Merge #267: New binary to parse torrent files (only for debugging pur…

…poses)

d9cdd65 feat: new binary to par torrent files (Jose Celano)

Pull request description:

  I'm trying to fix bug #266

  When I try to upload this torrent:

  https://academictorrents.com/details/3cd18ff2d3eec881207dcc5ca5a2c3a2a3afe462

  I get this error trying to parse it:

  ```
  InvalidType("Invalid Type: sequence (expected: `field identifier`)")
  ```

  I've tried to reproduce the error with a clean project:

  https://github.com/torrust/torrust-parse-torrent

  But It works.

  I've added a binary to reproduce the error in this project. You can run it with:

  ```
  cargo run --bin parse_torrent ./tests/fixtures/torrents/MC_GRID.zip-3cd18ff2d3eec881207dcc5ca5a2c3a2a3afe462.torrent
  ```

  Output:

  ```s
  Reading the torrent file ...
  Decoding torrent with standard serde implementation ...
  InvalidType("Invalid Type: sequence (expected: `field identifier`)")
  Error: Custom { kind: Other, error: "Error: invalid torrent!. Invalid Type: sequence (expected: `field identifier`)" }
  ```

  I need more ideas about how to solve this bug. I've checked the dependencies, and It does not work even if I use the same "serde" dependencies in this project.

  The torrent only has two different things:

  - The "pieces" field is big.
  - It has an extra field from BEP 19.

  I only have two more things to test:

  - ~~Create another torrent with a big "pieces" field. Only to check if the size is the problem~~. DONE.
  - Clone the "serve" crate and try to debug the code. I think the error is thrown [here](https://github.com/serde-rs/serde/blob/dad15b9fd0bef97b7a7c90a8a165b6ffbc682cae/serde/src/de/mod.rs#L1646). It seems the deserializer is expecting a file identifier (I guess for a Dictionary) and is getting a sequence.

Top commit has no ACKs.

Tree-SHA512: c9f02021801d492e34b7550662cfb6747bbf81f3724c3afdd3d92e22061066c400b721f35e80100d3253ff79fbda10d0bf0f7ea29df964f57ee97a1607b50fd3

.vscode/launch.json

@@ -0,0 +1,35 @@
+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Debug executable 'parse_torrent'",
+            "type": "cppdbg",
+            "request": "launch",
+            "program": "${workspaceFolder}/target/debug/parse_torrent",
+            "args": ["./tests/fixtures/torrents/MC_GRID.zip-3cd18ff2d3eec881207dcc5ca5a2c3a2a3afe462.torrent"],
+            "stopAtEntry": false,
+            "cwd": "${workspaceFolder}",
+            "environment": [],
+            "externalConsole": false,
+            "MIMode": "gdb",
+            "setupCommands": [
+                {
+                    "description": "Enable pretty-printing for gdb",
+                    "text": "-enable-pretty-printing",
+                    "ignoreFailures": true
+                }
+            ],
+            "preLaunchTask": "cargo build",
+            "miDebuggerPath": "/usr/bin/gdb",
+            "linux": {
+                "miDebuggerPath": "/usr/bin/gdb"
+            },
+            "windows": {
+                "miDebuggerPath": "C:\\MinGW\\bin\\gdb.exe"
+            },
+            "osx": {
+                "miDebuggerPath": "/usr/local/bin/gdb"
+            }
+        }
+    ]
+}

src/bin/parse_torrent.rs

@@ -0,0 +1,41 @@
+//! Command line tool to parse a torrent file and print the decoded torrent.
+//!
+//! It's only used for debugging purposes.
+use std::env;
+use std::fs::File;
+use std::io::{self, Read};
+
+use serde_bencode::de::from_bytes;
+use serde_bencode::value::Value as BValue;
+use torrust_index_backend::utils::parse_torrent;
+
+fn main() -> io::Result<()> {
+    let args: Vec<String> = env::args().collect();
+    if args.len() != 2 {
+        eprintln!("Usage:   cargo run --bin parse_torrent <PATH_TO_TORRENT_FILE>");
+        eprintln!("Example: cargo run --bin parse_torrent ./tests/fixtures/torrents/MC_GRID.zip-3cd18ff2d3eec881207dcc5ca5a2c3a2a3afe462.torrent");
+        std::process::exit(1);
+    }
+
+    println!("Reading the torrent file ...");
+
+    let mut file = File::open(&args[1])?;
+    let mut bytes = Vec::new();
+    file.read_to_end(&mut bytes)?;
+
+    println!("Decoding torrent with standard serde implementation ...");
+
+    match from_bytes::<BValue>(&bytes) {
+        Ok(_value) => match parse_torrent::decode_torrent(&bytes) {
+            Ok(torrent) => {
+                println!("Parsed torrent: \n{torrent:#?}");
+                Ok(())
+            }
+            Err(e) => Err(io::Error::new(io::ErrorKind::Other, format!("Error: invalid torrent!. {e}"))),
+        },
+        Err(e) => Err(io::Error::new(
+            io::ErrorKind::Other,
+            format!("Error: invalid bencode data!. {e}"),
+        )),
+    }
+}