer Graphics File Formats String Generation, SVG Advanced

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