Multithreaded HTTP/1.0 server in C with IPv6 support

Features

Supports HTTP/1.0 and HTTP/1.1 GET requests for static files.
- Implements a subset of the HTTP/1.0 specification.
- HTTP/1.1 is accepted in the request line for convenience as modern browsers default to this version string.
- Only the request line needs to be well-formed.
  - This server does not require, process, nor validate any further request headers.
  - Therefore, when reading the HTTP GET request, once a single CRLF is encountered at the end of a valid request line, the request parser state machine will transition to looking for 2x consecutive CRLF, which marks the end of a HTTP request as specified in RFC 1945.
    - The first CRLF of the 2x CRLF marking the request's end can also be the CRLF at the end of a valid request line. Thus a single request has a minimum of 2x CRLF in total, with 2 of these CRLFs being consecutive at the end of the request.
  - Since further request headers are unused, an alternative approach is possible as follows:
    - When reading the GET request, once a CRLF is encountered at the end of a valid request line, the request would be immediately accepted and processed.
    - This alternative approach would hence not wait until 2x consecutive CRLFs are reached (which would mark the end of a HTTP request as given by RFC 1945), thus marginally reducing latency (round-trip time) by replying earlier to requests with many additional headers.
Incrementally parses the request line by tracking the last-completed stage in per-request state machine, improving request processing performance.
Handles multiple simultaneous downloads up to the process thread limit through the use of a dedicated POSIX thread per request.
- To improve on this further, a thread pool could be used to avoid the per-process thread limit. Implementing green threads would be a further challenge!
Supports both IPv4 and IPv6! It is 2022 already.
Handles multi-packet requests: HTTP requests can be > 2KB in size (configurable), which is larger than a typical MTU.
Request and response types to encapsulate data, ensure separation of the request-parsing and response-building concerns, and improve readability. Response side-effects are performed only when the response struct has been fully populated.
Supports large files (larger than 2 GiB) - file sizes are limited only by the maximum supported by the file system (ext4: 16 TiB).
Performs zero-copy transfers from a file to the response socket using sendfile, reaching local download speeds to in excess of 3 GB/s on large files, saturating the read speed of a PCIe 3.0 NVMe SSD where the test files are located!
Protects against path escape attacks involving /../ or trailing /.., while also accepting and processing potentially-legitimate paths such as /folder../
Supports extremely long path names up to the system's max limits (255 chars per file folder, 4096 chars for the entire path on Linux).
Safe signal handling with correct use of sig_atomic_t - for example, keyboard interrupts sent through netcat will not remotely terminate the running server.
Supports timeouts on incomplete, idle requests.
No 3rd party dependencies. Uses only the C POSIX library.
Runs on amd64 Linux (any 64-bit CPU & Linux distribution should work, including arm64 CPUs).
Tests for well-formed and invalid requests written in Python 3 (version 3.7+ required).

Building

Clone this repository.
make

Running

./server [protocol number] [port number] [path to web root]

[protocol number]: 4 for IPv4 or 6 for IPv6
[port number] is a valid port number (8080, 9000, etc). Avoid using the well-known ports of 0-1023 inclusive, as they are reserved for the host OS and core services, and typically cannot be bound to without root access.
[path to web root] is a valid path e.g. ./www1 if the current directory is the root of this repo.

Testing

Before running any provided unit tests, stop any instance which has been bound to the same port (9000) to be used by the server instance launched during unit test setup.

Test results

A comprehensive list of test results is attached in proj2-final.txt. Note that these results and the comments are directed at commit SHA 20039d3df71cac80e9b33fa6e444169040cdaf91 - I've added a readme and improved the Makefile since, with no changes to the server functionality. The commit SHAs do not match those in proj2-final.txt after updating my git author email using git filter-repo.

Clearly, these tests that I wrote weren't for naught!

Netcat tests

These tests are designed to test the returned status of both well-formed and intentionally malformed requests, which should return 400 Bad Request, as well as the exact size of the response.

They also test that given these inputs, the server does not crash, segfault, leak memory, or otherwise do anything undesirable.

To run these tests:

Build the project as above.
Install nclib: pip3 install nclib.
In test_netcat_custom.py, configure the SKIP_TIMEOUT flag. If True, tests which expect a timeout outcome (such as sending an empty message) will not be run, reducing the total test duration.
Run the tests: python3 test_netcat_custom.py

Request tests

These test well-formed HTTP/1.0 or HTTP/1.1 GET requests (which also conform to the subset of the spec supported by this server) against the server. Key areas of focus are

Correct Content-Length and Content-Type header values
Correct actual size of response
Large file support
Path escape protection.